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Sample records for active membrane properties

  1. Investigation of membrane active properties and antiradical activity of gossypol and its derivatives

    Technology Transfer Automated Retrieval System (TEKTRAN)

    New asymmetrical derivatives of gossypol were synthesized. The antioxidant activity of gossypol and these derivatives was studied. The interaction of these compounds with modeled lipid membranes was also studied. It was found that the antioxidant effects and ability to interact with membranes was...

  2. Membrane-Active Properties and Antiradical Activity of Gossypol and Its Derivatives

    Technology Transfer Automated Retrieval System (TEKTRAN)

    New asymmetrical derivatives of gossypol were synthesized. The antioxidant activity of gossypol and these derivatives was studied. The interaction of these compounds with modeled lipid membranes was also studied. It was found that the antioxidant effects and ability to interact with membranes was...

  3. Passive and active membrane properties contribute to the temporal filtering properties of midbrain neurons in vivo.

    PubMed

    Fortune, E S; Rose, G J

    1997-05-15

    This study examined the contributions of passive and active membrane properties to the temporal selectivities of electrosensory neurons in vivo. The intracellular responses to time-varying (2-30 Hz) electrosensory stimulation and current injection of 27 neurons in the midbrain of the weakly electric fish Eigenmannia were recorded. Each neuron was filled with biocytin to reveal its anatomy. Neurons were divided into two biophysically distinct groups based on their frequency-dependent responses to sinusoidal current injection over the range 2-30 Hz. Fourteen neurons showed low-pass filtering, with a maximum decline in the amplitude of voltage responses of >2.6 dB (X = 4.30 dB, s = 1.10 dB) to sinusoidal current injection. These neurons also showed low-pass filtering of electrosensory information but with larger maximum declines in postsynaptic potential amplitude (X = 9.53 dB, s = 3.34 dB; n = 10). These neurons had broad dendritic arbors and relatively spiny dendrites. Five neurons showed all-pass filtering, having maximum decline in the amplitude of voltage responses of <2.0 dB (X = 1.16 dB, s = 0.61 dB). For electrosensory stimuli, however, these neurons showed low-, band-, or high-pass filtering. These neurons had small dendritic arbors and few or no spines. Voltage-dependent "active" conductances were revealed in eight neurons by using several levels of current clamp. In four of these neurons, the duration of the voltage-dependent conductances decreased in concert with the period of the electrosensory stimulus, whereas in the other four neurons the duration of the voltage-dependent conductances was relatively short (<30 msec) and nearly constant across sensory stimulation frequencies. These conductances enhanced the temporal filtering properties of neurons. PMID:9133400

  4. Barrier properties of poly(vinyl alcohol) membranes containing carbon nanotubes or activated carbon.

    PubMed

    Surdo, Erin M; Khan, Iftheker A; Choudhury, Atif A; Saleh, Navid B; Arnold, William A

    2011-04-15

    Carbon nanotube addition has been shown to improve the mechanical properties of some polymers. Because of their unique adsorptive properties, carbon nanotubes may also improve the barrier performance of polymers used in contaminant containment. This study compares the barrier performance of poly(vinyl alcohol) (PVA) membranes containing single-walled carbon nanotubes (SWCNTs) to that for PVA containing powdered activated carbon (PAC). Raw and surface-functionalized versions of each sorbent were tested for their abilities to adsorb 1,2,4-trichlorobenzene and Cu(2+), representing the important hydrophobic organic and heavy metal contaminant classes, as they diffused across the PVA. In both cases, PAC (for 1,2,4-trichlorobenzene) and functionalized PAC (for Cu(2+)) outperformed SWCNTs on a per mass basis by trapping more of the contaminants within the barrier membrane. Kinetics of sorption are important in evaluating barrier properties, and poor performance of SWCNT-containing membranes as 1,2,4-TCB barriers is attributed to kinetic limitations. PMID:21349636

  5. Salt stress in a membrane bioreactor: dynamics of sludge properties, membrane fouling and remediation through powdered activated carbon dosing.

    PubMed

    De Temmerman, L; Maere, T; Temmink, H; Zwijnenburg, A; Nopens, I

    2014-10-15

    Membrane bioreactors are a well-established technology for wastewater treatment. However, their efficiency is adversely impacted by membrane fouling, primarily inciting very conservative operations of installations that makes them less appealing from an economic perspective. This fouling propensity of the activated sludge is closely related to system disturbances. Therefore, improved insight into the impact of fouling is crucial towards increased membrane performance. In this work, the disturbance of a salt shock was investigated with respect to sludge composition and filterability in two parallel lab-scale membrane bioreactors. Several key sludge parameters (soluble microbial products, sludge-bound extracellular polymeric substances, supramicron particle size distributions (PSD), submicron particle concentrations) were intensively monitored prior to, during, and after a disturbance to investigate its impact as well as the potential governing mechanism. Upon salt addition, the supramicron PSD immediately shifted to smaller floc sizes, and the total fouling rate increased. Following a certain delay, an increase in submicron particles, supernatant proteins, and polysaccharides was observed as well as an increase in the irreversible membrane fouling rate. Recovery from the disturbance was evidenced with a simultaneous decrease in the above mentioned quantities. A similar experiment introducing powdered activated carbon (PAC) addition used for remediation resulted in either no or less significant changes in the above mentioned quantities, signifying its potential as a mitigation strategy. PMID:24999116

  6. In vivo antibacterial activity and pharmacological properties of the membrane-active glycopeptide antibiotic YV11455.

    PubMed

    Yarlagadda, Venkateswarlu; Konai, Mohini M; Manjunath, Goutham B; Prakash, Relekar G; Mani, Bhuvana; Paramanandham, Krishnamoorthy; Ranjan, Shome B; Ravikumar, Raju; Chakraborty, Subhankari P; Roy, Somenath; Haldar, Jayanta

    2015-06-01

    The membrane-active glycopeptide antibiotic YV11455 is a lipophilic cationic vancomycin analogue that demonstrates rapid and concentration-dependent killing of clinically relevant multidrug-resistant (MDR) Gram-positive bacteria in vitro. YV11455 was 2-fold and 54-270-fold more effective than vancomycin against clinical isolates of vancomycin-sensitive and vancomycin-resistant bacteria, respectively. In this study, the in vivo efficacy, pharmacodynamics, pharmacokinetics and acute toxicology of YV11455 were investigated. In vivo activity and pharmacodynamics were determined in the neutropenic mouse thigh infection model against meticillin-resistant Staphylococcus aureus (MRSA). YV11455 produced dose-dependent reductions in MRSA titres in thigh muscle. When administered intravenously, the 50% effective dose (ED(50)) for YV11455 against MRSA was found to be 3.3 mg/kg body weight, and titres were reduced by up to ca. 3log(10)CFU/g from pre-treatment values at a dosage of 12 mg/kg with single treatment. Single-dose pharmacokinetic studies demonstrated linear kinetics and a prolonged half-life, with an increase in drug exposure (area under the concentration-time curve) compared with vancomycin. The peak plasma concentration following an intravenous dose of 12 mg/kg was 543.5 μg/mL. Acute toxicology studies revealed that YV11455 did not cause any significant alterations in biochemical parameters or histological pictures related to major organs such as the liver and kidney at its pharmacodynamic endpoint (ED(3-log kill)). These findings collectively suggest that YV11455 could be used clinically for the treatment of infections caused by MDR Gram-positive bacteria. PMID:25900818

  7. Antimicrobial properties of membrane-active dodecapeptides derived from MSI-78.

    PubMed

    Monteiro, Claudia; Fernandes, Mariana; Pinheiro, Marina; Maia, Sílvia; Seabra, Catarina L; Ferreira-da-Silva, Frederico; Costa, Fabíola; Reis, Salette; Gomes, Paula; Martins, M Cristina L

    2015-05-01

    Antimicrobial peptides (AMPs) are a class of broad-spectrum antibiotics known by their ability to disrupt bacterial membranes and their low tendency to induce bacterial resistance, arising as excellent candidates to fight bacterial infections. In this study we aimed at designing short 12-mer AMPs, derived from a highly effective and broad spectrum synthetic AMP, MSI-78 (22 residues), by truncating this peptide at the N- and/or C-termini while spanning its entire sequence with 1 amino acid (aa) shifts. These designed peptides were evaluated regarding antimicrobial activity against selected gram-positive Staphylococcus strains and the gram-negative Pseudomonas aeruginosa (P. aeruginosa). The short 12-mer peptide CEM1 (GIGKFLKKAKKF) was identified as an excellent candidate to fight P. aeruginosa infections as it displays antimicrobial activity against this strain and selectivity, with negligible toxicity to mammalian cells even at high concentrations. However, in general most of the short 12-mer peptides tested showed a reduction in antimicrobial activity, an effect that was more pronounced for gram-positive Staphylococcus strains. Interestingly, CEM1 and a highly similar peptide differing by only one aa-shift (CEM2: IGKFLKKAKKFG), showed a remarkably contrasting AMP activity. These two peptides were chosen for a more detailed study regarding their mechanism of action, using several biophysical assays and simple membrane models that mimic the mammalian and bacterial lipid composition. We confirmed the correlation between peptide helicity and antimicrobial activity and propose a mechanism of action based on the disruption of the bacterial membrane permeability barrier. PMID:25680229

  8. Effects of DO levels on surface force, cell membrane properties and microbial community dynamics of activated sludge.

    PubMed

    Ma, Si-Jia; Ding, Li-Li; Huang, Hui; Geng, Jin-Ju; Xu, Ke; Zhang, Yan; Ren, Hong-Qiang

    2016-08-01

    In this paper, we employ atomic force microscopy (AFM), fluorescence recovery after photobleaching (FRAP) technique, phospholipid fatty acids (PLFA) and MiSeq analysis to study the effects of traditional dissolved oxygen (DO) levels (0.71-1.32mg/L, 2.13-3.02mg/L and 4.31-5.16mg/L) on surface force, cell membrane properties and microbial community dynamics of activated sludge. Results showed that low DO level enhanced the surface force and roughness of activated sludge; the medium DO level decreased cell membrane fluidity by reducing the synthesis of branched fatty acids in the cell membrane; high DO level resulted in the highest protein content in the effluent by EEM scanning. Abundance of Micropruina, Zoogloea and Nakamurella increased and Paracoccus and Rudaea decreased with the increase of DO levels. RDA analysis suggested that saturated fatty acids (SFA), anteiso-fatty acids (AFA) and iso-fatty acids (IFA) were closely related to effluent quality as well as some genera. PMID:27187569

  9. Rational modification of a dendrimeric peptide with antimicrobial activity: consequences on membrane-binding and biological properties.

    PubMed

    Batoni, Giovanna; Casu, Mariano; Giuliani, Andrea; Luca, Vincenzo; Maisetta, Giuseppantonio; Mangoni, Maria Luisa; Manzo, Giorgia; Pintus, Manuela; Pirri, Giovanna; Rinaldi, Andrea C; Scorciapino, Mariano A; Serra, Ilaria; Ulrich, Anne S; Wadhwani, Parvesh

    2016-03-01

    Peptide-based antibiotics might help containing the rising tide of antimicrobial resistance. We developed SB056, a semi-synthetic peptide with a dimeric dendrimer scaffold, active against both Gram-negative and Gram-positive bacteria. Being the mechanism of SB056 attributed to disruption of bacterial membranes, we enhanced the amphiphilic profile of the original, empirically derived sequence [WKKIRVRLSA-NH2] by interchanging the first two residues [KWKIRVRLSA-NH2], and explored the effects of this modification on the interaction of peptide, both in linear and dimeric forms, with model membranes and on antimicrobial activity. Results obtained against Escherichia coli and Staphylococcus aureus planktonic strains, with or without salts at physiological concentrations, confirmed the added value of dendrimeric structure over the linear one, especially at physiological ionic strength, and the impact of the higher amphipathicity obtained through sequence modification on enhancing peptide performances. SB056 peptides also displayed intriguing antibiofilm properties. Staphylococcus epidermidis was the most susceptible strain in sessile form, notably to optimized linear analog lin-SB056-1 and the wild-type dendrimer den-SB056. Membrane affinity of all peptides increased with the percentage of negatively charged lipids and was less influenced by the presence of salt in the case of dendrimeric peptides. The analog lin-SB056-1 displayed the highest overall affinity, even for zwitterionic PC bilayers. Thus, in addition to electrostatics, distribution of charged/polar and hydrophobic residues along the sequence might have a significant role in driving peptide-lipid interaction. Supporting this view, dendrimeric analog den-SB056-1 retained greater membrane affinity in the presence of salt than den-SB056, despite the fact that they bear exactly the same net positive charge. PMID:26614437

  10. Synthesis, antimicrobial activity, and membrane permeabilizing properties of C-terminally modified nisin conjugates accessed by CuAAC.

    PubMed

    Slootweg, Jack C; van der Wal, Steffen; Quarles van Ufford, H C; Breukink, Eefjan; Liskamp, Rob M J; Rijkers, Dirk T S

    2013-12-18

    Functionalization of the lantibiotic nisin with fluorescent reporter molecules is highly important for the understanding of its mode of action as a potent antimicrobial peptide. In addition to this, multimerization of nisin to obtain multivalent peptide constructs and conjugation of nisin to bioactive molecules or grafting it on surfaces can be attractive methods for interference with bacterial growth. Here, we report a convenient method for the synthesis of such nisin conjugates and show that these nisin derivatives retain both their antimicrobial activity and their membrane permeabilizing properties. The synthesis is based on the Cu(I)-catalyzed alkyne-azide cycloaddition reaction (CuAAC) as a bioorthogonal ligation method for large and unprotected peptides in which nisin was C-terminally modified with propargylamine and subsequently efficiently conjugated to a series of functionalized azides. Two fluorescently labeled nisin conjugates together with a dimeric nisin construct were prepared while membrane insertion as well as antimicrobial activity were unaffected by these modifications. This study shows that C-terminal modification of nisin does not deteriorate biological activity in sharp contrast to N-terminal modification and therefore C-terminally modified nisin analogues are valuable tools to study the antibacterial mode of action of nisin. Furthermore, the ability to use stoichiometric amounts of the azide containing molecule opens up possibilities for surface tethering and more complex multivalent structures. PMID:24266643

  11. Auxin-activated NADH oxidase activity of soybean plasma membranes is distinct from the constitutive plasma membrane NADH oxidase and exhibits prion-like properties

    NASA Technical Reports Server (NTRS)

    Morre, D. James; Morre, Dorothy M.; Ternes, Philipp

    2003-01-01

    The hormone-stimulated and growth-related cell surface hydroquinone (NADH) oxidase activity of etiolated hypocotyls of soybeans oscillates with a period of about 24 min or 60 times per 24-h day. Plasma membranes of soybean hypocotyls contain two such NADH oxidase activities that have been resolved by purification on concanavalin A columns. One in the apparent molecular weight range of 14-17 kDa is stimulated by the auxin herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The other is larger and unaffected by 2,4-D. The 2,4-D-stimulated activity absolutely requires 2,4-D for activity and exhibits a period length of about 24 min. Also exhibiting 24-min oscillations is the rate of cell enlargement induced by the addition of 2,4-D or the natural auxin indole-3-acetic acid (IAA). Immediately following 2,4-D or IAA addition, a very complex pattern of oscillations is frequently observed. However, after several hours a dominant 24-min period emerges at the expense of the constitutive activity. A recruitment process analogous to that exhibited by prions is postulated to explain this behavior.

  12. A pore-forming toxin requires a specific residue for its activity in membranes with particular physicochemical properties.

    PubMed

    Morante, Koldo; Caaveiro, Jose M M; Tanaka, Koji; González-Mañas, Juan Manuel; Tsumoto, Kouhei

    2015-04-24

    The physicochemical landscape of the bilayer modulates membrane protein function. Actinoporins are a family of potent hemolytic proteins from sea anemones acting at the membrane level. This family of cytolysins preferentially binds to target membranes containing sphingomyelin, where they form lytic pores giving rise to cell death. Although the cytolytic activity of the actinoporin fragaceatoxin C (FraC) is sensitive to vesicles made of various lipid compositions, it is far from clear how this toxin adjusts its mechanism of action to a broad range of physiochemical landscapes. Herein, we show that the conserved residue Phe-16 of FraC is critical for pore formation in cholesterol-rich membranes such as those of red blood cells. The interaction of a panel of muteins of Phe-16 with model membranes composed of raft-like lipid domains is inactivated in cholesterol-rich membranes but not in cholesterol-depleted membranes. These results indicate that actinoporins recognize different membrane environments, resulting in a wider repertoire of susceptible target membranes (and preys) for sea anemones. In addition, this study has unveiled promising candidates for the development of protein-based biosensors highly sensitive to the concentration of cholesterol within the membrane. PMID:25759390

  13. A Pore-Forming Toxin Requires a Specific Residue for Its Activity in Membranes with Particular Physicochemical Properties*

    PubMed Central

    Morante, Koldo; Caaveiro, Jose M. M.; Tanaka, Koji; González-Mañas, Juan Manuel; Tsumoto, Kouhei

    2015-01-01

    The physicochemical landscape of the bilayer modulates membrane protein function. Actinoporins are a family of potent hemolytic proteins from sea anemones acting at the membrane level. This family of cytolysins preferentially binds to target membranes containing sphingomyelin, where they form lytic pores giving rise to cell death. Although the cytolytic activity of the actinoporin fragaceatoxin C (FraC) is sensitive to vesicles made of various lipid compositions, it is far from clear how this toxin adjusts its mechanism of action to a broad range of physiochemical landscapes. Herein, we show that the conserved residue Phe-16 of FraC is critical for pore formation in cholesterol-rich membranes such as those of red blood cells. The interaction of a panel of muteins of Phe-16 with model membranes composed of raft-like lipid domains is inactivated in cholesterol-rich membranes but not in cholesterol-depleted membranes. These results indicate that actinoporins recognize different membrane environments, resulting in a wider repertoire of susceptible target membranes (and preys) for sea anemones. In addition, this study has unveiled promising candidates for the development of protein-based biosensors highly sensitive to the concentration of cholesterol within the membrane. PMID:25759390

  14. Modulation of neuronal activity and plasma membrane properties with low-power millimeter waves in organotypic cortical slices

    NASA Astrophysics Data System (ADS)

    Pikov, Victor; Arakaki, Xianghong; Harrington, Michael; Fraser, Scott E.; Siegel, Peter H.

    2010-08-01

    As millimeter waves (MMWs) are being increasingly used in communications and military applications, their potential effects on biological tissue has become an important issue for scientific inquiry. Specifically, several MMW effects on the whole-nerve activity were reported, but the underlying neuronal changes remain unexplored. This study used slices of cortical tissue to evaluate the MMW effects on individual pyramidal neurons under conditions mimicking their in vivo environment. The applied levels of MMW power are three orders of magnitude below the existing safe limit for human exposure of 1 mW cm-2. Surprisingly, even at these low power levels, MMWs were able to produce considerable changes in neuronal firing rate and plasma membrane properties. At the power density approaching 1 µW cm-2, 1 min of MMW exposure reduced the firing rate to one third of the pre-exposure level in four out of eight examined neurons. The width of the action potentials was narrowed by MMW exposure to 17% of the baseline value and the membrane input resistance decreased to 54% of the baseline value across all neurons. These effects were short lasting (2 min or less) and were accompanied by MMW-induced heating of the bath solution at 3 °C. Comparison of these results with previously published data on the effects of general bath heating of 10 °C indicated that MMW-induced effects cannot be fully attributed to heating and may involve specific MMW absorption by the tissue. Blocking of the intracellular Ca2+-mediated signaling did not significantly alter the MMW-induced neuronal responses suggesting that MMWs interacted directly with the neuronal plasma membrane. The presented results constitute the first demonstration of direct real-time monitoring of the impact of MMWs on nervous tissue at a microscopic scale. Implication of these findings for the therapeutic modulation of neuronal excitability is discussed.

  15. Active membrane phased array radar

    NASA Technical Reports Server (NTRS)

    Moussessian, Alina; Del Castillo, Linda; Huang, John; Sadowy, Greg; Hoffman, James; Smith, Phil; Hatake, Toshiro; Derksen, Chuck; Lopez, Bernardo; Caro, Ed

    2005-01-01

    We have developed the first membrane-based active phased array in L-band (1.26GHz). The array uses membrane compatible Transmit/Receive (T/R) modules (membrane T/R) for each antenna element. We use phase shifters within each T/R module for electronic beam steering. We will discuss the T/R module design and integration with the membrane, We will also present transmit and receive beam-steering results for the array.

  16. Membrane Elastic Properties and Cell Function

    PubMed Central

    Pontes, Bruno; Ayala, Yareni; Fonseca, Anna Carolina C.; Romão, Luciana F.; Amaral, Racκele F.; Salgado, Leonardo T.; Lima, Flavia R.; Farina, Marcos; Viana, Nathan B.; Moura-Neto, Vivaldo; Nussenzveig, H. Moysés

    2013-01-01

    Recent studies indicate that the cell membrane, interacting with its attached cytoskeleton, is an important regulator of cell function, exerting and responding to forces. We investigate this relationship by looking for connections between cell membrane elastic properties, especially surface tension and bending modulus, and cell function. Those properties are measured by pulling tethers from the cell membrane with optical tweezers. Their values are determined for all major cell types of the central nervous system, as well as for macrophage. Astrocytes and glioblastoma cells, which are considerably more dynamic than neurons, have substantially larger surface tensions. Resting microglia, which continually scan their environment through motility and protrusions, have the highest elastic constants, with values similar to those for resting macrophage. For both microglia and macrophage, we find a sharp softening of bending modulus between their resting and activated forms, which is very advantageous for their acquisition of phagocytic functions upon activation. We also determine the elastic constants of pure cell membrane, with no attached cytoskeleton. For all cell types, the presence of F-actin within tethers, contrary to conventional wisdom, is confirmed. Our findings suggest the existence of a close connection between membrane elastic constants and cell function. PMID:23844071

  17. Enzymatically active ultrathin pepsin membranes.

    PubMed

    Raaijmakers, Michiel J T; Schmidt, Thomas; Barth, Monika; Tutus, Murat; Benes, Nieck E; Wessling, Matthias

    2015-05-11

    Enzymatically active proteins enable efficient and specific cleavage reactions of peptide bonds. Covalent coupling of the enzymes permits immobilization, which in turn reduces autolysis-induced deactivation. Ultrathin pepsin membranes were prepared by facile interfacial polycondensation of pepsin and trimesoyl chloride. The pepsin membrane allows for simultaneous enzymatic conversion and selective removal of digestion products. The large water fluxes through the membrane expedite the transport of large molecules through the pepsin layers. The presented method enables the large-scale production of ultrathin, cross-linked, enzymatically active membranes. PMID:25779668

  18. Versatile Membrane Deformation Potential of Activated Pacsin

    PubMed Central

    Byrnes, Laura J.; Sondermann, Holger

    2012-01-01

    Endocytosis is a fundamental process in signaling and membrane trafficking. The formation of vesicles at the plasma membrane is mediated by the G protein dynamin that catalyzes the final fission step, the actin cytoskeleton, and proteins that sense or induce membrane curvature. One such protein, the F-BAR domain-containing protein pacsin, contributes to this process and has been shown to induce a spectrum of membrane morphologies, including tubules and tube constrictions in vitro. Full-length pacsin isoform 1 (pacsin-1) has reduced activity compared to its isolated F-BAR domain, implicating an inhibitory role for its C-terminal Src homology 3 (SH3) domain. Here we show that the autoinhibitory, intramolecular interactions in pacsin-1 can be released upon binding to the entire proline-rich domain (PRD) of dynamin-1, resulting in potent membrane deformation activity that is distinct from the isolated F-BAR domain. Most strikingly, we observe the generation of small, homogenous vesicles with the activated protein complex under certain experimental conditions. In addition, liposomes prepared with different methods yield distinct membrane deformation morphologies of BAR domain proteins and apparent activation barriers to pacsin-1's activity. Theoretical free energy calculations suggest bimodality of the protein-membrane system as a possible source for the different outcomes, which could account for the coexistence of energetically equivalent membrane structures induced by BAR domain-containing proteins in vitro. Taken together, our results suggest a versatile role for pacsin-1 in sculpting cellular membranes that is likely dependent both on protein structure and membrane properties. PMID:23236520

  19. Ligand-Dependent Conformations and Dynamics of the Serotonin 5-HT2A Receptor Determine Its Activation and Membrane-Driven Oligomerization Properties

    PubMed Central

    Shan, Jufang; Khelashvili, George; Mondal, Sayan; Mehler, Ernest L.; Weinstein, Harel

    2012-01-01

    From computational simulations of a serotonin 2A receptor (5-HT2AR) model complexed with pharmacologically and structurally diverse ligands we identify different conformational states and dynamics adopted by the receptor bound to the full agonist 5-HT, the partial agonist LSD, and the inverse agonist Ketanserin. The results from the unbiased all-atom molecular dynamics (MD) simulations show that the three ligands affect differently the known GPCR activation elements including the toggle switch at W6.48, the changes in the ionic lock between E6.30 and R3.50 of the DRY motif in TM3, and the dynamics of the NPxxY motif in TM7. The computational results uncover a sequence of steps connecting these experimentally-identified elements of GPCR activation. The differences among the properties of the receptor molecule interacting with the ligands correlate with their distinct pharmacological properties. Combining these results with quantitative analysis of membrane deformation obtained with our new method (Mondal et al, Biophysical Journal 2011), we show that distinct conformational rearrangements produced by the three ligands also elicit different responses in the surrounding membrane. The differential reorganization of the receptor environment is reflected in (i)-the involvement of cholesterol in the activation of the 5-HT2AR, and (ii)-different extents and patterns of membrane deformations. These findings are discussed in the context of their likely functional consequences and a predicted mechanism of ligand-specific GPCR oligomerization. PMID:22532793

  20. Proline transport across the intestinal microvillus membrane may be regulated by membrane physical properties.

    PubMed

    Sadowski, D C; Gibbs, D J; Meddings, J B

    1992-03-23

    There is now abundant evidence that integral membrane protein function may be modulated by the physical properties of membrane lipids. The intestinal brush border membrane represents a membrane system highly specialized for nutrient absorption and, thus, provides an opportunity to study the interaction between integral membrane transport proteins and their lipid environment. We have previously demonstrated that alterations in this environment may modulate the function of the sodium-dependent glucose transporter in terms of its affinity for glucose. In this communication we report that membrane lipid-protein interactions are distinctly different for the proline transport proteins. Maximal transport rates for L-proline by either the neutral brush border or imino transport systems are reduced 10-fold when the surrounding membrane environment is made more fluid over the physiological range that exists along the crypt-villus axis. Furthermore, in microvillus membrane vesicles prepared from enterocytes isolated from along the crypt-villus axis a similar gradient exists in the functional activity of these transport systems. This would imply that either the functional activity of these transporters are regulated by membrane physical properties or that the synthesis and insertion of these proteins is coordinated in concert with membrane physical properties as the enterocyte migrates up the crypt-villus axis. PMID:1567897

  1. A comparison of the physical, chemical, and biological properties of sludges from a complete-mix activated sludge reactor and a submerged membrane bioreactor.

    PubMed

    Merlo, Rion P; Trussell, R Shane; Hermanowicz, Slawomir W; Jenkins, David

    2007-03-01

    The properties of sludges from a pilot-scale submerged membrane bioreactor (SMBR) and two bench-scale complete-mix, activated sludge (CMAS) reactors treating municipal primary effluent were determined. Compared with the CMAS sludges, the SMBR sludge contained a higher amount of soluble microbial products (SMP) and colloidal material attributed to the use of a membrane for solid-liquid separation; a higher amount nocardioform bacteria, resulting from efficient foam trapping; and a lower amount of extracellular polymeric substances (EPS), possibly because there was no selective pressure for the sludge to settle. High aeration rates in both the CMAS and SMBR reactors produced sludges with higher numbers of smaller particles. Normalized capillary suction time values for the SMBR sludge were lower than for the CMAS sludges, possibly because of its lower EPS content. PMID:17469664

  2. Membrane optical activity: some facts and fallacies.

    PubMed

    Wallach, D F; Low, D A; Bertland, A V

    1973-11-01

    The circular dichroism of hypothetical, water-filled, spherical shells, 75-3500 nm in radius, with walls 7.5 nm thick, composed of poly(L-lysine) in various conformational proportions, and suspended in water, were computed from the known optical properties of this polypeptide by classical general light-scattering theory (Mie theory). Comparison of the computed curves of circular dichroism spectra with those of diverse membranes reveals large discrepancies below 215 nm and shows that light scattering does not adequately account for the optical activity of membranes containing appreciable proportions of nonhelical conformation. However, turbidity effects can explain the anomalies of membrane optical rotatory dispersion near 233 nm, if not uniquely so. We conclude that the optical activity of neither most soluble proteins nor membrane proteins can provide accurate conformational information when synthetic polypeptides are used as standards and list the reasons for this argument. We also show that present techniques to "correct" membrane optical activity are likely to produce additional artifact. PMID:4522300

  3. Thermodynamic properties of purple membrane.

    PubMed Central

    Marque, J; Eisenstein, L; Gratton, E; Sturtevant, J M; Hardy, C J

    1984-01-01

    We measured the density, expansivity, specific heat at constant pressure, and sound velocity of suspensions of purple membrane from Halobacterium halobium and their constituent buffers. From these quantities we calculated the apparent values for the density, expansivity, adiabatic compressibility, isothermal compressibility, specific heat at constant pressure, and specific heat at constant volume for the purple membrane. These results are discussed with respect to previously reported measurements on globular proteins and lipids. Our data suggest a simple additive model in which the protein and lipid molecules expand and compress independently of each other. However, this simple model seems to fail to describe the specific heat data. Our compressibility data suggest that bacteriorhodopsin in native purple membrane binds less water than many globular proteins in neutral aqueous solution, a finding consistent with the lipid surround of bacteriorhodopsin in purple membrane. PMID:6498271

  4. Mechano-capacitive properties of polarized membranes.

    PubMed

    Mosgaard, Lars D; Zecchi, Karis A; Heimburg, Thomas

    2015-10-28

    Biological membranes are capacitors that can be charged by applying a field across the membrane. The charges on the capacitor exert a force on the membrane that leads to electrostriction, i.e. a thinning of the membrane. Since the force is quadratic in voltage, negative and positive voltage have an identical influence on the physics of symmetric membranes. However, this is not the case for a membrane with an asymmetry leading to a permanent electric polarization. Positive and negative voltages of identical magnitude lead to different properties. Such an asymmetry can originate from a lipid composition that is different on the two monolayers of the membrane, or from membrane curvature. The latter effect is called 'flexoelectricity'. As a consequence of permanent polarization, the membrane capacitor is discharged at a voltage different from zero. This leads to interesting electrical phenomena such as outward or inward rectification of membrane permeability. Here, we introduce a generalized theoretical framework, that treats capacitance, polarization, flexoelectricity, piezoelectricity and thermoelectricity in the same language. We show applications to electrostriction, membrane permeability and piezoelectricity and thermoelectricity close to melting transitions, where such effects are especially pronounced. PMID:26324950

  5. Properties and performance of EUVL pellicle membranes

    NASA Astrophysics Data System (ADS)

    Gallagher, Emily E.; Vanpaemel, Johannes; Pollentier, Ivan; Zahedmanesh, Houman; Adelmann, Christoph; Huyghebaert, Cedric; Jonckheere, Rik; Lee, Jae Uk

    2015-10-01

    EUV mask protection during handling and exposure remains a challenge for high volume manufacturing using EUV scanners. A thin, transparent membrane can be mounted above the mask pattern so that any particle that falls onto the front of the mask is held out of focus and does not image. The fluoropolymer membranes that are compatible with 193nm lithography absorb too strongly at the 13.5nm EUV exposure wavelength to be considered. Initially, the industry planned to expose EUV masks without any pellicle; however, the time and cost of fabricating and qualifying an EUV mask is simply too high to risk decimating wafer yield each time a particle falls onto the mask pattern. Despite the challenges of identifying a membrane for EUV, the industry has returned to the pellicle concept for protection. EUVL pellicles have been in development for more than a decade and reasonable options exist. Meeting all pellicle requirements is difficult, so this type of risk-mitigation effort is needed to ensure that there is a viable high-volume manufacturing option. This paper first reviews the desired membrane properties for EUVL pellicles. Next, candidate materials are introduced based on reported properties and compatibility with fabrication. Finally a set of candidate membranes are fabricated. These membranes are screened using a simplified set of tests to assess their suitability as an EUV pellicle. EUV transmission, film stress, and film durability data are included. The results are presented along with general guidelines for pellicle membrane properties for EUV manufacturing.

  6. Ceramic ultrafiltration membranes with photocatalytic properties

    NASA Astrophysics Data System (ADS)

    Bell, Deborah Wildman

    The photocatalytic properties of ceramic ultrafilters have been utilized in the development of a novel in-situ membrane cleaning process for ultrafiltration membranes fabricated from titania. The use of the photoactive membrane layer mitigates the effects of foulants in the system, thereby yielding an increase in the observed overall flux without sacrificing rejection of the solute by the membrane. Photocatalytic membranes of titania supported on porous tubes of alpha-alumina were fabricated using sol-gel techniques. These membranes were developed on the basis of the results of two-level factorial experimental designs. Electron microscopy and x-ray spectrometry were employed to evaluate coverage of the support by the membrane, the thickness of the membrane, and the presence of defects in the membrane. The photocatalytic membrane system was characterized to determine both morphological and performance parameters. Morphological parameters included the pore diameters, Darcy coefficients, and the individual resistances associated with each of the porous layers comprising the composite photocatalytic membrane. Performance parameters included the nominal molecular weight cutoff values of the ceramic membranes, the rate of permeation of pure solvent in the presence and the absence of UV illumination through the porous layers of interest, and the ability of the photocatalytic membrane to resist fouling and maintain permselectivity in the presence of UV illumination. The photocatalytic membranes were used to ultrafilter aqueous solutions of polymeric organic foulants present at an initial concentration of 1 x 10-3 M. Formation of a gel layer of foulant on the surface of the membrane was observed in the presence and in the absence of UV radiation; however, the results of permeability experiments indicated that formation of this foulant layer was significantly retarded (by a factor of two) in the presence of UV radiation. Improvement in the flow rate of permeate through the

  7. How Membrane-Active Peptides Get into Lipid Membranes.

    PubMed

    Sani, Marc-Antoine; Separovic, Frances

    2016-06-21

    The structure-function relationship for a family of antimicrobial peptides (AMPs) from the skin of Australian tree frogs is discussed and compared with that of peptide toxins from bee and Australian scorpion venoms. Although these membrane-active peptides induce a similar cellular fate by disrupting the lipid bilayer integrity, their lytic activity is achieved via different modes of action, which are investigated in relation to amino acid sequence, secondary structure, and membrane lipid composition. In order to better understand what structural features govern the interaction between peptides and lipid membranes, cell-penetrating peptides (CPPs), which translocate through the membrane without compromising its integrity, are also discussed. AMPs possess membrane lytic activities that are naturally designed to target the cellular membrane of pathogens or competitors. They are extremely diverse in amino acid composition and often show specificity against a particular strain of microbe. Since our antibiotic arsenal is declining precariously in the face of the rise in multiantibiotic resistance, AMPs increasingly are seen as a promising alternative. In an effort to understand their molecular mechanism, biophysical studies of a myriad of AMPs have been reported, yet no unifying mechanism has emerged, rendering difficult the rational design of drug leads. Similarly, a wide variety of cytotoxic peptides are found in venoms, the best known being melittin, yet again, predicting their activity based on a particular amino acid composition or secondary structure remains elusive. A common feature of these membrane-active peptides is their preference for the lipid environment. Indeed, they are mainly unstructured in solution and, in the presence of lipid membranes, quickly adsorb onto the surface, change their secondary structure, eventually insert into the hydrophobic core of the membrane bilayer, and finally disrupt the bilayer integrity. These steps define the molecular

  8. Fluid transport by active elastic membranes

    NASA Astrophysics Data System (ADS)

    Evans, Arthur A.; Lauga, Eric

    2011-09-01

    A flexible membrane deforming its shape in time can self-propel in a viscous fluid. Alternatively, if the membrane is anchored, its deformation will lead to fluid transport. Past work in this area focused on situations where the deformation kinematics of the membrane were prescribed. Here we consider models where the deformation of the membrane is not prescribed, but instead the membrane is internally forced. Both the time-varying membrane shape and the resulting fluid motion result then from a balance between prescribed internal active stresses, internal passive resistance, and external viscous stresses. We introduce two specific models for such active internal forcing: one where a distribution of active bending moments is prescribed, and one where active inclusions exert normal stresses on the membrane by pumping fluid through it. In each case, we asymptotically calculate the membrane shape and the fluid transport velocities for small forcing amplitudes, and recover our results using scaling analysis.

  9. Nonequilibrium fluctuations, traveling waves, and instabilities in active membranes.

    PubMed

    Ramaswamy, S; Toner, J; Prost, J

    2000-04-10

    The stability of a flexible fluid membrane containing a distribution of mobile, active proteins (e.g., proton pumps) is shown to depend on the structure and functional asymmetry of the proteins. A stable active membrane is in a nonequilibrium steady state with height fluctuations whose statistical properties are governed by the protein activity. Disturbances are predicted to travel as waves at sufficiently long wavelength, with speed set by the normal velocity of the pumps. The unstable case involves a spontaneous, pump-driven undulation of the membrane, with clumping of the proteins in regions of high activity. PMID:11019123

  10. Viscoelastic properties of human tympanic membrane.

    PubMed

    Cheng, Tao; Dai, Chenkai; Gan, Rong Z

    2007-02-01

    The tympanic membrane or eardrum of human ear transfers sound waves into mechanical vibration from the external ear canal into the middle ear and cochlea. Mechanical properties of the tympanic membrane (TM) play an important role in sound transmission through the ear. Although limited resources about linear elastic properties of the TM are available in literature, there is a lack of measurement or modeling of viscoelastic properties of the TM at low stress levels. In this study, the uniaxial tensile, stress relaxation, and failure tests were conducted on fresh human cadaver TM specimens to explore mechanical properties of the TM. The experimental results were analyzed using the hyperelastic Ogden model and digital image correlation method. The constitutive equation and non-linear elastic properties of the TM were presented by functions of the stress and strain at the stress range from 0 to 1 MPa. Viscoelastic properties of the TM were described by the stress relaxation function and hysteresis. The results show that the uniaxial tensile test with the aid of digital image correlation analysis is a reliable and useful approach for measuring mechanical properties of ear tissues. The data presented in this paper contribute to ear biomechanics in both experimental measurement and theoretical analysis of ear tissues. PMID:17160465

  11. Dendrotoxin acceptor from bovine synaptic plasma membranes. Binding properties, purification and subunit composition of a putative constituent of certain voltage-activated K+ channels.

    PubMed Central

    Parcej, D N; Dolly, J O

    1989-01-01

    Dendrotoxin is a snake polypeptide that blocks selectively and potently certain voltage-sensitive, fast-activating K+ channels in the nervous system, where it binds with high affinity to membranous acceptors. Herein, the acceptor protein for dendrotoxin in bovine synaptic membranes is solubilized in active form and its complete purification achieved by affinity chromatography, involving a novel elution procedure. This putative K+-channel constituent is shown to be a large oligomeric glycoprotein containing two major subunits, with Mr values of 75,000 and 37,000. Images Fig. 2. PMID:2930493

  12. Properties of liposomal membranes containing lysolecithin.

    PubMed

    Kitagawa, T; Inoue, K; Nojima, S

    1976-06-01

    Liposomes have been prepared with lysolecithin (1-acyl-sn-3-glycerylphosphorylcholine), egg lecithin (3-sn-phosphatidylcholine), dicetyl phosphate, and cholesterol. The ability to function as a barrier to the diffusion of glucose marker and the sensitivities of the liposomes to hypotonic treatment and other reagents which modified the permeability were examined. Generally, lysolecithin incorporation decreased the effectiveness of the membranes as a barrier to glucose and made the membranes more "osmotically fragile." Cholesterol incorporation counteracted the effect of incorporated lysolecithin. The more cholesterol incorporated into liposomes, the more lysolecthin could be incorporated into the membrane without loss of function as a barrier. With more than 50 mole% of colesterol, lysolecithin alone could form membranes which were practically impermeable to glucose. The hemolytic activity of lysolecithin was affected by mixing with various lecithins or cholesterol. Liposomes containing lysolecithin, which have the ability to trap glucose marker, showed poor hemolytic activity, while lipid micelles with lysolecithin (which could trap little glucose) showed almost the same hemolytic activity as lysolecithin itself. There seems to be a close correlation between hemolytic activity and barrier function of lipid micelles. PMID:986392

  13. A common landscape for membrane-active peptides

    PubMed Central

    Last, Nicholas B; Schlamadinger, Diana E; Miranker, Andrew D

    2013-01-01

    Three families of membrane-active peptides are commonly found in nature and are classified according to their initial apparent activity. Antimicrobial peptides are ancient components of the innate immune system and typically act by disruption of microbial membranes leading to cell death. Amyloid peptides contribute to the pathology of diverse diseases from Alzheimer's to type II diabetes. Preamyloid states of these peptides can act as toxins by binding to and permeabilizing cellular membranes. Cell-penetrating peptides are natural or engineered short sequences that can spontaneously translocate across a membrane. Despite these differences in classification, many similarities in sequence, structure, and activity suggest that peptides from all three classes act through a small, common set of physical principles. Namely, these peptides alter the Brownian properties of phospholipid bilayers, enhancing the sampling of intrinsic fluctuations that include membrane defects. A complete energy landscape for such systems can be described by the innate membrane properties, differential partition, and the associated kinetics of peptides dividing between surface and defect regions of the bilayer. The goal of this review is to argue that the activities of these membrane-active families of peptides simply represent different facets of what is a shared energy landscape. PMID:23649542

  14. Designing Mimics of Membrane Active Proteins

    PubMed Central

    Sgolastra, Federica; deRonde, Brittany M.; Sarapas, Joel M.; Som, Abhigyan; Tew, Gregory N.

    2014-01-01

    CONSPECTUS As a semi-permeable barrier that controls the flux of biomolecules in and out the cell, the plasma membrane is critical in cell function and survival. Many proteins interact with the plasma membrane and modulate its physiology. Within this large landscape of membrane-active molecules, researchers have focused significant attention on two specific classes of peptides, antimicrobial peptides (AMPs) and cell penetrating peptides (CPPs) because of their unique properties. In this account, we describe our efforts over the last decade to build and understand synthetic mimics of antimicrobial peptides (SMAMPs). These endeavors represent one specific example of a much larger effort to understand how synthetic molecules interact with and manipulate the plasma membrane. Using both defined molecular weight oligomers and easier to produce, but heterogeneous, polymers, it has been possible to generate scaffolds with biological potency superior to the natural analogs. In one case, a compound has progressed through a phase II clinical trial for pan)staph infections. Modern biophysical assays highlighted the interplay between the synthetic scaffold and lipid composition leading to negative Gaussian curvature, a requirement for both pore formation and endosomal escape. The complexity of this interplay between lipids, bilayer components, and the scaffolds remains to be better resolved, but significant new insight has been provided. It is worthwhile to consider the various aspects of permeation and how these are related to ‘pore formation.’ More recently, our efforts have expanded toward protein transduction domains, or cell penetrating peptide, mimics. The combination of unique molecular scaffolds and guanidinium) rich side chains has produced an array of polymers with robust transduction (and delivery) activity. Being a new area, the fundamental interactions between these new scaffolds and the plasma membrane are just beginning to be understood. Negative Gaussian

  15. Interaction between active ruthenium complex [RuCl3(dppb)(VPy)] and phospholipid Langmuir monolayers: Effects on membrane electrical properties

    NASA Astrophysics Data System (ADS)

    Sandrino, B.; Wrobel, E. C.; Nobre, T. M.; Caseli, L.; Lazaro, S. R.; Júnior, A. C.; Garcia, J. R.; Oliveira, O. N.; Wohnrath, K.

    2016-04-01

    We report on the interaction between mer-[RuCl3(dppb)(VPy)] (dppb = 1,4-bis(diphenylphosphine)butane and VPy = 4-vinylpyridine) (RuVPy) and dipalmitoyl phosphatidyl serine (DPPS), in Langmuir and Langmuir-Blodgett (LB) films. Interaction of RuVPy with DPPS, which predominates in cancer cell membranes, should be weaker than for other phospholipids since RuVPy is less toxic to cancer cells than to healthy cells. Incorporation of RuVPy induced smaller changes in electrochemical properties of LB films of DPPS than for other phospholipids, but the same did not apply to surface pressure isotherms. This calls for caution in establishing correlations between effects from a single property and phenomena on cell membranes.

  16. Enzyme Activities in Polarized Cell Membranes

    PubMed Central

    Bass, L.; McIlroy, D. K.

    1968-01-01

    The theoretical pH dependence of enzyme activities in membranes of low dielectric constant is estimated. It is shown that in biological membranes some types of enzymes may attain a limiting pH sensitivity such that an increment of only 0.2 pH unit (sufficient to induce action potentials in squid axons) causes a relative activity change of over 25%. The transients of enzyme activity generated by membrane depolarization and by pH increments in the bathing solution are discussed in relation to the transients of nervous excitation. PMID:5641405

  17. Membrane-Binding and Enzymatic Properties of RPE65

    PubMed Central

    Kiser, Philip D.; Palczewski, Krzysztof

    2010-01-01

    Regeneration of visual pigments is essential for sustained visual function. Although the requirement for non-photochemical regeneration of the visual chromophore, 11-cis-retinal, was recognized early on, it was only recently that the trans to cis retinoid isomerase activity required for this process was assigned to a specific protein, a microsomal membrane enzyme called RPE65. In this review, we outline progress that has been made in the functional characterization of RPE65. We then discuss general concepts related to protein-membrane interactions and the mechanism of the retinoid isomerization reaction and describe some of the important biochemical and structural features of RPE65 with respect to its membrane-binding and enzymatic properties. PMID:20304090

  18. Active Nuclear Import of Membrane Proteins Revisited

    PubMed Central

    Laba, Justyna K.; Steen, Anton; Popken, Petra; Chernova, Alina; Poolman, Bert; Veenhoff, Liesbeth M.

    2015-01-01

    It is poorly understood how membrane proteins destined for the inner nuclear membrane pass the crowded environment of the Nuclear Pore Complex (NPC). For the Saccharomyces cerevisiae proteins Src1/Heh1 and Heh2, a transport mechanism was proposed where the transmembrane domains diffuse through the membrane while the extralumenal domains encoding a nuclear localization signal (NLS) and intrinsically disordered linker (L) are accompanied by transport factors and travel through the NPC. Here, we validate the proposed mechanism and explore and discuss alternative interpretations of the data. First, to disprove an interpretation where the membrane proteins become membrane embedded only after nuclear import, we present biochemical and localization data to support that the previously used, as well as newly designed reporter proteins are membrane-embedded irrespective of the presence of the sorting signals, the specific transmembrane domain (multipass or tail anchored), independent of GET, and also under conditions that the proteins are trapped in the NPC. Second, using the recently established size limit for passive diffusion of membrane proteins in yeast, and using an improved assay, we confirm active import of polytopic membrane protein with extralumenal soluble domains larger than those that can pass by diffusion on similar timescales. This reinforces that NLS-L dependent active transport is distinct from passive diffusion. Thirdly, we revisit the proposed route through the center of the NPC and conclude that the previously used trapping assay is, unfortunately, poorly suited to address the route through the NPC, and the route thus remains unresolved. Apart from the uncertainty about the route through the NPC, the data confirm active, transport factor dependent, nuclear transport of membrane-embedded mono- and polytopic membrane proteins in baker’s yeast. PMID:26473931

  19. Active Nuclear Import of Membrane Proteins Revisited.

    PubMed

    Laba, Justyna K; Steen, Anton; Popken, Petra; Chernova, Alina; Poolman, Bert; Veenhoff, Liesbeth M

    2015-01-01

    It is poorly understood how membrane proteins destined for the inner nuclear membrane pass the crowded environment of the Nuclear Pore Complex (NPC). For the Saccharomyces cerevisiae proteins Src1/Heh1 and Heh2, a transport mechanism was proposed where the transmembrane domains diffuse through the membrane while the extralumenal domains encoding a nuclear localization signal (NLS) and intrinsically disordered linker (L) are accompanied by transport factors and travel through the NPC. Here, we validate the proposed mechanism and explore and discuss alternative interpretations of the data. First, to disprove an interpretation where the membrane proteins become membrane embedded only after nuclear import, we present biochemical and localization data to support that the previously used, as well as newly designed reporter proteins are membrane-embedded irrespective of the presence of the sorting signals, the specific transmembrane domain (multipass or tail anchored), independent of GET, and also under conditions that the proteins are trapped in the NPC. Second, using the recently established size limit for passive diffusion of membrane proteins in yeast, and using an improved assay, we confirm active import of polytopic membrane protein with extralumenal soluble domains larger than those that can pass by diffusion on similar timescales. This reinforces that NLS-L dependent active transport is distinct from passive diffusion. Thirdly, we revisit the proposed route through the center of the NPC and conclude that the previously used trapping assay is, unfortunately, poorly suited to address the route through the NPC, and the route thus remains unresolved. Apart from the uncertainty about the route through the NPC, the data confirm active, transport factor dependent, nuclear transport of membrane-embedded mono- and polytopic membrane proteins in baker's yeast. PMID:26473931

  20. Radiation-Grafted Polymer Electrolyte Membranes for Water Electrolysis Cells: Evaluation of Key Membrane Properties.

    PubMed

    Albert, Albert; Barnett, Alejandro O; Thomassen, Magnus S; Schmidt, Thomas J; Gubler, Lorenz

    2015-10-14

    Radiation-grafted membranes can be considered an alternative to perfluorosulfonic acid (PFSA) membranes, such as Nafion, in a solid polymer electrolyte electrolyzer. Styrene, acrylonitrile, and 1,3-diisopropenylbenzene monomers are cografted into preirradiated 50 μm ethylene tetrafluoroethylene (ETFE) base film, followed by sulfonation to introduce proton exchange sites to the obtained grafted films. The incorporation of grafts throughout the thickness is demonstrated by scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX) analysis of the membrane cross-sections. The membranes are analyzed in terms of grafting kinetics, ion-exchange capacity (IEC), and water uptake. The key properties of radiation-grafted membranes and Nafion, such as gas crossover, area resistance, and mechanical properties, are evaluated and compared. The plot of hydrogen crossover versus area resistance of the membranes results in a property map that indicates the target areas for membrane development for electrolyzer applications. Tensile tests are performed to assess the mechanical properties of the membranes. Finally, these three properties are combined to establish a figure of merit, which indicates that radiation-grafted membranes obtained in the present study are promising candidates with properties superior to those of Nafion membranes. A water electrolysis cell test is performed as proof of principle, including a comparison to a commercial membrane electrode assembly (MEA). PMID:26393461

  1. Thioredoxin-like activity of thylakoid membranes

    SciTech Connect

    Ashton, A.R.; Brennan, T.; Anderson, L.E.

    1980-10-01

    The inactivation of pea leaf chloroplast glucose-6-phosphate dehydrogenase by dithiothreitol can be catalyzed by thioredoxin-like molecules that are present in chloroplasts. This thioredoxin activity occurs predominantly as a soluble species, but washed thylakoid membranes also exhibit some thioredoxin-like activity. The membrane-associated thioredoxin can be extracted by treatment with the detergent Triton X-100. The solubilized thioredoxing appears to have a molecular size similar to that of the soluble thioredoxin which catalyzes the same reaction. The thylakoid-bound activity constitutes only about 5% of the total chloroplast thioredoxin activity. The thioredoxin occurring in the membrane fraction cannot, however, be ascribed to the trapping of stroma since less than 0.1% of three stromal marker enzymes are found in the same thylakoid extract.

  2. Organelle morphogenesis by active membrane remodeling

    NASA Astrophysics Data System (ADS)

    Ramakrishnan, N.; Ipsen, John H.; Rao, Madan; Kumar, P. B. Sunil

    Intracellular organelles are subject to a steady flux of lipids and proteins through active, energy consuming transport processes. Active fission and fusion are promoted by GTPases, e.g., Arf-Coatamer and the Rab-Snare complexes, which both sense and generate local membrane curvature. Here we investigate through Dynamical Triangulation Monte Carlo simulations, the role that these active processes play in determining the morphology and compositional segregation in closed membranes. Our results suggest that the ramified morphologies of organelles observed in-vivo are a consequence of driven nonequilibrium processes rather than equilibrium forces.

  3. Monitoring membrane properties and apoptosis using membrane probes of the 3-hydroxyflavone family.

    PubMed

    Darwich, Zeinab; Klymchenko, Andrey S; Mély, Yves

    2014-01-01

    Environment-sensitive fluorescent membrane probes are attractive tools for investigating the membrane properties and their changes under perturbing conditions. Membrane probes of the 3-hydroxyflavone family are of particular interest due to their excited-state intramolecular proton transfer (ESIPT) reaction, which confers a dual emission highly sensitive to the polarity and hydration of the environment. In the present work, we will describe the protocols used with these probes in order to monitor the physicochemical properties of lipid membrane models and cell plasma membranes and to detect apoptosis. PMID:24108636

  4. Active membrane cholesterol as a physiological effector.

    PubMed

    Lange, Yvonne; Steck, Theodore L

    2016-09-01

    Sterols associate preferentially with plasma membrane sphingolipids and saturated phospholipids to form stoichiometric complexes. Cholesterol in molar excess of the capacity of these polar bilayer lipids has a high accessibility and fugacity; we call this fraction active cholesterol. This review first considers how active cholesterol serves as an upstream regulator of cellular sterol homeostasis. The mechanism appears to utilize the redistribution of active cholesterol down its diffusional gradient to the endoplasmic reticulum and mitochondria, where it binds multiple effectors and directs their feedback activity. We have also reviewed a broad literature in search of a role for active cholesterol (as opposed to bulk cholesterol or lipid domains such as rafts) in the activity of diverse membrane proteins. Several systems provide such evidence, implicating, in particular, caveolin-1, various kinds of ABC-type cholesterol transporters, solute transporters, receptors and ion channels. We suggest that this larger role for active cholesterol warrants close attention and can be tested easily. PMID:26874289

  5. Reconstitution of Membrane Proteins into Model Membranes: Seeking Better Ways to Retain Protein Activities

    PubMed Central

    Shen, Hsin-Hui; Lithgow, Trevor; Martin, Lisandra L.

    2013-01-01

    The function of any given biological membrane is determined largely by the specific set of integral membrane proteins embedded in it, and the peripheral membrane proteins attached to the membrane surface. The activity of these proteins, in turn, can be modulated by the phospholipid composition of the membrane. The reconstitution of membrane proteins into a model membrane allows investigation of individual features and activities of a given cell membrane component. However, the activity of membrane proteins is often difficult to sustain following reconstitution, since the composition of the model phospholipid bilayer differs from that of the native cell membrane. This review will discuss the reconstitution of membrane protein activities in four different types of model membrane—monolayers, supported lipid bilayers, liposomes and nanodiscs, comparing their advantages in membrane protein reconstitution. Variation in the surrounding model environments for these four different types of membrane layer can affect the three-dimensional structure of reconstituted proteins and may possibly lead to loss of the proteins activity. We also discuss examples where the same membrane proteins have been successfully reconstituted into two or more model membrane systems with comparison of the observed activity in each system. Understanding of the behavioral changes for proteins in model membrane systems after membrane reconstitution is often a prerequisite to protein research. It is essential to find better solutions for retaining membrane protein activities for measurement and characterization in vitro. PMID:23344058

  6. Active membranes studied by X-ray scattering.

    PubMed

    Giahi, A; El Alaoui Faris, M; Bassereau, P; Salditt, T

    2007-08-01

    In view of recent theories of "active" membranes, we have studied multilamellar phospholipid membrane stacks with reconstituted transmembrane protein bacteriorhodopsin (BR) under different illumination conditions by X-ray scattering. The light-active protein is considered as an active constituent which drives the system out of equilibrium and is predicted to change the collective fluctuation properties of the membranes. Using X-ray reflectivity, X-ray non-specular (diffuse) scattering, and grazing incidence scattering, we find no detectable change in the scattering curves when changing the illumination condition. In particular the intermembrane spacing d remains constant, after eliminating hydration-related artifacts by design of a suitable sample environment. The absence of any observable non-equilibrium effects in the experimental window is discussed in view of the relevant parameters and recent theories. PMID:17712523

  7. Polyvinylidenefluoride/carbon nanotubes mixed matrix membranes with tailored properties

    NASA Astrophysics Data System (ADS)

    Fontananova, Enrica; Grosso, Valentina; Aljlil, Saad A.; Bahattab, Mohammed A.; Vuono, Danilo; Di Profio, Gianluca; Drioli, Enrico

    2016-05-01

    Membrane operations are promising tools for efficient and environmentally friendly separations. However, the development of advanced membranes with tailored properties is a key issue to be addressed in order to better exploit the potentialities of membrane-based separations. An important approach toward this aim is the development of mixed matrix membranes in which an organic and an inorganic phase coexist in order to have synergic effects on membrane properties. The peculiar properties of carbon nanotubes (CNTs) such as high electrical and thermal conductivity, high strength and unique transport properties, has motivated a considerable effort to produce CNT-polymer composites in order to engineer membrane properties. In this work the roughness, wettability, morphology, crystalline phase and pore size of polyvinylidenefluoride (PVDF) membranes were tailored working on the membrane preparation conditions, as well as, by blending the polymer with multiwalled carbon nanotubes (MWCNTs). A study on the effect of concentration of the polymer, use of pore forming additives, type and concentration of MWCNTs (pristine and functionalized), was carried out. The results highlighted interesting relationships between membrane microstructure and composition, as well as, MWCNTs distribution, on transport and wettability properties, in the perspectives of a more efficient application of PVDF membranes in liquid phase separations.

  8. Influence of water and membrane microstructure on the transport properties of proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Siu, Ana Rosa

    Proton transport in proton exchange membranes (PEMs) depends on interaction between water and acid groups covalently bound to the polymer. Although the presence of water is important in maintaining the PEM's functions, a thorough understanding of this topic is still lacking. The objective of this work is to provide a better understanding of how the nature water, confined to ionic domains of the polymer, influences the membrane's ability to transport protons, methanol and water. Understanding this topic will facilitate development of new materials with favorable transport properties for fuel cells use. Five classes of polymer membranes were used in this work: polyacrylonitrile-graft-poly(styrenesulfonic) acid (PAN-g-macPSSA); poly(vinylidene difluoride) irradiation-graft-poly(styrenesulfonic) acid (PVDF-g-PSSA); poly(ethylenetetrafluoroethylene) irradiation-graft-poly(styrenesulfonic) acid (ETFE-gPSSA); PVDF-g-PSSA with hydroxyethylmethacrylate (HEMA); and perfluorosulfonic acid membrane (Nafion). The nature of water within the polymers (freezable versus non-freezable states) was measured by systematically freezing samples, and observing the temperature at which water freezes and the amount of heat released in the process. Freezing water-swollen membranes resulted in a 4-fold decrease in the proton conductivity of the PEM. Activation energies of proton transport before and after freezing were ˜ 0.15 eV and 0.5 eV, consistent with proton transport through liquid water and bound water, respectively. Reducing the content of water in membrane samples decreased the amount of freezable and non-freezable water. Calorimetric measurements of membranes in various degrees of hydration showed that water molecules became non-freezable when lambda, (water molecules per sulfonic acid group) was less than ˜14. Proton conduction through membranes containing only non-freezable water was demonstrated to be feasible. Diffusion experiments showed that the permeability of methanol

  9. Membrane has high urea-rejection properties

    NASA Technical Reports Server (NTRS)

    Johnson, C. C.; Wydeven, T.

    1977-01-01

    Membranes are synthesized from ethylene and nitrogen in RF plasma at low power, gas-flow rates, and pressure. Ethylene and nitrogen are used because flow rate and partial pressure of each gas can be independently controlled to produce optimum conditions for synthesizing membrane. Membrane is particularly useful in recycling and purifying water.

  10. Process for restoring membrane permeation properties

    DOEpatents

    Pinnau, Ingo; Toy, Lora G.; Casillas, Carlos G.

    1997-05-20

    A process for restoring the selectivity of high-flee-volume, glassy polymer membranes for condensable components over less-condensable components or non-condensable components of a gas mixture. The process involves exposing the membrane to suitable sorbent vapor, such as propane or butane, thereby reopening the microvoids that make up the free volume. The selectivity of an aged membrane may be restored to 70-100% of its original value. The selectivity of a membrane which is known to age over time can also be maintained by keeping the membrane in a vapor environment when it is not in use.

  11. Process for restoring membrane permeation properties

    DOEpatents

    Pinnau, I.; Toy, L.G.; Casillas, C.G.

    1997-05-20

    A process is described for restoring the selectivity of high-free-volume, glassy polymer membranes for condensable components over less-condensable components or non-condensable components of a gas mixture. The process involves exposing the membrane to suitable sorbent vapor, such as propane or butane, thereby reopening the microvoids that make up the free volume. The selectivity of an aged membrane may be restored to 70--100% of its original value. The selectivity of a membrane which is known to age over time can also be maintained by keeping the membrane in a vapor environment when it is not in use. 8 figs.

  12. High flux and antifouling properties of negatively charged membrane for dyeing wastewater treatment by membrane distillation.

    PubMed

    An, Alicia Kyoungjin; Guo, Jiaxin; Jeong, Sanghyun; Lee, Eui-Jong; Tabatabai, S Assiyeh Alizadeh; Leiknes, TorOve

    2016-10-15

    This study investigated the applicability of membrane distillation (MD) to treat dyeing wastewater discharged by the textile industry. Four different dyes containing methylene blue (MB), crystal violet (CV), acid red 18 (AR18), and acid yellow 36 (AY36) were tested. Two types of hydrophobic membranes made of polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) were used. The membranes were characterized by testing against each dye (foulant-foulant) and the membrane-dye (membrane-foulant) interfacial interactions and their mechanisms were identified. The MD membranes possessed negative charges, which facilitated the treatment of acid and azo dyes of the same charge and showed higher fluxes. In addition, PTFE membrane reduced the wettability with higher hydrophobicity of the membrane surface. The PTFE membrane evidenced especially its resistant to dye absorption, as its strong negative charge and chemical structure caused a flake-like (loose) dye-dye structure to form on the membrane surface rather than in the membrane pores. This also enabled the recovery of flux and membrane properties by water flushing (WF), thereby direct-contact MD with PTFE membrane treating 100 mg/L of dye mixtures showed stable flux and superior color removal during five days operation. Thus, MD shows a potential for stable long-term operation in conjunction with a simple membrane cleaning process, and its suitability in dyeing wastewater treatment. PMID:27486044

  13. Improved antifouling properties of polyamide nanofiltration membranes by reducing the density of surface carboxyl groups.

    PubMed

    Mo, Yinghui; Tiraferri, Alberto; Yip, Ngai Yin; Adout, Atar; Huang, Xia; Elimelech, Menachem

    2012-12-18

    Carboxyls are inherent functional groups of thin-film composite polyamide nanofiltration (NF) membranes, which may play a role in membrane performance and fouling. Their surface presence is attributed to incomplete reaction of acyl chloride monomers during the membrane active layer synthesis by interfacial polymerization. In order to unravel the effect of carboxyl group density on organic fouling, NF membranes were fabricated by reacting piperazine (PIP) with either isophthaloyl chloride (IPC) or the more commonly used trimesoyl chloride (TMC). Fouling experiments were conducted with alginate as a model hydrophilic organic foulant in a solution, simulating the composition of municipal secondary effluent. Improved antifouling properties were observed for the IPC membrane, which exhibited lower flux decline (40%) and significantly greater fouling reversibility or cleaning efficiency (74%) than the TMC membrane (51% flux decline and 40% cleaning efficiency). Surface characterization revealed that there was a substantial difference in the density of surface carboxyl groups between the IPC and TMC membranes, while other surface properties were comparable. The role of carboxyl groups was elucidated by measurements of foulant-surface intermolecular forces by atomic force microscopy, which showed lower adhesion forces and rupture distances for the IPC membrane compared to TMC membranes in the presence of calcium ions in solution. Our results demonstrated that a decrease in surface carboxyl group density of polyamide membranes fabricated with IPC monomers can prevent calcium bridging with alginate and, thus, improve membrane antifouling properties. PMID:23205860

  14. Effect of Hydroperoxides on Red Blood Cell Membrane Mechanical Properties

    PubMed Central

    Hale, John P.; Winlove, C. Peter; Petrov, Peter G.

    2011-01-01

    We investigate the effect of oxidative stress on red blood cell membrane mechanical properties in vitro using detailed analysis of the membrane thermal fluctuation spectrum. Two different oxidants, the cytosol-soluble hydrogen peroxide and the membrane-soluble cumene hydroperoxide, are used, and their effects on the membrane bending elastic modulus, surface tension, strength of confinement due to the membrane skeleton, and 2D shear elastic modulus are measured. We find that both oxidants alter significantly the membrane elastic properties, but their effects differ qualitatively and quantitatively. While hydrogen peroxide mainly affects the elasticity of the membrane protein skeleton (increasing the membrane shear modulus), cumene hydroperoxide has an impact on both membrane skeleton and lipid bilayer mechanical properties, as can be seen from the increased values of the shear and bending elastic moduli. The biologically important implication of these results is that the effects of oxidative stress on the biophysical properties, and hence the physiological functions, of the cell membrane depend on the nature of the oxidative agent. Thermal fluctuation spectroscopy provides a means of characterizing these different effects, potentially in a clinical milieu. PMID:22004746

  15. Supported phospholipid/alkanethiol biomimetic membranes: insulating properties.

    PubMed Central

    Plant, A L; Gueguetchkeri, M; Yap, W

    1994-01-01

    A novel model lipid bilayer membrane is prepared by the addition of phospholipid vesicles to alkanethiol monolayers on gold. This supported hybrid bilayer membrane is rugged, easily and reproducibly prepared in the absence of organic solvent, and is stable for very long periods of time. We have characterized the insulating characteristics of this membrane by examining the rate of electron transfer and by impedance spectroscopy. Supported hybrid bilayers formed from phospholipids and alkanethiols are pinhole-free and demonstrate measured values of conductivity and resistivity which are within an order of magnitude of that reported for black lipid membranes. Capacitance values suggest a dielectric constant of 2.7 for phospholipid membranes in the absence of organic solvent. The protein toxin, melittin, destroys the insulating capability of the phospholipid layer without significantly altering the bilayer structure. This model membrane will allow the assessment of the effect of lipid membrane perturbants on the insulating properties of natural lipid membranes. PMID:7811924

  16. Activation of Membrane Cholesterol by 63 Amphipaths†

    PubMed Central

    Lange, Yvonne; Ye, Jin; Duban, Mark-Eugene; Steck, Theodore L.

    2009-01-01

    A few membrane-intercalating amphipaths have been observed to stimulate the interaction of cholesterol with cholesterol oxidase, saponin and cyclodextrin, presumably by displacing cholesterol laterally from its phospholipid complexes. We now report that this effect, referred to as cholesterol activation, occurs with dozens of other amphipaths, including alkanols, saturated and cis- and trans-unsaturated fatty acids, fatty acid methyl esters, sphingosine derivatives, terpenes, alkyl ethers, ketones, aromatics and cyclic alkyl derivatives. The apparent potency of the agents tested ranged from 3 μM to 7 mM and generally paralleled their octanol/water partition coefficients, except that relative potency declined for compounds with> 10 carbons. Some small amphipaths activated cholesterol at a membrane concentration of ~3 moles per 100 moles bilayer lipids, about equimolar with the cholesterol they displaced. Lysophosphatidylserine countered the effects of all these agents, consistent with its ability to reduce the pool of active membrane cholesterol. Various amphipaths stabilized red cells against the hemolysis elicited by cholesterol depletion, presumably by substituting for the extracted sterol. The number and location of cis and trans fatty acid unsaturations and the absolute stereochemistry of enantiomer pairs had only small effects on amphipath potency. Nevertheless, potency varied ~7-fold within a group of diverse agents with similar partition coefficients. We infer that a wide variety of amphipaths can displace membrane cholesterol by competing stoichiometrically but with only limited specificity for its weak association with phospholipids. Any number of other drugs and experimental agents might do the same. PMID:19655814

  17. Membrane activity of biomimetic facially amphiphilic antibiotics.

    PubMed

    Arnt, Lachelle; Rennie, Jason R; Linser, Sebastian; Willumeit, Regine; Tew, Gregory N

    2006-03-01

    Membranes are a central feature of all biological systems, and their ability to control many cellular processes is critically important. As a result, a better understanding of how molecules bind to and select between biological membranes is an active area of research. Antimicrobial host defense peptides are known to be membrane-active and, in many cases, exhibit discrimination between prokaryotic and eukaryotic cells. The design of synthetic molecules that capture the biological activity of these natural peptides has been shown. In this report, the interaction between our biomimetic structures and different biological membranes is reported using both model vesicle and in vitro bacterial cell experiments. Compound 1 induces 12% leakage at 20 microg/mL against phosphatidylglycerol (PG)-phosphatidylethanolamine (PE) vesicles vs only 3% leakage at 200 microg/mL against phosphatidyl-L-serine (PS)-phosphatidylcholine (PC) vesicles. Similarly, a 40% reduction in fluorescence is measured in lipid movement experiments for PG-PE compared to 10% for PS-PC at 600 s. A 30 degrees C increase in the phase transition of stearoyl-oleoyl-phosphatidylserine is observed in the presence of 1. These results show that lipid composition is more important for selectivity than overall net charge. Additionally, the overall concentration of a given lipid is another important factor. An effort is made to connect model vesicle studies with in vitro data and naturally occurring lipid compositions. PMID:16494408

  18. The properties of an ion selective enzymatic asymmetric synthetic membrane.

    NASA Technical Reports Server (NTRS)

    Mitz, M. A.

    1971-01-01

    With the aid of a simple model membrane system, the properties of cellulose enzymes and of membrane selectivity and pump-like action are considered. The model is based on materials possibly present on a primitive earth, as well as on a membrane able to sort or concentrate these materials. An overview of the model membrane system is presented in terms of how it is constructed, what its properties are, and what to expect in performance characteristics. The model system is shown to be useful for studying the selective and in some cases accelerated transfer of nutrients and metabolites.

  19. Relating rejection of trace organic contaminants to membrane properties in forward osmosis: measurements, modelling and implications.

    PubMed

    Xie, Ming; Nghiem, Long D; Price, William E; Elimelech, Menachem

    2014-02-01

    This study elucidates the relationship between membrane properties and the rejection of trace organic contaminants (TrOCs) in forward osmosis (FO). An asymmetric cellulose triacetate (CTA) and a thin-film composite (TFC) polyamide FO membrane were used for this investigation. The effective average pore radius (rp), selective barrier thickness over porosity parameter (l/ε), surface charge, support layer structural parameter (S), pure water permeability coefficient (A) and salt (NaCl) permeability coefficient (B) of the two membranes were systematically characterised. Results show that measured rejection of TrOCs as a function of permeate water flux can be well described by the pore hindrance transport model. This observation represents the first successful application of this model, which was developed for pressure-driven nanofiltration, to an osmotically-driven membrane process. The rejection of charged TrOCs by the CTA and TFC membranes was high and was governed by both electrostatic repulsion and steric hindrance. The TFC membrane exhibited higher rejection of neutral TrOCs with low molecular weight than the CTA membrane, although the estimated pore size of the TFC membrane (0.42 nm) was slightly larger than that of the CTA membrane (0.37 nm). This higher rejection of neutral TrOCs by the TFC membrane is likely attributed to its active layer properties, namely a more effective active layer structure, as indicated by a larger l/ε parameter, and pore hydration induced by the negative surface charge. PMID:24345822

  20. Ionic transport properties of template-synthesized gold nanotube membranes

    NASA Astrophysics Data System (ADS)

    Gao, Peng

    Ionic transport in nanotubes exhibits unique properties due to the strong interactions between ions and the nanotube surface. The main objective of my research is to explore and regulate the ionic transport in gold nanotube membranes. Chapter 1 overviews a versatile method of fabricating nanostructured materials, called the template synthesis. Important parameters of the template synthesis are introduced such as templates and deposition methods. The template synthesis method is used to prepare membranes used in this dissertation. Chapter 2 describes a method to increase the ionic conductivity in membranes containing gold nanotubes with small diameter (4 nm). The gold nanotube membrane is prepared by the electroless plating of gold in a commercially available polycarbonate membrane. Voltages are applied to the gold nanotube membrane and fixed charges are injected on the gold nanotube walls. We show that ionic conductivity of the gold nanotube membrane can be enhanced in aqueous potassium chloride (KCl) solution at negative applied voltages. When the most negative voltage (-0.8 V vs. Ag/AgCl) is applied to the membrane, the ionic conductivity of the solution inside the gold nanotube (94 mS.cm-1) is comparable to that of 1 M aqueous KCl, over two orders of magnitude higher than that of the 0.01 M KCl contacting the membrane. Chapter 3 explores another important transport property of the gold nanotube membrane -- ion permselectivity. When the permselective membrane separates two electrolyte solutions at different concentrations, a membrane potential is developed and measured by the potentiometric method. Surface charge density and the ion mobilities are estimated by fitting the experimental data with a pre-existing model. The surface charge density of the gold nanotube membrane in this research is estimated to be 2 muC/cm2. Chapter 4 describes voltage-controlled ionic transport in a gold/polypyrrole membrane doped with sodium dodecylbenzene sulfonate (DBS). Polypyrrole

  1. Calcium Modulation of Plant Plasma Membrane-Bound Atpase Activities

    NASA Technical Reports Server (NTRS)

    Caldwell, C.

    1983-01-01

    The kinetic properties of barley enzyme are discussed and compared with those of other plants. Possibilities for calcium transport in the plasma membrane by proton pump and ATPase-dependent calcium pumps are explored. Topics covered include the ph phase of the enzyme; high affinity of barley for calcium; temperature dependence, activation enthalpy, and the types of ATPase catalytic sites. Attention is given to lipids which are both screened and bound by calcium. Studies show that barley has a calmodulin activated ATPase that is found in the presence of magnesium and calcium.

  2. Properties of Plasma Membrane from Pea Root Seedlings under Altered Gravity

    NASA Astrophysics Data System (ADS)

    Klymchuk, D.; Baranenko, V.; Vorobyova, T. V.; Kurylenko, I.; Chyzhykova, O.; Dubovoy, V.

    In this study, the properties of pea (Pisum sativum L.) plasma membrane were examined to determine how the membrane structure and functions are regulated in response to clinorotation (2 rev/min) conditions. Membrane preparations enriched by plasma membrane vesicles were obtained by aqueous two-phase partitioning from 6-day seedling roots. The specific characteristics of H^+-ATPase, lípid composition and peroxidation intensity as well as fluidity of lipid bilayer were analysed. ATP hydrolytic activity was inhibited by ortovanadate and was insensitive to aside and nitrate in sealed plasma membrane vesicles isolated from both clinorotated and control seedlings. Plasma membrane vesicles from clinorotated seedlings in comparison to controls were characterised by increase in the total lipid/protein ratio, ATP hydrolytic activity and intensifying of lipid peroxidation. Sitosterol and campesterol were the predominant free sterol species. Clinorotated seedlings contained a slightly higher level of unsaturated fatty acid than controls. Plasma membrane vesicles were labelled with pyrene and fluorescence originating from monomeric (I_M) molecules and excimeric (I_E) aggregates were measured. The calculated I_E/I_M values were higher in clinorotated seedlings compared with controls reflecting the reduction in membrane microviscosity. The involvement of the changes in plasma membrane lipid content and composition, fluidity and H^+-ATPase activity in response of pea seedlings to altered gravity is discussed.

  3. O-(carboxymethyl)-chitosan nanofiltration membrane surface functionalized with graphene oxide nanosheets for enhanced desalting properties.

    PubMed

    Wang, Jiali; Gao, Xueli; Wang, Jian; Wei, Yi; Li, Zhaokui; Gao, Congjie

    2015-02-25

    A novel O-(carboxymethyl)-chitosan (OCMC) nanofiltration (NF) membrane is developed via surface functionalization with graphene oxide (GO) nanosheets to enhance desalting properties. Using ring-opening polymerization between epoxy groups of GO nanosheets and amino groups of OCMC active layer, GO nanosheets are irreversibly bound to the membrane. The OCMC NF membranes surface-functionalized with GO nanosheets are characterized by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, contact angle analyzer, and zeta potential analyzer. The membranes exhibit not only higher permeability but also better salt rejections than the pristine membranes and the commercial NF membranes; besides, the desalting properties are enhanced with the concentration of GO nanosheets increasing. Furthermore, the transport mechanism of GO-OCMC NF membranes reveals that the nanoporous structure of GO-OCMC functional layer and size exclusion and electrostatic repulsion of water nanochannels formed by GO nanosheets lead to the membranes possessing enhanced desalting properties. PMID:25635511

  4. Structured microparticles with tailored properties produced by membrane emulsification.

    PubMed

    Vladisavljević, Goran T

    2015-11-01

    This paper provides an overview of membrane emulsification routes for fabrication of structured microparticles with tailored properties for specific applications. Direct (bottom-up) and premix (top-down) membrane emulsification processes are discussed including operational, formulation and membrane factors that control the droplet size and droplet generation regimes. A special emphasis was put on different methods of controlled shear generation on membrane surface, such as cross flow on the membrane surface, swirl flow, forward and backward flow pulsations in the continuous phase and membrane oscillations and rotations. Droplets produced by membrane emulsification can be used for synthesis of particles with versatile morphology (solid and hollow, matrix and core/shell, spherical and non-spherical, porous and coherent, composite and homogeneous), which can be surface functionalised and coated or loaded with macromolecules, nanoparticles, quantum dots, drugs, phase change materials and high molecular weight gases to achieve controlled/targeted drug release and impart special optical, chemical, electrical, acoustic, thermal and magnetic properties. The template emulsions including metal-in-oil, solid-in-oil-in-water, oil-in-oil, multilayer, and Pickering emulsions can be produced with high encapsulation efficiency of encapsulated materials and narrow size distribution and transformed into structured particles using a variety of solidification processes, such as polymerisation (suspension, mini-emulsion, interfacial and in-situ), ionic gelation, chemical crosslinking, melt solidification, internal phase separation, layer-by-layer electrostatic deposition, particle self-assembly, complex coacervation, spray drying, sol-gel processing, and molecular imprinting. Particles fabricated from droplets produced by membrane emulsification include nanoclusters, colloidosomes, carbon aerogel particles, nanoshells, polymeric (molecularly imprinted, hypercrosslinked, Janus and core

  5. Reverse osmosis membrane of high urea rejection properties. [water purification

    NASA Technical Reports Server (NTRS)

    Johnson, C. C.; Wydeven, T. J. (Inventor)

    1980-01-01

    Polymeric membranes suitable for use in reverse osmosis water purification because of their high urea and salt rejection properties are prepared by generating a plasma of an unsaturated hydrocarbon monomer and nitrogen gas from an electrical source. A polymeric membrane is formed by depositing a polymer of the unsaturated monomer from the plasma onto a substrate, so that nitrogen from the nitrogen gas is incorporated within the polymer in a chemically combined form.

  6. Effect of defoliant (butiphose) on morpho-physiological properties and enzyme systems of natural membranes.

    PubMed

    Mirakhmedov, A K; Ochilov, K R; Sagatova, G A; Khan, M Z; Khole, V

    1989-03-01

    Butiphose (Tributyltritiophosphate, (C4H9S)3PO) a commonly used defoliant in cotton growing regions of USSR, caused extensive alterations in morphological features of erythrocyte and nuclear membranes and affected the permeability properties of rat liver mitochondrial membrane. It disrupted Ca2+ transport system and other energy dependent processes in mitochondria. A reduction in the activity of cytochrome-c-oxidase and NAD.H-oxidase was also observed. PMID:2606532

  7. Mechanical and water sorption properties of nafion and composite nafion/titanium dioxide membranes for polymer electrolyte membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Satterfield, May Barclay

    The mechanical properties of the membranes used in polymer electrolyte membrane fuel cells are important to the performance and longevity of the cell. The speed and extent of membrane water uptake depend on the membrane's viscoelastic mechanical properties, which are themselves dependent on membrane hydration, and increased hydration improves membrane proton conductivity and fuel cell performance. Membrane mechanical properties also affect durability and cell longevity, preventing membrane failure from stresses induced by changing temperature and water content during operational cycling. Further, membrane creep and stress-relaxation can change the extent of membrane/electrode contact, also changing cell behavior. New composite membrane materials have exhibited superior performance in fuel cells, and it is suspected that improved mechanical properties are responsible. Studies of polymer electrolyte membrane (PEM) fuel cell dynamics using Nafion membranes have demonstrated the importance of membrane mechanical properties, swelling and water-absorption behavior to cell performance. Nonlinear and delayed dynamic responses to changing operating parameters were unexpected, but reminiscent of polymer viscoelastic behavior and water sorption dynamics, illustrating the need to better understand membrane properties to design and operate fuel cells. Further, Nafion/TiO2 composite membranes developed by the Princeton Chemistry Department improve fuel cell performance, which may be due to changes in membrane microstructure and enhanced mechanical properties. Mechanical properties, stress-relaxation behavior, water sorption and desorption rates and pressures exerted during hydration by a confined membrane have been measured for Nafion and for Nafion/TiO2 composite membranes. Mechanical properties, including the Young's modulus and limits of elastic deformation are dependent on temperature and membrane water content. The Young's modulus decreases with increasing water content and

  8. Antiviral activity of squalamine: Role of electrostatic membrane binding

    NASA Astrophysics Data System (ADS)

    Beckerman, Bernard; Qu, Wei; Mishra, Abhijit; Zasloff, Michael; Wong, Gerard; Luijten, Erik

    2012-02-01

    Recent workootnotetextM. Zasloff et al., Proc. Nat. Acad. Sci. (USA) 108, 15978 (2011). has demonstrated that squalamine, a molecule found in the liver of sharks, exhibits broad-spectrum antiviral properties. It has been proposed that this activity results from the charge-density matching of squalamine and phospholipid membranes, causing squalamine to bind to membranes and displace proteins such as Rac1 that are crucial for the viral replication cycle. Here we investigate this hypothesis by numerical simulation of a coarse-grained model for the competition between Rac1 and squalamine in binding affinity to a flat lipid bilayer. We perform free-energy calculations to test the ability of squalamine to condense stacked bilayer systems and thereby displace bulkier Rac1 molecules. We directly compare our findings to small-angle x-ray scattering results for the same setup.

  9. Alterations in the activities of hepatic plasma-membrane and microsomal enzymes during liver regeneration.

    PubMed Central

    Deliconstantinos, G; Ramantanis, G

    1983-01-01

    A marked increase in the activities of rat liver plasma-membrane (Na+ + K+)-stimulated ATPase and microsomal Ca2+-stimulated ATPase was observed 18h after partial hepatectomy. Lipid analyses for both membrane preparations reveal that in partially hepatectomized rats the cholesterol and sphingomyelin content are decreased with a subsequent decrease in the cholesterol/phospholipid molar ratio compared with those of sham-operated animals. Changes in the allosteric properties of plasma-membrane (Na+ + K+)-stimulated ATPase by F- (as reflected by changes in the Hill coefficient) indicated a fluidization of the lipid bilayer of both membrane preparations in 18 h-regenerating liver. The amphipathic dodecyl glucoside incorporated into the hepatic plasma membranes evoked a marked increase in the (Na+ + K+)-stimulated ATPase and 5'-nucleotidase activities. The lack of effect of the glucoside on the Lubrol-PX-solubilized 5'-nucleotidase indicates that changes in the activities of the membrane-bound enzymes caused by the glucoside are due to modulation of the membrane fluidity. Dodecyl glucoside appears to increase the membrane fluidity, evaluated through changes in the Hill coefficient for plasma-membrane (Na+ + K+)-stimulated ATPase. The biological significance of these data is discussed in terms of the differences and changes in the interaction of membrane-bound enzymes with membrane lipids during liver regeneration. PMID:6309144

  10. Membrane perturbing properties of sucrose polyesters.

    PubMed

    McManus, G G; Buchanan, G W; Jarrell, H C; Epand, R M; Epand, R F; Cheetham, J J

    2001-02-01

    Sucrose polyester (SPE), in the form of sucrose octaesters and sucrose hexaesters of palmitic (16:0), stearic (18:0), oleic (18:1cis), and linoleic (18:2cis) acids, have many uses. Applications include: a non-caloric fat substitute, detoxification agent, and oral contrast agent for human abdominal (MRI) magnetic resonance imaging. However, it has been shown that the ingestion of SPE was shown to generate a depletion of physiologically important lipidic vitamins and other lipophilic molecules. In order to better understand, at the molecular level, the type of interaction between SPE and lipid membrane, we have, first synthesized different type of labelled and non-labelled SPEs. Secondly, we have studied the effect of SPEs on multilamellar dispersions of dielaidoylphosphatidylethanolamine (DEPE) and dipalmitoylphosphocholine (DPPC) as a function of temperature, SPE composition and concentration. The effects of SPEs were studied by differential scanning calorimetry (DSC), X-ray diffraction, 2H and 31P NMR spectroscopy. At low concentration (< 1 mol%) all of the SPEs lowered the bilayer to the inverted hexagonal phase transition temperature of DEPE and induced the formation of a cubic phase in a composition dependent manner. At the same low concentration, SPEs in DPPC induce the formation of a non-bilayer phase as seen by 31P NMR. Order parameter measurements of DPPC-d62/SPE mixtures show that the SPE effect on the DPPC monolayer thickness is dependent on the SPE, concentration, chains length and saturation level. At higher concentration (> or = 10 mol%) SPE are very potent DEPE bilayer to HII phase transition promoters, although at that concentration the SPE have lost the ability to form cubic phases. SPEs have profound effects on the phase behaviour of model membrane systems, and may be important to consider when developing current and potential industrial and medical applications. PMID:11269937

  11. Water uptake, ionic conductivity and swelling properties of anion-exchange membrane

    SciTech Connect

    Duan, QJ; Ge, SH; Wang, CY

    2013-12-01

    Water uptake, ionic conductivity and dimensional change of the anion-exchange membrane made by Tokuyama Corporation (A201 membrane) are investigated at different temperatures and water activities. Specifically, the amount of water taken up by membranes exposed to water vapor and membranes soaked in liquid water is determined. The water uptake of the A201 membrane increases with water content as well as temperature. In addition, water sorption data shows Schroeder's paradox for the AEMs investigated. The swelling properties of the A201 membrane exhibit improved dimensional stability compared with Nafion membrane. Water sorption of the A201 membrane occurs with a substantial negative excess volume of mixing. The threshold value of hydrophilic fraction in the A201 membrane for ionic conductivity is around 0.34, above which, the conductivity begins to rise quickly. This indicates that a change in the connectivity of the hydrophilic domains occurs when hydrophilic fraction approaches 0.34. (C) 2013 Elsevier B.V. All rights reserved.

  12. Membrane protein properties revealed through data-rich electrostatics calculations

    PubMed Central

    Guerriero, Christopher J.; Brodsky, Jeffrey L.; Grabe, Michael

    2015-01-01

    SUMMARY The electrostatic properties of membrane proteins often reveal many of their key biophysical characteristics, such as ion channel selectivity and the stability of charged membrane-spanning segments. The Poisson-Boltzmann (PB) equation is the gold standard for calculating protein electrostatics, and the software APBSmem enables the solution of the PB equation in the presence of a membrane. Here, we describe significant advances to APBSmem including: full automation of system setup, per-residue energy decomposition, incorporation of PDB2PQR, calculation of membrane induced pKa shifts, calculation of non-polar energies, and command-line scripting for large scale calculations. We highlight these new features with calculations carried out on a number of membrane proteins, including the recently solved structure of the ion channel TRPV1 and a large survey of 1,614 membrane proteins of known structure. This survey provides a comprehensive list of residues with large electrostatic penalties for being embedded in the membrane potentially revealing interesting functional information. PMID:26118532

  13. Structure and physical properties of biomembranes and model membranes

    NASA Astrophysics Data System (ADS)

    Hianik, T.

    2006-12-01

    Biomembranes belong to the most important structures of the cell and the cell organels. They play not only structural role of the barrier separating the external and internal part of the membrane but contain also various functional molecules, like receptors, ionic channels, carriers and enzymes. The cell membrane also preserves non-equillibrium state in a cell which is crucial for maintaining its excitability and other signaling functions. The growing interest to the biomembranes is also due to their unique physical properties. From physical point of view the biomembranes, that are composed of lipid bilayer into which are incorporated integral proteins and on their surface are anchored peripheral proteins and polysaccharides, represent liquid scrystal of smectic type. The biomembranes are characterized by anisotropy of structural and physical properties. The complex structure of biomembranes makes the study of their physical properties rather difficult. Therefore several model systems that mimic the structure of biomembranes were developed. Among them the lipid monolayers at an air-water interphase, bilayer lipid membranes (BLM), supported bilayer lipid membranes (sBLM) and liposomes are most known. This work is focused on the introduction into the "physical word" of the biomembranes and their models. After introduction to the membrane structure and the history of its establishment, the physical properties of the biomembranes and their models areare stepwise presented. The most focus is on the properties of lipid monolayers, BLM, sBLM and liposomes that were most detailed studied. This contribution has tutorial character that may be usefull for undergraduate and graduate students in the area of biophysics, biochemistry, molecular biology and bioengineering, however it contains also original work of the author and his co-worker and PhD students, that may be usefull also for specialists working in the field of biomembranes and model membranes.

  14. Gender differences in alcohol-induced oxidative stress and altered membrane properties in erythrocytes of rats.

    PubMed

    Reddy, Kindinti Rameshwar; Reddy, Vaddi Damodara; Padmavathi, Pannuru; Kavitha, Godugu; Saradamma, Bulle; Varadacharyulu, N C

    2013-02-01

    Alcohol-induced oxidative stress leads to imbalance between reactive oxygen species (ROS) and the antioxidant defense system, resulting in oxidative damage to membrane components such as lipids and proteins, ultimately altering membrane properties. In this study, we assessed oxidative stress status and alterations in erythrocyte membrane properties in alcohol-administered rats with respect to gender difference. Alcohol (20% v/v) administered rats of both genders showed significant changes in plasma lipid profile with elevated nitrite/nitrate levels. Furthermore, alcohol-administration significantly decreased erythrocyte antioxidant enzymes and enhanced erythrocyte membrane lipid peroxidation, cholesterol/phospholipid (C/P) ratio and Na+/K(+)-ATPase activity in both males and females. Besides, anisotropic studies revealed that alcohol-administration significantly decreased erythrocyte membrane fluidity. In conclusion, alcohol-administration significantly increased oxidative stress by decreasing antioxidant status, and subsequent generation of ROS altered membrane properties by altering fluidity and Na+/K(+)-ATPase activity. Female rats were more vulnerable to alcohol-induced biochemical and biophysical changes in plasma and erythrocyte including oxidative stress than male rats. PMID:23617072

  15. Effect of membrane tension on the physical properties of DOPC lipid bilayer membrane

    PubMed Central

    Reddy, A. Srinivas; Warshaviak, Dora Toledo; Chachisvilis, Mirianas

    2013-01-01

    Molecular dynamics simulations of a dioleoylphosphocholine (DOPC) lipid bilayer were performed to explore its mechanosensitivity. Variations in the bilayer properties, such as area per lipid, volume, thickness, hydration depth (HD), hydration thickness (HT), lateral diffusion coefficient, and changes in lipid structural order were computed in the membrane tension range 0 to 15 dyn/cm. We determined that an increase in membrane tension results in a decrease in the bilayer thickness and HD of ∼5% and ∼5.7% respectively, whereas area per lipid, volume, and HT/HD increased by 6.8%, 2.4%, and 5% respectively. The changes in lipid conformation and orientation were characterized using orientational (S2) and deuterium (SCD) order parameters. Upon increase of membrane tension both order parameters indicated an increase in lipid disorder by 10– 20%, mostly in the tail end region of the hydrophobic chains. The effect of membrane tension on lipid lateral diffusion in the DOPC bilayer was analyzed on three different time scales corresponding to inertial motion, anomalous diffusion and normal diffusion. The results showed that lateral diffusion of lipid molecules is anomalous in nature due to the non-exponential distribution of waiting times. The anomalous and normal diffusion coefficients increased by 20% and 52% when the membrane tension changed from 0 to 15 dyn/cm, respectively. In conclusion, our studies showed that membrane tension causes relatively significant changes in the area per lipid, volume, polarity, membrane thickness, and fluidity of the membrane suggesting multiple mechanisms by which mechanical perturbation of the membrane could trigger mechanosensitive response in cells. PMID:22588133

  16. Plant pentacyclic triterpenic acids as modulators of lipid membrane physical properties.

    PubMed

    Prades, Jesús; Vögler, Oliver; Alemany, Regina; Gomez-Florit, Manuel; Funari, Sérgio S; Ruiz-Gutiérrez, Valentina; Barceló, Francisca

    2011-03-01

    Free triterpenic acids (TTPs) present in plants are bioactive compounds exhibiting multiple nutriceutical activities. The underlying molecular mechanisms have only been examined in part and mainly focused on anti-inflammatory properties, cancer and cardiovascular diseases, in all of which TTPs frequently affect membrane-related proteins. Based on the structural characteristics of TTPs, we assume that their effect on biophysical properties of cell membranes could play a role for their biological activity. In this context, our study is focused on the compounds, oleanolic (3β-hydroxy-12-oleanen-28-oic acid, OLA), maslinic (2α,3β-dihydroxy-12-oleanen-28-oic acid, MSL) and ursolic ((3β)-3-hydroxyurs-12-en-28-oic acid, URL) as the most important TTPs present in orujo olive oil. X-ray diffraction, differential scanning calorimetry, (31)P nuclear magnetic resonance and Laurdan fluorescence data provide experimental evidence that OLA, MSL and URL altered the structural properties of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and DPPC-Cholesterol (Cho) rich membranes, being located into the polar-hydrophobic interphase. Specifically, in DPPC membranes, TTPs altered the structural order of the L(β'), phase without destabilizing the lipid bilayer. The existence of a nonbilayer isotropic phase in coexistence with the liquid crystalline L(α) phase, as observed in DPPC:URL samples, indicated the presence of lipid structures with high curvature (probably inverted micelles). In DPPC:Cho membranes, TTPs affected the membrane phase properties increasing the Laurdan GP values above 40°C. MSL and URL induced segregation of Cho within the bilayer, in contrast to OLA, that reduced the structural organization of the membrane. These results strengthen the relevance of TTP interactions with cell membranes as a molecular mechanism underlying their broad spectrum of biological effects. PMID:21167812

  17. Detecting Extracellular Carbonic Anhydrase Activity Using Membrane Inlet Mass Spectrometry

    PubMed Central

    Delacruz, Joannalyn; Mikulski, Rose; Tu, Chingkuang; Li, Ying; Wang, Hai; Shiverick, Kathleen T.; Frost, Susan C.; Horenstein, Nicole A.; Silverman, David N.

    2010-01-01

    Current research into the function of carbonic anhydrases in cell physiology emphasizes the role of membrane-bound carbonic anhydrases, such as carbonic anhydrase IX that has been identified in malignant tumors and is associated with extracellular acidification as a response to hypoxia. We present here a mass spectrometric method to determine the extent to which total carbonic anhydrase activity is due to extracellular carbonic anhydrase in whole cell preparations. The method is based on the biphasic rate of depletion of 18O from CO2 measured by membrane inlet mass spectrometry. The slopes of the biphasic depletion are a sensitive measure of the presence of carbonic anhydrase outside and inside of the cells. This property is demonstrated here using suspensions of human red cells in which external carbonic anhydrase was added to the suspending solution. It is also applied to breast and prostate cancer cells which both express exofacial carbonic anhydrase IX. Inhibition of external carbonic anhydrase is achieved by use of a membrane impermeant inhibitor that was synthesized for this purpose, p-aminomethylbenzenesulfonamide attached to a polyethyleneglycol polymer. PMID:20417171

  18. Improving the Performance and Antifouling Properties of Thin-Film Composite Membranes for Water Separation Technologies

    NASA Astrophysics Data System (ADS)

    Tiraferri, Alberto

    Membrane-based water separation processes utilize semi-permeable membranes to retain dissolved solids and contaminants. Deployment of these technologies for desalination and wastewater reuse has the potential to sustainably increase the supply of potable, agricultural, and industrial water. Despite considerable development of semi-permeable membranes in the last decades, several design obstacles hampering their progress have yet to be overcome. Specifically, major membrane improvements are currently sought with respect to their performance and productivity, as well as their resistance to fouling. This dissertation research aims at the advancement of semi-permeable membranes by rational optimization of their design to: (i) understand and improve their transport properties and (ii) reduce fouling by organic molecules and delay biofouling by microorganisms. In particular, thin-film composite polyamide membranes for both reverse osmosis and forward osmosis processes are the main target of the investigation. The structural and physicochemical properties of thin-film composite membranes are both characterized and tailored through implementation of original techniques and novel functionalization protocols. The membrane structure and morphology are rationally modified to enhance the mass transport within the support layer. The influence of fabrication conditions on support layer formation and on its final structure is elucidated. The intricate interrelationship among the performance of the different layers of the composite membrane is highlighted and a new protocol is developed to characterize the transport properties of membranes deployed in forward osmosis processes. Novel approaches to impart targeted properties to the active surface of thin-film composite membranes are also proposed. The functionalization is achieved by exploiting the inherent moieties of the polyamide layer to irreversibly bind nanomaterials with desired properties. An experimental method to determine

  19. Water permeation through Nafion membranes: the role of water activity.

    PubMed

    Majsztrik, Paul; Bocarsly, Andrew; Benziger, Jay

    2008-12-25

    The permeation of water through 1100 equivalent weight Nation membranes has been measured for film thicknesses of 51-254 microm, temperatures of 30-80 degrees C, and water activities (a(w)) from 0.3 to 1 (liquid water). Water permeation coefficients increased with water content in Nafion. For feed side water activity in the range 0 < a(w) < 0.8, permeation coefficients increased linearly with water activity and scaled inversely with membrane thickness. The permeation coefficients were independent of membrane thickness when the feed side of the membrane was in contact with liquid water (a(w) = 1). The permeation coefficient for a 127 microm thick membrane increased by a factor of 10 between contacting the feed side of the membrane to water vapor (a(w) = 0.9) compared to liquid water (a(w) = 1). Water permeation couples interfacial transport across the fluid membrane interface with water transport through the hydrophilic phase of Nafion. At low water activity the hydrophilic volume fraction is small and permeation is limited by water diffusion. The volume fraction of the hydrophilic phase increases with water activity, increasing water transport. As a(w) --> 1, the effective transport rate increased by almost an order of magnitude, resulting in a change of the limiting transport resistance from water permeation across the membrane to interfacial mass transport at the gas/membrane interface. PMID:19053672

  20. Influences of acid-base property of membrane on interfacial interactions related with membrane fouling in a membrane bioreactor based on thermodynamic assessment.

    PubMed

    Zhao, Leihong; Qu, Xiaolu; Zhang, Meijia; Lin, Hongjun; Zhou, Xiaoling; Liao, Bao-Qiang; Mei, Rongwu; Hong, Huachang

    2016-08-01

    Failure of membrane hydrophobicity in predicting membrane fouling requires a more reliable indicator. In this study, influences of membrane acid base (AB) property on interfacial interactions in two different interaction scenarios in a submerged membrane bioreactor (MBR) were studied according to thermodynamic approaches. It was found that both the polyvinylidene fluoride (PVDF) membrane and foulant samples in the MBR had relatively high electron donor (γ(-)) component and low electron acceptor (γ(+)) component. For both of interaction scenarios, AB interaction was the major component of the total interaction. The results showed that, the total interaction monotonically decreased with membrane γ(-), while was marginally affected by membrane γ(+), suggesting that γ(-) could act as a reliable indicator for membrane fouling prediction. This study suggested that membrane modification for fouling mitigation should orient to improving membrane surface γ(-) component rather than hydrophilicity. PMID:27155263

  1. How Lipid Membranes Affect Pore Forming Toxin Activity.

    PubMed

    Rojko, Nejc; Anderluh, Gregor

    2015-12-15

    Pore forming toxins (PFTs) evolved to permeate the plasma membrane of target cells. This is achieved in a multistep mechanism that usually involves binding of soluble protein monomer to the lipid membrane, oligomerization at the plane of the membrane, and insertion of part of the polypeptide chain across the lipid membrane to form a conductive channel. Introduced pores allow uncontrolled transport of solutes across the membrane, inflicting damage to the target cell. PFTs are usually studied from the perspective of structure-function relationships, often neglecting the important role of the bulk membrane properties on the PFT mechanism of action. In this Account, we discuss how membrane lateral heterogeneity, thickness, and fluidity influence the pore forming process of PFTs. In general, lipid molecules are more accessible for binding in fluid membranes due to steric reasons. When PFT specifically binds ordered domains, it usually recognizes a specific lipid distribution pattern, like sphingomyelin (SM) clusters or SM/cholesterol complexes, and not individual lipid species. Lipid domains were also suggested to act as an additional concentration platform facilitating PFT oligomerization, but this is yet to be shown. The last stage in PFT action is the insertion of the transmembrane segment across the membranes to build the transmembrane pore walls. Conformational changes are a spontaneous process, and sufficient free energy has to be available for efficient membrane penetration. Therefore, fluid bilayers are permeabilized more readily in comparison to highly ordered and thicker liquid ordered lipid phase (Lo). Energetically more costly insertion into the Lo phase can be driven by the hydrophobic mismatch between the thinner liquid disordered phase (Ld) and large protein complexes, which are unable to tilt like single transmembrane segments. In the case of proteolipid pores, membrane properties can directly modulate pore size, stability, and even selectivity. Finally

  2. The Structural Basis of Cholesterol Activity in Membranes

    SciTech Connect

    Olsen, Brett N.; Bielska, Agata; Lee, Tiffany; Daily, Michael D.; Covey, Douglas F.; Schlesinger, Paul H.; Baker, Nathan A.; Ory, Daniel S.

    2013-10-15

    Although the majority of free cellular cholesterol is present in the plasma membrane, cholesterol homeostasis is principally regulated through sterol-sensing proteins that reside in the cholesterol-poor endoplasmic reticulum (ER). In response to acute cholesterol loading or depletion, there is rapid equilibration between the ER and plasma membrane cholesterol pools, suggesting a biophysical model in which the availability of plasma membrane cholesterol for trafficking to internal membranes modulates ER membrane behavior. Previous studies have predominantly examined cholesterol availability in terms of binding to extramembrane acceptors, but have provided limited insight into the structural changes underlying cholesterol activation. In this study, we use both molecular dynamics simulations and experimental membrane systems to examine the behavior of cholesterol in membrane bilayers. We find that cholesterol depth within the bilayer provides a reasonable structural metric for cholesterol availability and that this is correlated with cholesterol-acceptor binding. Further, the distribution of cholesterol availability in our simulations is continuous rather than divided into distinct available and unavailable pools. This data provide support for a revised cholesterol activation model in which activation is driven not by saturation of membrane-cholesterol interactions but rather by bulk membrane remodeling that reduces membrane-cholesterol affinity.

  3. Recent trends in the tuning of polymersomes' membrane properties.

    PubMed

    Le Meins, J-F; Sandre, O; Lecommandoux, S

    2011-02-01

    "Polymersomes" are vesicular structures made from the self-assembly of block copolymers. Such structures present outstanding interest for different applications such as micro- or nano-reactor, drug release or can simply be used as tool for understanding basic biological mechanisms. The use of polymersomes in such applications is strongly related to the way their membrane properties are controlled and tuned either by a precise molecular design of the constituting block or by addition of specific components inside the membrane (formulation approaches). Typical membrane properties of polymersomes obtained from the self-assembly of "coil coil" block copolymer since the end of the nineties will be first briefly reviewed and compared to those of their lipidic analogues, named liposomes. Therefore the different approaches able to modulate their permeability, mechanical properties or ability to release loaded drugs, using macromolecular engineering or formulations, are detailed. To conclude, the most recent advances to modulate the polymersomes' properties and systems that appear very promising especially for biomedical application or for the development of complex and bio-mimetic structures are presented. PMID:21337017

  4. Development of active-transport membrane devices

    SciTech Connect

    Laciak, D.V.

    1994-07-01

    This report introduces the concept of Air Products` AT membranes for the separation of NH{sub 3} and CO{sub 2} from process gas streams and presents results from the first year fabrication concept development studies.

  5. Polymer electrolyte membranes from fluorinated polyisoprene-block-sulfonated polystyrene: Membrane structure and transport properties

    SciTech Connect

    Sodeye, Akinbode; Huang, Tianzi; Gido, Samuel; Mays, Jimmy

    2011-01-01

    With a view to optimizing morphology and ultimately properties, membranes have been cast from relatively inexpensive block copolymer ionomers of fluorinated polyisoprene-block-sulfonated polystyrene (FISS) with various sulfonation levels, in both the acid form and the cesium neutralized form. The morphology of these membranes was characterized by transmission electron microscopy and ultra-small angle X-ray scattering, as well as water uptake, proton conductivity and methanol permeability within the temperature range from 20 to 60 C. Random phase separated morphologies were obtained for all samples except the cesium sample with 50 mol% sulfonation. The transport properties increased with increasing degree of sulfonation and temperature for all samples. The acid form samples absorbed more water than the cesium samples with a maximum swelling of 595% recorded at 60 C for the acid sample having 50 mol% sulfonation. Methanol permeability for the latter sample was more than an order of magnitude less than for Nafion 112 but so was the proton conductivity within the plane of the membrane at 20 C. Across the plane of the membrane this sample had half the conductivity of Nafion 112 at 60 C.

  6. Active membrane having uniform physico-chemically functionalized ion channels

    DOEpatents

    Gerald, II, Rex E; Ruscic, Katarina J; Sears, Devin N; Smith, Luis J; Klingler, Robert J; Rathke, Jerome W

    2012-09-24

    The present invention relates to a physicochemically-active porous membrane for electrochemical cells that purports dual functions: an electronic insulator (separator) and a unidirectional ion-transporter (electrolyte). The electrochemical cell membrane is activated for the transport of ions by contiguous ion coordination sites on the interior two-dimensional surfaces of the trans-membrane unidirectional pores. One dimension of the pore surface has a macroscopic length (1 nm-1000 .mu.m) and is directed parallel to the direction of an electric field, which is produced between the cathode and the anode electrodes of an electrochemical cell. The membrane material is designed to have physicochemical interaction with ions. Control of the extent of the interactions between the ions and the interior pore walls of the membrane and other materials, chemicals, or structures contained within the pores provides adjustability of the ionic conductivity of the membrane.

  7. Characterization of antibacterial polyethersulfone membranes using the Respiration Activity Monitoring System (RAMOS).

    PubMed

    Kochan, Jozef; Scheidle, Marco; van Erkel, Joost; Bikel, Matías; Büchs, Jochen; Wong, John Erik; Melin, Thomas; Wessling, Matthias

    2012-10-15

    Membranes with antibacterial properties were developed using surface modification of polyethersulfone ultrafiltration membranes. Three different modification strategies using polyelectrolyte layer-by-layer (LbL) technique are described. The first strategy relying on the intrinsic antibacterial properties of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(ethylenimine) (PEI) exhibits only little antibacterial effects. The other two strategies contain silver in both ionic (Ag(+)) and metallic (Ag(0)) form. Ag(+) embedded into negatively charged poly(sodium 4-styrene sulfonate) (PSS) layers totally inhibits bacterial growth. Ag(0) nanoparticles were introduced to the membrane surface by LbL deposition of chitosan- and poly(methacrylic acid) - sodium salt (PMA)-capped silver nanoparticles and subsequent UV or heat treatment. Antibacterial properties of the modified membranes were quantified by a new method based on the Respiration Activity Monitoring System (RAMOS), whereby the oxygen transfer rates (OTR) of E. coli K12 cultures on the membranes were monitored online. As opposed to colony forming counting method RAMOS yields more quantitative and reliable data on the antibacterial effect of membrane modification. Ag-imprinted polyelectrolyte film composed of chitosan (Ag(0))/PMA(Ag(0))/chitosan(Ag(0)) was found to be the most promising among the tested membranes. Further investigation revealed that the concentration and equal distribution of silver in the membrane surface plays an important role in bacterial growth inhibition. PMID:22884245

  8. Membrane stretching triggers mechanosensitive Ca2+ channel activation in Chara.

    PubMed

    Kaneko, Toshiyuki; Takahashi, Naoya; Kikuyama, Munehiro

    2009-03-01

    In order to confirm that mechanosensitive Ca(2+) channels are activated by membrane stretching, we stretched or compressed the plasma membrane of Chara by applying osmotic shrinkage or swelling of the cell by varying the osmotic potential of the bathing medium. Aequorin studies revealed that treatments causing membrane stretching induced a transient but large increase in cytoplasmic concentration of Ca(2+) (Delta[Ca(2+)](c)). However, the observed Delta[Ca(2+)](c) decreased during the treatments, resulting in membrane compression. A second experiment was carried out to study the relationship between changes in membrane potential (DeltaE(m)) and stretching or compression of the plasma membrane. Significant DeltaE(m) values, often accompanied by an action potential, were observed during the initial exchange of the bathing medium from a hypotonic medium to a hypertonic one (plasmolysis). DeltaE(m) appears to be triggered by a partial stretching of the membrane as it was peeled from the cell wall. After plasmolysis, other exchanges from hypertonic to hypotonic media, with their accompanying membrane stretching, always induced large DeltaE(m) values and were often accompanied by an action potential. By contrast, action potentials were scarcely observed during other exchanges from hypotonic to hypertonic solutions (=membrane compression). Thus, we concluded that activation of the mechanosensitive channels is triggered by membrane stretching in Chara. PMID:19234734

  9. Lachesana tarabaevi, an expert in membrane-active toxins.

    PubMed

    Kuzmenkov, Alexey I; Sachkova, Maria Y; Kovalchuk, Sergey I; Grishin, Eugene V; Vassilevski, Alexander A

    2016-08-15

    In the present study, we show that venom of the ant spider Lachesana tarabaevi is unique in terms of molecular composition and toxicity. Whereas venom of most spiders studied is rich in disulfide-containing neurotoxic peptides, L. tarabaevi relies on the production of linear (no disulfide bridges) cytolytic polypeptides. We performed full-scale peptidomic examination of L. tarabaevi venom supported by cDNA library analysis. As a result, we identified several dozen components, and a majority (∼80% of total venom protein) exhibited membrane-active properties. In total, 33 membrane-interacting polypeptides (length of 18-79 amino acid residues) comprise five major groups: repetitive polypeptide elements (Rpe), latarcins (Ltc), met-lysines (MLys), cyto-insectotoxins (CIT) and latartoxins (LtTx). Rpe are short (18 residues) amphiphilic molecules that are encoded by the same genes as antimicrobial peptides Ltc 4a and 4b. Isolation of Rpe confirms the validity of the iPQM (inverted processing quadruplet motif) proposed to mark the cleavage sites in spider toxin precursors that are processed into several mature chains. MLys (51 residues) present 'idealized' amphiphilicity when modelled in a helical wheel projection with sharply demarcated sectors of hydrophobic, cationic and anionic residues. Four families of CIT (61-79 residues) are the primary weapon of the spider, accounting for its venom toxicity. Toxins from the CIT 1 and 2 families have a modular structure consisting of two shorter Ltc-like peptides. We demonstrate that in CIT 1a, these two parts act in synergy when they are covalently linked. This finding supports the assumption that CIT have evolved through the joining of two shorter membrane-active peptides into one larger molecule. PMID:27287558

  10. Preparation of polysaccharide loaded collagen membrane with anti-oxidative activity.

    PubMed

    Shu, Zibin; Ding, Shengli; He, Xiaohong; Dai, Xuemei; Xiao, Qian; Yang, Min; Leng, Xue; Ma, Yanshun; Yang, Hua

    2015-01-01

    The scavenging activity of polysaccharides from Lycium barbarum, Lentinus edodes and Ganoderma Lucidum Karst to DPPH free radicals was investigated. It was found that among the three polysaccharides, Lycium barbarum polysaccharides (LBP) exhibits the best scavenging activity. Polysaccharide loaded collagen membranes were prepared by mixing LBP with collagen, starch, glycerol, sodium carboxymethyl cellulose and glutaraldehyde. In vitro drug release from membranes was evaluated. With increasing the immersion time, the release rate first increases and then slows down. Meanwhile, the scavenging activity to DPPH radicals exhibits similar variation, in agreement with a good release effect of the membrane. The optimal formulation of collagen membrane and preparation parameters were obtained considering the overall properties and the scavenging activity to radicals. PMID:26406078

  11. Modification of polyethylene terephthalate track membrane properties by ammonia plasma

    NASA Astrophysics Data System (ADS)

    Kravets, Lyubov; Dmitriev, Serguei; Dinescu, George; Lazea, Andrada; Raiciu, Eric

    2004-09-01

    The properties of polyethylene terephthalate track membranes (PET TM) exposed to ammonia are investigated. The influence of the conditions of plasma treatment on the basic characteristics of the membranes, namely pore size and shape, wettability, water permeability, is studied. PET TM of the thickness of 10 μ m with the effective pore diameter of 0.215 μ m (pore density 2\\cdot 10^8 cm-2) were under study. The plasma treatment was performed on a plasma-chemical installation realizing a RF-discharge on the frequency 13.56 MHz. The process was conducted in a dynamic mode. Before delivering vapours of the plasma forming gas, the chamber was beforehand vacuumed down to residual pressure of 10-2 Torr. One side of the membranes was subjected to plasma. The discharge parameters (gas pressure in the vacuum chamber, discharge power) and the duration of plasma action were varied. It has been figured out that when treating the membranes in plasma of the explored gas there are two competing processes: etching of a polymeric matrix and deposition of a polymeric layer on their surface. It has been shown that at a short time of plasma action and low values of the discharge parameters, an etching process is mainly observed. Decrease in the thickness of the membranes and increase in the effective pore diameter testifies it. A result of the gas-discharge etching is also a hydrophilization of the TM surface stipulated by formation of polar function groups in the points of breaking chemical bonds. Here the value of the water contact angle of surface decreases down to 45-50 degrees in some cases. It has been shown that at a longer action of the plasma and increase of the discharge parameters, as accumulation in the chamber of etch products takes place, a process of deposition of a polymeric film becomes dominating, and it is proved by increasing the width of the membranes and changing their color. The value of the water contact angle of surface in this case is grown and, depending

  12. Functional Implications of Plasma Membrane Condensation for T Cell Activation

    PubMed Central

    Quinn, Carmel M.; Engelhardt, Karin; Williamson, David; Grewal, Thomas; Jessup, Wendy; Harder, Thomas; Gaus, Katharina

    2008-01-01

    The T lymphocyte plasma membrane condenses at the site of activation but the functional significance of this receptor-mediated membrane reorganization is not yet known. Here we demonstrate that membrane condensation at the T cell activation sites can be inhibited by incorporation of the oxysterol 7-ketocholesterol (7KC), which is known to prevent the formation of raft-like liquid-ordered domains in model membranes. We enriched T cells with 7KC, or cholesterol as control, to assess the importance of membrane condensation for T cell activation. Upon 7KC treatment, T cell antigen receptor (TCR) triggered calcium fluxes and early tyrosine phosphorylation events appear unaltered. However, signaling complexes form less efficiently on the cell surface, fewer phosphorylated signaling proteins are retained in the plasma membrane and actin restructuring at activation sites is impaired in 7KC-enriched cells resulting in compromised downstream activation responses. Our data emphasizes lipids as an important medium for the organization at T cell activation sites and strongly indicates that membrane condensation is an important element of the T cell activation process. PMID:18509459

  13. Molecular Details of Membrane Fluidity Changes during Apoptosis and Relationship to Phospholipase A2 Activity

    PubMed Central

    Gibbons, Elizabeth; Pickett, Katalyn R.; Streeter, Michael C.; Warcup, Ashley O.; Nelson, Jennifer; Judd, Allan M.; Bell, John D.

    2012-01-01

    Summary Secretory phospholipase A2 exhibits much greater activity toward apoptotic versus healthy cells. Various plasma membrane changes responsible for this phenomenon have been proposed, including biophysical alterations described as “membrane fluidity” and “order.” Understanding of these membrane perturbations was refined by applying studies with model membranes to fluorescence measurements during thapsigargin-induced apoptosis of S49 cells using probes specific for the plasma membrane: Patman and trimethylammonium-diphenylhexatriene. Alterations in emission properties of these probes corresponded with enhanced susceptibility of the cells to hydrolysis by secretory phospholipase A2. By applying a quantitative model, additional information was extracted from the kinetics of Patman equilibration with the membrane. Taken together, these data suggested that the phospholipids of apoptotic membranes display greater spacing between adjacent headgroups, reduced interactions between neighboring lipid tails, and increased penetration of water among the heads. The phase transition of artificial bilayers was used to calibrate quantitatively the relationship between probe fluorescence and the energy of interlipid interactions. This analysis was applied to results from apoptotic cells to estimate the frequency with which phospholipids protrude sufficiently at the membrane surface to enter the enzyme’s active site. The data suggested that this frequency increases 50–100-fold as membranes become susceptible to hydrolysis during apoptosis. PMID:22967861

  14. Network and neuronal membrane properties in hybrid networks reciprocally regulate selectivity to rapid thalamocortical inputs.

    PubMed

    Pesavento, Michael J; Pinto, David J

    2012-11-01

    Rapidly changing environments require rapid processing from sensory inputs. Varying deflection velocities of a rodent's primary facial vibrissa cause varying temporal neuronal activity profiles within the ventral posteromedial thalamic nucleus. Local neuron populations in a single somatosensory layer 4 barrel transform sparsely coded input into a spike count based on the input's temporal profile. We investigate this transformation by creating a barrel-like hybrid network with whole cell recordings of in vitro neurons from a cortical slice preparation, embedding the biological neuron in the simulated network by presenting virtual synaptic conductances via a conductance clamp. Utilizing the hybrid network, we examine the reciprocal network properties (local excitatory and inhibitory synaptic convergence) and neuronal membrane properties (input resistance) by altering the barrel population response to diverse thalamic input. In the presence of local network input, neurons are more selective to thalamic input timing; this arises from strong feedforward inhibition. Strongly inhibitory (damping) network regimes are more selective to timing and less selective to the magnitude of input but require stronger initial input. Input selectivity relies heavily on the different membrane properties of excitatory and inhibitory neurons. When inhibitory and excitatory neurons had identical membrane properties, the sensitivity of in vitro neurons to temporal vs. magnitude features of input was substantially reduced. Increasing the mean leak conductance of the inhibitory cells decreased the network's temporal sensitivity, whereas increasing excitatory leak conductance enhanced magnitude sensitivity. Local network synapses are essential in shaping thalamic input, and differing membrane properties of functional classes reciprocally modulate this effect. PMID:22896716

  15. Development and modulation of intrinsic membrane properties control the temporal precision of auditory brain stem neurons.

    PubMed

    Franzen, Delwen L; Gleiss, Sarah A; Berger, Christina; Kümpfbeck, Franziska S; Ammer, Julian J; Felmy, Felix

    2015-01-15

    Passive and active membrane properties determine the voltage responses of neurons. Within the auditory brain stem, refinements in these intrinsic properties during late postnatal development usually generate short integration times and precise action-potential generation. This developmentally acquired temporal precision is crucial for auditory signal processing. How the interactions of these intrinsic properties develop in concert to enable auditory neurons to transfer information with high temporal precision has not yet been elucidated in detail. Here, we show how the developmental interaction of intrinsic membrane parameters generates high firing precision. We performed in vitro recordings from neurons of postnatal days 9-28 in the ventral nucleus of the lateral lemniscus of Mongolian gerbils, an auditory brain stem structure that converts excitatory to inhibitory information with high temporal precision. During this developmental period, the input resistance and capacitance decrease, and action potentials acquire faster kinetics and enhanced precision. Depending on the stimulation time course, the input resistance and capacitance contribute differentially to action-potential thresholds. The decrease in input resistance, however, is sufficient to explain the enhanced action-potential precision. Alterations in passive membrane properties also interact with a developmental change in potassium currents to generate the emergence of the mature firing pattern, characteristic of coincidence-detector neurons. Cholinergic receptor-mediated depolarizations further modulate this intrinsic excitability profile by eliciting changes in the threshold and firing pattern, irrespective of the developmental stage. Thus our findings reveal how intrinsic membrane properties interact developmentally to promote temporally precise information processing. PMID:25355963

  16. Preparation of the superhydrophobic nano-hybrid membrane containing carbon nanotube based on chitosan and its antibacterial activity.

    PubMed

    Song, Kaili; Gao, Aiqin; Cheng, Xi; Xie, Kongliang

    2015-10-01

    The functional nano-hybrid surface containing multi-walled carbon nanotubes (MWCNT) on chitosan incorporated with the cationic chitosan (C-CS), MWCNTs and silicon couple agent (KH-560) was designed and prepared. The nano-hybrid membranes (NHM) containing MWCNTs were modified by perfluorooctanesulfonyl fluoride (PFOSF). The superhydrophobic multi-functional membranes with biological activity and superhydrophobic surface were obtained. The incorporated MWCNTs improved the roughness of the nano-hybrid membranes. The perfluorinated end groups of the nano-hybrid membrane surface provided low energy surface. The antibacterial activity, surface superhydrophobicity and mechanical property of the perfluorinated nano-hybrid membranes (PFNM) were discussed. Their morphological structures and surface ingredients were characterized by energy dispersive X-ray spectrometer (SEM-EDX). The PFNMs had excellent antibacterial property and superhydrophobicity. The novel nano-hybrid membranes with excellent antibacterial, superhydrophbic, and mechanical properties have potential applications in the food engineering, bioengineering fields and medical materials. PMID:26076639

  17. Physical Effects of Buckwheat Extract on Biological Membrane In Vitro and Its Protective Properties.

    PubMed

    Włoch, Aleksandra; Strugała, Paulina; Pruchnik, Hanna; Żyłka, Romuald; Oszmiański, Jan; Kleszczyńska, Halina

    2016-04-01

    Buckwheat is a valuable source of many biologically active compounds and nutrients. It has properties that reduce blood cholesterol levels, and so reduces the risk of atherosclerosis, seals the capillaries, and lowers blood pressure. The aim of the study was to determine quantitative and qualitative characteristics of polyphenols contained in extracts from buckwheat husks and stalks, the biological activity of the extracts, and biophysical effects of their interaction with the erythrocyte membrane, treated as a model of the cell. An analysis of the extract's composition has shown that buckwheat husk and stalk extracts are a rich source of polyphenolic compounds, the stalk extracts showing more compounds than the husk extract. The study allowed to determine the location which incorporated polyphenols occupy in the erythrocyte membrane and changes in the membrane properties caused by them. It was found that the extracts do not induce hemolysis of red blood cells, causing an increase in osmotic resistance of erythrocytes. They affect mainly the hydrophilic region by changing the degree of order of the polar heads of lipids, but do little to change the fluidity of the membrane and its hydration. The results showed also that polyphenolic substances included in the extracts well protect the membranes of red blood cells against oxidation and exhibit anti-inflammatory effect. PMID:26581904

  18. Changes in physicochemical and transport properties of a reverse osmosis membrane exposed to chloraminated seawater.

    PubMed

    Valentino, Lauren; Renkens, Tennie; Maugin, Thomas; Croué, Jean-Philippe; Mariñas, Benito J

    2015-02-17

    This study contributed to improving our understanding of how disinfectants, applied to control biofouling of reverse osmosis (RO) membranes, result in membrane performance degradation. We investigated changes in physicochemical properties and permeation performance of a RO membrane with fully aromatic polyamide (PA) active layer. Membrane samples were exposed to varying concentrations of monochloramine, bromide, and iodide in both synthetic and natural seawater. Elemental analysis of the membrane active layer by Rutherford backscattering spectrometry (RBS) revealed the incorporation of bromine and iodine into the polyamide. The kinetics of polyamide bromination were first order with respect to the concentration of the secondary oxidizing agent Br2 for the conditions investigated. Halogenated membranes were characterized after treatment with a reducing agent and heavy ion probes to reveal the occurrence of irreversible ring halogenation and an increase in carboxylic groups, the latter produced as a result of amide bond cleavage. Finally, permeation experiments revealed increases in both water permeability and salt passage as a result of oxidative damage. PMID:25590510

  19. Elastic Properties of Polymerised and Fluid Membranes Under Stress

    NASA Astrophysics Data System (ADS)

    Shillcock, Julian Charles

    The stability of a living cell relies on the properties and interrelations of its constituent parts. The fluid bilayer surrounding the cell separates the cytoplasm inside the cell from the extracellular environment. A cross-linked network of proteins within the cytoplasm supports the fluid bilayer and contributes to the cell's elasticity. Three properties relating to the behaviour of a model fluid bilayer and polymerised network are investigated by Monte Carlo simulation: the phase behaviour of a system of discotic liquid crystal molecules, the elastic properties of a model polymerised network, and the stability and rupture of a model fluid membrane. The isotropic to nematic transition induced by hydrostatic pressure in a system of discotic liquid cystal molecules in three dimensions is presented. The study concentrates on the phase behaviour resulting from the anisotropy of the disks. The transition is present for disks whose thickness to radius ratio is less than 40%, but is absent for thicker disks. A more specialised model of disks restricted to intersect a planar interface between two immiscible fluids is investigated, but has no isotropic -nematic phase transition at finite temperature. The elastic properties of a two-dimensional, triangulated network of Hookean springs are investigated as a function of temperature and applied tension. The compression modulus decreases, and the shear modulus increases, as the tension on the network is increased. The elastic properties of self-avoiding networks at low temperature are well described by a mean field theory. When the self-avoidance constraint is removed, the network undergoes a phase transition to a collapsed state of small area as the tension is reduced to zero. Both types of network show an unstable expansion of their area when the stretching tension exceeds a specified value. Both networks also have the unusual property (referred to as a negative Poisson ratio) of expanding transversely when stretched

  20. Antibacterial property and mechanism of a novel Pu-erh tea nanofibrous membrane.

    PubMed

    Su, Yajuan; Zhang, Chenlu; Wang, Yan; Li, Ping

    2012-02-01

    Pu-erh tea is made via a natural fermentation process. In this study, Pu-erh tea was used as a raw material for nanomaterials preparation and as an antibacterial agent. Antibacterial activities on Escherichia coli of Pu-erh tea, Pu-erh tea powder (PTP) of different sizes, and Pu-erh tea residual powder were firstly determined, respectively. With polyvinyl alcohol as the carrier, through an electrospinning technique, different kinds of nanofibrous membranes were obtained from the extract of Pu-erh tea and nano-PTP (NPTP), and their antibacterial properties and mechanism against E. coli were evaluated. The results showed better antibacterial activity with smaller PTP particles, the nano-sized particles had the best effects, and the MIC of NPTP was 13.5 mg/mL. When NPTP was in nanofibrous membranes, the antibacterial activity decreased slightly, but increased with modification by ZnO. Pu-erh tea in nanofibrous membranes damaged the E. coli cell membranes and caused leakage of K(+) and enzymes. What is more is that damage of the cell walls led to the leakage of fluorescent proteins from enhanced green fluorescence protein-expressing E. coli. These results indicate that the Pu-erh tea nanofibrous membranes had good antibacterial activities against E. coli, which may provide a promising application of novel antibacterial materials. PMID:21858494

  1. Membrane properties of the smooth-muscle fibres of the guinea-pig portal vein.

    PubMed

    Ito, Y; Kuriyama, H

    1971-05-01

    The membrane activities and the various characteristic constants of the smooth-muscle membrane of the guinea-pig portal vein were investigated with the micro-electrode technique.1. The mean membrane potential was -37 mV. Spontaneous discharges appeared as regular bursts of short trains of spikes alternating with silent periods, as a mixture of single spikes and bursts of spikes appearing continuously, or as regular spikes with low frequency.2. Spontaneous spikes with overshoot were frequently observed. The maximum rate of rise of the spike was 3.7 V/sec. The shapes of the spikes were classified into three different types, i.e. pace-maker type of spike, monophasic spike and spike with a hump during the falling phase.3. Tetrodotoxin (10(-5) g/ml.) did not influence the patterns of the spontaneous train discharges nor the shape of the spike.4. Extracellularly applied outward current elicited spikes which were either monophasic or had a hump on the falling phase. Inward current elicited break excitation of the spike.5. Current-voltage relations, produced by application of inward current pulses to the tissue and measured at various distances from the stimulating partition, were linear.6. The smooth-muscle membrane of portal vein showed cable-like properties. The mean space constant of the membrane was 0.52 mm; the mean time constant of the membrane calculated from the electrotonic potential was 330 msec.7. Conduction velocity of the spike measured by insertion of two micro-electrodes was 0.58 cm/sec.8. The time constant of the foot of the propagated spike was 27 msec. The time constant of the membrane calculated from the time constant of the foot of the spike and the conduction velocity was 310 msec.9. The membrane properties of longitudinal smooth muscle of the portal vein were discussed in comparison with other veins and various visceral smooth muscles. PMID:5580862

  2. Phosphocreatine Interacts with Phospholipids, Affects Membrane Properties and Exerts Membrane-Protective Effects

    PubMed Central

    Tokarska-Schlattner, Malgorzata; Epand, Raquel F.; Meiler, Flurina; Zandomeneghi, Giorgia; Neumann, Dietbert; Widmer, Hans R.; Meier, Beat H.; Epand, Richard M.; Saks, Valdur; Wallimann, Theo; Schlattner, Uwe

    2012-01-01

    A broad spectrum of beneficial effects has been ascribed to creatine (Cr), phosphocreatine (PCr) and their cyclic analogues cyclo-(cCr) and phospho-cyclocreatine (PcCr). Cr is widely used as nutritional supplement in sports and increasingly also as adjuvant treatment for pathologies such as myopathies and a plethora of neurodegenerative diseases. Additionally, Cr and its cyclic analogues have been proposed for anti-cancer treatment. The mechanisms involved in these pleiotropic effects are still controversial and far from being understood. The reversible conversion of Cr and ATP into PCr and ADP by creatine kinase, generating highly diffusible PCr energy reserves, is certainly an important element. However, some protective effects of Cr and analogues cannot be satisfactorily explained solely by effects on the cellular energy state. Here we used mainly liposome model systems to provide evidence for interaction of PCr and PcCr with different zwitterionic phospholipids by applying four independent, complementary biochemical and biophysical assays: (i) chemical binding assay, (ii) surface plasmon resonance spectroscopy (SPR), (iii) solid-state 31P-NMR, and (iv) differential scanning calorimetry (DSC). SPR revealed low affinity PCr/phospholipid interaction that additionally induced changes in liposome shape as indicated by NMR and SPR. Additionally, DSC revealed evidence for membrane packing effects by PCr, as seen by altered lipid phase transition. Finally, PCr efficiently protected against membrane permeabilization in two different model systems: liposome-permeabilization by the membrane-active peptide melittin, and erythrocyte hemolysis by the oxidative drug doxorubicin, hypoosmotic stress or the mild detergent saponin. These findings suggest a new molecular basis for non-energy related functions of PCr and its cyclic analogue. PCr/phospholipid interaction and alteration of membrane structure may not only protect cellular membranes against various insults, but could

  3. An Extended Membrane System with Active Membranes to Solve Automatic Fuzzy Clustering Problems.

    PubMed

    Peng, Hong; Wang, Jun; Shi, Peng; Pérez-Jiménez, Mario J; Riscos-Núñez, Agustín

    2016-05-01

    This paper focuses on automatic fuzzy clustering problem and proposes a novel automatic fuzzy clustering method that employs an extended membrane system with active membranes that has been designed as its computing framework. The extended membrane system has a dynamic membrane structure; since membranes can evolve, it is particularly suitable for processing the automatic fuzzy clustering problem. A modification of a differential evolution (DE) mechanism was developed as evolution rules for objects according to membrane structure and object communication mechanisms. Under the control of both the object's evolution-communication mechanism and the membrane evolution mechanism, the extended membrane system can effectively determine the most appropriate number of clusters as well as the corresponding optimal cluster centers. The proposed method was evaluated over 13 benchmark problems and was compared with four state-of-the-art automatic clustering methods, two recently developed clustering methods and six classification techniques. The comparison results demonstrate the superiority of the proposed method in terms of effectiveness and robustness. PMID:26790484

  4. Structural Model of Active Bax at the Membrane

    PubMed Central

    Bleicken, Stephanie; Jeschke, Gunnar; Stegmueller, Carolin; Salvador-Gallego, Raquel; García-Sáez, Ana J.; Bordignon, Enrica

    2016-01-01

    Bax plays a central role in the mitochondrial pathway of apoptosis. Upon activation, cytosolic Bax monomers oligomerize on the surface of mitochondria and change conformation concertedly to punch holes into the outer membrane. The subsequent release of cytochrome c initiates cell death. However, the structure of membrane-inserted Bax and its mechanism of action remain largely unknown. Here, we propose a 3D model of active Bax at the membrane based on double electron-electron resonance (DEER) spectroscopy in liposomes and isolated mitochondria. We show that active Bax is organized at the membrane as assemblies of dimers. In addition to a stable dimerization domain, each monomer contains a more flexible piercing domain involved in interdimer interactions and pore formation. The most important structural change during Bax activation is the opening of the hairpin formed by helices 5 and 6, which adopts a clamp-like conformation central to the mechanism of mitochondrial permeabilization. PMID:25458844

  5. Effect of lipid head group interactions on membrane properties and membrane-induced cationic β-hairpin folding.

    PubMed

    Ganesan, Sai J; Xu, Hongcheng; Matysiak, Silvina

    2016-07-21

    Stages in POPS membrane induced SVS-1 folding. One key characteristic of mIFs is the dielectric gradient and subsequently, electrostatic potential that arises from dipolar interactions in the head group region. In this work, we present a coarse-grained (CG) model for anionic and zwitterionic lipids that accounts for dipolar intricacies in the head group region. Prior work on adding dipolar interactions in a coarse grained (CG) model for peptides enabled us to achieve α/β secondary structure content de novo, without any added bias. We have now extended this idea to lipids. To mimic dipolar interactions, two dummy particles with opposite charges are added to CG polar beads. These two dummy charges represent a fluctuating dipole that introduces structural polarization into the head group region. We have used POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) and POPS (1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-l-serine) as our model lipids. We characterize structural, dynamic, and dielectric properties of our CG bilayer, along with the effect of monovalent ions. We observe head group dipoles to play a significant role in membrane dielectric gradient and lipid clustering induced by dipole-dipole interactions in POPS lipids. In addition, we studied membrane-induced peptide folding of a cationic antimicrobial peptide with anticancer activity, SVS-1. We find that membrane-induced peptide folding is driven by both (a) cooperativity in peptide self-interaction and (b) cooperativity in membrane-peptide interaction. In particular, dipolar interactions between the peptide backbone and lipid head groups contribute to stabilizing folded conformations. PMID:27165814

  6. Quantum description of nanoantenna properties of a graphene membrane

    NASA Astrophysics Data System (ADS)

    Firsova, N. E.; Firsov, Yu. A.

    2016-06-01

    We considered a graphene membrane irradiated by a weak activating periodic electric field in the terahertz range. We used the quantum approach based on the time-dependent density matrix method to analyze the graphene electromagnetic response. For this goal the exact solution was found for the graphene membrane density matrix equation in linear approximation on the external field. On this basis the induced current was studied and then we obtained the formula for quantum conductivity as a function of external field frequency and temperature. The found formula for the conductivity corrected the one obtained in 2007 by Gusynin, Sharapov and Carbotte (Phys. Rev. B, 75 (2007) 165407). The corrected formula allowed to see that the graphene membrane was an oscillating contour, its fundamental eigenfrequency coinciding with a singularity point of the conductivity. The obtained formula allowed us also to calculate the graphene membrane quantum inductivity and capacitance. So in effect we demonstrated that the graphene membrane could be used as an antenna or a transistor. It was shown also that its eigenfrequency could be tuned by doping as its value was found to depend on electrons concentration. It was obtained that the eigenfrequency could be tuned in a rather large terahertz-infrared frequency range as electrons concentration in graphene may differ considerably. The found dependence on concentration is consistent with experiments. The presented formula for conductivity can be used to correct the SPPs Dispersion Relation and for the description of radiation process. It would be useful to take the obtained results into account when constructing devices containing a graphene membrane nanoantenna. Such project could make it possible to create wireless communications among nanosystems. This would be a promising research area of energy harvesting applications.

  7. Intrinsic membrane properties determine hippocampal differential firing pattern in vivo in anesthetized rats.

    PubMed

    Kowalski, Janina; Gan, Jian; Jonas, Peter; Pernía-Andrade, Alejandro J

    2016-05-01

    The hippocampus plays a key role in learning and memory. Previous studies suggested that the main types of principal neurons, dentate gyrus granule cells (GCs), CA3 pyramidal neurons, and CA1 pyramidal neurons, differ in their activity pattern, with sparse firing in GCs and more frequent firing in CA3 and CA1 pyramidal neurons. It has been assumed but never shown that such different activity may be caused by differential synaptic excitation. To test this hypothesis, we performed high-resolution whole-cell patch-clamp recordings in anesthetized rats in vivo. In contrast to previous in vitro data, both CA3 and CA1 pyramidal neurons fired action potentials spontaneously, with a frequency of ∼3-6 Hz, whereas GCs were silent. Furthermore, both CA3 and CA1 cells primarily fired in bursts. To determine the underlying mechanisms, we quantitatively assessed the frequency of spontaneous excitatory synaptic input, the passive membrane properties, and the active membrane characteristics. Surprisingly, GCs showed comparable synaptic excitation to CA3 and CA1 cells and the highest ratio of excitation versus hyperpolarizing inhibition. Thus, differential synaptic excitation is not responsible for differences in firing. Moreover, the three types of hippocampal neurons markedly differed in their passive properties. While GCs showed the most negative membrane potential, CA3 pyramidal neurons had the highest input resistance and the slowest membrane time constant. The three types of neurons also differed in the active membrane characteristics. GCs showed the highest action potential threshold, but displayed the largest gain of the input-output curves. In conclusion, our results reveal that differential firing of the three main types of hippocampal principal neurons in vivo is not primarily caused by differences in the characteristics of the synaptic input, but by the distinct properties of synaptic integration and input-output transformation. © 2015 The Authors Hippocampus

  8. [Immunotropic and immunogenic properties of Burkholderia pseudomallei surface and membrane antigens].

    PubMed

    Piven', N N; Rybkin, V S; Plekhanova, N G; Zhukova, S I; Viktorov, D V; Avrorova, I V; Demediuk, E A; Drefs, N M; Popov, S F

    2001-01-01

    The immunotropic and immunogenic properties of some chromatographic fractions of B. pseudomallei surface antigenic complex, as well as the preparations of B. pseudomallei outer and cytoplasmic membranes, were studied. The difference between the biopolymers under study in cytotoxicity, humoral and cell-mediated immunity characteristics, phagocytic activity were established. Some antigenic fractions (B, C, C1, H) showed perceptible protective activity (25-60%) in experiments on mice infected with B. pseudomallei virulent strain. One of the preparations of cytoplasmic membrane (CM-1) was also found to have protective properties (30%). Complex immunization with the antigenic complexes under study, introduced in combination with the immunomodulating agent Bromantan, was shown to enhance the protective effect. PMID:11236497

  9. Biological Activity of Blackcurrant Extracts (Ribes nigrum L.) in Relation to Erythrocyte Membranes

    PubMed Central

    Cyboran, Sylwia; Żyłka, Romuald; Oszmiański, Jan; Kleszczyńska, Halina

    2014-01-01

    Compounds contained in fruits and leaves of blackcurrant (Ribes nigrum L.) are known as agents acting preventively and therapeutically on the organism. The HPLC analysis showed they are rich in polyphenol anthocyanins in fruits and flavonoids in leaves, that have antioxidant activity and are beneficial for health. The aim of the research was to determine the effect of blackcurrant fruit and leaf extracts on the physical properties of the erythrocyte membranes and assess their antioxidant properties. The effect of the extracts on osmotic resistance, shape of erythrocytes and hemolytic and antioxidant activity of the extracts were examined with spectrophotometric methods. The FTIR investigation showed that extracts modify the erythrocyte membrane and protect it against free radicals induced by UV radiation. The results show that the extracts do not induce hemolysis and even protect erythrocytes against the harmful action of UVC radiation, while slightly strengthening the membrane and inducing echinocytes. The compounds contained in the extracts do not penetrate into the hydrophobic region, but bind to the membrane surface inducing small changes in the packing arrangement of the polar head groups of membrane lipids. The extracts have a high antioxidant activity. Their presence on the surface of the erythrocyte membrane entails protection against free radicals. PMID:24527456

  10. Neuronal Activation by GPI-Linked Neuroligin-1 Displayed in Synthetic Lipid Bilayer Membranes

    PubMed Central

    Baksh, Michael M.; Groves, Jay T.; Dean, Camin; Pautot, Sophie; DeMaria, Shannon; Isacoff, Ehud

    2006-01-01

    We have characterized, in vitro, interactions between hippocampal neuronal cells and silica microbeads coated with synthetic, fluid, lipid bilayer membranes containing the glycosylphosphatidyl inositol (GPI)-linked extracellular domain of the postsynaptic membrane protein neuroligin-1. These bilayer–neuroligin-1 beads activated neuronal cells to form presynaptic nerve terminals at the point of contact in a manner similar to that observed for live PC12 cells, ectopically expressing the full length neuroligin-1. The synthetic membranes exhibited biological activity at neuroligin-1 densities of ∼1 to 6 proteins/μm2. Polyolycarbonate beads with neuroligin-1 covalently attached to the surface failed to activate neurons despite the fact that neuroligin-1 binding activity is preserved. This implies that a lipid membrane environment is likely to be essential for neuroligin-1 activity. This technique allows the study of isolated proteins in an environment that has physical properties resembling those of a cell surface; proteins can diffuse freely within the membrane, retain their in vivo orientations, and are in a nondenatured state. In addition, the synthetic membrane environment affords control over both lipid and protein composition. This technology is easily implemented and can be applied to a wide variety of cellular studies. PMID:16262338

  11. Ammonia-Activated Mesoporous Carbon Membranes for Gas Separations

    SciTech Connect

    Mahurin, Shannon Mark; Lee, Jeseung; Wang, Xiqing; Dai, Sheng

    2011-01-01

    Porous carbon membranes, which generally show improved chemical and thermal stability compared to polymer membranes, have been used in gas separations for many years. In this work, we show that the post-synthesis ammonia treatment of porous carbon at elevated temperature can improve the permeance and selectivity of these membranes for the separation of carbon dioxide and hydrocarbons from permanent gases. Hierarchically structured porous carbon membranes were exposed to ammonia gas at temperatures ranging from 850 C to 950 C for up to 10 min and the N{sub 2}, CO{sub 2}, and C{sub 3}H{sub 6} permeances were measured for these different membranes. Higher treatment temperatures and longer exposure times resulted in higher gas permeance values. In addition, CO{sub 2}/N{sub 2} and C{sub 3}H{sub 6}/N{sub 2} selectivities increased by a factor of 2 as the treatment temperature and time increased up to a temperature and time of 900 C, 10 min. Higher temperatures showed increased permeance but decreased selectivity indicating excess pore activation. Nitrogen adsorption measurements show that the ammonia treatment increased the porosity of the membrane while elemental analysis revealed the presence of nitrogen-containing surface functionalities in the treated carbon membranes. Thus, ammonia treatment at high temperature provides a controlled method to introduce both added microporosity and surface functionality to enhance gas separations performance of porous carbon membranes.

  12. Bilayer Membrane Modulation of Membrane Type 1 Matrix Metalloproteinase (MT1-MMP) Structure and Proteolytic Activity.

    PubMed

    Cerofolini, Linda; Amar, Sabrina; Lauer, Janelle L; Martelli, Tommaso; Fragai, Marco; Luchinat, Claudio; Fields, Gregg B

    2016-01-01

    Cell surface proteolysis is an integral yet poorly understood physiological process. The present study has examined how the pericellular collagenase membrane-type 1 matrix metalloproteinase (MT1-MMP) and membrane-mimicking environments interplay in substrate binding and processing. NMR derived structural models indicate that MT1-MMP transiently associates with bicelles and cells through distinct residues in blades III and IV of its hemopexin-like domain, while binding of collagen-like triple-helices occurs within blades I and II of this domain. Examination of simultaneous membrane interaction and triple-helix binding revealed a possible regulation of proteolysis due to steric effects of the membrane. At bicelle concentrations of 1%, enzymatic activity towards triple-helices was increased 1.5-fold. A single mutation in the putative membrane interaction region of MT1-MMP (Ser466Pro) resulted in lower enzyme activation by bicelles. An initial structural framework has thus been developed to define the role(s) of cell membranes in modulating proteolysis. PMID:27405411

  13. Bilayer Membrane Modulation of Membrane Type 1 Matrix Metalloproteinase (MT1-MMP) Structure and Proteolytic Activity

    PubMed Central

    Cerofolini, Linda; Amar, Sabrina; Lauer, Janelle L.; Martelli, Tommaso; Fragai, Marco; Luchinat, Claudio; Fields, Gregg B.

    2016-01-01

    Cell surface proteolysis is an integral yet poorly understood physiological process. The present study has examined how the pericellular collagenase membrane-type 1 matrix metalloproteinase (MT1-MMP) and membrane-mimicking environments interplay in substrate binding and processing. NMR derived structural models indicate that MT1-MMP transiently associates with bicelles and cells through distinct residues in blades III and IV of its hemopexin-like domain, while binding of collagen-like triple-helices occurs within blades I and II of this domain. Examination of simultaneous membrane interaction and triple-helix binding revealed a possible regulation of proteolysis due to steric effects of the membrane. At bicelle concentrations of 1%, enzymatic activity towards triple-helices was increased 1.5-fold. A single mutation in the putative membrane interaction region of MT1-MMP (Ser466Pro) resulted in lower enzyme activation by bicelles. An initial structural framework has thus been developed to define the role(s) of cell membranes in modulating proteolysis. PMID:27405411

  14. Membrane activity of the phospholipase C-δ1 pleckstrin homology (PH) domain

    PubMed Central

    2005-01-01

    PH-PLCδ1 [the PH domain (pleckstrin homology domain) of PLCδ1 (phospholipase C-δ1)] is among the best-characterized phosphoinositide-binding domains. PH-PLCδ1 binds with high specificity to the headgroup of PtdIns(4,5)P2, but little is known about its interfacial properties. In the present study, we show that PH-PLCδ1 is also membrane-active and can insert significantly into PtdIns(4,5)P2-containing monolayers at physiological (bilayer-equivalent) surface pressures. However, this membrane activity appears to involve interactions distinct from those that target PH-PLCδ1 to the PtdIns(4,5)P2 headgroup. Whereas the majority of PtdIns(4,5)P2-bound PH-PLCδ1 can be displaced by adding excess of soluble headgroup [Ins(1,4,5)P3], membrane activity of PH-PLCδ1 cannot. PH-PLCδ1 differs from other phosphoinositide-binding domains in that its membrane insertion does not require that the phosphoinositide-binding site be occupied. Significant monolayer insertion remains when the phosphoinositide-binding site is mutated, and PH-PLCδ1 can insert into monolayers that contain no PtdIns(4,5)P2 at all. Our results suggest a model in which reversible membrane binding of PH-PLCδ1, mediated by PtdIns(4,5)P2 or other acidic phospholipids, occurs without membrane insertion. Accumulation of the PH domain at the membrane surface enhances the efficiency of insertion, but does not significantly affect its extent, whereas the presence of phosphatidylethanolamine and cholesterol in the lipid mixture promotes the extent of insertion. This is the first report of membrane activity in an isolated PH domain and has implications for understanding the membrane targeting by this common type of domain. PMID:15755258

  15. Modeling and vibration control of an active membrane mirror

    NASA Astrophysics Data System (ADS)

    Ruggiero, Eric J.; Inman, Daniel J.

    2009-09-01

    The future of space satellite technology lies in ultra-large mirrors and radar apertures for significant improvements in imaging and communication bandwidths. The availability of optical-quality membranes drives a parallel effort for structural models that can capture the dominant dynamics of large, ultra-flexible satellite payloads. Unfortunately, the inherent flexibility of membrane mirrors wreaks havoc with the payload's on-orbit stability and maneuverability. One possible means of controlling these undesirable dynamics is by embedding active piezoelectric ceramics near the boundary of the membrane mirror. In doing so, active feedback control can be used to eliminate detrimental vibration, perform static shape control, and evaluate the health of the structure. The overall motivation of the present work is to design a control system using distributed bimorph actuators to eliminate any detrimental vibration of the membrane mirror. As a basis for this study, a piezoceramic wafer was attached in a bimorph configuration near the boundary of a tensioned rectangular membrane sample. A finite element model of the system was developed to capture the relevant system dynamics from 0 to 300 Hz. The finite element model was compared against experimental results, and fair agreement found. Using the validated finite element models, structural control using linear quadratic regulator control techniques was then used to numerically demonstrate effective vibration control. Typical results show that less than 12 V of actuation voltage is required to eliminate detrimental vibration of the membrane samples in less than 15 ms. The functional gains of the active system are also derived and presented. These spatially descriptive control terms dictate favorable regions within the membrane domain for placing sensors and can be used as a design guideline for structural control applications. The results of the present work demonstrate that thin plate theory is an appropriate modeling

  16. Cytotoxic bile acids, but not cytoprotective species, inhibit the ordering effect of cholesterol in model membranes at physiologically active concentrations.

    PubMed

    Mello-Vieira, João; Sousa, Tânia; Coutinho, Ana; Fedorov, Aleksander; Lucas, Susana D; Moreira, Rui; Castro, Rui E; Rodrigues, Cecília M P; Prieto, Manuel; Fernandes, Fábio

    2013-09-01

    Submillimolar concentrations of cytotoxic bile acids (BAs) induce cell death via apoptosis. On the other hand, several cytoprotective BAs were shown to prevent apoptosis in the same concentration range. Still, the mechanisms by which BAs trigger these opposite signaling effects remain unclear. This study was aimed to determine if cytotoxic and cytoprotective BAs, at physiologically active concentrations, are able to modulate the biophysical properties of lipid membranes, potentially translating into changes in the apoptotic threshold of cells. Binding of BAs to membranes was assessed through the variation of fluorescence parameters of suitable derivatized BAs. These derivatives partitioned with higher affinity to liquid disordered than to the cholesterol-enriched liquid ordered domains. Unlabeled BAs were also shown to have a superficial location upon interaction with the lipid membrane. Additionally, the interaction of cytotoxic BAs with membranes resulted in membrane expansion, as concluded from FRET data. Moreover, it was shown that cytotoxic BAs were able to significantly disrupt the ordering of the membrane by cholesterol at physiologically active concentrations of the BA, an effect not associated with cholesterol removal. On the other hand, cytoprotective bile acids had no effect on membrane properties. It was concluded that, given the observed effects on membrane rigidity, the apoptotic activity of cytotoxic BAs could be potentially associated with changes in plasma membrane organization (e.g. modulation of lipid domains) or with an increase in mitochondrial membrane affinity for apoptotic proteins. PMID:23747364

  17. Controlled change of transport properties of poly(ethylene terephthalate) track membranes by plasma method

    NASA Astrophysics Data System (ADS)

    Kravets, L. I.; Dmitriev, S. N.; Drachev, A. I.; Gilman, A. B.; Lazea, A.; Dinescu, G.

    2007-04-01

    A process of plasma polymerization of dimethylaniline and acrylic acid vapours on the surface of poly(ethylene terephthalate) track membranes has been investigated. The surface and hydrodynamic properties of the composite membranes produced in this case have been studied. It is shown that the water permeability of the obtained polymeric membranes can be controlled by changing the filtrate pH. Membranes with such properties can be used for controllable drug delivery and in sensor control.

  18. Membrane Changes Associated with Platelet Activation

    PubMed Central

    George, James N.; Lyons, Roger M.; Morgan, Rebecca K.

    1980-01-01

    The effect of aggregation and secretion on membrane proteins was studied in washed human platelets. Reversible aggregation without secretion was stimulated by ADP and secretion without aggregation was stimulated by thrombin in the presence of EDTA. No loss of platelet surface glycoproteins occurred during reversible ADP-induced platelet aggregation, as measured by quantitative polyacrylamide gel electrophoresis analysis of platelets that were labeled with 125I-diazotized diiodosulfanilic acid (DD125ISA) before ADP stimulation. Also, no new proteins became exposed on the platelet surface after ADP aggregation, as determined by DD125ISA labeling after stimulation. Thrombin-induced platelet secretion also caused no loss of platelet surface glycoproteins. However, after platelet secretion two new proteins were labeled by DD125ISA: (a) actin and (b) the 149,000-mol wt glycoprotein (termed GP-G), which is contained in platelet granules and secreted in response to thrombin. The identity of DD125ISA-labeled actin was confirmed by four criteria: (a) comigration with actin in three different sodium dodecyl sulfate-polyacrylamide gel electrophoresis systems, (b) elution from a particulate fraction in low ionic strength buffer, (c) co-migration with actin in isoelectric focusing, and (d) binding to DNase I. The identity of actin and its appearance on the platelet surface after thrombin-induced secretion was also demonstrated by the greater binding of an anti-actin antibody to thrombin-treated platelets, measured with 125I-staphylococcal protein A. Therefore, major platelet membrane changes occur after secretion but not after reversible aggregation. The platelet surface changes occurring with secretion may be important in the formation of irreversible platelet aggregates and in the final retraction of the blood clot. Images PMID:6772667

  19. Multiple sources of carbonic anhydrase activity in pea thylakoids: soluble and membrane-bound forms.

    PubMed

    Rudenko, Natalia N; Ignatova, Lyudmila K; Ivanov, Boris N

    2007-01-01

    Carbonic anhydrase (CA) activity of pea thylakoids, thylakoid membranes enriched with photosystem I (PSI-membranes), or photosystem II (PSII-membranes) as well as both supernatant and pellet after precipitation of thylakoids treated with detergent Triton X-100 were studied. CA activity of thylakoids in the presence of varying concentrations of Triton X-100 had two maxima, at Triton/chlorophyll (triton/Chl) ratios of 0.3 and 1.0. CA activities of PSI-membranes and PSII-membranes had only one maximum each, at Triton/Chl ratio 0.3 or 1.0, respectively. Two CAs with characteristics of the membrane-bound proteins and one CA with characteristics of the soluble proteins were found in the medium after thylakoids were incubated with Triton. One of the first two CAs had mobility in PAAG after native electrophoresis the same as that of CA residing in PSI-membranes, and the other CA had mobility the same as the mobility of CA residing in PSII-membranes, but the latter was different from CA situated in PSII core-complex (Ignatova et al. 2006 Biochemistry (Moscow) 71:525-532). The properties of the "soluble" CA removed from thylakoids were different from the properties of the known soluble CAs of plant cell: apparent molecular mass was about 262 kD and it was three orders more sensitive to the specific CA inhibitor, ethoxyzolamide, than soluble stromal CA. The data are discussed as indicating the presence of, at least, four CAs in pea thylakoids. PMID:17347907

  20. Carnitine palmitoyltransferase in human erythrocyte membrane. Properties and malonyl-CoA sensitivity.

    PubMed Central

    Ramsay, R R; Mancinelli, G; Arduini, A

    1991-01-01

    Carnitine palmitoyltransferase located in the erythrocyte plasma membrane is sensitive to inhibition by malonyl-CoA and 2-bromopalmitoyl-CoA plus carnitine. Although this inhibition and other properties suggest similarities to the intracellular enzymes in other tissues, no cross-reaction was observed with antisera to the peroxisomal or to the mitochondrial inner-membrane enzyme. The activity was solubilized by and was stable in Triton X-100, which destroys the enzymes found in microsomes and in the mitochondrial outer membrane. The substrate specificity is broader than for the intracellular enzymes, the activities with stearoyl-CoA (114%) and arachidonoyl-CoA (97%) being equal to that with palmitoyl-CoA, and the activities with linoleoyl-CoA (44%) and erucoyl-CoA (46%) about half that with palmitoyl-CoA. The function of this carnitine palmitoyltransferase is probably to buffer the acyl-CoA present in the erythrocyte for turnover of the fatty acyl groups of the membrane lipids. PMID:2039446

  1. The physicochemical properties of polyurethane membranes determined by swelling measurements

    NASA Astrophysics Data System (ADS)

    Ciobanu, Gabriela; Carja, Gabriela; Apostolescu, Gabriela; Apostolescu, Nicolae

    2009-01-01

    In this work, we have dispersed SAPO-5 zeolite particles in polyurethane matrix for preparation of porous mixed matrix membranes. The goal of work is the determination of the cohesive energy density for unfilled- and zeolite - filled polyurethane membranes. Experimental determination of cohesive energy density values for the prepared membranes is obtained by measuring the swelling coefficients in water and several alcohols (methanol, ethanol, propanol and butanol). The solubility parameters of the membranes are also calculated. For the unfilled membranes the corresponded values of cohesive energy density and solubility parameter increase in comparison to those of the filled membranes. All the tested membranes show a tendency to swell with ethanol.

  2. Characterization and adsorption properties of eggshells and eggshell membrane.

    PubMed

    Tsai, W T; Yang, J M; Lai, C W; Cheng, Y H; Lin, C C; Yeh, C W

    2006-02-01

    The objective of this work was to study the chemical and physical characterization of eggshell and eggshell membrane particles prepared from the hen eggshell waste. Under the characterization measurements investigated, it was found that the pore structures of the two biomaterials belong to a typical Type II, indicating that they should be basically characteristic of nonporous materials or materials with macropores or open voids. Further, the chemical composition of the resulting eggshell particle was strongly associated with the presence of carbonate minerals from the Fourier transform infrared (FTIR) spectra. In contrast to the resulting eggshell membrane particle, the presence of functional groups of amines and amides was observable because of its chemical composition of fibrous proteins. From the isotherm data of methylene blue at 25 degrees C, the Freundlich model yielded a somewhat better fit than the Langmuir model. The adsorption isotherms revealed the eggshell biosorbents could only uptake the basic dye of less than 1.0mg/g in aqueous medium, which was attributed to their poor pore properties. PMID:15896954

  3. Tailored fibro-porous structure of electrospun polyurethane membranes, their size-dependent properties and trans-membrane glucose diffusion

    PubMed Central

    Wang, Ning; Burugapalli, Krishna; Song, Wenhui; Halls, Justin; Moussy, Francis; Zheng, Yudong; Ma, Yanxuan; Wu, Zhentao; Li, Kang

    2012-01-01

    The aim of this study was to develop polyurethane (PU) based fibro-porous membranes and to investigate the size-effect of hierarchical porous structure on permeability and surface properties of the developed electrospun membranes. Non-woven Selectophore™ PU membranes having tailored fibre diameters, pore sizes, and thickness were spun using electrospinning, and their chemical, physical and glucose permeability properties were characterised. Solvents, solution concentration, applied voltage, flow rate and distance to collector, each were systematically investigated, and electrospinning conditions for tailoring fibre diameters were identified. Membranes having average fibre diameters – 347, 738 and 1102 nm were characterized, revealing average pore sizes of 800, 870 and 1060 nm and pore volumes of 44, 63 and 68% respectively. Hydrophobicity increased with increasing fibre diameter and porosity. Effective diffusion coefficients for glucose transport across the electrospun membranes varied as a function of thickness and porosity, indicating high flux rates for mass transport. Electrospun PU membranes having significantly high pore volumes, extensively interconnected porosity and tailorable properties compared to conventional solvent cast membranes can find applications as coatings for sensors requiring analyte exchange. PMID:23170040

  4. Membrane fouling potentials and cellular properties of bacteria isolated from fouled membranes in a MBR treating municipal wastewater.

    PubMed

    Ishizaki, So; Fukushima, Toshikazu; Ishii, Satoshi; Okabe, Satoshi

    2016-09-01

    Membrane fouling remains a major challenge for wider application of membrane bioreactors (MBRs) to wastewater treatment. Membrane fouling is mainly caused by microorganisms and their excreted microbial products. For development of more effective control strategies, it is important to identify and characterize the microorganisms that are responsible for membrane fouling. In this study, 41 bacterial strains were isolated from fouled microfiltration membranes in a pilot-scale MBR treating real municipal wastewater, and their membrane fouling potentials were directly measured using bench-scale cross-flow membrane filtration systems (CFMFSs) and related to their cellular properties. It was found that the fouling potential was highly strain dependent, suggesting that bacterial identification at the strain level is essential to identify key fouling-causing bacteria (FCB). The FCB showed some common cellular properties. The most prominent feature of FCB was that they formed convex colonies having swollen podgy shape and smooth lustrous surfaces with high water, hydrophilic organic matter and carbohydrate content. However, general and rigid biofilm formation potential as determined by microtiter plates and cell surface properties (i.e., hydrophobicity and surface charge) did not correlate with the fouling potential in this study. These results suggest that the fouling potential should be directly evaluated under filtration conditions, and the colony water content could be a useful indicator to identify the FCB. PMID:27232989

  5. Cholesterol modulates alkaline phosphatase activity of rat intestinal microvillus membranes.

    PubMed

    Brasitus, T A; Dahiya, R; Dudeja, P K; Bissonnette, B M

    1988-06-25

    Experiments were conducted, using a nonspecific lipid transfer protein, to vary the cholesterol/phospholipid molar ratio of rat proximal small intestinal microvillus membranes in order to assess the possible role of cholesterol in modulating enzymatic activities of this plasma membrane. Cholesterol/phospholipid molar ratios from 0.71 to 1.30 were produced from a normal value of 1.05 by incubation with the transfer protein and an excess of either phosphatidylcholine or cholesterol/phosphatidylcholine liposomes for 60 min at 37 degrees C. Cholesterol loading or depletion of the membranes was accompanied by a decrease or increase, respectively, in their lipid fluidity, as assessed by steady-state fluorescence polarization techniques using the lipid-soluble fluorophore 1,6-diphenyl-1,3,5-hexatriene. Increasing the cholesterol/phospholipid molar ratio also decreased alkaline phosphatase specific activity by approximately 20-30%, whereas decreasing this ratio increased this enzymatic activity by 20-30%. Sucrase, maltase, and lactase specific activities were not affected in these same preparations. Since the changes in alkaline phosphatase activity could be secondary to alterations in fluidity, cholesterol, or both, additional experiments were performed using benzyl alcohol, a known fluidizer. Benzyl alcohol (25 mM) restored the fluidity of cholesterol-enriched preparations to control levels, did not change the cholesterol/phospholipid molar ratio, and failed to alter alkaline phosphatase activity. These findings, therefore, indicate that alterations in the cholesterol content and cholesterol/phospholipid molar ratio of microvillus membranes can modulate alkaline phosphatase but not sucrase, maltase, or lactase activities. Moreover, membrane fluidity does not appear to be an important physiological regulator of these enzymatic activities. PMID:3379034

  6. Membrane Thinning and Thickening Induced by Membrane-Active Amphipathic Peptides.

    PubMed

    Grage, Stephan L; Afonin, Sergii; Kara, Sezgin; Buth, Gernot; Ulrich, Anne S

    2016-01-01

    Membrane thinning has been discussed as a fundamental mechanism by which antimicrobial peptides can perturb cellular membranes. To understand which factors play a role in this process, we compared several amphipathic peptides with different structures, sizes and functions in their influence on the lipid bilayer thickness. PGLa and magainin 2 from X. laevis were studied as typical representatives of antimicrobial cationic amphipathic α-helices. A 1:1 mixture of these peptides, which is known to possess synergistically enhanced activity, allowed us to evaluate whether and how this synergistic interaction correlates with changes in membrane thickness. Other systems investigated here include the α-helical stress-response peptide TisB from E. coli (which forms membrane-spanning dimers), as well as gramicidin S from A. migulanus (a natural antibiotic), and BP100 (designer-made antimicrobial and cell penetrating peptide). The latter two are very short, with a circular β-pleated and a compact α-helical structure, respectively. Solid-state (2)H-NMR and grazing incidence small angle X-ray scattering (GISAXS) on oriented phospholipid bilayers were used as complementary techniques to access the hydrophobic thickness as well as the bilayer-bilayer repeat distance including the water layer in between. This way, we found that magainin 2, gramicidin S, and BP100 induced membrane thinning, as expected for amphiphilic peptides residing in the polar/apolar interface of the bilayer. PGLa, on the other hand, decreased the hydrophobic thickness only at very high peptide:lipid ratios, and did not change the bilayer-bilayer repeat distance. TisB even caused an increase in the hydrophobic thickness and repeat distance. When reconstituted as a mixture, PGLa and magainin 2 showed a moderate thinning effect which was less than that of magainin 2 alone, hence their synergistically enhanced activity does not seem to correlate with a modulation of membrane thickness. Overall, the absence of

  7. A membrane-type acoustic metamaterial with adjustable acoustic properties

    NASA Astrophysics Data System (ADS)

    Langfeldt, F.; Riecken, J.; Gleine, W.; von Estorff, O.

    2016-07-01

    A new realization of a membrane-type acoustic metamaterial (MAM) with adjustable sound transmission properties is presented. The proposed design distinguishes itself from other realizations by a stacked arrangement of two MAMs which is inflated using pressurized air. The static pressurization leads to large nonlinear deformations and, consequently, geometrical stiffening of the MAMs which is exploited to adjust the eigenmodes and sound transmission loss of the structure. A theoretical analysis of the proposed inflatable MAM design using numerical and analytical models is performed in order to identify two important mechanisms, namely the shifting of the eigenfrequencies and modal residuals due to the pressurization, responsible for the transmission loss adjustment. Analytical formulas are provided for predicting the eigenmode shifting and normal incidence sound transmission loss of inflated single and double MAMs using the concept of effective mass. The investigations are concluded with results from a test sample measurement inside an impedance tube, which confirm the theoretical predictions.

  8. Hydrodynamic and Membrane Binding Properties of Purified Rous Sarcoma Virus Gag Protein

    PubMed Central

    Nanda, Hirsh; Fang, Xianyang; Wen, Yi; Barros, Marilia; Wang, Yun-Xing; Rein, Alan; Vogt, Volker M.

    2015-01-01

    ABSTRACT Previously, no retroviral Gag protein has been highly purified in milligram quantities and in a biologically relevant and active form. We have purified Rous sarcoma virus (RSV) Gag protein and in parallel several truncation mutants of Gag and have studied their biophysical properties and membrane interactions in vitro. RSV Gag is unusual in that it is not naturally myristoylated. From its ability to assemble into virus-like particles in vitro, we infer that RSV Gag is biologically active. By size exclusion chromatography and small-angle X-ray scattering, Gag in solution appears extended and flexible, in contrast to previous reports on unmyristoylated HIV-1 Gag, which is compact. However, by neutron reflectometry measurements of RSV Gag bound to a supported bilayer, the protein appears to adopt a more compact, folded-over conformation. At physiological ionic strength, purified Gag binds strongly to liposomes containing acidic lipids. This interaction is stimulated by physiological levels of phosphatidylinositol-(4,5)-bisphosphate [PI(4,5)P2] and by cholesterol. However, unlike HIV-1 Gag, RSV Gag shows no sensitivity to acyl chain saturation. In contrast with full-length RSV Gag, the purified MA domain of Gag binds to liposomes only weakly. Similarly, both an N-terminally truncated version of Gag that is missing the MA domain and a C-terminally truncated version that is missing the NC domain bind only weakly. These results imply that NC contributes to membrane interaction in vitro, either by directly contacting acidic lipids or by promoting Gag multimerization. IMPORTANCE Retroviruses like HIV assemble at and bud from the plasma membrane of cells. Assembly requires the interaction between thousands of Gag molecules to form a lattice. Previous work indicated that lattice formation at the plasma membrane is influenced by the conformation of monomeric HIV. We have extended this work to the more tractable RSV Gag. Our results show that RSV Gag is highly flexible

  9. Spatially distinct and metabolically active membrane domain in mycobacteria.

    PubMed

    Hayashi, Jennifer M; Luo, Chu-Yuan; Mayfield, Jacob A; Hsu, Tsungda; Fukuda, Takeshi; Walfield, Andrew L; Giffen, Samantha R; Leszyk, John D; Baer, Christina E; Bennion, Owen T; Madduri, Ashoka; Shaffer, Scott A; Aldridge, Bree B; Sassetti, Christopher M; Sandler, Steven J; Kinoshita, Taroh; Moody, D Branch; Morita, Yasu S

    2016-05-10

    Protected from host immune attack and antibiotic penetration by their unique cell envelope, mycobacterial pathogens cause devastating human diseases such as tuberculosis. Seamless coordination of cell growth with cell envelope elongation at the pole maintains this barrier. Unraveling this spatiotemporal regulation is a potential strategy for controlling mycobacterial infections. Our biochemical analysis previously revealed two functionally distinct membrane fractions in Mycobacterium smegmatis cell lysates: plasma membrane tightly associated with the cell wall (PM-CW) and a distinct fraction of pure membrane free of cell wall components (PMf). To provide further insight into the functions of these membrane fractions, we took the approach of comparative proteomics and identified more than 300 proteins specifically associated with the PMf, including essential enzymes involved in cell envelope synthesis such as a mannosyltransferase, Ppm1, and a galactosyltransferase, GlfT2. Furthermore, comparative lipidomics revealed the distinct lipid composition of the PMf, with specific association of key cell envelope biosynthetic precursors. Live-imaging fluorescence microscopy visualized the PMf as patches of membrane spatially distinct from the PM-CW and notably enriched in the pole of the growing cells. Taken together, our study provides the basis for assigning the PMf as a spatiotemporally distinct and metabolically active membrane domain involved in cell envelope biogenesis. PMID:27114527

  10. Large-Aperture Membrane Active Phased-Array Antennas

    NASA Technical Reports Server (NTRS)

    Karasik, Boris; McGrath, William; Leduc, Henry

    2009-01-01

    Large-aperture phased-array microwave antennas supported by membranes are being developed for use in spaceborne interferometric synthetic aperture radar systems. There may also be terrestrial uses for such antennas supported on stationary membranes, large balloons, and blimps. These antennas are expected to have areal mass densities of about 2 kg/sq m, satisfying a need for lightweight alternatives to conventional rigid phased-array antennas, which have typical areal mass densities between 8 and 15 kg/sq m. The differences in areal mass densities translate to substantial differences in total mass in contemplated applications involving aperture areas as large as 400 sq m. A membrane phased-array antenna includes patch antenna elements in a repeating pattern. All previously reported membrane antennas were passive antennas; this is the first active membrane antenna that includes transmitting/receiving (T/R) electronic circuits as integral parts. Other integral parts of the antenna include a network of radio-frequency (RF) feed lines (more specifically, a corporate feed network) and of bias and control lines, all in the form of flexible copper strip conductors on flexible polymeric membranes. Each unit cell of a prototype antenna (see Figure 1) contains a patch antenna element and a compact T/R module that is compatible with flexible membrane circuitry. There are two membrane layers separated by a 12.7-mm air gap. Each membrane layer is made from a commercially available flexible circuit material that, as supplied, comprises a 127-micron-thick polyimide dielectric layer clad on both sides with 17.5-micron-thick copper layers. The copper layers are patterned into RF, bias, and control conductors. The T/R module is located on the back side of the ground plane and is RF-coupled to the patch element via a slot. The T/R module is a hybrid multilayer module assembled and packaged independently and attached to the membrane array. At the time of reporting the information for

  11. Pervaporation properties of dense polyamide-6 membranes in separation of water-ethanol mixtures

    SciTech Connect

    Kujawski, W.; Waczynski, M.; Lasota, M.

    1996-04-01

    Several dense polyamide-6 membranes were prepared by casting 7 wt% and/or 10 wt% solutions of polymer in trifluoroethanol. The cast membranes were dried at different temperatures from 25 to 80{degrees}C. Sorption and pervaporation properties of PA-6 membranes in water-ethanol mixtures were obtained. The data obtained showed that water was preferentially sorbed into the membrane and transported through the membrane; however, the pervaporation selectivity factor {alpha}{sup PV} was close to unity at higher concentrations. The selectivity parameters in pervaporation were improved for membranes obtained from 10 wt% polymer and dried at higher temperatures.

  12. Preparation and properties of PLGA nanofiber membranes reinforced with cellulose nanocrystals.

    PubMed

    Mo, Yunfei; Guo, Rui; Liu, Jianghui; Lan, Yong; Zhang, Yi; Xue, Wei; Zhang, Yuanming

    2015-08-01

    Although extensively used in the fields of drug-carrier and tissue engineering, the biocompatibility and mechanical properties of polylactide-polyglycolide (PLGA) nanofiber membranes still limit their applications. The objective of this study was to improve their utility by introducing cellulose nanocrystals (CNCs) into PLGA nanofiber membranes. PLGA and PLGA/CNC composite nanofiber membranes were prepared via electrospinning, and the morphology and thermodynamic and mechanical properties of these nanofiber membranes were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The cytocompatibility and cellular responses of the nanofiber membranes were also studied by WST-1 assay, SEM, and confocal laser scanning microscopy (CLSM). Incorporation of CNCs (1, 3, 5, and 7 wt.%) increased the average fiber diameter of the prepared nanofiber membranes from 100 nm (neat PLGA) to ∼400 nm (PLGA/7 wt.% CNC) and improved the thermal stability of the nanofiber membranes. Among the PLGA/CNC composite nanofiber membranes, those loaded with 7 wt.% CNC nanofiber membranes had the best mechanical properties, which were similar to those of human skin. Cell culture results showed that the PLGA/CNC composite nanofiber membranes had better cytocompatibility and facilitated fibroblast adhesion, spreading, and proliferation compared with neat PLGA nanofiber membranes. These preliminary results suggest that PLGA/CNC composite nanofiber membranes are promising new materials for the field of skin tissue engineering. PMID:26047881

  13. Importance of Membrane Structural Integrity for RPE65 Retinoid Isomerization Activity*

    PubMed Central

    Golczak, Marcin; Kiser, Philip D.; Lodowski, David T.; Maeda, Akiko; Palczewski, Krzysztof

    2010-01-01

    Regeneration of visual chromophore in the vertebrate visual cycle involves the retinal pigment epithelium-specific protein RPE65, the key enzyme catalyzing the cleavage and isomerization of all-trans-retinyl fatty acid esters to 11-cis-retinol. Although RPE65 has no predicted membrane spanning domains, this protein predominantly associates with microsomal fractions isolated from bovine retinal pigment epithelium (RPE). We have re-examined the nature of RPE65 interactions with native microsomal membranes by using extraction and phase separation experiments. We observe that hydrophobic interactions are the dominant forces that promote RPE65 association with these membranes. These results are consistent with the crystallographic model of RPE65, which features a large lipophilic surface that surrounds the entrance to the catalytic site of this enzyme and likely interacts with the hydrophobic core of the endoplasmic reticulum membrane. Moreover, we report a critical role for phospholipid membranes in preserving the retinoid isomerization activity and physical properties of RPE65. Isomerase activity measured in bovine RPE was highly sensitive to phospholipase A2 treatment, but the observed decline in 11-cis-retinol production did not directly reflect inhibition by products of lipid hydrolysis. Instead, a direct correlation between the kinetics of phospholipid hydrolysis and retinoid isomerization suggests that the lipid membrane structure is critical for RPE65 enzymatic activity. We also provide evidence that RPE65 operates in a multiprotein complex with retinol dehydrogenase 5 and retinal G protein-coupled receptor in RPE microsomes. Modifications in the phospholipid environment affecting interactions with these protein components may be responsible for the alterations in retinoid metabolism observed in phospholipid-depleted RPE microsomes. Thus, our results indicate that the enzymatic activity of native RPE65 strongly depends on its membrane binding and phospholipid

  14. Ultrathin and stable active layer of dense composite membrane enabled by poly(dopamine).

    PubMed

    Li, Ben; Liu, Wanpeng; Jiang, Zhongyi; Dong, Xiao; Wang, Baoyi; Zhong, Yurong

    2009-07-01

    We demonstrate that dopamine is able to self-polymerize and adhere firmly onto the substrate, which can create a hierarchical structure comprising an ultrathin active layer and a porous support layer. Such an approach opens a novel way to fabricating highly efficient and stable composite materials including composite membranes. More specifically, in this study the composite membranes are fabricated by simply dipping microporous substrate in aqueous dopamine solution under mild conditions. Nanoindentation measurement reveals the tight adhesion of dopamine onto microporous substrate, which is ascribed to numerous pi-pi and hydrogen-bonding interactions. The chemical composition of the active layer is analyzed by XPS, which demonstrates the self-polymerization of dopamine. The water contact angle of the dopamine coated membranes is reduced remarkably compared with that of the uncoated counterpart. Stylus profiler measurements display that the poly(dopamine) thickness increases as the coating time increases. FESEM images of the membranes' cross section show that an active layer (<100 nm) is deposited on the porous polysulfone (PS) substrate. Positron annihilation spectroscopy (PAS) is introduced to probe the fractional free volume properties throughout the cross section of the composite membranes and reveal that after dopamine double-coating the active layer becomes thicker and more compact. Moreover, pH and concentration of the dopamine solution exert notable influence on the fractional free volume of the composite membranes. The as-prepared membranes are tentatively employed for pervaporative desulfurization and exhibits satisfying separation performance as well as durability. This facile, versatile, and efficient approach enables a promising prospect for the wide applications of such novel kinds of ultrathin composite materials. PMID:19366196

  15. Importance of Membrane Structural Integrity for RPE65 Retinoid Isomerization Activity

    SciTech Connect

    Golczak, Marcin; Kiser, Philip D.; Lodowski, David T.; Maeda, Akiko; Palczewski, Krzysztof

    2010-04-05

    Regeneration of visual chromophore in the vertebrate visual cycle involves the retinal pigment epithelium-specific protein RPE65, the key enzyme catalyzing the cleavage and isomerization of all-trans-retinyl fatty acid esters to 11-cis-retinol. Although RPE65 has no predicted membrane spanning domains, this protein predominantly associates with microsomal fractions isolated from bovine retinal pigment epithelium (RPE). We have re-examined the nature of RPE65 interactions with native microsomal membranes by using extraction and phase separation experiments. We observe that hydrophobic interactions are the dominant forces that promote RPE65 association with these membranes. These results are consistent with the crystallographic model of RPE65, which features a large lipophilic surface that surrounds the entrance to the catalytic site of this enzyme and likely interacts with the hydrophobic core of the endoplasmic reticulum membrane. Moreover, we report a critical role for phospholipid membranes in preserving the retinoid isomerization activity and physical properties of RPE65. Isomerase activity measured in bovine RPE was highly sensitive to phospholipase A{sup 2} treatment, but the observed decline in 11-cis-retinol production did not directly reflect inhibition by products of lipid hydrolysis. Instead, a direct correlation between the kinetics of phospholipid hydrolysis and retinoid isomerization suggests that the lipid membrane structure is critical for RPE65 enzymatic activity. We also provide evidence that RPE65 operates in a multiprotein complex with retinol dehydrogenase 5 and retinal G protein-coupled receptor in RPE microsomes. Modifications in the phospholipid environment affecting interactions with these protein components may be responsible for the alterations in retinoid metabolism observed in phospholipid-depleted RPE microsomes. Thus, our results indicate that the enzymatic activity of native RPE65 strongly depends on its membrane binding and

  16. Nature of the charged headgroup determines the fusogenic potential and membrane properties of lithocholic acid phospholipids.

    PubMed

    Bhargava, Priyanshu; Singh, Manish; Sreekanth, Vedagopuram; Bajaj, Avinash

    2014-08-01

    Phospholipids play a crucial role in many cellular processes ranging from selective membrane permeability, to membrane fission and fusion, to cellular signaling. Headgroups of phospholipids determine the membrane properties and fusogenicity of these lipids with target cell membranes. We studied the fusogenic and membrane properties of phospholipids possessing unnatural charged headgroups with model membranes using laurdan based membrane hydration studies, DPH based membrane fluidity, and differential scanning calorimetry. We unravel that fusogenicity, membrane hydration, and fluidity of membranes are strongly contingent on the nature of the phospholipid charged headgroup. Our studies unraveled that introduction of bulky headgroups like dimethylamino pyridine induces maximum membrane hydration and perturbations with high fusogenicity as compared to small headgroup based phospholipids. These phospholipids also have the capability of high retention in DPPC membranes. Hydration and fluidity of these phospholipid-doped DPPC membranes are contingent on the nature of the charged headgroup. This study would help in future design of phospholipid based nanomaterials for effective drug delivery. PMID:25029367

  17. Property Blocks: Games and Activities.

    ERIC Educational Resources Information Center

    Humphreys, Alan, Ed.; Dailey, Jean, Ed.

    This pamphlet describes the property blocks produced by MINNEMAST, and discusses their use in the development of thinking processes. Classification systems, including block diagrams and tree diagrams, are discussed. Sixteen classroom activities and eleven games which use the blocks are described. Suggestions to the teacher for further reading are…

  18. Alterations of Red Cell Membrane Properties in Nneuroacanthocytosis

    PubMed Central

    Siegl, Claudia; Hamminger, Patricia; Jank, Herbert; Ahting, Uwe; Bader, Benedikt; Danek, Adrian; Gregory, Allison; Hartig, Monika; Hayflick, Susan; Hermann, Andreas; Prokisch, Holger; Sammler, Esther M.; Yapici, Zuhal; Prohaska, Rainer; Salzer, Ulrich

    2013-01-01

    Neuroacanthocytosis (NA) refers to a group of heterogenous, rare genetic disorders, namely chorea acanthocytosis (ChAc), McLeod syndrome (MLS), Huntington’s disease-like 2 (HDL2) and pantothenate kinase associated neurodegeneration (PKAN), that mainly affect the basal ganglia and are associated with similar neurological symptoms. PKAN is also assigned to a group of rare neurodegenerative diseases, known as NBIA (neurodegeneration with brain iron accumulation), associated with iron accumulation in the basal ganglia and progressive movement disorder. Acanthocytosis, the occurrence of misshaped erythrocytes with thorny protrusions, is frequently observed in ChAc and MLS patients but less prevalent in PKAN (about 10%) and HDL2 patients. The pathological factors that lead to the formation of the acanthocytic red blood cell shape are currently unknown. The aim of this study was to determine whether NA/NBIA acanthocytes differ in their functionality from normal erythrocytes. Several flow-cytometry-based assays were applied to test the physiological responses of the plasma membrane, namely drug-induced endocytosis, phosphatidylserine exposure and calcium uptake upon treatment with lysophosphatidic acid. ChAc red cell samples clearly showed a reduced response in drug-induced endovesiculation, lysophosphatidic acid-induced phosphatidylserine exposure, and calcium uptake. Impaired responses were also observed in acanthocyte-positive NBIA (PKAN) red cells but not in patient cells without shape abnormalities. These data suggest an “acanthocytic state” of the red cell where alterations in functional and interdependent membrane properties arise together with an acanthocytic cell shape. Further elucidation of the aberrant molecular mechanisms that cause this acanthocytic state may possibly help to evaluate the pathological pathways leading to neurodegeneration. PMID:24098554

  19. Alterations of red cell membrane properties in neuroacanthocytosis.

    PubMed

    Siegl, Claudia; Hamminger, Patricia; Jank, Herbert; Ahting, Uwe; Bader, Benedikt; Danek, Adrian; Gregory, Allison; Hartig, Monika; Hayflick, Susan; Hermann, Andreas; Prokisch, Holger; Sammler, Esther M; Yapici, Zuhal; Prohaska, Rainer; Salzer, Ulrich

    2013-01-01

    Neuroacanthocytosis (NA) refers to a group of heterogenous, rare genetic disorders, namely chorea acanthocytosis (ChAc), McLeod syndrome (MLS), Huntington's disease-like 2 (HDL2) and pantothenate kinase associated neurodegeneration (PKAN), that mainly affect the basal ganglia and are associated with similar neurological symptoms. PKAN is also assigned to a group of rare neurodegenerative diseases, known as NBIA (neurodegeneration with brain iron accumulation), associated with iron accumulation in the basal ganglia and progressive movement disorder. Acanthocytosis, the occurrence of misshaped erythrocytes with thorny protrusions, is frequently observed in ChAc and MLS patients but less prevalent in PKAN (about 10%) and HDL2 patients. The pathological factors that lead to the formation of the acanthocytic red blood cell shape are currently unknown. The aim of this study was to determine whether NA/NBIA acanthocytes differ in their functionality from normal erythrocytes. Several flow-cytometry-based assays were applied to test the physiological responses of the plasma membrane, namely drug-induced endocytosis, phosphatidylserine exposure and calcium uptake upon treatment with lysophosphatidic acid. ChAc red cell samples clearly showed a reduced response in drug-induced endovesiculation, lysophosphatidic acid-induced phosphatidylserine exposure, and calcium uptake. Impaired responses were also observed in acanthocyte-positive NBIA (PKAN) red cells but not in patient cells without shape abnormalities. These data suggest an "acanthocytic state" of the red cell where alterations in functional and interdependent membrane properties arise together with an acanthocytic cell shape. Further elucidation of the aberrant molecular mechanisms that cause this acanthocytic state may possibly help to evaluate the pathological pathways leading to neurodegeneration. PMID:24098554

  20. Measuring Cysteine Cathepsin Activity to Detect Lysosomal Membrane Permeabilization.

    PubMed

    Repnik, Urška; Česen, Maruša Hafner; Turk, Boris

    2016-01-01

    During lysosomal membrane permeabilization (LMP), lysosomal lumenal contents can be released into the cytosol. Small molecules are more likely to be released, and cysteine cathepsins, with mature forms possessing a mass of 25-30 kDa, are among the smallest lumenal lysosomal enzymes. In addition, specific substrates for cysteine cathepsins are available to investigators, and therefore the measurement of the cathepsin activity as a hallmark of LMP works well. Here, we present a protocol for measuring the activity of these enzymes after selective plasma membrane permeabilization with a low concentration of digitonin and after total cell membrane lysis with a high concentration of digitonin. A fluorogenic substrate can be added either directly to the well with lysed cells to show LMP or to the cell-free extract to show that the lysosomal membrane has been sufficiently destabilized to allow the translocation of lysosomal enzymes. Although the content of lysosomal cysteine cathepsins differs between cell lines, this method has general applicability, is sensitive, and has high throughput. The presented protocol shows how to measure cysteine cathepsin activity in the presence of lysed cells and also in cell-free extracts. Depending on the aim of the study, one or both types of measurements can be performed. PMID:27140915

  1. Membrane phase characteristics control NA-CATH activity.

    PubMed

    Samuel, Robin; Gillmor, Susan

    2016-09-01

    Our studies presented in this report focus on the behavior of NA-CATH, an α-helical cathelicidin antimicrobial peptide, originally discovered in the Naja atra snake. It has demonstrated high potency against gram-positive and gram-negative bacteria with minimal hemolysis. Here we examine the kinetics, behaviors and potential mechanisms of the peptide in the presence of membrane liposome, modeling Escherichia coli, whose membrane exhibits distinct lipid phases. To understand NA-CATH interactions, the role of lipid phases is critical. We test three different lipid compositions to detangle the effect of phase on NA-CATH's activity using a series of leakage experiments. From these studies, we observe that NA-CATH changes from membrane disruption to pore-based lysing, depending on phases and lipid composition. This behavior also plays a major role in its kinetics. PMID:27216315

  2. Membrane-active macromolecules resensitize NDM-1 gram-negative clinical isolates to tetracycline antibiotics.

    PubMed

    Uppu, Divakara S S M; Manjunath, Goutham B; Yarlagadda, Venkateswarlu; Kaviyil, Jyothi E; Ravikumar, Raju; Paramanandham, Krishnamoorthy; Shome, Bibek R; Haldar, Jayanta

    2015-01-01

    Gram-negative 'superbugs' such as New Delhi metallo-beta-lactamase-1 (blaNDM-1) producing pathogens have become world's major public health threats. Development of molecular strategies that can rehabilitate the 'old antibiotics' and halt the antibiotic resistance is a promising approach to target them. We report membrane-active macromolecules (MAMs) that restore the antibacterial efficacy (enhancement by >80-1250 fold) of tetracycline antibiotics towards blaNDM-1 Klebsiella pneumonia and blaNDM-1 Escherichia coli clinical isolates. Organismic studies showed that bacteria had an increased and faster uptake of tetracycline in the presence of MAMs which is attributed to the mechanism of re-sensitization. Moreover, bacteria did not develop resistance to MAMs and MAMs stalled the development of bacterial resistance to tetracycline. MAMs displayed membrane-active properties such as dissipation of membrane potential and membrane-permeabilization that enabled higher uptake of tetracycline in bacteria. In-vivo toxicity studies displayed good safety profiles and preliminary in-vivo antibacterial efficacy studies showed that mice treated with MAMs in combination with antibiotics had significantly decreased bacterial burden compared to the untreated mice. This report of re-instating the efficacy of the antibiotics towards blaNDM-1 pathogens using membrane-active molecules advocates their potential for synergistic co-delivery of antibiotics to combat Gram-negative superbugs. PMID:25789871

  3. Evidence of steroid hormone activity in the chorioallantoic membrane of a Turtle (Pseudemys nelsoni).

    PubMed

    Cruze, Lori; Hamlin, Heather J; Kohno, Satomi; McCoy, Michael W; Guillette, Louis J

    2013-06-01

    Endocrine properties of extraembryonic membranes have traditionally been viewed as a characteristic of placental amniotes. However, our laboratory recently demonstrated that this ability extends to the extraembryonic membranes of two oviparous amniotes (chicken and alligator) indicating that endocrine extraembryonic membranes are not an innovation of placental amniotes and suggesting that this could be a shared amniote characteristic. In this study, we test our hypothesis that the chorioallantoic membrane (CAM) obtained from non-archosaurian obligate oviparous amniotes such as turtles, have the potential for steroid hormone activity. To investigate synthesis of a major placental hormone, we performed explant culture and found that the turtle CAM synthesizes progesterone in vitro in the presence of a steroid precursor. In addition, to examine whether the CAM has the ability to respond to steroid signaling, we quantified mRNA expression of the progesterone, androgen, and two estrogen receptors. Finally, to determine if steroid receptor mRNA is translated to protein, we performed immunolocalization of the progesterone receptor. Our data demonstrate that the turtle CAM exhibits steroid synthesis and has steroid hormone signaling capabilities. To that end, steroid hormone activity has now been demonstrated in the CAMs of three oviparous species that represent three independent lineages within oviparous Reptilia that have never exhibited viviparity; thus these data support our hypothesis that endocrine activity of extraembryonic membranes is a conserved trait of Amniota. PMID:23458289

  4. Membrane-Active Macromolecules Resensitize NDM-1 Gram-Negative Clinical Isolates to Tetracycline Antibiotics

    PubMed Central

    Uppu, Divakara S. S. M.; Manjunath, Goutham B.; Yarlagadda, Venkateswarlu; Kaviyil, Jyothi E.; Ravikumar, Raju; Paramanandham, Krishnamoorthy; Shome, Bibek R.; Haldar, Jayanta

    2015-01-01

    Gram-negative ‘superbugs’ such as New Delhi metallo-beta-lactamase-1 (blaNDM-1) producing pathogens have become world’s major public health threats. Development of molecular strategies that can rehabilitate the ‘old antibiotics’ and halt the antibiotic resistance is a promising approach to target them. We report membrane-active macromolecules (MAMs) that restore the antibacterial efficacy (enhancement by >80-1250 fold) of tetracycline antibiotics towards blaNDM-1 Klebsiella pneumonia and blaNDM-1 Escherichia coli clinical isolates. Organismic studies showed that bacteria had an increased and faster uptake of tetracycline in the presence of MAMs which is attributed to the mechanism of re-sensitization. Moreover, bacteria did not develop resistance to MAMs and MAMs stalled the development of bacterial resistance to tetracycline. MAMs displayed membrane-active properties such as dissipation of membrane potential and membrane-permeabilization that enabled higher uptake of tetracycline in bacteria. In-vivo toxicity studies displayed good safety profiles and preliminary in-vivo antibacterial efficacy studies showed that mice treated with MAMs in combination with antibiotics had significantly decreased bacterial burden compared to the untreated mice. This report of re-instating the efficacy of the antibiotics towards blaNDM-1 pathogens using membrane-active molecules advocates their potential for synergistic co-delivery of antibiotics to combat Gram-negative superbugs. PMID:25789871

  5. How To Functionalize Ceramics by Perfluoroalkylsilanes for Membrane Separation Process? Properties and Application of Hydrophobized Ceramic Membranes.

    PubMed

    Kujawa, Joanna; Cerneaux, Sophie; Kujawski, Wojciech; Bryjak, Marek; Kujawski, Jan

    2016-03-23

    The combination of microscopic (atomic force microscopy and scanning electron microscopy) and goniometric (static and dynamic measurements) techniques, and surface characterization (surface free energy determination, critical surface tension, liquid entry pressure, hydraulic permeability) was implemented to discuss the influence of perfluoroalkylsilanes structure and grafting time on the physicochemistry of the created hydrophobic surfaces on the titania ceramic membranes of 5 kD and 300 kD. The impact of molecular structure of perfluoroalkylsilanes modifiers (possessing from 6 to 12 carbon atoms in the fluorinated part of the alkyl chain) and the time of the functionalization process in the range of 5 to 35 h was studied. Based on the scanning electron microscopy with energy-dispersive X-ray spectroscopy, it was found that the localization of grafting molecules depends on the membrane pore size (5 kD or 300 kD). In the case of 5 kD titania membranes, modifiers are attached mainly on the surface and only partially inside the membrane pores, whereas, for 300 kD membranes, the perfluoroalkylsilanes molecules are present within the whole porous structure of the membranes. The application of 4 various types of PFAS molecules enabled for interesting observations and remarks. It was explained how to obtain ceramic membrane surfaces with controlled material (contact angle, roughness, contact angle hysteresis) and separation properties. Highly hydrophobic surfaces with low values of contact angle hysteresis and low roughness were obtained. These surfaces possessed also low values of critical surface tension, which means that surfaces are highly resistant to wetting. This finding is crucial in membrane applicability in separation processes. The obtained and characterized hydrophobic membranes were subsequently applied in air-gap membrane distillation processes. All membranes were very efficient in MD processes, showing good transport and selective properties (∼99% of Na

  6. Effect of Amphotericin B antibiotic on the properties of model lipid membrane

    NASA Astrophysics Data System (ADS)

    Kiryakova, S.; Dencheva-Zarkova, M.; Genova, J.

    2014-12-01

    Model membranes formed from natural and synthetic lipids are an interesting object for scientific investigations due to their similarity to biological cell membrane and their simple structure with controlled composition and properties. Amphotericin B is an important polyene antifungal antibiotic, used for treatment of systemic fungal infections. It is known from the literature that the studied antibiotic has a substantial effect on the transmembrane ionic channel structures. When applied to the lipid membranes it has the tendency to create pores and in this way to affect the structure and the properties of the membrane lipid bilayer. In this work the thermally induced shape fluctuations of giant quasi-spherical liposomes have been used to study the influence of polyene antibiotic amphotericin B on the elastic properties of model lipid membranes. It have been shown experimentally that the presence of 3 mol % of AmB in the lipid membrane reduces the bending elasticity of the lipid membrane for both studied cases: pure SOPC membrane and mixed SOPC-Cholesterol membrane. Interaction of the amphotericin B with bilayer lipid membranes containing channels have been studied in this work. Model membranes were self-assembled using the patch-clamp and tip-dip patch clamp technique. We have found that amphotericin B is an ionophore and reduces the resistance of the lipid bilayer.

  7. Structure-property relationships of anionic permselective membranes. [Fe/Cr redox storage batteries

    SciTech Connect

    Arnold, C. Jr.

    1983-01-01

    Anionic exchange membranes are used in Fe/Cr redox storage batteries to separate the anolyte from the catholyte and provide electrical continuity. Membranes with lower area resistivity, higher selectivity and reduced susceptibility toward fouling are required to improve the efficiency and lifetime of these batteries. In order to develop improved membrane, a better understanding of the relationships between these properties and such structural parameters as degree of crosslinking, ion exchange capacity and porosity were needed. The primary objective of this work was to define the structure-property relationships of anionic permselective membranes. A secondary goal was to develop empirical models which can be used to predict membrane performance. This kind of information should be useful for the development of improved membranes. To accomplish these goals a factorial study was carried out with model membranes. These membranes were designed in such a way that all three structural parameters could be varied independently. In this paper it will be shown how this approach not only provided models which could be used to predict membrane performance, but also how one of the model membrane exhibited better properties than state-of-the-art membranes.

  8. Functional specializations of primary auditory afferents on the Mauthner cells: interactions between membrane and synaptic properties.

    PubMed

    Curti, Sebastian; Pereda, Alberto E

    2010-01-01

    Primary auditory afferents are usually perceived as passive, timing-preserving, lines of communication. Contrasting this view, a special class of auditory afferents to teleost Mauthner cells, a command neuron that organizes tail-flip escape responses, undergoes potentiation of their mixed (electrical and chemical) synapses in response to high frequency cellular activity. This property is likely to represent a mechanism of input sensitization as these neurons provide the Mauthner cell with essential information for the initiation of an escape response. We review here the anatomical and physiological specializations of these identifiable auditory afferents. In particular, we discuss how their membrane and synaptic properties act in concert to more efficaciously activate the Mauthner cells. The striking functional specializations of these neurons suggest that primary auditory afferents might be capable of more sophisticated contributions to auditory processing than has been generally recognized. PMID:19941953

  9. Composite membranes prepared from cation exchange membranes and polyaniline and their transport properties in electrodialysis

    SciTech Connect

    Sata, Tshikatsu; Ishii, Yuuko; Kawamura, Kohei; Matsusaki, Koji

    1999-02-01

    A cation exchange membrane was modified with polyaniline by polymerizing aniline with ammonium peroxodisulfate on the membrane surfaces, producing a membrane with polyaniline layers on both surfaces or a membrane with a single polyaniline layer on the surface. The modified membranes, composite membranes, showed sodium ion permselectivity in electrodialysis compared with divalent cations at an optimum polymerization time. The electronic conductivity of dry membranes showed a maximum (ca. 5 {times} 10{sup {minus}3} S/cm) at the same polymerization time as the time to attain a maximum value of the sodium ion permselectivity. Because emeraldine-based polyaniline is conductive and has a cationic charge, the sodium ion permselectivity is based on the difference in the electrostatic repulsion forces of the cationic charge on the membrane surface of a desalting side to divalent cations and sodium ions. In fact, the selective permeation of sodium ions appeared only when the layer faced the desalting side of the membrane, and was affected by dissociation of polyaniline. Further oxidized polyaniline, pernigraniline-based polyaniline, did not affect the permselectivity between cations, and the diffusion coefficient of neutral molecules, urea, increased with increasing polymerization time. Sodium ion permselectivity was maintained with repeated electrodialysis.

  10. Preparation of hydrophilic vinyl chloride copolymer hollow fiber membranes with antifouling properties

    NASA Astrophysics Data System (ADS)

    Rajabzadeh, Saeid; Sano, Rie; Ishigami, Toru; Kakihana, Yuriko; Ohmukai, Yoshikage; Matsuyama, Hideto

    2015-01-01

    Hydrophilic vinyl chloride copolymer hollow fiber membranes with antifouling properties were prepared from brominated vinyl chloride-hydroxyethyl methacrylate copolymer (poly(VC-co-HEMA-Br)). The base membrane was grafted with two different zwitterionic monomers, (2-methacryloyloxyethylphosphorylcholine) (MPC) and [2-(methacryloyloxy) ethyl] dimethyl (3-sulfopropyl) ammonium hydroxide) (MEDSAH), and poly(ethylene glycol) methyl ether methacrylate (PEGMA). The effect of the grafting on the base membrane hydrophilicity and antifouling properties was investigated. For comparison of the results, the pure water permeabilities and pore sizes at the outer surfaces of the grafted hollow fiber membranes were controlled to be similar. A poly(VC-co-HEMA-Br) hollow fiber membrane with similar pure water permeability and pore size was also prepared as a control membrane. A BSA solution was used as a model fouling solution for evaluation of the antifouling properties. Grafting with zwitterionic monomers and PEGMA improved the antifouling properties compared with the control membrane. The PEGMA grafted membrane showed the best antifouling properties among the grafted membranes

  11. Shape-dependent bactericidal activity of copper oxide nanoparticle mediated by DNA and membrane damage

    SciTech Connect

    Laha, Dipranjan; Pramanik, Arindam; Laskar, Aparna; Jana, Madhurya; Pramanik, Panchanan; Karmakar, Parimal

    2014-11-15

    Highlights: • Spherical and sheet shaped copper oxide nanoparticles were synthesized. • Physical characterizations of these nanoparticles were done by TEM, DLS, XRD, FTIR. • They showed shape dependent antibacterial activity on different bacterial strain. • They induced both membrane damage and ROS mediated DNA damage in bacteria. - Abstract: In this work, we synthesized spherical and sheet shaped copper oxide nanoparticles and their physical characterizations were done by the X-ray diffraction, fourier transform infrared spectroscopy, transmission electron microscopy and dynamic light scattering. The antibacterial activity of these nanoparticles was determined on both gram positive and gram negative bacterial. Spherical shaped copper oxide nanoparticles showed more antibacterial property on gram positive bacteria where as sheet shaped copper oxide nanoparticles are more active on gram negative bacteria. We also demonstrated that copper oxide nanoparticles produced reactive oxygen species in both gram negative and gram positive bacteria. Furthermore, they induced membrane damage as determined by atomic force microscopy and scanning electron microscopy. Thus production of and membrane damage are major mechanisms of the bactericidal activity of these copper oxide nanoparticles. Finally it was concluded that antibacterial activity of nanoparticles depend on physicochemical properties of copper oxide nanoparticles and bacterial strain.

  12. A packed bed membrane reactor for production of biodiesel using activated carbon supported catalyst.

    PubMed

    Baroutian, Saeid; Aroua, Mohamed K; Raman, Abdul Aziz A; Sulaiman, Nik M N

    2011-01-01

    In this study, a novel continuous reactor has been developed to produce high quality methyl esters (biodiesel) from palm oil. A microporous TiO2/Al2O3 membrane was packed with potassium hydroxide catalyst supported on palm shell activated carbon. The central composite design (CCD) of response surface methodology (RSM) was employed to investigate the effects of reaction temperature, catalyst amount and cross flow circulation velocity on the production of biodiesel in the packed bed membrane reactor. The highest conversion of palm oil to biodiesel in the reactor was obtained at 70 °C employing 157.04 g catalyst per unit volume of the reactor and 0.21 cm/s cross flow circulation velocity. The physical and chemical properties of the produced biodiesel were determined and compared with the standard specifications. High quality palm oil biodiesel was produced by combination of heterogeneous alkali transesterification and separation processes in the packed bed membrane reactor. PMID:20888219

  13. Some properties and applications of thin self-supporting polymer membranes.

    PubMed

    Korn, U; Rav-Noy, Z; Shtrikman, S

    1978-10-01

    Membranes as thin as 500 A were produced from many plastic materials and transferred to frames with dimensions of several centimeters. The self-supporting membranes were obtained using simple-dip-coating techniques. In some cases additional plasma polymerized layers were applied. These membranes can withstand several procedures of photolithography and chemical processing. The mechanical properties of the membranes are similar to that of the bulk material. Some typical applications are described. These applications include the use of the membranes as substrates for thermoelectric detectors and also as beamsplitters and windows for cells employed in CO(2) laser spectroscopy. PMID:18698977

  14. Properties of stellar activity cycles

    NASA Astrophysics Data System (ADS)

    Korhonen, Heidi

    2015-08-01

    The current photometric datasets, that span decades, allow for studying long-term magentic cycles on active stars. Complementary Ca H&K observations give information also on the cycles of normal solar-like stars, which have significantly smaller, and less easily detectable, spots. In recent years, high precision space-based observations, for example from the Kepler satellite, have allowed also to study the sunspot-like spot sizes in other stars. In this talk I will review what is known about the properties of the cyclic stellar activity in other stars than our Sun, and also discuss the future prospects in this field.

  15. Modification of the properties of biological membrane and its protection against oxidation by Actinidia arguta leaf extract.

    PubMed

    Cyboran, Sylwia; Oszmiański, Jan; Kleszczyńska, Halina

    2014-09-01

    The aim of the study was to determine the polyphenol composition and biological activity of an extract from the leaves of kiwi. Antioxidant and hemolytic activity of the extract were examined, as well as its effect on the physical properties of the erythrocyte membrane such as osmotic resistance, membrane fluidity, and packing order of its hydrophilic area. Antioxidant activity of the extract was determined in relation to the erythrocyte membrane oxidized with free radicals induced by UVB and UVC radiation and the compound AAPH. Chromatographic, spectrophotometric and fluorimetric methods were applied in the research. The obtained results showed that kiwi leaves are a rich source of polyphenolic substances, mainly catechins and their dimers, which do not induce red blood cell hemolysis but make them stronger and more resistant to changes in medium tonicity. Substances contained in the extract effectively protect erythrocyte membranes against oxidation induced by physicochemical factors, the effectiveness of the protection depending on the concentration and type of free radical inducer. In addition, the study showed that the kiwi extract increases fluidity of the erythrocyte membrane and causes an increase in packing disorder in the hydrophilic membrane area. The changes seem to be due to the presence of polyphenolic substances in the extract, mainly in the region of the polar heads of lipids, where they can form a barrier protecting the membrane against diffusion of free radicals to the membrane interior. The effects of the extract evidenced by the present research, in particular protection of the biological membrane against free radicals induced by physicochemical agents, make it a potential valuable food additive, to enrich it with polyphenolic compounds that inhibit lipid oxidation in food exposed to UVB radiation. Supplementing the organism with substances contained in kiwi leaves is expected to provide protection against many diseases that develop as a result

  16. Properties of ganglioside GM1 in phosphatidylcholine bilayer membranes.

    PubMed

    Reed, R A; Shipley, G G

    1996-03-01

    Gangliosides have been shown to function as cell surface receptors, as well as participating in cell growth, differentiation, and transformation. In spite of their multiple biological functions, relatively little is known about their structure and physical properties in membrane systems. The thermotropic and structural properties of ganglioside GM1 alone and in a binary system with 1,2-dipalmitoyl phosphatidylcholine (DPPC) have been investigated by differential scanning calorimetry (DSC) and x-ray diffraction. By DSC hydrated GM1 undergoes a broad endothermic transition TM = 26 degrees C (delta H = 1.7 kcal/mol GM1). X-ray diffraction below (-2 degrees C) and above (51 degrees C) this transition indicates a micellar structure with changes occurring only in the wide angle region of the diffraction pattern (relatively sharp reflection at 1/4.12 A-1 at -2 degrees C; more diffuse reflection at 1/4.41 A-1 at 51 degrees C). In hydrated binary mixtures with DPPC, incorporation of GM1 (0-30 mol%; zone 1) decreases the enthalpy of the DPPC pretransition at low molar compositions while increasing the TM of both the pre- and main transitions (limiting values, 39 and 44 degrees C, respectively). X-ray diffraction studies indicate the presence of a single bilayer gel phase in zone 1 that can undergo chain melting to an L alpha bilayer phase. A detailed hydration study of GM1 (5.7 mol %)/DPPC indicated a conversion of the DPPC bilayer gel phase to an infinite swelling system in zone 1 due to the presence of the negatively charged sialic acid moiety of GM1. At 30-61 mol % GM1 (zone 2), two calorimetric transitions are observed at 44 and 47 degrees C, suggesting the presence of two phases. The lower transition reflects the bilayer gel --> L alpha transition (zone 1), whereas the upper transition appears to be a consequence of the formation of a nonbilayer, micellar or hexagonal phase, although the structure of this phase has not been defined by x-ray diffraction. At > 61 mol % GM

  17. Membrane anchoring of diacylglycerol-lactones substituted with rigid hydrophobic acyl domains correlates with biological activities

    PubMed Central

    Raifman, Or; Kolusheva, Sofiya; Comin, Maria J.; Kedei, Noemi; Lewin, Nancy E.; Blumberg, Peter M.; Marquez, Victor E.; Jelinek, Raz

    2009-01-01

    Summary Synthetic diacylglycerol lactones (DAG-lactones) are effective modulators of critical cellular signaling pathways, downstream of the lipophilic second messenger diacylglycerol, that activate a host of protein kinase C (PKC) isozymes as well as other non-kinase proteins that share with PKC similar C1 membrane-targeting domains. A fundamental determinant of the biological activity of these amphiphilic molecules is the nature of their interactions with cellular membranes. This study characterizes the membrane interactions and bilayer anchoring of a series of DAG-lactones in which the hydrophobic moiety is a “molecular rod”, namely a rigid 4-[2-(R-phenyl)ethynyl]benzoate moiety in the acyl position. Application of assays employing chromatic biomimetic vesicles and biophysical techniques reveals that the mode of membrane anchoring of the DAG-lactone derivatives was markedly affected by the presence of the hydrophobic diphenyl rod and by the size of the functional unit displayed at the terminus of the rod. Two primary mechanisms of interaction were observed: surface binding of the DAG-lactones at the lipid/water interface and deep insertion of the ligands into the alkyl core of the lipid bilayer. These membrane-insertion properties could explain the different patterns of PKC translocation from cytosol to membranes induced by the molecular-rod DAG-lactones. This investigation emphasizes that the side-residues of DAG-lactones, rather than simply conferring hydrophobicity, profoundly influence membrane interactions and in that fashion may further contribute to the diversity of biological actions of these synthetic biomimetic ligands. PMID:19961537

  18. Polyethersulfone/polyacrylonitrile blended ultrafiltration membranes: preparation, morphology and filtration properties.

    PubMed

    Pasaoglu, Mehmet Emin; Guclu, Serkan; Koyuncu, Ismail

    2016-01-01

    Polyethersulfone (PES)/polyacrylonitrile (PAN) membranes have been paid attention among membrane research subjects. However, very few studies are included in the literature. In our study, asymmetric ultrafiltration (UF) membranes were prepared from blends of PES/PAN with phase inversion method using water as coagulation bath. Polyvinylpyrrolidone (PVP) with Mw of 10,000 Da was used as pore former agent. N,N-dimethylformamide was used as solvent. The effects of different percentage of PVP and PES/PAN composition on morphology and water filtration properties were investigated. Membrane performances were examined using pure water and lake water filtration studies. Performances of pure water were less with the addition of PAN into the PES polymer casting solutions. However, long-term water filtration tests showed that PES/PAN blend membranes anti-fouling properties were much higher than the neat PES membranes. The contact angles of PES/PAN membranes were lower than neat PES membranes because of PAN addition in PES polymer casting solutions. Furthermore, it was found that PES/PAN blend UF membranes' dynamic mechanical analysis properties in terms of Young's modules were less than neat PES membrane because of decreasing amount of PES polymer. PMID:27508379

  19. Aluminum ions alter the function of non-specific phospholipase C through the changes in plasma membrane physical properties.

    PubMed

    Pejchar, Přemysl; Martinec, Jan

    2015-01-01

    The first indication of the aluminum (Al) toxicity in plants growing in acidic soils is the cessation of root growth, but the detailed mechanism of Al effect is unknown. Here we examined the impact of Al stress on the activity of non-specific phospholipase C (NPC) in the connection with the processes related to the plasma membrane using fluorescently labeled phosphatidylcholine. We observed a rapid and significant decrease of labeled diacylglycerol (DAG), product of NPC activity, in Arabidopsis seedlings treated with AlCl₃. Interestingly, an application of the membrane fluidizer, benzyl alcohol, restored the level of DAG during Al treatment. Our observations suggest that the activity of NPC is affected by Al-induced changes in plasma membrane physical properties. PMID:26024014

  20. Aluminum ions alter the function of non-specific phospholipase C through the changes in plasma membrane physical properties

    PubMed Central

    Pejchar, Přemysl; Martinec, Jan

    2015-01-01

    The first indication of the aluminum (Al) toxicity in plants growing in acidic soils is the cessation of root growth, but the detailed mechanism of Al effect is unknown. Here we examined the impact of Al stress on the activity of non-specific phospholipase C (NPC) in the connection with the processes related to the plasma membrane using fluorescently labeled phosphatidylcholine. We observed a rapid and significant decrease of labeled diacylglycerol (DAG), product of NPC activity, in Arabidopsis seedlings treated with AlCl3. Interestingly, an application of the membrane fluidizer, benzyl alcohol, restored the level of DAG during Al treatment. Our observations suggest that the activity of NPC is affected by Al-induced changes in plasma membrane physical properties. PMID:26024014

  1. Quantifying the lateral lipid domain properties in erythrocyte ghost membranes using EPR-spectra decomposition.

    PubMed

    Arsov, Zoran; Schara, Milan; Strancar, Janez

    2002-07-01

    Using EPR spectroscopy a typical lateral domain structure was detected in the membranes of spin-labeled bovine erythrocyte ghosts. The spectral parameters were determined by decomposing the EPR spectrum into three spectral components and tuned by a hybrid-evolutionary-optimization method. In our experiments the lateral domain structure and its properties were influenced by the variation in the temperature and by the addition of n-butanol. The specific responses of the particular domain types were detected. For the most-ordered domain type a break was seen in the temperature dependence of its order parameter, while the order parameters of the two less-ordered domain types exhibited a continuous decrease. Below the break-point temperature the alcohol-induced membrane fluidity variation is mainly a consequence of the change in the proportions of the least- and the most-ordered domain type and not the change of the domain-type ordering or dynamics (with n-butanol concentration). On the other hand, the fluidity variation above the break-point temperature arises from both types of changes. Interestingly, the proportion of the domain type that has its order parameter between that of the least- and the most-ordered domain type remains almost constant with concentration as well as with temperature, which implies its stability. Such characterization of the lateral membrane domain structure could be beneficial when considering the lipid-protein interactions, because it can be assumed that the activity of the membrane-bound enzyme depends on the properties of the particular domain type. PMID:12202132

  2. A flexible nanofiber-based membrane with superhydrophobic pinning properties.

    PubMed

    Hu, Luyang; Zhang, Shanmei; Zhang, Yumin; Li, Benxia

    2016-06-15

    A nanofiber-based TiO2(B)/carbon nanofiber membrane has been synthesized by a facile and effective route that incorporates electrospinning approach with hydrothermal method. The prepared membrane shows high flexibility and hydrophilicity. After treatment with a low surface energy fluorosilane, the obtained superhydrophobic surface endows the membrane a high adhesive force due to the hybrid microstructure of TiO2(B) nanotubes and nanoplates on fibers. A water droplet on the surface of the membrane appears spherical in shape, which cannot roll off even when the membrane is bent and turned upside down. When a water droplet dropped from a certain height above the tilt membrane, the rolled water droplet can be stopped after a small displacement. In addition, a 12μl water droplet can be quickly captured from a hydrophobic surface by curvature change of the superhydrophobic TiO2(B)/carbon nanofiber membrane. The membrane with excellent static and dynamic pinning performance to water may be expected to apply to biomedical and microfluidic devices. PMID:27038279

  3. Preparation and gas separation properties of zeolite T membrane.

    PubMed

    Cui, Ying; Kita, Hidetoshi; Okamoto, Ken-ichi

    2003-09-01

    Zeolite T membranes were synthesized on tubular porous mullite tubes by hydrothermal synthesis. The membranes selectively permeated carbon dioxide from CO2/CH4 and CO2/N2 mixtures with high separation performances, which were due to combined effects of molecular sieving and competitive adsorption. PMID:13678177

  4. Physically Gelled Room-Temperature Ionic Liquid-Based Composite Membranes for CO2/N-2 Separation: Effect of Composition and Thickness on Membrane Properties and Performance

    SciTech Connect

    Nguyen, PT; Voss, BA; Wiesenauer, EF; Gin, DL; Nobe, RD

    2013-07-03

    An aspartame-based, low molecular-weight organic gelator (LMOG) was used to form melt-infused and composite membranes with two different imidazolium-based room-temperature ionic liquids (RTILs) for CO2 separation from N-2. Previous work demonstrated that LMOGs can gel RTILs at low, loading levels, and this aspartame-based LMOG was selected because it has been reported to gel a large number of RTILs. The imidazolium-based RTILs were used because of their inherent good properties for CO2/light gas separations. Analysis of the resulting bulk RTIL/LMOG physical gels showed that these materials have high sol-gel transition temperatures (ca. 135 degrees C) suitable for flue gas applications. Gas permeabilities and burst pressure measurements of thick, melt infused membranes revealed a trade-off between high CO2 permeabilities and good mechanical stability as a function of the LMOG loading. Defect-free, composite membranes of the gelled RTILs were successfully fabricated by choosing an appropriate porous membrane support (hydrophobic PTFE) using a suitable coating technique (roller coating). The thicknesses of the applied composite gel layers ranged from 10.3 to 20.7 mu m, which represents an order of magnitude decrease in active layer thickness, compared to the original melt-infused gel RTIL membranes.

  5. Ion implantation: effect on flux and rejection properties of NF membranes.

    PubMed

    Abitoye, Joshua Olufemi; Mukherjee, J Parna; Jones, Kimberly

    2005-09-01

    Nanofiltration (NF) membranes typically carry a net electric charge, enabling electrostatic interactions to play a pivotal role in the rejection of species such as metals, nitrates, and other charged contaminants. In this study, two types of polymeric NF membranes, polyamide and cellulose acetate, were modified by ion implantation to increase the effective surface charge of the membranes. The modified membranes contain implanted ions in the membrane matrix, inducing a discrete, permanent charge in the active membrane layer. The presence of a permanent charge in the membrane matrix allows for increased electrostatic repulsive forces throughout the entire pH range. Streaming potential measurements were conducted as a function of pH for the modified and unmodified membranes to determine the effect of ion implantation on the zeta potential of the membranes. Rejection experiments were performed in order to quantify the effect of increased electrostatic repulsion on ion rejection, and flux measurements quantified the effect of the modification on permeability. Results indicate that electrostatic interactions near the membrane surface can affect rejection; however, the extent of the effect of increased membrane charge depends on physical-chemical characteristics of the membrane. Increased negative zeta potential of the modified membranes resulted in slightly higher rejection of salts with divalent co-ions from the membrane, with less increase observed with salts of monovalent co-ions. Modified membranes were less permeable than the unmodified membranes. Results of this research hold implications in membrane synthesis and modification studies as well as choice of membranes for water treatment applications. PMID:16190203

  6. The adrenal specific toxicant mitotane directly interacts with lipid membranes and alters membrane properties depending on lipid composition.

    PubMed

    Scheidt, Holger A; Haralampiev, Ivan; Theisgen, Stephan; Schirbel, Andreas; Sbiera, Silviu; Huster, Daniel; Kroiss, Matthias; Müller, Peter

    2016-06-15

    Mitotane (o,p'.-DDD) is an orphan drug approved for the treatment of adrenocortical carcinoma. The mechanisms, which are responsible for this activity of the drug, are not completely understood. It can be hypothesized that an impact of mitotane is mediated by the interaction with cellular membranes. However, an interaction of mitotane with (lipid) membranes has not yet been investigated in detail. Here, we characterized the interaction of mitotane and its main metabolite o,p'-dichlorodiphenyldichloroacetic acid (o,p'-DDA) with lipid membranes by applying a variety of biophysical approaches of nuclear magnetic resonance, electron spin resonance, and fluorescence spectroscopy. We found that mitotane and o,p'-DDA bind to lipid membranes by inserting into the lipid-water interface of the bilayer. Mitotane but not o,p'-DDA directly causes a disturbance of bilayer structure leading to an increased permeability of the membrane for polar molecules. Mitotane induced alterations of the membrane integrity required the presence of phosphatidylethanolamine and/or cholesterol. Collectively, our data for the first time characterize the impact of mitotane on the lipid membrane structure and dynamics, which may contribute to a better understanding of specific mitotane effects and side effects. PMID:27002491

  7. Photosynthesis Activates Plasma Membrane H+-ATPase via Sugar Accumulation.

    PubMed

    Okumura, Masaki; Inoue, Shin-Ichiro; Kuwata, Keiko; Kinoshita, Toshinori

    2016-05-01

    Plant plasma membrane H(+)-ATPase acts as a primary transporter via proton pumping and regulates diverse physiological responses by controlling secondary solute transport, pH homeostasis, and membrane potential. Phosphorylation of the penultimate threonine and the subsequent binding of 14-3-3 proteins in the carboxyl terminus of the enzyme are required for H(+)-ATPase activation. We showed previously that photosynthesis induces phosphorylation of the penultimate threonine in the nonvascular bryophyte Marchantia polymorpha However, (1) whether this response is conserved in vascular plants and (2) the process by which photosynthesis regulates H(+)-ATPase phosphorylation at the plasma membrane remain unresolved issues. Here, we report that photosynthesis induced the phosphorylation and activation of H(+)-ATPase in Arabidopsis (Arabidopsis thaliana) leaves via sugar accumulation. Light reversibly phosphorylated leaf H(+)-ATPase, and this process was inhibited by pharmacological and genetic suppression of photosynthesis. Immunohistochemical and biochemical analyses indicated that light-induced phosphorylation of H(+)-ATPase occurred autonomously in mesophyll cells. We also show that the phosphorylation status of H(+)-ATPase and photosynthetic sugar accumulation in leaves were positively correlated and that sugar treatment promoted phosphorylation. Furthermore, light-induced phosphorylation of H(+)-ATPase was strongly suppressed in a double mutant defective in ADP-glucose pyrophosphorylase and triose phosphate/phosphate translocator (adg1-1 tpt-2); these mutations strongly inhibited endogenous sugar accumulation. Overall, we show that photosynthesis activated H(+)-ATPase via sugar production in the mesophyll cells of vascular plants. Our work provides new insight into signaling from chloroplasts to the plasma membrane ion transport mechanism. PMID:27016447

  8. Mechanical Properties of Two-Dimensional Alkanethiol-Coated Gold Nanoparticle Membranes

    NASA Astrophysics Data System (ADS)

    Salerno, K. Michael; Bolintineanu, Dan S.; Lane, J. Matthew D.; Grest, Gary S.

    2014-03-01

    Membranes formed from nanoparticle monolayers have been shown to have mechanical properties that may make them suitable for use in micro-scale devices. Metallic-core nanoparticles with short, organic ligands can form membranes with dimensions up to several micrometers, with large elastic moduli. Experimental tests of membranes with different cores and ligands indicate that ligand length as well as core-ligand and ligand-ligand interactions can influence membrane mechanical response. We use explicit-atom molecular dynamics simulations to examine the properties of membranes formed from a two-dimensional hexagonal array of alkanethiol-coated Au nanoparticles. Results are presented for nanoparticle core diameters from 4-6nm, ligand lengths of 10-18 units and carboxyl and methyl end groups, all of which influence the mechanical properties of the membranes. Knowledge of how microstructure and composition influence membrane properties could lead to efficient membrane manufacture with improved mechanical properties. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  9. Effect of unsaturations on the physical properties of a model membrane with the highly polyunsaturated docosahexaenoic fatty acid

    NASA Astrophysics Data System (ADS)

    Saiz, Leonor; Klein, Michael L.

    2001-03-01

    Polyunsaturated fatty acids are an essential component of biomembranes. The docosahexaenoic fatty acid (DHA), in particular, is found in high concentrations in retinal and neuronal tissue and in the olfactory bulb. Furthermore, it is well known the ability of DHA rich membranes to modulate membrane protein function, in some situations, by modifying the membrane physical properties. A particularly well studied situation is the DHA effect onthe activity of the visual receptor (protein) rhodopsin. Here, we study at a microscopic level this type of complex systems under physiological conditions. In this way, we can probe the molecular origin of the peculiarities that the system confers to membranes. To this purpose, the structure of a fully hydrated mixed (saturated/polyunsaturated) chain lipid bilayer in the biologically relevant liquid crystalline phase has been examined by performing molecular dynamics simulations. The model membrane, a 1-stearoyl- 2-docosahexaenoic- sn-glycero- 3-phosphatidylcholine (18:0/22:6 PC) lipid bilayer, was investigated at room temperature and ambient pressure and the results obtained in the nanosecond time scale were in good agreement with the available experimental data. Among the effects of the multiple unsaturations on the physical properties of these membranes, we focus on the enhanced permeability to water and small organic solvents, the decreased area compressibility modulus, and the domain formation and chain segregation.

  10. Removal properties of human enteric viruses in a pilot-scale membrane bioreactor (MBR) process.

    PubMed

    Miura, Takayuki; Okabe, Satoshi; Nakahara, Yoshihito; Sano, Daisuke

    2015-05-15

    In order to evaluate removal properties of human enteric viruses from wastewater by a membrane bioreactor (MBR), influent, anoxic and oxic mixed liquor, and membrane effluent samples were collected in a pilot-scale anoxic-oxic MBR process for 16 months, and concentrations of enteroviruses, norovirus GII, and sapoviruses were determined by real-time PCR using murine norovirus as a process control. Mixed liquor samples were separated into liquid and solid phases by centrifugation, and viruses in the bulk solution and those associated with mixed liquor suspended solids (MLSS) were quantified. Enteroviruses, norovirus GII, and sapoviruses were detected in the influent throughout the sampling period (geometrical mean, 4.0, 3.1, and 4.4 log copies/mL, respectively). Enterovirus concentrations in the solid phase of mixed liquor were generally lower than those in the liquid phase, and the mean log reduction value between influent and anoxic mixed liquor was 0.40 log units. In contrast, norovirus GII and sapovirus concentrations in the solid phase were equal to or higher than those in the liquid phase, and higher log reduction values (1.3 and 1.1 log units, respectively) were observed between influent and anoxic mixed liquor. This suggested that enteroviruses were less associated with MLSS than norovirus GII and sapoviruses, resulting in lower enterovirus removal in the activated sludge process. Enteroviruses and norovirus GII were detected in the MBR effluent but sapoviruses were not in any effluent samples. When MLSS concentration was reduced to 50-60% of a normal operation level, passages of enteroviruses and norovirus GII through a PVDF microfiltration membrane were observed. Since rejection of viruses by the membrane was not related to trans-membrane pressure which was monitored as a parameter of membrane fouling, the results indicated that adsorption to MLSS plays an important role in virus removal by an MBR, and removal properties vary by viruses reflecting different

  11. Properties of novel polyvinyl alcohol/cellulose nanocrystals/silver nanoparticles blend membranes.

    PubMed

    Xu, Xu; Yang, Yi-Qin; Xing, Ying-Ying; Yang, Jiu-Fang; Wang, Shi-Fa

    2013-11-01

    Novel polyvinyl alcohol (PVA) blend membranes containing cellulose nanocrystals (CNs) and silver nanoparticles (AgNPs) were prepared via a simple method. CNs were prepared by sulfuric acid treatment of microcrystalline cellulose. AgNO3 aqueous solution mixed with the CNs aqueous suspension and was reduced by NaBH4 at room temperature. Purified CNs/AgNPs nanocomposites as functional fillers mixed with polyvinyl alcohol to prepare blend membrane. The morphology, mechanical properties, and antibacterial activities of PVA/CNs/AgNPs composite films were investigated. The PVA/CNs/AgNPs composite films were stable and homogeneous. The tensile strength of PVA was increased from 57.02 MPa to 81.21 MPa when filled with CNs/AgNPs. Antibacterial ratio of PVA/CNs/AgNPs composite against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus was 96.9% and 88.2%, respectively. The CNs/AgNPs nanocomposites could be applied as bi-functional nanofillers within PVA to improve the mechanical properties and antibacterial activities. PMID:24053842

  12. Comparison of the properties of membranes produced with alginate and chitosan from mushroom and from shrimp.

    PubMed

    Bierhalz, Andréa C K; Westin, Cecília Buzatto; Moraes, Ângela Maria

    2016-10-01

    Dense and porous chitosan-alginate membranes (1:1 in mass) useful as coverages of skin wounds treated through cell therapy were produced using chitosan of different chain sizes from fungal (white mushrooms) and animal (shrimp shells) sources. Porous materials were obtained by adding the surfactant Poloxamer 188 to the formulations. The influence of chitosan type on membranes physicochemical properties and toxicity to fibroblasts was evaluated. Porosity was noticed to be more pronounced in membranes obtained with fungal chitosan and increased with its molecular mass. These formulations showed the highest values of thickness, roughness, opacity, liquid uptake and water vapor permeability. The membranes were not toxic to fibroblasts, but the lowest cytotoxicity values (0.16-0.21%) were observed for membranes prepared with fungal chitosan in the presence of surfactant. In conclusion, it is possible to replace chitosan from animal sources by chitosan of fungal origin to produce membranes with negligible cytotoxicity while maintaining appropriate physicochemical properties. PMID:27240752

  13. Water adsorption properties controlled by coating/filling ordered mesoporous silica inside cellulose membranes.

    PubMed

    Kimura, Tatsuo

    2013-09-28

    Porous organic membranes have been utilized as hard templates not only for replication of porous macrostructures but also for fabrication of hierarchical porous solids through infiltration of precursor solutions in ordered mesoporous materials. However, such organic membranes are usually burned out as sacrificial skeletons by calcination. In addition, replicated macropores are too big to enhance properties due to inorganic oxide frameworks. In this study, when cellulose membranes were used as organic membranes, a coating/filling technology of ordered mesoporous silicas was proposed and the water adsorption-desorption properties were directly investigated by using the composite membranes after extraction of nonionic surfactants used. The composite membranes possessed enough adsorption capacity for water, which will be potentially useful for improving total energy efficiency in heat-pump and desiccant air conditioning systems. PMID:23925426

  14. Mechanical properties of the plasma membrane of isolated plant protoplasts

    SciTech Connect

    Wolfe, J.; Steponkus, P.L.

    1983-01-01

    The volume of isolated protoplasts of rye (Secale cereale L. cv Puma) in a suspending solution at constant concentration is shown to be negligibly changed by tensions in the plasma membrane which approach that tension necessary to lyse them. This allows a detailed investigation of the plasma membrane stress-strain relation by micropipette aspiration. Over periods less than a second, the membrane behaves as an elastic two-dimensional fluid with an area modulus of elasticity of 230 millinewtons per meter. Over longer periods, the stress-strain relation approaches a surface energy law--the resting tension is independent of area and has a value of the order 100 micronewtons per meter. Over longer periods the untensioned area, which is defined as the area that would be occupied by the molecules in the membrane at any given time if the tension were zero, increases with time under large imposed tensions and decreases under sufficiently small tension. It is proposed that these long term responses are the result of exchange of material between the plane of the membrane and a reservoir of membrane material. The irreversibility of large contractions in area is demonstrated directly, and the behavior of protoplasts during osmotically induced cycles of contraction and expansion is explained in terms of the membrane stress-strain relation.

  15. Cyclohexane triones, novel membrane-active antibacterial agents.

    PubMed Central

    Lloyd, W J; Broadhurst, A V; Hall, M J; Andrews, K J; Barber, W E; Wong-Kai-In, P

    1988-01-01

    The cyclohexane triones are a novel group of synthetic antibacterial agents that are active against gram-positive bacteria, Haemophilus influenzae, and Mycobacterium smegmatis. In general, these compounds behaved in a manner similar to that of hexachlorophene, inhibiting the transport of low-molecular-weight hydrophilic substances into bacteria. Unlike cationic detergents, such as chlorhexidine, they did not cause disruption of the bacterial cytoplasmic membrane over a short time period. The most potent antibacterial cyclohexane trione studied had a reduced ability to inhibit solute transport in comparison with certain less active analogs. Cyclohexane triones may express more than a single type of antibacterial effect. PMID:3137860

  16. Formulation and process optimization of multiparticulate pulsatile system delivered by osmotic pressure-activated rupturable membrane.

    PubMed

    Hung, Sheng-Feng; Hsieh, Chien-Ming; Chen, Ying-Chen; Lin, Cheng-Mao; Ho, Hsiu-O; Sheu, Ming-Thau

    2015-03-01

    In this study, a multiparticulate pulsatile drug delivery system activated by a rupturable controlled-release membrane (Eudragit(®) RS) via osmotic pressure (with NaCl as the osmogent) was developed and characterized for omeprazole, omeprazole sodium, and propranolol HCl which have different water solubilities. Multiparticulates in pellet form for incorporation with or without the osmogent were manufactured by three methods and then used to coat a polymeric membrane. Results demonstrated that drug/osmogent-containing pellets manufactured by the extrusion/spheronization method with incorporation of the osmogent were optimal. The lag time (tL) to initiate pulsatile release is regulated by tL=l(2)/(6×D), which is dependent on the coating levels (l(2)) and plasticizer content (D). The pulsatile release pattern was found to be dependent on the osmotic pressure (osmogent), drug solubility, and mechanical properties of the polymeric membrane (elasticity and toughness). Omeprazole with lower water solubility could not generate sufficient osmotic pressure to create a crack in the membrane to activate pulsatile release, whereas the two other model drugs with higher solubilities could. But adsorption of omeprazole sodium on Eudragit(®) RS via charge-charge interactions led the its incomplete release. Finally, with 4% osmogent of NaCl added, a lag time in a range from 0 to 12h proportionally regulated by varying both the membrane thickness and plasticizer level initiated the complete pulsatile release of propranolol HCl. In conclusion, a multiparticulate pulsatile drug delivery system activated by a rupturable controlled-release membrane via osmotic pressure was successfully developed, and clinical applications of chronotherapy with drugs like propranolol HCl are expected. PMID:25575473

  17. High-pressure stainless steel active membrane microvalves

    NASA Astrophysics Data System (ADS)

    Sharma, G.; Svensson, S.; Ogden, S.; Klintberg, L.; Hjort, K.

    2011-07-01

    In this work, high-pressure membrane microvalves have been designed, manufactured and evaluated. The valves were able to withstand back-pressures of 200 bar with a response time of less than 0.6 s. These stainless steel valves, manufactured with back-end batch production, utilize the large volume expansion coupled to the solid-liquid phase transition in paraffin wax. When membrane materials were evaluated, parylene coated stainless steel was found to be the best choice as compared to polydimethylsiloxane and polyimide. Also, the influence of the orifice placement and diameter is included in this work. If the orifice is placed too close to the rim of the membrane, the valve can stay sealed even after turning the power off, and the valve will not open until the pressure in the system is released. The developed steel valves, evaluated for both water and air, provide excellent properties in terms of mechanical stability, ease of fabrication, and low cost. Possible applications include sampling at high pressures, chemical microreactors, high performance liquid chromatography, pneumatics, and hydraulics.

  18. Chemical Modulation of the Biological Activity of Reutericyclin: a Membrane-Active Antibiotic from Lactobacillus reuteri

    PubMed Central

    Cherian, Philip T.; Wu, Xiaoqian; Maddox, Marcus M.; Singh, Aman P.; Lee, Richard E.; Hurdle, Julian G.

    2014-01-01

    Whilst the development of membrane-active antibiotics is now an attractive therapeutic concept, progress in this area is disadvantaged by poor knowledge of the structure-activity relationship (SAR) required for optimizing molecules to selectively target bacteria. This prompted us to explore the SAR of the Lactobacillus reuteri membrane-active antibiotic reutericyclin, modifying three key positions about its tetramic acid core. The SAR revealed that lipophilic analogs were generally more active against Gram-positive pathogens, but introduction of polar and charged substituents diminished their activity. This was confirmed by cytometric assays showing that inactive compounds failed to dissipate the membrane potential. Radiolabeled substrate assays indicated that dissipation of the membrane potential by active reutericyclins correlated with inhibition of macromolecular synthesis in cells. However, compounds with good antibacterial activities also showed cytotoxicity against Vero cells and hemolytic activity. Although this study highlights the challenge of optimizing membrane-active antibiotics, it shows that by increasing antibacterial potency the selectivity index could be widened, allowing use of lower non-cytotoxic doses. PMID:24739957

  19. Molecular dynamics simulations of lipid membranes with lateral force: rupture and dynamic properties.

    PubMed

    Xie, Jun Yu; Ding, Guang Hong; Karttunen, Mikko

    2014-03-01

    Membranes' response to lateral tension, and eventual rupture, remains poorly understood. In this study, pure dipalmitoylphosphatidylcholine (DPPC) lipid bilayers, under tension/pressure, were studied using molecular dynamics (MD) simulations. The irreversible membrane breakdown is demonstrated to depend on the amplitude of lateral tension, loading rate, and the size of the bilayer. In all of our simulations, -200bar lateral pressure was found to be enough to rupture lipid membrane regardless of the loading rate or the membrane size. Loading rate and membrane size had a significant impact on rupture. A variety of dynamic properties of lipid molecules, probability distribution of area per lipid particularly, have been determined, and found to be fundamental for describing membrane behavior in detail, thus providing the quantitative description for the requirement of membrane rupture. PMID:24374317

  20. Decoupling Mechanical and Ion Transport Properties in Polymer Electrolyte Membranes

    NASA Astrophysics Data System (ADS)

    McIntosh, Lucas D.

    Polymer electrolytes are mixtures of a polar polymer and salt, in which the polymer replaces small molecule solvents and provides a dielectric medium so that ions can dissociate and migrate under the influence of an external electric field. Beginning in the 1970s, research in polymer electrolytes has been primarily motivated by their promise to advance electrochemical energy storage and conversion devices, such as lithium ion batteries, flexible organic solar cells, and anhydrous fuel cells. In particular, polymer electrolyte membranes (PEMs) can improve both safety and energy density by eliminating small molecule, volatile solvents and enabling an all-solid-state design of electrochemical cells. The outstanding challenge in the field of polymer electrolytes is to maximize ionic conductivity while simultaneously addressing orthogonal mechanical properties, such as modulus, fracture toughness, or high temperature creep resistance. The crux of the challenge is that flexible, polar polymers best-suited for polymer electrolytes (e.g., poly(ethylene oxide)) offer little in the way of mechanical robustness. Similarly, polymers typically associated with superior mechanical performance (e.g., poly(methyl methacrylate)) slow ion transport due to their glassy polymer matrix. The design strategy is therefore to employ structured electrolytes that exhibit distinct conducting and mechanically robust phases on length scales of tens of nanometers. This thesis reports a remarkably simple, yet versatile synthetic strategy---termed polymerization-induced phase separation, or PIPS---to prepare PEMs exhibiting an unprecedented combination of both high conductivity and high modulus. This performance is enabled by co-continuous, isotropic networks of poly(ethylene oxide)/ionic liquid and highly crosslinked polystyrene. A suite of in situ, time-resolved experiments were performed to investigate the mechanism by which this network morphology forms, and it appears to be tied to the

  1. Scolopendin 2, a cationic antimicrobial peptide from centipede, and its membrane-active mechanism.

    PubMed

    Lee, Heejeong; Hwang, Jae-Sam; Lee, Jaeho; Kim, Jae Il; Lee, Dong Gun

    2015-02-01

    Scolopendin 2 is a 16-mer peptide (AGLQFPVGRIGRLLRK) derived from the centipede Scolopendra subspinipes mutilans. We observed that this peptide exhibited antimicrobial activity in a salt-dependent manner against various fungal and bacterial pathogens and showed no hemolytic effect in the range of 1.6 μM to 100 μM. Circular dichroism analysis showed that the peptide has an α-helical properties. Furthermore, we determined the mechanism(s) of action using flow cytometry and by investigating the release of intracellular potassium. The results showed that the peptide permeabilized the membranes of Escherichia coli O157 and Candida albicans, resulting in loss of intracellular potassium ions. Additionally, bis-(1,3-dibutylbarbituric acid) trimethine oxonol and 3,3'-dipropylthiacarbocyanine iodide assays showed that the peptide caused membrane depolarization. Using giant unilamellar vesicles encapsulating calcein and large unilamellar vesicles containing fluorescein isothiocyanate-dextran, which were similar in composition to typical E. coli O157 and C. albicans membranes, we demonstrated that scolopendin 2 disrupts membranes, resulting in a pore size between 4.8 nm and 5.0 nm. Thus, we have demonstrated that a cationic antimicrobial peptide, scolopendin 2, exerts its broad-spectrum antimicrobial effects by forming pores in the cell membrane. PMID:25462167

  2. Ti3C2Tx Filler Effect on the Proton Conduction Property of Polymer Electrolyte Membrane.

    PubMed

    Liu, Yahua; Zhang, Jiakui; Zhang, Xiang; Li, Yifan; Wang, Jingtao

    2016-08-10

    Conductive polymer electrolyte membranes are increasingly attractive for a wide range of applications in hydrogen-relevant devices, for instance hydrogen fuel cells. In this study, two-dimensional Ti3C2Tx, a typical representative of the recently developed MXene family, is synthesized and employed as a universal filler for its features of large specific surface area, high aspect ratio, and sufficient terminated -OH groups. The Ti3C2Tx is incorporated into polymer matrix to explore its function on membrane microstructure and proton conduction property. Both phase-separated (acidic Nafion and sulfonated poly(ether ether ketone)) and non-phase-separated (basic chitosan) polymers are utilized as membrane matrixes. The microstructures, physicochemical properties, and proton conduction properties of the membranes are extensively investigated. It is demonstrated that Ti3C2Tx generates significant promotion effect on proton conduction of the composite membrane by facilitating both vehicle-type and Grotthuss-type proton transfer, yielding several times increased proton conductivity for every polymer-based composite membrane under various conditions, and the composite membrane achieves elevated hydrogen fuel cell performance. The stable Ti3C2Tx also reinforces the thermal and mechanical stabilities of these composite membranes. Since the MXene family includes more than 70 members, this exploration is expected to open up new perspectives for expanding their applications, especially as membrane modifiers and proton conductors. PMID:27430190

  3. Preparation and properties of homogeneous-reinforced polyvinylidene fluoride hollow fiber membrane

    NASA Astrophysics Data System (ADS)

    Zhang, Xuliang; Xiao, Changfa; Hu, Xiaoyu; Bai, Qianqian

    2013-01-01

    Homogeneous-reinforced (HR) polyvinylidene fluoride (PVDF) hollow fiber membranes include PVDF polymer solutions (coating layer) and the matrix membrane prepared through the dry-wet spinning process. The performance of HR membranes varies with the polymer concentration in the polymer solutions and is characterized in terms of pure water flux, rejection of protein, porosity, infiltration property, a mechanical strength test, and morphology observations by a field emission scanning electron microscope (FESEM). The results of this study indicate that the tensile strength of the HR PVDF membranes decreases slights compared with that of the matrix membrane, but the elongation at break increases much more and the hollow fiber membranes are endowed with better flexibility performance. The HR PVDF hollow fiber membranes have a favorable interfacial bonding between the coating layer and the matrix membrane, as shown by FESEM. The infiltration property is characterized by the contact angle experiments. Pure water flux decreases while the rejection ratio with an increase in polymer concentration increasing. The protein solution flux of the HR PVDF membranes is higher than that of the matrix membrane after 100 min of infiltration.

  4. SEPARATION PROPERTIES OF SURFACE MODIFIED SILICA SUPPORTED LIQUID MEMBRANES FOR DIVALENT METAL REMOVAL/RECOVERY

    EPA Science Inventory

    The synthesis and separation properties of a mesoporous silica supported liquid membrane (SLM) were studied. The membranes consisted of a silica layer, from dip-coated colloidal silica, on a a-alumina support, modified with DCDMS (dichlorodimethyl silane) to add surface methyl g...

  5. Antibacterial activities of surface modified electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) fibrous membranes

    NASA Astrophysics Data System (ADS)

    Yao, Chen; Li, Xinsong; Neoh, K. G.; Shi, Zhilong; Kang, E. T.

    2009-01-01

    Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membrane, with its excellent chemical and mechanical properties, has good potential for broad applications. However, due to its hydrophobic nature, microbial colonization is commonly encountered. In this work, electrospun PVDF-HFP fibrous membranes were surface modified by poly(4-vinyl- N-alkylpyridinium bromide) to achieve antibacterial activities. The membranes were first subjected to plasma pretreatment followed by UV-induced surface graft copolymerization of 4-vinylpyridine (4VP) and quaternization of the grafted pyridine groups with hexylbromide. The chemical composition of the surface modified PVDF-HFP electrospun membranes was studied by X-ray photoelectron spectroscopy (XPS). The morphology and mechanical properties of pristine and surface modified PVDF-HFP fibrous membranes were characterized by scanning electron microscopy (SEM) and tensile test, respectively. The antibacterial activities of the modified electrospun PVDF-HFP fibrous membranes were assessed against Gram-positive Staphylococcus aureus ( S. aureus) and Gram-negative Escherichia coli ( E. coli). The results showed that the PVDF-HFP fibrous membranes modified with quaternized pyridinium groups are highly effective against both bacteria with killing efficiency as high as 99.9999%.

  6. Study on the effects of nylon-chitosan-blended membranes on the spheroid-forming activity of human melanocytes.

    PubMed

    Lin, Sung-Jan; Hsiao, Wen-Chu; Jee, Shiou-Hwa; Yu, Hsin-Su; Tsai, Tsen-Fang; Lai, Juin-Yih; Young, Tai-Horng

    2006-10-01

    Though reported limitedly in tissue engineering, modification of cellular functions can be achieved by culturing them into multicellular spheroids. We have shown melanocytes form spheroids on chitosan surface. However, how biomaterials promote spheroid formation has never been systemically investigated. In this work, nylon, which inhibits melanocyte spheroid formation, and chitosan, which promotes melanocyte spheroid formation, are used to prepare nylon/chitosan-blended membranes. Membranes composed of pure nylon, pure chitosan and various ratios of nylon and chitosan are employed to examine their effects on spheroid formation. Melanocytes show better adhesion to nylon membranes than that to chitosan membranes. In blended membranes, as more nylon is incorporated, cell adhesion increases and the trend for spheroid formation decreases. Melanocytes can only form spheroids on membranes with poorer cell adhesion. Examining the surface of the blended membranes shows phase separation of nylon and chitosan. As nylon content increases, the nylon phase on the membrane surface increases and thereby enhances cell adhesion. The opposite trend for cell adhesion and spheroid formation substantiates our hypothesis of spheroid formation on biomaterials: a balance between cell-substrate interaction and cell-cell interaction. The decrease in cell-substrate interaction tilts the balance to a state more favorable for spheroid formation. Our work can serve as a model to investigate the relative strengths of cell-cell and cell-substrate interactions and also pave way to design blended membranes with desired physical properties while preserving the spheroid-forming activity. PMID:16777216

  7. Transport properties of track-etched membranes having variable effective pore-lengths

    NASA Astrophysics Data System (ADS)

    Nguyen, Quoc Hung; Ali, Mubarak; Nasir, Saima; Ensinger, Wolfgang

    2015-12-01

    The transport rate of molecules through polymeric membranes is normally limited because of their micrometer-scale thickness which restricts their suitability for more practical application. To study the effect of effective pore length on the transport behavior, polymer membranes containing cylindrical and asymmetric-shaped nanopores were prepared through a two-step ion track-etching technique. Permeation experiments were performed separately to investigate the transport properties (molecular flux and selectivity) of these track-etched membranes. The permeation data shows that the molecular flux across membranes containing asymmetric nanopores is higher compared to those having cylindrical pores. On the other hand, the cylindrical pore membranes exhibit higher selectivity than asymmetric pores for the permeation of charged molecules across the membrane. Current-voltage (I-V) measurements of single-pore membranes further verify that asymmetric pores exhibit lower resistance for the flow of ions and therefore show higher currents than cylindrical pores. Moreover, unmodified and polyethyleneimine (PEI) modified asymmetric-shaped pore membranes were successfully used for the separation of cationic and anionic analyte molecules from their mixture, respectively. In this study, two distinct effects (pore geometry and pore density, i.e. number of pores cm-2), which mainly influence membrane selectivity and molecular transport rates, were thoroughly investigated in order to optimize the membrane performance. In this context, we believe that membranes with high molecular transport rates could readily find their application in molecular separation and controlled drug delivery processes.

  8. Transport properties of track-etched membranes having variable effective pore-lengths.

    PubMed

    Nguyen, Quoc Hung; Ali, Mubarak; Nasir, Saima; Ensinger, Wolfgang

    2015-12-01

    The transport rate of molecules through polymeric membranes is normally limited because of their micrometer-scale thickness which restricts their suitability for more practical application. To study the effect of effective pore length on the transport behavior, polymer membranes containing cylindrical and asymmetric-shaped nanopores were prepared through a two-step ion track-etching technique. Permeation experiments were performed separately to investigate the transport properties (molecular flux and selectivity) of these track-etched membranes. The permeation data shows that the molecular flux across membranes containing asymmetric nanopores is higher compared to those having cylindrical pores. On the other hand, the cylindrical pore membranes exhibit higher selectivity than asymmetric pores for the permeation of charged molecules across the membrane. Current-voltage (I-V) measurements of single-pore membranes further verify that asymmetric pores exhibit lower resistance for the flow of ions and therefore show higher currents than cylindrical pores. Moreover, unmodified and polyethyleneimine (PEI) modified asymmetric-shaped pore membranes were successfully used for the separation of cationic and anionic analyte molecules from their mixture, respectively. In this study, two distinct effects (pore geometry and pore density, i.e. number of pores cm(-2)), which mainly influence membrane selectivity and molecular transport rates, were thoroughly investigated in order to optimize the membrane performance. In this context, we believe that membranes with high molecular transport rates could readily find their application in molecular separation and controlled drug delivery processes. PMID:26553245

  9. Modulation of Erythrocyte Plasma Membrane Redox System Activity by Curcumin

    PubMed Central

    Singh, Prabhakar; Kesharwani, Rajesh Kumar; Misra, Krishna; Rizvi, Syed Ibrahim

    2016-01-01

    Plasma membrane redox system (PMRS) is an electron transport chain system ubiquitously present throughout all cell types. It transfers electron from intracellular substrates to extracellular acceptors for regulation of redox status. Curcumin, isolated from Curcuma longa, has modulatory effects on cellular physiology due to its membrane interaction ability and antioxidant potential. The present study investigates the effect of curcumin on PMRS activity of erythrocytes isolated from Wistar rats in vitro and in vivo and validated through an in silico docking simulation study using Molegro Virtual Docker (MVD). Effects of curcumin were also evaluated on level of glutathione (GSH) and the oxidant potential of plasma measured in terms of plasma ferric equivalent oxidative potentials (PFEOP). Results show that curcumin significantly (p < 0.01) downregulated the PMRS activity in a dose-dependent manner. Molecular docking results suggest that curcumin interacts with amino acids at the active site cavity of cytochrome b5 reductase, a key constituent of PMRS. Curcumin also increased the GSH level in erythrocytes and plasma while simultaneously decreasing the oxidant potential (PFEOP) of plasma. Altered PMRS activity and redox status are associated with the pathophysiology of several health complications including aging and diabetes; hence, the above finding may explain part of the role of curcumin in health beneficial effects. PMID:26904287

  10. Omniphobic Membrane for Robust Membrane Distillation

    SciTech Connect

    Lin, SH; Nejati, S; Boo, C; Hu, YX; Osuji, CO; Ehmelech, M

    2014-11-01

    In this work, we fabricate an omniphobic microporous membrane for membrane distillation (MD) by modifying a hydrophilic glass fiber membrane with silica nanoparticles followed by surface fluorination and polymer coating. The modified glass fiber membrane exhibits an anti-wetting property not only against water but also against low surface tension organic solvents that easily wet a hydrophobic polytetrafluoroethylene (PTFE) membrane that is commonly used in MD applications. By comparing the performance of the PTFE and omniphobic membranes in direct contact MD experiments in the presence of a surfactant (sodium dodecyl sulfate, SDS), we show that SDS wets the hydrophobic PTFE membrane but not the omniphobic membrane. Our results suggest that omniphobic membranes are critical for MD applications with feed waters containing surface active species, such as oil and gas produced water, to prevent membrane pore wetting.

  11. [Study of antioxidant and membrane activity of rosmarinic acid using different model systems].

    PubMed

    Popov, A M; Osipov, A N; Korepanova, E A; Krivoshapko, O N; Artiukov, A A

    2013-01-01

    Rosmarinic acid is found in many species of different families of higher plants and its chemical structure is phenol propanoid with various biological activity. In this paper, we conducted a comparative study of antioxidant (radical-scavenging) properties of rosmarinic acid in systems of 2,2'-azo-bis(2-methylpropionamidin)dihydrochloride-luminol and hemoglobin-hydrogen peroxide-lu- minol, determined its protective potential in preventing peroxidation of linoleic acid, and evaluated the effect on the permeability of planar bilayer lipid membranes. Linoleic acid peroxidation was assessed by iron-thiocyanate method. In these studies, trolox was used as a reference antioxidant, and ascorbic acid, and dihydroquercetin were taken as standards. Rosmarinic acid is significantly superior to trolox, ascorbic acid and dihydroquercetin in the tests for antioxidant activity in the systems studied, as well as in inhibition of linoleic acid peroxidation. According to their activity the investigated substances can be arranged in the following order: rosmarinic acid > dihydroquercetin trolox > ascorbic acid. Rosmarinic acid does not cause significant changes in the permeability of planar bilayer membranes in a dose range of 0.5 to 10 mkg/mL. Antioxidant activity of rosmarinic acid is due to the neutralization of reactive oxygen species and/or luminol radicals generated in model systems. The observed features of the antioxidant and membrane activity of rosmarinic acid, which may underlie the previously mentioned pharmacological effects are discussed. PMID:25481945

  12. [Study of antioxidant and membrane activity of rosmarinic acid using different model systems].

    PubMed

    2013-01-01

    Rosmarinic acid is found in many species of different families of higher plants and its chemical structure is phenol propanoid with various biological activity. In this paper, we conducted a comparative study of antioxidant (radical-scavenging) properties of rosmarinic acid in systems of 2,2'-azo-bis(2-methylpropionamidin)dihydrochloride-luminol and hemoglobin-hydrogen peroxide-lu- minol, determined its protective potential in preventing peroxidation of linoleic acid, and evaluated the effect on the permeability of planar bilayer lipid membranes. Linoleic acid peroxidation was assessed by iron-thiocyanate method. In these studies, trolox was used as a reference antioxidant, and ascorbic acid, and dihydroquercetin were taken as standards. Rosmarinic acid is significantly superior to trolox, ascorbic acid and dihydroquercetin in the tests for antioxidant activity in the systems studied, as well as in inhibition of linoleic acid peroxidation. According to their activity the investigated substances can be arranged in the following order: rosmarinic acid > dihydroquercetin trolox > ascorbic acid. Rosmarinic acid does not cause significant changes in the permeability of planar bilayer membranes in a dose range of 0.5 to 10 mkg/mL. Antioxidant activity of rosmarinic acid is due to the neutralization of reactive oxygen species and/or luminol radicals generated in model systems. The observed features of the antioxidant and membrane activity of rosmarinic acid, which may underlie the previously mentioned pharmacological effects are discussed. PMID:25508797

  13. Different metabolic activity in placental and reflected regions of the human amniotic membrane.

    PubMed

    Banerjee, Asmita; Weidinger, Adelheid; Hofer, Martin; Steinborn, Ralf; Lindenmair, Andrea; Hennerbichler-Lugscheider, Simone; Eibl, Johann; Redl, Heinz; Kozlov, Andrey V; Wolbank, Susanne

    2015-11-01

    Cells of the human amniotic membrane (hAM) have stem cell characteristics with low immunogenicity and anti-inflammatory properties. While hAM is an excellent source for tissue engineering, so far, its sub-regions have not been taken into account. We show that placental and reflected hAM differ distinctly in morphology and functional activity, as the placental region has significantly higher mitochondrial activity, however significantly less reactive oxygen species. Since mitochondria may participate in processes such as cell rescue, we speculate that amniotic sub-regions may have different potential for tissue regeneration, which may be crucial for clinical applications. PMID:26386652

  14. Influence of protein bulk properties on membrane surface coverage during immobilization.

    PubMed

    Militano, Francesca; Poerio, Teresa; Mazzei, Rosalinda; Piacentini, Emma; Gugliuzza, Annarosa; Giorno, Lidietta

    2016-07-01

    Biomolecules immobilization is a key factor for many biotechnological applications. For this purpose, the covalent immobilization of bovine serum albumin (BSA), lipase from Candida rugosa and protein G on differently functionalized regenerated cellulose membranes was investigated. Dynamic light scattering and electrophoresis measurements carried out on biomolecules in solution indicated the presence of monomers, dimers and trimers for both BSA and protein G, while large aggregates were observed for lipase. The immobilization rate and the surface coverage on functionalized regenerated cellulose membranes were studied as a function of biomolecule concentration. Results indicated that the saturation coverage of BSA and protein G was concentration independent (immobilized protein amount of 2.40±0.03mg/g and 2.65±0.07mg/g, respectively). Otherwise, a different immobilization kinetics trend was obtained for lipase, for which the immobilized amount increases as a function of time without reaching a saturation value. Atomic force microscopy (AFM) micrographs showed the formation of monolayers for both BSA and protein G on the membrane surface, while a multilayer structure is found for lipase, in agreement with the trends observed in the related immobilization kinetics. As a result, the morphology of the proteins layer on the membrane surface seems to be strictly dependent on the proteins behavior in solution. Besides, the surface coverage has been described for BSA and protein G by the pseudo second order models, the results indicating the surface reaction as the controlling step of immobilization kinetics. Finally, enzyme activity and binding capacity studies indicated the preservation of the biomolecule functional properties. PMID:27022871

  15. Location and Effects of an Antitumoral Catechin on the Structural Properties of Phosphatidylethanolamine Membranes.

    PubMed

    Casado, Francisco; Teruel, José A; Casado, Santiago; Ortiz, Antonio; Rodríguez-López, José N; Aranda, Francisco J

    2016-01-01

    Green tea catechins exhibit high diversity of biological effects including antioncogenic properties, and there is enormous interest in their potential use in the treatment of a number of pathologies. It is recognized that the mechanism underlying the activity of catechins relay in part in processes related to the membrane, and many studies revealed that the ability of catechins to interact with lipids plays a probably necessary role in their mechanism of action. We present in this work the characterization of the interaction between an antitumoral synthetically modified catechin (3-O-(3,4,5-trimethoxybenzoyl)-(-)-catechin, TMCG) and dimiristoylphosphatidyl-ethanolamine (DMPE) membranes using an array of biophysical techniques which include differential scanning calorimetry, X-ray diffraction, infrared spectroscopy, atomic force microscopy, and molecular dynamics simulations. We found that TMCG incorporate into DMPE bilayers perturbing the thermotropic transition from the gel to the fluid state forming enriched domains which separated into different gel phases. TMCG does not influence the overall bilayer assembly of phosphatidylethanolamine systems but it manages to influence the interfacial region of the membrane and slightly decrease the interlamellar repeat distance of the bilayer. TMCG seems to be located in the interior of the phosphatidylethanolamine bilayer with the methoxy groups being in the deepest position and some portion of the molecule interacting with the water interface. We believe that the reported interactions are significant not only from the point of view of the known antitumoral effect of TMCG, but also might contribute to understanding the basic molecular mechanism of the biological effects of the catechins found at the membrane level. PMID:27347914

  16. Membrane-Active Peptides and the Clustering of Anionic Lipids

    PubMed Central

    Wadhwani, P.; Epand, R.F.; Heidenreich, N.; Bürck, J.; Ulrich, A.S.; Epand, R.M.

    2012-01-01

    There is some overlap in the biological activities of cell-penetrating peptides (CPPs) and antimicrobial peptides (AMPs). We compared nine AMPs, seven CPPs, and a fusion peptide with regard to their ability to cluster anionic lipids in a mixture mimicking the cytoplasmic membrane of Gram-negative bacteria, as measured by differential scanning calorimetry. We also studied their bacteriostatic effect on several bacterial strains, and examined their conformational changes upon membrane binding using circular dichroism. A remarkable correlation was found between the net positive charge of the peptides and their capacity to induce anionic lipid clustering, which was independent of their secondary structure. Among the peptides studied, six AMPs and four CPPs were found to have strong anionic lipid clustering activity. These peptides also had bacteriostatic activity against several strains (particularly Gram-negative Escherichia coli) that are sensitive to lipid clustering agents. AMPs and CPPs that did not cluster anionic lipids were not toxic to E. coli. As shown previously for several types of AMPs, anionic lipid clustering likely contributes to the mechanism of antibacterial action of highly cationic CPPs. The same mechanism could explain the escape of CPPs from intracellular endosomes that are enriched with anionic lipids. PMID:22853904

  17. Hydrodynamic collective effects of active proteins in biological membranes.

    PubMed

    Koyano, Yuki; Kitahata, Hiroyuki; Mikhailov, Alexander S

    2016-08-01

    Lipid bilayers forming biological membranes are known to behave as viscous two-dimensional fluids on submicrometer scales; usually they contain a large number of active protein inclusions. Recently, it was shown [A. S. Mikhailov and R. Kapral, Proc. Natl. Acad. Sci. USA 112, E3639 (2015)PNASA60027-842410.1073/pnas.1506825112] that such active proteins should induce nonthermal fluctuating lipid flows leading to diffusion enhancement and chemotaxislike drift for passive inclusions in biomembranes. Here, a detailed analytical and numerical investigation of such effects is performed. The attention is focused on the situations when proteins are concentrated within lipid rafts. We demonstrate that passive particles tend to become attracted by active rafts and are accumulated inside them. PMID:27627343

  18. Effect of clofibrate on the enzyme activity of rat liver plasma membranes.

    PubMed

    Renaud, G; Foliot, A; Marais, J; Infante, R

    1980-03-15

    The activity of 3 plasma membranes marker enzymes (5'-nucleotidase, Mg++-ATPase and alkaline phosphodiesterase-I) was determined in plasma membranes isolated from liver of control and of clofibrate-treated rats. A complete indentity of plasma membranes enzyme activity in the 2 groups of experimental animals was observed for the 3 enzymes studied. PMID:6102923

  19. On Physical Properties of Tetraether Lipid Membranes: Effects of Cyclopentane Rings

    PubMed Central

    Chong, Parkson Lee-Gau; Ayesa, Umme; Prakash Daswani, Varsha; Hur, Ellah Chay

    2012-01-01

    This paper reviews the recent findings related to the physical properties of tetraether lipid membranes, with special attention to the effects of the number, position, and configuration of cyclopentane rings on membrane properties. We discuss the findings obtained from liposomes and monolayers, composed of naturally occurring archaeal tetraether lipids and synthetic tetraethers as well as the results from computer simulations. It appears that the number, position, and stereochemistry of cyclopentane rings in the dibiphytanyl chains of tetraether lipids have significant influence on packing tightness, lipid conformation, membrane thickness and organization, and headgroup hydration/orientation. PMID:23028246

  20. Ligand structure and mechanical properties of single-nanoparticle thick membranes

    DOE PAGESBeta

    Salerno, Kenneth Michael; Bolintineanu, Dan S.; Lane, J. Matthew D.; Grest, Gary S.

    2015-06-16

    We believe that the high mechanical stiffness of single-nanoparticle-thick membranes is the result of the local structure of ligand coatings that mediate interactions between nanoparticles. These ligand structures are not directly observable experimentally. We use molecular dynamics simulations to observe variations in ligand structure and simultaneously measure variations in membrane mechanical properties. We have shown previously that ligand end group has a large impact on ligand structure and membrane mechanical properties. Here we introduce and apply quantitative molecular structure measures to these membranes and extend analysis to multiple nanoparticle core sizes and ligand lengths. Simulations of nanoparticle membranes with amore » nanoparticle core diameter of 4 or 6 nm, a ligand length of 11 or 17 methylenes, and either carboxyl (COOH) or methyl (CH3) ligand end groups are presented. In carboxyl-terminated ligand systems, structure and interactions are dominated by an end-to-end orientation of ligands. In methyl-terminated ligand systems large ordered ligand structures form, but nanoparticle interactions are dominated by disordered, partially interdigitated ligands. Core size and ligand length also affect both ligand arrangement within the membrane and the membrane's macroscopic mechanical response, but are secondary to the role of the ligand end group. Additionally, the particular end group (COOH or CH3) alters the nature of how ligand length, in turn, affects the membrane properties. The effect of core size does not depend on the ligand end group, with larger cores always leading to stiffer membranes. Asymmetry in the stress and ligand density is observed in membranes during preparation at a water-vapor interface, with the stress asymmetry persisting in all membranes after drying.« less

  1. Ligand structure and mechanical properties of single-nanoparticle thick membranes

    SciTech Connect

    Salerno, Kenneth Michael; Bolintineanu, Dan S.; Lane, J. Matthew D.; Grest, Gary S.

    2015-06-16

    We believe that the high mechanical stiffness of single-nanoparticle-thick membranes is the result of the local structure of ligand coatings that mediate interactions between nanoparticles. These ligand structures are not directly observable experimentally. We use molecular dynamics simulations to observe variations in ligand structure and simultaneously measure variations in membrane mechanical properties. We have shown previously that ligand end group has a large impact on ligand structure and membrane mechanical properties. Here we introduce and apply quantitative molecular structure measures to these membranes and extend analysis to multiple nanoparticle core sizes and ligand lengths. Simulations of nanoparticle membranes with a nanoparticle core diameter of 4 or 6 nm, a ligand length of 11 or 17 methylenes, and either carboxyl (COOH) or methyl (CH3) ligand end groups are presented. In carboxyl-terminated ligand systems, structure and interactions are dominated by an end-to-end orientation of ligands. In methyl-terminated ligand systems large ordered ligand structures form, but nanoparticle interactions are dominated by disordered, partially interdigitated ligands. Core size and ligand length also affect both ligand arrangement within the membrane and the membrane's macroscopic mechanical response, but are secondary to the role of the ligand end group. Additionally, the particular end group (COOH or CH3) alters the nature of how ligand length, in turn, affects the membrane properties. The effect of core size does not depend on the ligand end group, with larger cores always leading to stiffer membranes. Asymmetry in the stress and ligand density is observed in membranes during preparation at a water-vapor interface, with the stress asymmetry persisting in all membranes after drying.

  2. Fundamental Studies of Assembly and Mechanical Properties of Lipid Bilayer Membranes and Unilamellar Vesicles

    NASA Astrophysics Data System (ADS)

    Wang, Xi

    This dissertation work focuses on: (i) obtaining a phospholipid bilayer membrane (LBM)/conducting electrode system with low defect density and optimized rigidity; (ii) investigating vesicle stability and mechanical properties. LBM is a simplified yet representative cell membrane model. LBMs assembled on conductive surfaces can probe protein-LBM interactions activities electrochemically. Sterically stabilized vesicles could be used as cell models or for drug delivery. The main challenges for LBM assembly on gold are vesicles do not spontaneously rupture to form LBMs on gold and the roughness of the gold substrate has considerable influence on molecular film defect density. In this study, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) vesicles were functionalized with 1,2-distearoyl-sn-glycero-3-phosphoethanolamine- N-poly(ethylene glycol)-2000-N-[3-(2-pyridyldithio)propionate] (DSPE-PEG-PDP) to yield stable LBMs on gold without surface modification. A template-stripping method was used to obtain atomically flat and pristine gold surfaces. The critical force to initiate vesicle rupture decreases with increasing DSPE-PEG-PDP concentration, indicating that gold-thiolate bonding between DSPE-PEG-PDP and gold substrates promotes LBM formation. Mechanical properties of LBMs and vesicles were investigated as a function of DSPE-PEG-PDP concentration via Atomic Force Microscopy. The elastic moduli of LBMs were determined with DSPE-PEG-PDP concentration ranging from 0mol% to 24mol% and were found to depend on PEG chain conformation. Incorporating DSPE-PEG-PDP molecules with PEG in mushroom conformation results in a decrease of LBM rigidity, while incorporating PEG in brush conformation leads to LBM stiffening. Contrarily, mechanical properties of functionalized vesicles did not vary significantly by varying DSPE-PEG-PDP concentration. LBM with tunable rigidity by adjusting DSPE-PEG-PDP concentration provides a versatile cell membrane model for studying protein or

  3. Glucose transport and microvillus membrane physical properties along the crypt-villus axis of the rabbit.

    PubMed Central

    Meddings, J B; DeSouza, D; Goel, M; Thiesen, S

    1990-01-01

    Both transport function and microvillus membrane physical properties evolve as the enterocyte matures and migrates up the crypt-villus axis. We isolated enriched fractions of villus tip, mid-villus, and crypt enterocytes from which microvillus membrane vesicles were prepared. Using this material we characterized the alterations that occur in microvillus membrane fluidity as the rabbit enterocyte matures and correlated these with kinetic studies of glucose transport. With increasing maturity the microvillus membrane becomes more rigid due to both an increase in the cholesterol/phospholipid ratio and alterations in individual phospholipid subclasses. Maximal rates of glucose transport were greatest in microvillus membrane vesicles prepared from mature cells. However, the glucose concentration producing half-maximal rates of transport (Km) was significantly lower in crypt microvillus membrane vesicles, suggesting that a distinct glucose transporter existed in crypt enterocytes. This distinction disappeared when differences between membrane lipid environments were removed. By fluidizing villus-tip microvillus membrane vesicles, in vitro, to levels seen in the crypt microvillus membrane, we observed a reduction in the Km of this transport system. These data suggest that the kinetic characteristics of the sodium-dependent glucose transporter are dependent upon its local membrane environment. Images PMID:2318967

  4. Glucocorticoid-induced alterations in mitochondrial membrane properties and respiration in childhood acute lymphoblastic leukemia.

    PubMed

    Eberhart, Karin; Rainer, Johannes; Bindreither, Daniel; Ritter, Ireen; Gnaiger, Erich; Kofler, Reinhard; Oefner, Peter J; Renner, Kathrin

    2011-06-01

    Mitochondria are signal-integrating organelles involved in cell death induction. Mitochondrial alterations and reduction in energy metabolism have been previously reported in the context of glucocorticoid (GC)-triggered apoptosis, although the mechanism is not yet clarified. We analyzed mitochondrial function in a GC-sensitive precursor B-cell acute lymphoblastic leukemia (ALL) model as well as in GC-sensitive and GC-resistant T-ALL model systems. Respiratory activity was preserved in intact GC-sensitive cells up to 24h under treatment with 100 nM dexamethasone before depression of mitochondrial respiration occurred. Severe repression of mitochondrial respiratory function was observed after permeabilization of the cell membrane and provision of exogenous substrates. Several mitochondrial metabolite and protein transporters and two subunits of the ATP synthase were downregulated in the T-ALL and in the precursor B-ALL model at the gene expression level under dexamethasone treatment. These data could partly be confirmed in ALL lymphoblasts from patients, dependent on the molecular abnormality in the ALL cells. GC-resistant cell lines did not show any of these defects after dexamethasone treatment. In conclusion, in GC-sensitive ALL cells, dexamethasone induces changes in membrane properties that together with the reduced expression of mitochondrial transporters of substrates and proteins may lead to repressed mitochondrial respiratory activity and lower ATP levels that contribute to GC-induced apoptosis. PMID:21237131

  5. Basement membrane stiffening promotes retinal endothelial activation associated with diabetes.

    PubMed

    Yang, Xiao; Scott, Harry A; Monickaraj, Finny; Xu, Jun; Ardekani, Soroush; Nitta, Carolina F; Cabrera, Andrea; McGuire, Paul G; Mohideen, Umar; Das, Arup; Ghosh, Kaustabh

    2016-02-01

    Endothelial activation is a hallmark of the high-glucose (HG)-induced retinal inflammation associated with diabetic retinopathy (DR). However, precisely how HG induces retinal endothelial activation is not fully understood. We hypothesized that HG-induced up-regulation of lysyl oxidase (LOX), a collagen-cross-linking enzyme, in retinal capillary endothelial cells (ECs) enhances subendothelial basement membrane (BM) stiffness, which, in turn, promotes retinal EC activation. Diabetic C57BL/6 mice exhibiting a 70 and 50% increase in retinal intercellular adhesion molecule (ICAM)-1 expression and leukocyte accumulation, respectively, demonstrated a 2-fold increase in the levels of BM collagen IV and LOX, key determinants of capillary BM stiffness. Using atomic force microscopy, we confirmed that HG significantly enhances LOX-dependent subendothelial matrix stiffness in vitro, which correlated with an ∼2.5-fold increase in endothelial ICAM-1 expression, a 4-fold greater monocyte-EC adhesion, and an ∼2-fold alteration in endothelial NO (decrease) and NF-κB activation (increase). Inhibition of LOX-dependent subendothelial matrix stiffening alone suppressed HG-induced retinal EC activation. Finally, using synthetic matrices of tunable stiffness, we demonstrated that subendothelial matrix stiffening is necessary and sufficient to promote EC activation. These findings implicate BM stiffening as a critical determinant of HG-induced retinal EC activation and provide a rationale for examining BM stiffness and underlying mechanotransduction pathways as therapeutic targets for diabetic retinopathy. PMID:26443820

  6. Thinking in Terms of Structure-Activity-Relationships (T-SAR): A Tool to Better Understand Nanofiltration Membranes

    PubMed Central

    Fernández, José F.; Jastorff, Bernd; Störmann, Reinhold; Stolte, Stefan; Thöming, Jorg

    2011-01-01

    A frontier to be conquered in the field of membrane technology is related to the very limited scientific base for the rational and task-specific design of membranes. This is especially true for nanofiltration membranes with properties that are based on several solute-membrane interaction mechanisms. “Thinking in terms of Structure-Activity-Relationships” (T-SAR) is a methodology which applies a systematic analysis of a chemical entity based on its structural formula. However, the analysis become more complex with increasing size of the molecules considered. In this study, T-SAR was combined with classical membrane characterization methods, resulting in a new methodology which allowed us not only to explain membrane characteristics, but also provides evidence for the importance of the chemical structure for separation performance. We demonstrate an application of the combined approach and its potential to discover stereochemistry, molecular interaction potentials, and reactivity of two FilmTec nanofiltration membranes (NF-90 and NF-270). Based on these results, it was possible to predict both properties and performance in the recovery of hydrophobic ionic liquids from aqueous solution. PMID:24957730

  7. Influence of decavanadate on rat synaptic plasma membrane ATPases activity.

    PubMed

    Krstić, Danijela; Colović, Mirjana; Bosnjaković-Pavlović, Nada; Spasojević-De Bire, Anne; Vasić, Vesna

    2009-09-01

    The in vitro influence of decameric vanadate species on Na+/K+-ATPase, plasma membrane Ca2+-ATPase (PMCA)-calcium pump and ecto-ATPase activity, using rat synaptic plasma membrane (SPM) as model system was investigated, whereas the commercial porcine cerebral cortex Na+/K+-ATPase served as a reference. The thermal behaviour of the synthesized decavanadate (V10) has been studied by differential scanning calorimetry and thermogravimetric analysis, while the type of polyvanadate anion was identified using the IR spectroscopy. The concentration-dependent responses to V10 of all enzymes were obtained. The half-maximum inhibitory concentration (IC50) of the enzyme activity was achieved at (4.74 +/- 1.15) x 10(-7) mol/l for SPM Na+/K+-ATPase, (1.30 +/- 0.10) x 10(-6) mol/l for commercial Na+/K+-ATPase and (3.13 +/- 1.70) x 10(-8) mol/l for Ca2+-ATPase, while ecto-ATPase is significantly less sensitive toward V10 (IC50 = (1.05 +/- 0.10) x 10(-4) mol/l) than investigated P-type ATPases. Kinetic analysis showed that V10 inhibited Na+/K+-ATPase by reducing the maximum enzymatic velocity and apparent affinity for ATP (increasing K(m) value), implying a mixed mode of interaction between V10 and P-type ATPases. PMID:20037196

  8. Dramatic nano-fluidic properties of carbon nanotube membranes as a platform for protein channel mimetics

    NASA Astrophysics Data System (ADS)

    Hinds, Bruce

    2013-03-01

    Carbon nanotubes have three key attributes that make them of great interest for novel membrane applications: 1) atomically flat graphite surface allows for ideal fluid slip boundary conditions and extremely fast flow rates 2) the cutting process to open CNTs inherently places functional chemistry at CNT core entrance for chemical selectivity and 3) CNT are electrically conductive allowing for electrochemical reactions and application of electric fields gradients at CNT tips. Pressure driven flux of a variety of solvents (H2O, hexane, decane ethanol, methanol) are 4-5 orders of magnitude higher than conventional Newtonian flow [Nature 2005, 438, 44] due to atomically flat graphite planes inducing nearly ideal slip conditions. However this is eliminated with selective chemical functionalization [ACS Nano 2011 5(5) 3867-3877] needed to give chemical selectivity. These unique properties allow us to explore the hypothesis of producing ``Gatekeeper'' membranes that mimic natural protein channels to actively pump through rapid nm-scale channels. With anionic tip functionality strong electroosmotic flow is induced by unimpeded cation flow with similar 10,000 fold enhancements [Nature Nano 2012 7(2) 133-39]. With enhanced power efficiency, carbon nanotube membranes were employed as the active element of a switchable transdermal drug delivery device that can facilitate more effective treatments of drug abuse and addiction. Recently methods to deposit Pt monolayers on CNT surface have been developed making for highly efficient catalytic platforms. Discussed are other applications of CNT protein channel mimetics, for large area robust engineering platforms, including water purification, flow battery energy storage, and biochemical/biomass separations. DOE EPSCoR (DE-FG02-07ER46375) and DARPA, W911NF-09-1-0267

  9. Selective flow-induced vesicle rupture to sort by membrane mechanical properties

    PubMed Central

    Pommella, Angelo; Brooks, Nicholas J.; Seddon, John M.; Garbin, Valeria

    2015-01-01

    Vesicle and cell rupture caused by large viscous stresses in ultrasonication is central to biomedical and bioprocessing applications. The flow-induced opening of lipid membranes can be exploited to deliver drugs into cells, or to recover products from cells, provided that it can be obtained in a controlled fashion. Here we demonstrate that differences in lipid membrane and vesicle properties can enable selective flow-induced vesicle break-up. We obtained vesicle populations with different membrane properties by using different lipids (SOPC, DOPC, or POPC) and lipid:cholesterol mixtures (SOPC:chol and DOPC:chol). We subjected vesicles to large deformations in the acoustic microstreaming flow generated by ultrasound-driven microbubbles. By simultaneously deforming vesicles with different properties in the same flow, we determined the conditions in which rupture is selective with respect to the membrane stretching elasticity. We also investigated the effect of vesicle radius and excess area on the threshold for rupture, and identified conditions for robust selectivity based solely on the mechanical properties of the membrane. Our work should enable new sorting mechanisms based on the difference in membrane composition and mechanical properties between different vesicles, capsules, or cells. PMID:26302783

  10. Conformational activation of visual rhodopsin in native disc membranes.

    PubMed

    Malmerberg, Erik; M Bovee-Geurts, Petra H; Katona, Gergely; Deupi, Xavier; Arnlund, David; Wickstrand, Cecilia; Johansson, Linda C; Westenhoff, Sebastian; Nazarenko, Elena; Schertler, Gebhard F X; Menzel, Andreas; de Grip, Willem J; Neutze, Richard

    2015-03-10

    Rhodopsin is the G protein-coupled receptor (GPCR) that serves as a dim-light receptor for vision in vertebrates. We probed light-induced conformational changes in rhodopsin in its native membrane environment at room temperature using time-resolved wide-angle x-ray scattering. We observed a rapid conformational transition that is consistent with an outward tilt of the cytoplasmic portion of transmembrane helix 6 concomitant with an inward movement of the cytoplasmic portion of transmembrane helix 5. These movements were considerably larger than those reported from the basis of crystal structures of activated rhodopsin, implying that light activation of rhodopsin involves a more extended conformational change than was previously suggested. PMID:25759477

  11. Model Membrane and Cell Studies of Antimicrobial Activity of Melittin Analogues.

    PubMed

    Jamasbi, Elaheh; Mularski, Anna; Separovic, Frances

    2016-01-01

    Melittin is a 26 residue peptide and the major component of bee (Apis mellifera) venom. Although melittin has both anticancer and antimicrobial properties, utilization has been limited due to its high lytic activity against eukaryotic cells. The mechanism of this lytic activity remains unclear but several mechanisms have been proposed, including pore formation or a detergent like mechanism, which result in lysis of cell membranes. Several analogues of melittin have been synthesized to further understand the role of specific residues in its antimicrobial and lytic activity. Melittin analogues that have a proline residue substituted for an alanine, lysine or cysteine have been studied with both model membrane systems and living cells. These studies have revealed that the proline residue plays a critical role in antimicrobial activity and cytotoxicity. Analogues lacking the proline residue and dimers of these analogues displayed decreased cytotoxicity and minimum inhibition concentrations. Several mutant studies have shown that, when key substitutions are made, the resultant peptides have more activity in terms of pore formation than the native melittin. Designing analogues that retain antimicrobial and anticancer activity while minimizing haemolytic activity will be a promising way to utilize melittin as a potential therapeutic agent. PMID:26139117

  12. Preparation and Properties of Nano-Hydroxyapatite/Gelatin/Poly(vinyl alcohol) Composite Membrane.

    PubMed

    Liao, Haotian; Shi, Kun; Peng, Jinrong; Qu, Ying; Liao, Jinfeng; Qian, Zhiyong

    2015-06-01

    In this study, the bone-like composite membrane based on blends of gelatin (Gel), nano-hydroxyapatite (n-HA) and poly(vinyl alcohol) (PVA) was fabricated by solvent casting and evaporation methods. The effect of n-HA content and the ratio of Gel/PVA on the properties of the composite was investigated. The Gel/PVA and n-HA/Gel/PVA composite membranes were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), water contact angle measurement and scanning electron microscopy (SEM). The mechanical properties of the composites were determined by tensile tests. The as prepared composite membranes exhibited hydrophobility, the water contact angle of composite membrane was 126.6 when its mass ratio of n-HA/Gel/PVA was 10/50/40. The tensile strength of composite membranes was greatly increased due to the introduction of n-HA, and the tensile strength was increased to 74.92 MPa when the mass ratio of n-HA/Gel/PVA was 10/50/40. SEM observation indicated that n-HA was dispersed in the membranes and a sea-island structure was formed in the n-HA/Gel/PVA composite membranes, resulting in a significant increase in tensile strength. The as-prepared n-HA/Gel/PVA composite membranes may be applied in the field of bone tissue engineering. PMID:26369028

  13. Non steroidal anti-inflammatory drugs modulate the physicochemical properties of plasma membrane in experimental colorectal cancer: a fluorescence spectroscopic study.

    PubMed

    Vaish, Vivek; Sanyal, Sankar Nath

    2011-12-01

    According to "fluid-mosaic model," plasma membrane is a bilayer constituted by phospholipids which regulates the various cellular activities governed by many proteins and enzymes. Any chemical, biochemical, or physical factor has to interact with the bilayer in order to regulate the cellular metabolism where various physicochemical properties of membrane, i.e., polarization, fluidity, electrostatic potential, and phase state may get affected. In this study, we have observed the in vivo effects of a pro-carcinogen 1,2-dimethylhydrazine dihydrochloride (DMH) and the two non steroidal anti-inflammatory drugs (NSAIDs); sulindac and celecoxib on various properties of the plasma membrane of colonocytes, i.e., electric potential, fluidity, anisotropy, microviscosity, lateral diffusion, and phase state in the experimentally induced colorectal cancer. A number of fluorescence probes were utilized like membrane fluidity and anisotropy by 1,6-diphenyl-1,3,5-hexatriene, membrane microviscosity by Pyrene, membrane electric potential by merocyanine 540, lateral diffusion by N-NBD-PE, and phase state by Laurdan. It is observed that membrane phospholipids are less densely packed and therefore, the membrane is more fluid in case of carcinogenesis produced by DMH than control. But NSAIDs are effective in reverting back the membrane toward normal state when co-administered with DMH. The membrane becomes less fluid, composed of low electric potential phospholipids whose lateral diffusion is being prohibited and the membrane stays mostly in relative gel phase. It may be stated that sulindac and celecoxib, the two NSAIDs may exert their anti-neoplastic role in colorectal cancer via modifying the physicochemical properties of the membranes. PMID:21725642

  14. Ceramic membranes for catalytic membrane reactors with high ionic conductivities and low expansion properties

    DOEpatents

    Mackay, Richard; Sammells, Anthony F.

    2000-01-01

    Ceramics of the composition: Ln.sub.x Sr.sub.2-x-y Ca.sub.y B.sub.z M.sub.2-z O.sub.5+.delta. where Ln is an element selected from the fblock lanthanide elements and yttrium or mixtures thereof; B is an element selected from Al, Ga, In or mixtures thereof; M is a d-block transition element of mixtures thereof; 0.01.ltoreq.x.ltoreq.1.0; 0.01.ltoreq.y.ltoreq.0.7; 0.01.ltoreq.z.ltoreq.1.0 and .delta. is a number that varies to maintain charge neutrality are provided. These ceramics are useful in ceramic membranes and exhibit high ionic conductivity, high chemical stability under catalytic membrane reactor conditions and low coefficients of expansion. The materials of the invention are particularly useful in producing synthesis gas.

  15. The effect of membrane parameters on the properties of the nerve impulse.

    NASA Technical Reports Server (NTRS)

    Sabah, N. H.; Leibovic, K. N.

    1972-01-01

    The effect of varying some membrane parameters is explored, basing the investigation on computer simulation of the Hodgkin-Huxley equations for the squid giant axon, including variations in the membrane capacitance, conductances, and the rate constants. It is shown that by reducing the degree of regeneration in the excitable membrane, the character of the nerve signal can be smoothly changed from that of the axonal spike to essentially electrotonic spread, with all gradations in between. The reduction in the degree of regeneration can most simply be brought about by a decrease in the density of active membrane patches.

  16. Signaling Network Triggers and Membrane Physical Properties Control the Actin Cytoskeleton-Driven Isotropic Phase of Cell Spreading

    PubMed Central

    Rangamani, Padmini; Fardin, Marc-Antoine; Xiong, Yuguang; Lipshtat, Azi; Rossier, Olivier; Sheetz, Michael P.; Iyengar, Ravi

    2011-01-01

    Cell spreading is regulated by signaling from the integrin receptors that activate intracellular signaling pathways to control actin filament regulatory proteins. We developed a hybrid model of whole-cell spreading in which we modeled the integrin signaling network as ordinary differential equations in multiple compartments, and cell spreading as a three-dimensional stochastic model. The computed activity of the signaling network, represented as time-dependent activity levels of the actin filament regulatory proteins, is used to drive the filament dynamics. We analyzed the hybrid model to understand the role of signaling during the isotropic phase of fibroblasts spreading on fibronectin-coated surfaces. Simulations showed that the isotropic phase of spreading depends on integrin signaling to initiate spreading but not to maintain the spreading dynamics. Simulations predicted that signal flow in the absence of Cdc42 or WASP would reduce the spreading rate but would not affect the shape evolution of the spreading cell. These predictions were verified experimentally. Computational analyses showed that the rate of spreading and the evolution of cell shape are largely controlled by the membrane surface load and membrane bending rigidity, and changing information flow through the integrin signaling network has little effect. Overall, the plasma membrane acts as a damper such that only ∼5% of the actin dynamics capability is needed for isotropic spreading. Thus, the biophysical properties of the plasma membrane can condense varying levels of signaling network activities into a single cohesive macroscopic cellular behavior. PMID:21320428

  17. Membrane stretch and cytoplasmic Ca2+ independently modulate stretch-activated BK channel activity.

    PubMed

    Zhao, Hu-Cheng; Agula, Hasi; Zhang, Wei; Wang, Fa; Sokabe, Masahiro; Li, Lu-Ming

    2010-11-16

    Large conductance Ca(2+)-activated K(+) (BK) channels are responsible for changes in chemical and physical signals such as Ca(2+), Mg(2+) and membrane potentials. Previously, we reported that a BK channel cloned from chick heart (SAKCaC) is activated by membrane stretch. Molecular cloning and subsequent functional characterization of SAKCaC have shown that both the membrane stretch and intracellular Ca(2+) signal allosterically regulate the channel activity via the linker of the gating ring complex. Here we investigate how these two gating principles interact with each other. We found that stretch force activated SAKCaC in the absence of cytoplasmic Ca(2+). Lack of Ca(2+) bowl (a calcium binding motif) in SAKCaC diminished the Ca(2+)-dependent activation, but the mechanosensitivity of channel was intact. We also found that the abrogation of STREX (a proposed mechanosensing apparatus) in SAKCaC abolished the mechanosensitivity without altering the Ca(2+) sensitivity of channels. These observations indicate that membrane stretch and intracellular Ca(2+) could independently modulate SAKCaC activity. PMID:20673577

  18. Effects of sterilization methods on the physical, chemical, and biological properties of silk fibroin membranes.

    PubMed

    de Moraes, Mariana Agostini; Weska, Raquel Farias; Beppu, Marisa Masumi

    2014-05-01

    Silk fibroin has been widely explored for many biomedical applications, due to its biocompatibility and biodegradability. Sterilization is a fundamental step in biomaterials processing and it must not jeopardize the functionality of medical devices. The aim of this study was to analyze the influence of different sterilization methods in the physical, chemical, and biological characteristics of dense and porous silk fibroin membranes. Silk fibroin membranes were treated by several procedures: immersion in 70% ethanol solution, ultraviolet radiation, autoclave, ethylene oxide, and gamma radiation, and were analyzed by scanning electron microscopy, Fourier-transformed infrared spectroscopy (FTIR), X-ray diffraction, tensile strength and in vitro cytotoxicity to Chinese hamster ovary cells. The results indicated that the sterilization methods did not cause perceivable morphological changes in the membranes and the membranes were not toxic to cells. The sterilization methods that used organic solvent or an increased humidity and/or temperature (70% ethanol, autoclave, and ethylene oxide) increased the silk II content in the membranes: the dense membranes became more brittle, while the porous membranes showed increased strength at break. Membranes that underwent sterilization by UV and gamma radiation presented properties similar to the nonsterilized membranes, mainly for tensile strength and FTIR results. PMID:24259492

  19. Enzymatic activation of cellulose acetate membrane for reducing of protein fouling.

    PubMed

    Koseoglu-Imer, Derya Y; Dizge, Nadir; Koyuncu, Ismail

    2012-04-01

    In this study, the surface of cellulose acetate (CA) ultrafiltration membrane was activated with serine protease (Savinase) enzyme to reduce protein fouling. Enzyme molecules were covalently immobilized with glutaraldehyde (cross-linking agent) onto the surface of CA membranes. The membrane activation was verified using filtration experiments and morphological analysis. Scanning electron microscopy (SEM) images and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy of the activated membrane when compared with raw membrane were confirmed that the enzyme was immobilized onto the membrane surface. The immobilization efficiencies changed from 13.2 to 41.2% according to the enzyme ratios from 2.5 to 10.0 mg/mL. However, the permeability values decreased from 232±6 to 121±4 L/m(2) h bar with increasing enzyme concentration from 2.5 to 10.0 mg/mL. In fouling experiments, bovine serum albumin (BSA) was used as the protein model solution and activated sludge was used as the model biological sludge. Enzyme-activated membranes exhibited good filtration performances and protein rejection efficiencies were compared with raw CA membrane. Also the relative flux reduction (RFR) ratios of membranes were calculated as 97% and 88% for raw CA and enzyme-activated membranes (5 mg/mL savinase), respectively. The membrane activated with Savinase enzyme could be proposed as a surface treatment method before filtration to mitigate protein fouling. PMID:22218336

  20. The bacteriocin AS-48 requires dimer dissociation followed by hydrophobic interactions with the membrane for antibacterial activity.

    PubMed

    Cebrián, Rubén; Martínez-Bueno, Manuel; Valdivia, Eva; Albert, Armando; Maqueda, Mercedes; Sánchez-Barrena, María José

    2015-05-01

    The molecular mechanism underlining the antibacterial activity of the bacteriocin AS-48 is not known, and two different and opposite alternatives have been proposed. Available data suggested that the interaction of positively charged amino acids of AS-48 with the membrane would produce membrane destabilization and disruption. Alternatively, it has been proposed that AS-48 activity could rely on the effective insertion of the bacteriocin into the membrane. The biological and structural properties of the AS-48G13K/L40K double mutant were investigated to shed light on this subject. Compared with the wild type, the mutant protein suffered an important reduction in the antibacterial activity. Biochemical and structural studies of AS-48G13K/L40K mutant suggest the basis of its decreased antimicrobial activity. Lipid cosedimentation assays showed that the membrane affinity of AS-48G13K/L40K is 12-fold lower than that observed for the wild type. L40K mutation is responsible for this reduced membrane affinity and thus, hydrophobic interactions are involved in membrane association. Furthermore, the high-resolution crystal structure of AS-48G13K/L40K, together with the study of its dimeric character in solution showed that G13K stabilizes the inactive water-soluble dimer, which displays a reduced dipole moment. Our data suggest that the cumulative effect of these three affected properties reduces AS-48 activity, and point out that the bactericidal effect is achieved by the electrostatically driven approach of the inactive water-soluble dimer towards the membrane, followed by the dissociation and insertion of the protein into the lipid bilayer. PMID:25816760

  1. Low temperature alters plasma membrane lipid composition and ATPase activity of pineapple fruit during blackheart development.

    PubMed

    Zhou, Yuchan; Pan, Xiaoping; Qu, Hongxia; Underhill, Steven J R

    2014-02-01

    Plasma membrane (PM) plays central role in triggering primary responses to chilling injury and sustaining cellular homeostasis. Characterising response of membrane lipids to low temperature can provide important information for identifying early causal factors contributing to chilling injury. To this end, PM lipid composition and ATPase activity were assessed in pineapple fruit (Ananas comosus) in relation to the effect of low temperature on the development of blackheart, a form of chilling injury. Chilling temperature at 10 °C induced blackheart development in concurrence with increase in electrolyte leakage. PM ATPase activity was decreased after 1 week at low temperature, followed by a further decrease after 2 weeks. The enzyme activity was not changed during 25 °C storage. Loss of total PM phospholipids was found during postharvest senescence, but more reduction was shown from storage at 10 °C. Phosphatidylcholine and phosphatidylethanolamine were the predominant PM phospholipid species. Low temperature increased the level of phosphatidic acid but decreased the level of phosphatidylinositol. Both phospholipid species were not changed during storage at 25 °C. Postharvest storage at both temperatures decreased the levels of C18:3 and C16:1, and increased level of C18:1. Low temperature decreased the level of C18:2 and increased the level of C14:0. Exogenous application of phosphatidic acid was found to inhibit the PM ATPase activity of pineapple fruit in vitro. Modification of membrane lipid composition and its effect on the functional property of plasma membrane at low temperature were discussed in correlation with their roles in blackheart development of pineapple fruit. PMID:24390546

  2. Cytolytic activity in T cell clones derived from human synovial rheumatoid membrane: inhibition by synovial fluid.

    PubMed Central

    Miltenburg, A M; Van Laar, J M; De Kuiper, P; Daha, M R; Breedveld, F C

    1990-01-01

    A panel of T cell clones was derived from the synovial membrane of a patient with rheumatoid arthritis (RA). We investigated whether T cell clones with cytolytic properties were present and whether T cell cytotoxicity was influenced by the presence of synovial fluid. These issues were studied using anti-CD3 and lectin-induced cytotoxicity assays. The majority of the T cell clones derived from the synovial membrane showed cytotoxic properties although non-cytotoxic clones were also found. Three clones (N11, N6 and N15) showed strong cytotoxicity (more than 40% lysis at an effector-to-target cell ratio of 10:1) whereas three clones (N16, N4 and N14) were non-cytotoxic (less than 20% lysis at an effector-to-target cell ratio of 10:1). The induction of cytotoxicity in the anti-CD3-driven system was shown to be dependent on the dose of anti-CD3 present. When synovial fluid was added to these assays a strong inhibition of cytotoxicity was found. This inhibition of cytotoxicity was found with synovial fluid samples of RA patients, as well as with non-RA synovial fluids. Both anti-CD3 and lectin-dependent cytotoxicity assays were strongly inhibited. In conclusion, T cell clones with cytotoxic activity can be isolated from rheumatoid synovial membrane. In the presence of synovial fluid these cytotoxic cells are inhibited to exert their cytotoxic function. PMID:2148285

  3. Integrated carboxylic carbon nanotube pathways with membranes for voltage-activated humidity detection and microclimate regulation.

    PubMed

    Pingitore, V; Miriello, D; Drioli, E; Gugliuzza, A

    2015-06-14

    This work describes some single walled carboxylic carbon nanotubes with outstanding transport properties when assembled in a 3D microarray working like a humidity membrane-sensor and an adjustable moisture regulator. Combined nano-assembly approaches are used to build up a better quality pathway through which assisted-charge and mass transport synchronically takes place. The structure-electrical response relationship is found, while controllable and tunable donor-acceptor interactions established at material interfaces are regarded as key factors for the accomplishment of charge transportation, enhanced electrical responses and adjustable moisture exchange. Raman and infrared spectroscopy provides indications about the fine structural and chemical features of the hybrid-composite membranes, resulting in perfect agreement with related morphology and electrical properties. Enhanced and modular electrical response to changes in the surrounding atmosphere is concerned with doping events, while assisted moisture regulation is discussed in relation to swelling and hopping actions. The electro-activated hybrid-composite membrane proposed in this work can be regarded as an attractive 'sense-to-act' precursor for smart long-distance monitoring systems with capability to adapt itself and provide local comfortable microenvironments. PMID:25939404

  4. Cassava root membrane proteome reveals activities during storage root maturation.

    PubMed

    Naconsie, Maliwan; Lertpanyasampatha, Manassawe; Viboonjun, Unchera; Netrphan, Supatcharee; Kuwano, Masayoshi; Ogasawara, Naotake; Narangajavana, Jarunya

    2016-01-01

    Cassava (Manihot esculenta Crantz) is one of the most important crops of Thailand. Its storage roots are used as food, feed, starch production, and be the important source for biofuel and biodegradable plastic production. Despite the importance of cassava storage roots, little is known about the mechanisms involved in their formation. This present study has focused on comparison of the expression profiles of cassava root proteome at various developmental stages using two-dimensional gel electrophoresis and LC-MS/MS. Based on an anatomical study using Toluidine Blue, the secondary growth was confirmed to be essential during the development of cassava storage root. To investigate biochemical processes occurring during storage root maturation, soluble and membrane proteins were isolated from storage roots harvested from 3-, 6-, 9-, and 12-month-old cassava plants. The proteins with differential expression pattern were analysed and identified to be associated with 8 functional groups: protein folding and degradation, energy, metabolism, secondary metabolism, stress response, transport facilitation, cytoskeleton, and unclassified function. The expression profiling of membrane proteins revealed the proteins involved in protein folding and degradation, energy, and cell structure were highly expressed during early stages of development. Integration of these data along with the information available in genome and transcriptome databases is critical to expand knowledge obtained solely from the field of proteomics. Possible role of identified proteins were discussed in relation with the activities during storage root maturation in cassava. PMID:26547558

  5. Preparation of Chemically-Tailored Copolymer Membranes with Tunable Ion Transport Properties.

    PubMed

    Qu, Siyi; Dilenschneider, Theodore; Phillip, William A

    2015-09-01

    Membranes derived from copolymer materials are a promising platform due to their straightforward fabrication and small yet tunable pore structures. However, most current applications of these membranes are limited to the size-selective filtration of solutes. In this study, to advance the utility of copolymer membranes beyond size-selective filtrations, a poly(acrylonitrile-r-oligo(ethylene glycol) methyl ether methacrylate-r-glycidyl methacrylate) (P(AN-r-OEGMA-r-GMA)) copolymer is used to fabricate membranes that can be chemically modified via straightforward schemes. The P(AN-r-OEGMA-r-GMA) copolymer is cast into asymmetric membranes using a nonsolvent induced phase separation technique. Then, the surface charge of the membrane is modified to tailor its performance for nanofiltration applications. The oxirane groups of the glycidyl methacrylate (GMA) moiety that line the pore walls of the membrane allows for both positively charged and negatively charged moieties to be introduced directly without any prior activation. Notably, the highly size-selective nanostructure of the copolymer materials is retained throughout the functionalization processes. Specifically, amine moieties are attached to the pore walls using the aminolysis of the oxirane groups. The resulting amine-functionalized membrane is positively charged and rejects up to 87% of the salt dissolved in a 10 mM magnesium chloride feed solution. Further modification of the amine-functionalized membrane with 4-sulfophenyl isothiocyanate results in pore walls lined by sulfonic acid moieties. These negatively charged membranes reject up to 90% of a 10 mM sodium sulfate feed solution. Throughout the modification scheme, the membrane permeability remains equal to 1.5 L m(-2) h(-1) bar(-1) and the rejection of neutral solutes (i.e., sucrose and poly(ethylene oxide)) is consistent with the membrane having a single well-defined pore diameter of ∼5 nm. The performance of the membrane as a function of ion valence

  6. Effects of non-thermal plasma on the electrical properties of an erythrocyte membrane

    NASA Astrophysics Data System (ADS)

    Lee, Jin Young; Baik, Ku Youn; Kim, Tae Soo; Lim, Jaekwan; Uhm, Han S.; Choi, Eun Ha

    2015-09-01

    Non-thermal plasma is used here for membrane oxidation and permeabilization in which the electrical properties of an erythrocyte membrane are investigated after treatments. The zeta potential as measured by electrophoresis shows the increased negativity of the membrane surface potential (Ψs). The secondary electron emission coefficient ( γ) measured by a focused ion beam shows a decrease in the dipole potential (Ψd) of lipid molecules. The voltage-sensitive fluorescent intensity as measured by flow cytometry shows a decrease in the trans-membrane potential (ΔΨ) through the lipid bilayer membrane. These results allow us to take a step forward to unveil the complex events occurring in plasma-treated cells.

  7. Liquid but Durable: Molecular Dynamics Simulations Explain the Unique Properties of Archaeal-Like Membranes

    NASA Astrophysics Data System (ADS)

    Chugunov, Anton O.; Volynsky, Pavel E.; Krylov, Nikolay A.; Boldyrev, Ivan A.; Efremov, Roman G.

    2014-12-01

    Archaeal plasma membranes appear to be extremely durable and almost impermeable to water and ions, in contrast to the membranes of Bacteria and Eucaryota. Additionally, they remain liquid within a temperature range of 0-100°C. These are the properties that have most likely determined the evolutionary fate of Archaea, and it may be possible for bionanotechnology to adopt these from nature. In this work, we use molecular dynamics simulations to assess at the atomistic level the structure and dynamics of a series of model archaeal membranes with lipids that have tetraether chemical nature and ``branched'' hydrophobic tails. We conclude that the branched structure defines dense packing and low water permeability of archaeal-like membranes, while at the same time ensuring a liquid-crystalline state, which is vital for living cells. This makes tetraether lipid systems promising in bionanotechnology and material science, namely for design of new and unique membrane nanosystems.

  8. Liquid but durable: molecular dynamics simulations explain the unique properties of archaeal-like membranes.

    PubMed

    Chugunov, Anton O; Volynsky, Pavel E; Krylov, Nikolay A; Boldyrev, Ivan A; Efremov, Roman G

    2014-01-01

    Archaeal plasma membranes appear to be extremely durable and almost impermeable to water and ions, in contrast to the membranes of Bacteria and Eucaryota. Additionally, they remain liquid within a temperature range of 0-100°C. These are the properties that have most likely determined the evolutionary fate of Archaea, and it may be possible for bionanotechnology to adopt these from nature. In this work, we use molecular dynamics simulations to assess at the atomistic level the structure and dynamics of a series of model archaeal membranes with lipids that have tetraether chemical nature and "branched" hydrophobic tails. We conclude that the branched structure defines dense packing and low water permeability of archaeal-like membranes, while at the same time ensuring a liquid-crystalline state, which is vital for living cells. This makes tetraether lipid systems promising in bionanotechnology and material science, namely for design of new and unique membrane nanosystems. PMID:25501042

  9. Structure, morphology and properties of genipin-crosslinked carboxymethylchitosan porous membranes.

    PubMed

    Fiamingo, Anderson; Campana-Filho, Sergio Paulo

    2016-06-01

    Highly porous genipin cross-linked membranes of carboxymethylchitosan exhibiting different crosslinking degree (3%membranes were able to adsorb high amounts of PBS and presented high ultimate tensile strength and elongation-at-break the lower the crosslinking degree and the higher the molecular of the parent carboxymethylchitosan. Particularly, the membrane prepared from high molecular weight carboxymethylchitosan displayed higher swelling ratio (17.5g/g), ultimate tensile strength (≥300kPa) and elongation-at-break (≥65%). The susceptibility to lysozyme degradation depends only on the crosslinking degree of the membranes, the degradation rate being faster the lower the crosslinking degree. The preparation of lightly genipin cross-linked carboxymethylchitosan membranes displaying appropriated properties to fulfill specific applications as biomaterials is envisaged by using high molecular weight carboxymethylchitosan. PMID:27083355

  10. Liquid but Durable: Molecular Dynamics Simulations Explain the Unique Properties of Archaeal-Like Membranes

    PubMed Central

    Chugunov, Anton O.; Volynsky, Pavel E.; Krylov, Nikolay A.; Boldyrev, Ivan A.; Efremov, Roman G.

    2014-01-01

    Archaeal plasma membranes appear to be extremely durable and almost impermeable to water and ions, in contrast to the membranes of Bacteria and Eucaryota. Additionally, they remain liquid within a temperature range of 0–100°C. These are the properties that have most likely determined the evolutionary fate of Archaea, and it may be possible for bionanotechnology to adopt these from nature. In this work, we use molecular dynamics simulations to assess at the atomistic level the structure and dynamics of a series of model archaeal membranes with lipids that have tetraether chemical nature and “branched” hydrophobic tails. We conclude that the branched structure defines dense packing and low water permeability of archaeal-like membranes, while at the same time ensuring a liquid-crystalline state, which is vital for living cells. This makes tetraether lipid systems promising in bionanotechnology and material science, namely for design of new and unique membrane nanosystems. PMID:25501042

  11. Physiochemical Properties of Aluminum Adjuvants Elicit Differing Reorganization of Phospholipid Domains in Model Membranes.

    PubMed

    Antúnez, Lorena R; Livingston, Andrea; Berkland, Cory; Dhar, Prajnaparamita

    2016-05-01

    Most vaccines contain aluminum adjuvants; however, their exact mechanism of action remains unclear. A novel mechanism by Shi and colleagues proposes aluminum adjuvants may enhance immune activation by binding and reorganizing lipids that are key components of lipid rafts. To better understand the specificity of interaction between aluminum adjuvants and the cell membrane lipids, we present a biophysical study of lipid domain clustering in simple model phospholipid monolayers containing dipalmitoyl-phosphatidylcholine (DPPC) and dioleoyl-phosphatidylcholine (DOPC) exposed to two aluminum adjuvants, Alhydrogel and Adju-Phos. Surface pressure measurements and fluorescence microscopy images verified aluminum adjuvant-induced increase in lipid domain size, even in the key lipid raft components. Additionally, adjuvant induced lipid clustering differed based on the physicochemical properties of the adjuvants. Alhydrogel appeared to reduce monolayer compressibility and insert into the monolayer, while Adju-Phos induced more significant changes in domain size, without compromising the integrity of the monolayer. The Alhydrogel and Adju-Phos-mediated reorganization of phospholipid domains reported here supports the new mechanistic paradigm proposed by Shi and co-workers, and further suggests that lipid clustering is induced even in simple phospholipid membranes. The results present the basis for future exploration into lipid-mediated mechanisms of action for adjuvants. PMID:26998680

  12. Functional, photochemically active, and chemically asymmetric membranes by interfacial polymerization of derivatized multifunctional prepolymers

    DOEpatents

    Lonsdale, H.K.; Wamser, C.C.

    1990-04-17

    The preparation of a novel class of thin film membranes by interfacial polymerization is disclosed, said membranes incorporating as part of their polymeric structure the functionality of monomeric or oligomeric precursors. Specific embodiments include porphyrin and phthalocyanine derivatives that are photochemically or electrochemically active, as well as chemically asymmetric membranes.

  13. Functional, photochemically active, and chemically asymmetric membranes by interfacial polymerization of derivatized multifunctional prepolymers

    DOEpatents

    Lonsdale, Harold K.; Wamser, Carl C.

    1990-01-01

    The preparation of a novel class of thin film membranes by interfacial polymerization is disclosed, said membranes incorporating as part of their polymeric structure the functionality of monomeric or oligomeric precursors. Specific embodiments include porphyrin and phthalocyanine derivatives that are photochemically or electrochemically active, as well as chemically asymmetric membranes.

  14. Fusicoccin Binding to Its Plasma Membrane Receptor and the Activation of the Plasma Membrane H+-ATPase

    PubMed Central

    De Michelis, Maria Ida; Pugliarello, Maria Chiara; Rasi-Caldogno, Franca

    1989-01-01

    The characteristics of fusicoccin binding were investigated in microsomes from 24-h-old radish (Raphanus sativus L.) seedlings. The time course of fusicoccin binding depended on fusicoccin concentration: equilibrium was reached much faster at 10 nanomolar fusicoccin than at 0.3 nanomolar fusicoccin. Scatchard analysis of equilibrium binding as a function of fusicoccin concentration indicated a single class of receptor sites with a Kd of 1.8 nanomolar and a site density of 6.3 picomoles per milligram protein. Similar values (Kd 1.7 nanomolar and site density 7 picomoles per milligram protein) were obtained from the analysis of the dependence of equilibrium binding on membrane concentration at fixed fusicoccin concentrations. Fusicoccin binding comigrated with the plasma membrane H+-ATPase in an equilibrium sucrose density gradient: both activities formed a sharp peak (1.18 grams per milliliter) clearly distinct from that of markers of other membranes which all peaked at lower densities. The saturation profiles of fusicoccin binding and of fusicoccin-induced activation of the plasma membrane H+-ATPase, measured under identical conditions, were similar, supporting the view that fusicoccin-induced activation of the plasma membrane H+-ATPase is mediated by fusicoccin binding to its plasma membrane receptor. PMID:16666723

  15. Experimental study on the microstructure and nanomechanical properties of the wing membrane of dragonfly

    NASA Astrophysics Data System (ADS)

    Xiao, Kewei; Bai, Ke; Wang, Wensheng; Song, Fan

    2007-06-01

    Detailed investigations on the microstructure and the mechanical properties of the wing membrane of the dragonfly are carried out. It is found that in the direction of the thickness the membrane was divided into three layers rather than a single entity as traditionally considered, and on the surfaces the membrane displays a random distribution rough microstructure that is composed of numerous nanometer scale columns coated by the cuticle wax secreted. The characteristics of the surface structure are measured and described. The mechanical properties of the membranes taken separately from the wings of live and dead dragonflies are investigated by the nanoindentation technique. The Young’s moduli obtained here are approximately two times greater than the previous result, and the reasons that yield the difference are discussed.

  16. Red wine activates plasma membrane redox system in human erythrocytes.

    PubMed

    Tedesco, Idolo; Moccia, Stefania; Volpe, Silvestro; Alfieri, Giovanna; Strollo, Daniela; Bilotto, Stefania; Spagnuolo, Carmela; Di Renzo, Massimo; Aquino, Rita P; Russo, Gian Luigi

    2016-05-01

    In the present study, we report that polyphenols present in red wine obtained by a controlled microvinification process are able to protect human erythrocytes from oxidative stress and to activate Plasma Membrane Redox System (PMRS). Human plasma obtained from healthy subjects was incubated in the presence of whole red wine at a concentration corresponding to 9.13-73 μg/ml gallic acid equivalents to verify the capacity to protect against hypochlorous acid (HOCl)-induced plasma oxidation and to minimize chloramine formation. Red wine reduced hemolysis and chloramine formation induced by HOCl of 40 and 35%, respectively. PMRS present on human erythrocytes transfers electrons from intracellular molecules to extracellular electron acceptors. We demonstrated that whole red wine activated PMRS activity in human erythrocytes isolated from donors in a dose-dependent manner with a maximum at about 70-100 μg/ml gallic acid equivalents. We also showed that red wine increased glutathione (GSH) levels and erythrocytic antioxidant capacity, measured by 2,2-diphenyl-1-picrylhydrazyl (DPPH) quenching assay. Furthermore, we reported that GSH played a crucial role in regulating PMRS activity in erythrocytes. In fact, the effect of iodoacetamide, an alkylating agent that induces depletion of intracellular GSH, was completely counteracted by red wine. Bioactive compounds present in red wine, such as gallic acid, resveratrol, catechin, and quercetin were unable to activate PMRS when tested at the concentrations normally present in aged red wines. On the contrary, the increase of PMRS activity was associated with the anthocyanin fraction, suggesting the capacity of this class of compounds to positively modulate PMRS enzymatic activity. PMID:26866566

  17. Biologically Inspired Photocatalytically Active Membranes for Water Treatment

    NASA Astrophysics Data System (ADS)

    Kinsinger, Nichola M.

    There is an alarming increase of a variety of new chemicals that are now being discharged into the wastewater system causing increased concern for public health and safety because many are not removed by typical wastewater treatment practices. Titanium Dioxide (TiO2) is a heterogeneous photocatalytic material that rapidly and completely mineralizing organics without harmful byproducts. TiO2 is synthesized by various methods, which lack the necessary control of crystal size, phase, and morphological features that yield optimized semiconductor materials. Mineralizing organisms demonstrate how nature can produce elegant structures at room temperature through controlled organic-mineral interactions. Here, we utilize biologically-inspired scaffolds to template the nucleation and growth of inorganic materials such as TiO2, which aid in controlling the size and phase of these particles and ultimately, their properties. Nanosized rutile and anatase particles were synthesized under solution conditions at relatively low temperatures and mild pH conditions. The effects of reaction conditions on phase and grain size were investigated and discussed from coordination chemistry and coarsening mechanisms. Photocatalytic characterization of TiO2 phase mixtures was performed to investigate their synergistic effect. The suspension conditions of these catalytic nanomaterials were modulated to optimize the degradation rate of organic analytes. Through the addition of an organic scaffold during the synthesis reaction, a mechanically robust (elastic) composite material containing TiO2 nanoparticles was produced. This composite was subsequently heat-treated to produce a porous, high surface area TiO2 nanoparticulate membrane. Processing conditions were investigated to characterize the growth and phase transformation of TiO2, which ultimately impacts photocatalytic performance. These bulk porous TiO2 structures can be fabricated and tailored to act as stand-alone photocatalytic membranes

  18. Spatial variations in membrane properties in the intact rat lens.

    PubMed Central

    Baldo, G J; Mathias, R T

    1992-01-01

    We have used linear frequency domain techniques to measure impedance at various locations and depths in the intact rat lens. The data are used to obtain best-fit solutions to a new electrical model based on lens structure, allowing us to estimate localized conductances of surface cell membranes (Gs), fiber cell membranes (gm), and gap junctions (Gj) as functions of position. We find that gm is small and fairly uniform throughout the lens (2.02 +/- 0.58 microS/cm2); for the anterior surface-epithelial cells Gs = 1.26 +/- 0.19 mS/cm2; for the posterior surface differentiating fiber cells Gs = 0.46 +/- 0.04 mS/cm2. Thus, Gs varies about the equator in a stepwise fashion. Gj between fiber cells at locations interior to 80% of the radius is fairly uniform (0.75 S/cm2); but in the outer 20% Gj varies smoothly and symmetrically from both poles (0.66 S/cm2) to equator (5.95 S/cm2). This pattern of variation in Gj is similar to the pattern of inward and outward currents reported by Robinson and Patterson (1983. Curr. Eye Res. 2:843-847). We therefore suggest that the nonuniform distribution of functional gap junctions, not the surface cell conductance or Na/K pumps, may be responsible for directing these current flows. Gap junctional uncoupling during exposure to elevated calcium and acidification was also examined. High calcium (20 mM, with the calcium ionophore A23187) produced modest (twofold) irreversible uncoupling along with large, irreversible decreases in membrane potential. We did not pursue this further. Acidification with 20 and 100% CO2-bubbled Tyrode's produced 5- and 15-fold reversible uncoupling, respectively, only in the outer 20% of the lens radius. The remaining inner 80% of the lens gap junctions seemed resistant to the acidification and did not uncouple. PMID:1420894

  19. Branched phospholipids render lipid vesicles more susceptible to membrane-active peptides.

    PubMed

    Mitchell, Natalie J; Seaton, Pamela; Pokorny, Antje

    2016-05-01

    Iso- and anteiso-branched lipids are abundant in the cytoplasmic membranes of bacteria. Their function is assumed to be similar to that of unsaturated lipids in other organisms - to maintain the membrane in a fluid state. However, the presence of terminally branched membrane lipids is likely to impact other membrane properties as well. For instance, lipid acyl chain structure has been shown to influence the activity of antimicrobial peptides. Moreover, the development of resistance to antimicrobial agents in Staphylococcus aureus is accompanied by a shift in the fatty acid composition toward a higher fraction of anteiso-branched lipids. Little is known about how branched lipids and the location of the branch point affect the activity of membrane-active peptides. We hypothesized that bilayers containing lipids with low phase transition temperatures would tend to exclude peptides and be less susceptible to peptide-induced perturbation than those made from higher temperature melting lipids. To test this hypothesis, we synthesized a series of asymmetric phospholipids that only differ in the type of fatty acid esterified at the sn-2 position of the lipid glycerol backbone. We tested the influence of acyl chain structure on peptide activity by measuring the kinetics of release from dye-encapsulated lipid vesicles made from these synthetic lipids. The results were compared to those obtained using vesicles made from S. aureus and Staphylococcus sciuri membrane lipid extracts. Anteiso-branched phospholipids, which melt at very low temperatures, produced lipid vesicles that were only slightly less susceptible to peptide-induced dye release than those made from the iso-branched isomer. However, liposomes made from bacterial phospholipid extracts were generally much more resistant to peptide-induced perturbation than those made from any of the synthetic lipids. The results suggest that the increase in the fraction of anteiso-branched fatty acids in antibiotic-resistant strains

  20. Shielding membrane surface carboxyl groups by covalent-binding graphene oxide to improve anti-fouling property and the simultaneous promotion of flux.

    PubMed

    Han, Jing-Long; Xia, Xue; Tao, Yu; Yun, Hui; Hou, Ya-Nan; Zhao, Chang-Wei; Luo, Qin; Cheng, Hao-Yi; Wang, Ai-Jie

    2016-10-01

    Graphene oxide (GO) is an excellent material for membrane surface modification. However, little is known about how and to what extent surface functional groups change after GO modification influence membrane anti-fouling properties. Carboxyl is an inherent functional group on polyamide or other similar membranes. Multivalent cations in wastewater secondary effluent can bridge with carboxyls on membrane surfaces and organic foulants, resulting in serious membrane fouling. In this study, carboxyls of a polydopamine (pDA)/1,3,5-benzenetricarbonyl trichloride (TMC) active layer are shielded by covalently-bound GO. The process is mediated by N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC)/N-hydroxysuccinimide (NHS). For GO containing low quantities of carboxyls, X-ray photoelectron spectroscopy (XPS) and zeta potential analyzer test results reveal that the carboxyl density decreased by 52.3% compare to the pDA/TMC membrane after GO modification. Fouling experiments shows that the flux only slightly declines in the GO functionalized membrane (19.0%), compared with the pDA/TMC membrane (36.0%) after fouling. In addition, during GO modification process the pDA/TMC active layer also become harder and thinner with the aid of EDC/NHS. So the pure water permeability increases from 56.3 ± 18.2 to 103.7 ± 12.0 LMH/MPa. Our results provide new insights for membrane modification work in water treatment and other related fields. PMID:27479294

  1. Immobilization of tris(2 pyridyl) methylamine in a PVC-Membrane Sensor and Characterization of the Membrane Properties

    PubMed Central

    2012-01-01

    Background Due to the increasing industrial use of titanium compounds, its determination is the subject of considerable efforts. The ionophore or membrane active recognition is the most important component of any polymeric membrane sensor. The sensor’s response depends on the ionophore and bonding between the ionophore and the target ion. Ionophores with molecule-sized dimensions containing cavities or semi-cavities can surround the target ion. The bond between the ionophore and target ion gives different selectivity and sensitivity toward the other ions. Therefore, ionophores with different binding strengths can be used in the sensor. Results In the present work, poly (vinyl chloride) (PVC) based membrane incorporating tris (2 pyridyl) methylamine (tpm) as an ionophore has been prepared and explored as a titanium(III) selective sensor. Conclusions The strengths of the ion–ionophore (Ti(OH)2+-tpm) interactions and the role of ionophore on membrane were tested by various techniques such as elemental analysis, UV–vis, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and powder X-ray diffraction (XRD). All data approved the successful incorporation of organic group via covalent bond. PMID:22564322

  2. Plasma deposition of silver nanoparticles on ultrafiltration membranes: antibacterial and anti-biofouling properties

    PubMed Central

    Cruz, Mercedes Cecilia; Ruano, Gustavo; Wolf, Marcus; Hecker, Dominic; Vidaurre, Elza Castro; Schmittgens, Ralph; Rajal, Verónica Beatriz

    2015-01-01

    A novel and versatile plasma reactor was used to modify Polyethersulphone commercial membranes. The equipment was applied to: i) functionalize the membranes with low-temperature plasmas, ii) deposit a film of poly(methyl methacrylate) (PMMA) by Plasma Enhanced Chemical Vapor Deposition (PECVD) and, iii) deposit silver nanoparticles (SNP) by Gas Flow Sputtering. Each modification process was performed in the same reactor consecutively, without exposure of the membranes to atmospheric air. Scanning electron microscopy and transmission electron microscopy were used to characterize the particles and modified membranes. SNP are evenly distributed on the membrane surface. Particle fixation and transport inside membranes were assessed before- and after-washing assays by X-ray photoelectron spectroscopy depth profiling analysis. PMMA addition improved SNP fixation. Plasma-treated membranes showed higher hydrophilicity. Anti-biofouling activity was successfully achieved against Gram-positive (Enterococcus faecalis) and -negative (Salmonella Typhimurium) bacteria. Therefore, disinfection by ultrafiltration showed substantial resistance to biofouling. The post-synthesis functionalization process developed provides a more efficient fabrication route for anti-biofouling and anti-bacterial membranes used in the water treatment field. To the best of our knowledge, this is the first report of a gas phase condensation process combined with a PECVD procedure in order to deposit SNP on commercial membranes to inhibit biofouling formation. PMID:26166926

  3. Membrane lipid physical state and modulation of the Na+,Mg2+-ATPase activity in Acholeplasma laidlawii B.

    PubMed Central

    Silvius, J R; McElhaney, R N

    1980-01-01

    Careful analysis of the Arrhenius plot of the Na+,Mg2+-ATPase (ATP pyrophosphohydrolase, EC 3.6.1.8) activity in Acholeplasma laidlawii B membranes of varying fatty acid composition has been combined with differential thermal analysis of the membrane lipid phase transitions to evaluate the effects of membrane lipid properties on the enzyme activity. Our results indicate that the enzyme is active only in association with liquid-crystalline lipids, exhibiting a significant heat capacity of activation, delta Cp++, for the ATP hydrolytic reaction in this case. Quantitative analyses of Arrhenius plots for the enzyme activity in membranes whose lipids exhibit a gel-to-liquid-crystalline phase transition in the physiological temperature range suggest that the ATPase is inactivated when its boundary lipids undergo a phase transition that is driven by the bulk lipid phase transition but is less cooperative than the latter. Our results suggest that the familiar "biphasic linear" Arrhenius plots obtained for many membrane enzymes may in fact have a more complex shape, analysis of which can furnish useful information regarding the behavior of the enzyme molecule. Images PMID:6445554

  4. Temperature effects on nanostructure and mechanical properties of single-nanoparticle thick membranes.

    DOE PAGESBeta

    Salerno, Kenneth Michael; Grest, Gary S.

    2015-04-30

    In this study, the properties of mechanically stable single-nanoparticle (NP)-thick membranes have largely been studied at room temperature. How these membranes soften as nanoparticle ligands disorder with increasing temperature is unknown. Molecular dynamics simulations are used to probe the temperature dependence of the mechanical and nanostructural properties of nanoparticle membranes made of 6 nm diameter Au nanoparticles coated with dodecanethiol ligands and terminated with either methyl (CH3) or carboxyl (COOH) terminal groups. For methyl-terminated ligands, interactions along the alkane chain provide mechanical stiffness, with a Young's modulus of 1.7 GPa at 300 K. For carboxyl-terminated chains, end-group interactions are significant,more » producing stiffer membranes at all temperatures, with a Young's modulus of 3.8 GPa at 300 K. For both end-group types, membrane stiffness is reduced to zero at about 400 K. Ligand structure and mechanical properties of membranes at 300 K that have been annealed at 400 K are comparable to samples that do not undergo thermal annealing.« less

  5. Temperature effects on nanostructure and mechanical properties of single-nanoparticle thick membranes.

    SciTech Connect

    Salerno, Kenneth Michael; Grest, Gary S.

    2015-04-30

    In this study, the properties of mechanically stable single-nanoparticle (NP)-thick membranes have largely been studied at room temperature. How these membranes soften as nanoparticle ligands disorder with increasing temperature is unknown. Molecular dynamics simulations are used to probe the temperature dependence of the mechanical and nanostructural properties of nanoparticle membranes made of 6 nm diameter Au nanoparticles coated with dodecanethiol ligands and terminated with either methyl (CH3) or carboxyl (COOH) terminal groups. For methyl-terminated ligands, interactions along the alkane chain provide mechanical stiffness, with a Young's modulus of 1.7 GPa at 300 K. For carboxyl-terminated chains, end-group interactions are significant, producing stiffer membranes at all temperatures, with a Young's modulus of 3.8 GPa at 300 K. For both end-group types, membrane stiffness is reduced to zero at about 400 K. Ligand structure and mechanical properties of membranes at 300 K that have been annealed at 400 K are comparable to samples that do not undergo thermal annealing.

  6. Structure and transport properties of ethylcellulose membranes with different types and granulation of magnetic powder

    NASA Astrophysics Data System (ADS)

    Krasowska, Monika; Strzelewicz, Anna; Rybak, Aleksandra; Dudek, Gabriela; Cieśla, Michał

    2016-06-01

    Structure and transport properties of ethylcellulose membranes with dispersed magnetic powder were investigated. The study mainly focused on diffusion, which is one of the transport mechanisms. The transport properties depend on many parameters like: polymeric matrix used, type of powder, its amount and granulation. The structure of the pattern formed by magnetic particles in the membrane matrix was studied. Description of the system was based on the phenomenological and molecular (random walk on a fractal lattice) approaches. Two parameters were calculated: the fractal dimension of random walk dw, and the fractal dimension of membrane structure df. The knowledge of both parameters made it possible to use the generalized equation of diffusion on the fractal structure obtained by Metzler et al. The research was carried out to determine the influence of magnetic powder granulation on the transport properties. The results showed that the random walk within the membranes of the smallest magnetic powder granulation was of the most subdiffusive character. Detailed investigation and quantitative description of gas transport through the membranes enables designing the membranes to be used in air oxygen enrichment.

  7. Red Blood Cell Susceptibility to Pneumolysin: CORRELATION WITH MEMBRANE BIOCHEMICAL AND PHYSICAL PROPERTIES.

    PubMed

    Bokori-Brown, Monika; Petrov, Peter G; Khafaji, Mawya A; Mughal, Muhammad K; Naylor, Claire E; Shore, Angela C; Gooding, Kim M; Casanova, Francesco; Mitchell, Tim J; Titball, Richard W; Winlove, C Peter

    2016-05-01

    This study investigated the effect of the biochemical and biophysical properties of the plasma membrane as well as membrane morphology on the susceptibility of human red blood cells to the cholesterol-dependent cytolysin pneumolysin, a key virulence factor of Streptococcus pneumoniae, using single cell studies. We show a correlation between the physical properties of the membrane (bending rigidity and surface and dipole electrostatic potentials) and the susceptibility of red blood cells to pneumolysin-induced hemolysis. We demonstrate that biochemical modifications of the membrane induced by oxidative stress, lipid scrambling, and artificial cell aging modulate the cell response to the toxin. We provide evidence that the diversity of response to pneumolysin in diabetic red blood cells correlates with levels of glycated hemoglobin and that the mechanical properties of the red blood cell plasma membrane are altered in diabetes. Finally, we show that diabetic red blood cells are more resistant to pneumolysin and the related toxin perfringolysin O relative to healthy red blood cells. Taken together, these studies indicate that the diversity of cell response to pneumolysin within a population of human red blood cells is influenced by the biophysical and biochemical status of the plasma membrane and the chemical and/or oxidative stress pre-history of the cell. PMID:26984406

  8. Hydrophilicity and antifouling property of membrane materials from cellulose acetate/polyethersulfone in DMAc.

    PubMed

    Sun, Zhonghua; Chen, Fushan

    2016-10-01

    In this study, cellulose acetate (CA) was blended with polyethersulfone (PES) to endow the ultrafiltration membrane with the improved hydrophilicity and antifouling property by using N,N-dimethylacetamide (DMAc) as the solvent. The effects of blend composition and evaporation time on the mechanical strength and pure water flux were investigated. It was found that the optimal composition of the casting solution was: 18wt% (PES), 4wt% (Polyvinylpyrrolidone K30), 3wt% (CA) and 20s (Evaporation time). The characteristics of CA-PES blend membranes were investigated through the methods of contact angle goniometer, antifouling property, compatibility, thermo gravimetric analysis and SEM. The results showed that the hydrophilicity and antifouling property of CA-PES ultrafiltration membranes were enhanced in comparison with the pure PES membranes. The CA-PES membranes exhibited semi-compatibility and good thermal stability below 270°C. This study provided a potential industrial application prospect of CA-PES membranes prepared in DMAc. PMID:27211301

  9. A nanohybrid membrane with lipid bilayer-like properties utilized as a conductimetric saccharin sensor.

    PubMed

    Chalkias, Nikolaos G; Giannelis, Emmanuel P

    2007-10-31

    Since their introduction, artificial lipid bilayer membranes were used in a wide array of applications, such as sensors, biocompatible materials and study-models of the cell's outer boundary. Here, we present a nanohybrid membrane using an inorganic host and amphiphilic organic molecules with lipid bilayer-like properties. The stability of the presented mimetic membrane is significantly improved when compared to existing methods. The nanohybrid membrane exhibited two thermotropic phases corresponding to the L(alpha) and L(beta) phases that lipid bilayer membranes are known to adopt. Integration of cholesterol molecules into the nanohybrid membrane lead to the same qualitative effects as in lipid bilayers, including expansion of the bilayer spacing and decrease of the L(alpha) to L(beta) transition enthalpy. To further illustrate the similarities of the synthesized membrane with a lipid bilayer, the ability of the nanohybrid membrane to function as saccharin conductimetric sensor was evaluated. The lower limit of detection of the sensor was 6 microM and the linear range of response was from 20 to 400 microM. PMID:17548189

  10. Salt transport properties of model reverse osmosis membranes using electrochemical impedance spectroscopy

    NASA Astrophysics Data System (ADS)

    Feldman, Kathleen; Chan, Edwin; Stafford, Gery; Stafford, Christopher

    With the increasing shortage of clean water, efficient purification technologies including membrane separations are becoming critical. The main requirement of reverse osmosis in particular is to maximize water permeability while minimizing salt permeability. Such performance optimization has typically taken place through trial and error approaches. In this work, key salt transport metrics are instead measured in model reverse osmosis membranes using electrochemical impedance spectroscopy (EIS). As shown previously, EIS can provide both the membrane resistance Rm and membrane capacitance Cm, with Rm directly related to salt permeability. The membranes are fabricated in a molecular layer by layer approach, which allows for control over such parameters as thickness, surface and bulk chemistry, and network geometry/connectivity. Rm, and therefore salt permeability, follows the expected trends with thickness and membrane area but shows unusual behavior when the network geometry is systematically varied. By connecting intrinsic material properties such as the salt permeability with macroscopic performance measures we can begin to establish design rules for improving membrane efficiency and facilitate the creation of next-generation separation membranes.

  11. In vitro erythrocyte membrane stabilization properties of Carica papaya L. leaf extracts

    PubMed Central

    Ranasinghe, Priyanga; Ranasinghe, Pathmasiri; Abeysekera, W. P. Kaushalya M.; Premakumara, G. A. Sirimal; Perera, Yashasvi S.; Gurugama, Padmalal; Gunatilake, Saman B.

    2012-01-01

    Background: Carica papaya L. fruit juice and leaf extracts are known to have many beneficial medical properties. Recent reports have claimed possible beneficial effects of C. papaya L. leaf juice in treating patients with dengue viral infections. This study aims to evaluate the membrane stabilization potential of C. papaya L. leaf extracts using an in vitro hemolytic assay. Materials and Methods: The study was conducted in between June and August 2010. Two milliliters of blood from healthy volunteers and patients with serologically confirmed current dengue infection were freshly collected and used in the assays. Fresh papaya leaves at three different maturity stages (immature, partly matured, and matured) were cleaned with distilled water, crushed, and the juice was extracted with 10 ml of cold distilled water. Freshly prepared cold water extracts of papaya leaves (1 ml containing 30 μl of papaya leaf extracts, 20 μl from 40% erythrocytes suspension, and 950 μl of phosphate buffered saline) were used in the heat-induced and hypotonic-induced hemolytic assays. In dose response experiments, six different concentrations (9.375, 18.75, 37.5, 75, 150, and 300 μg/ml) of freeze dried extracts of the partly matured leaves were used. Membrane stabilization properties were investigated with heat-induced and hypotonicity-induced hemolysis assays. Results: Extracts of papaya leaves of all three maturity levels showed a significant reduction in heat-induced hemolysis compared to controls (P < 0.05). Papaya leaf extracts of all three maturity levels showed more than 25% inhibition at a concentration of 37.5 μg/ml. The highest inhibition of heat-induced hemolysis was observed at 37.5 μg/ml. Inhibition activity of different maturity levels was not significantly (P < 0.05) different from one another. Heat-induced hemolysis inhibition activity did not demonstrate a linear dose response relationship. At 37.5 μg/ml concentration of the extract, a marked inhibition of

  12. Intrinsic membrane properties and inhibitory synaptic input of kenyon cells as mechanisms for sparse coding?

    PubMed

    Demmer, Heike; Kloppenburg, Peter

    2009-09-01

    The insect mushroom bodies (MBs) are multimodal signal processing centers and are essential for olfactory learning. Electrophysiological recordings from the MBs' principal component neurons, the Kenyon cells (KCs), showed a sparse representation of olfactory signals. It has been proposed that the intrinsic and synaptic properties of the KC circuitry combine to reduce the firing of action potentials and to generate relatively brief windows for synaptic integration in the KCs, thus causing them to operate as coincidence detectors. To better understand the ionic mechanisms that mediate the KC intrinsic firing properties, we used whole cell patch-clamp recordings from KCs in the adult, intact brain of Periplaneta americana to analyze voltage- and/or Ca2+-dependent inward (ICa, INa) and outward currents [IA, IK(V), IK,ST, IO(Ca)]. In general the currents had properties similar to those of currents in other insect neurons. Certain functional parameters of ICa and IO(Ca), however, had unusually high values, allowing them to assist sparse coding. ICa had a low-activation threshold and a very high current density compared with those of ICa in other insect neurons. Together these parameters make ICa suitable for boosting and sharpening the excitatory postsynaptic potentials as reported in previous studies. IO(Ca) also had a large current density and a very depolarized activation threshold. In combination, the large ICa and IO(Ca) are likely to mediate the strong spike frequency adaptation. These intrinsic properties of the KCs are likely to be supported by their tonic, inhibitory synaptic input, which was revealed by specific GABA antagonists and which contributes significantly to the hyperpolarized membrane potential at rest. PMID:19553491

  13. Surface functionalization of thin-film composite membranes with copper nanoparticles for antimicrobial surface properties.

    PubMed

    Ben-Sasson, Moshe; Zodrow, Katherine R; Genggeng, Qi; Kang, Yan; Giannelis, Emmanuel P; Elimelech, Menachem

    2014-01-01

    Biofouling is a major operational challenge in reverse osmosis (RO) desalination, motivating a search for improved biofouling control strategies. Copper, long known for its antibacterial activity and relatively low cost, is an attractive potential biocidal agent. In this paper, we present a method for loading copper nanoparticles (Cu-NPs) on the surface of a thin-film composite (TFC) polyamide RO membrane. Cu-NPs were synthesized using polyethyleneimine (PEI) as a capping agent, resulting in particles with an average radius of 34 nm and a copper content between 39 and 49 wt.%. The positive charge of the Cu-NPs imparted by the PEI allowed a simple electrostatic functionalization of the negatively charged RO membrane. We confirmed functionalization and irreversible binding of the Cu-NPs to the membrane surface with SEM and XPS after exposing the membrane to bath sonication. We also demonstrated that Cu-NP functionalization can be repeated after the Cu-NPs dissolve from the membrane surface. The Cu-NP functionalization had minimal impact on the intrinsic membrane transport parameters. Surface hydrophilicity and surface roughness were also maintained, and the membrane surface charge became positive after functionalization. The functionalized membrane exhibited significant antibacterial activity, leading to an 80-95% reduction in the number of attached live bacteria for three different model bacterial strains. Challenges associated with this functionalization method and its implementation in RO desalination are discussed. PMID:24308843

  14. Porous CS based membranes with improved antimicrobial properties for the treatment of infected wound in veterinary applications.

    PubMed

    Tonda-Turo, C; Ruini, F; Argentati, M; Di Girolamo, N; Robino, P; Nebbia, P; Ciardelli, G

    2016-03-01

    Recently, much attention has been given to the use of innovative solution for the treatment of infected wounds in animals. Current applied treatments are often un-effective leading to infection propagation and animal death. Novel engineered membranes based on chitosan (CS) can be prepared to combine local antimicrobial effect, high flexibility and easy manipulation. In this work, CS crosslinked porous membranes with improved antimicrobial properties were prepared via freeze-drying technique to promote wound healing and to reduce the bacterial proliferation in infected injuries. Silver nanoparticles (AgNPs) and gentamicin sulfate (GS) were incorporated into the CS matrices to impart antibacterial properties on a wild range of strains. CS based porous membranes were tested for their physicochemical, thermal, mechanical as well as swelling and degradation behavior at physiological condition. Additionally, GS release profile was investigated, showing a moderate burst effect in the first days followed by a decreasing release rate which it was maintained for at least 56 days. Moreover, porous membranes loaded with GS or AgNPs showed good bactericidal activity against both of Gram-positive and Gram-negative bacteria. The bacterial strains used in this work were collected in chelonians after carapace injuries to better mimic the environment after trauma. PMID:26706548

  15. The Lipopeptide Antibiotic Paenibacterin Binds to the Bacterial Outer Membrane and Exerts Bactericidal Activity through Cytoplasmic Membrane Damage

    PubMed Central

    Huang, En

    2014-01-01

    Paenibacterin is a broad-spectrum lipopeptide antimicrobial agent produced by Paenibacillus thiaminolyticus OSY-SE. The compound consists of a cyclic 13-residue peptide and an N-terminal C15 fatty acyl chain. The mechanism of action of paenibacterin against Escherichia coli and Staphylococcus aureus was investigated in this study. The cationic lipopeptide paenibacterin showed a strong affinity for the negatively charged lipopolysaccharides (LPS) from the outer membrane of Gram-negative bacteria. Addition of LPS (100 μg/ml) completely eliminated the antimicrobial activity of paenibacterin against E. coli. The electrostatic interaction between paenibacterin and LPS may have displaced the divalent cations on the LPS network and thus facilitated the uptake of antibiotic into Gram-negative cells. Paenibacterin also damaged the bacterial cytoplasmic membrane, as evidenced by the depolarization of membrane potential and leakage of intracellular potassium ions from cells of E. coli and S. aureus. Therefore, the bactericidal activity of paenibacterin is attributed to disruption of the outer membrane of Gram-negative bacteria and damage of the cytoplasmic membrane of both Gram-negative and Gram-positive bacteria. Despite the evidence of membrane damage, this study does not rule out additional bactericidal mechanisms potentially exerted by paenibacterin. PMID:24561581

  16. NPA binding activity is peripheral to the plasma membrane and is associated with the cytoskeleton.

    PubMed Central

    Cox, D N; Muday, G K

    1994-01-01

    N-1-Naphthylphthalamic acid (NPA) binding activity is released into the supernatant when plasma membranes are subjected to high-salt treatment, indicating that this activity is peripherally associated with the membrane. Extraction of plasma membrane vesicles with Triton X-100 resulted in retention of NPA binding activity in the detergent-insoluble cytoskeletal pellet. Treatment of this pellet with KI released NPA binding activity, actin, and alpha-tubulin. Dialysis to remove KI led to the repolymerization of cytoskeletal elements and movement of NPA binding activity into an insoluble cytoskeletal pellet. NPA binding activity partitioned into the detergent-insoluble cytoskeletal pellet obtained from both zucchini and maize membranes and was released from these pellets by KI treatment. Treatment of a cytoskeletal pellet with cytochalasin B doubled NPA binding activity in the resulting supernatant. Together, these experiments indicate that NPA binding activity is peripherally associated with the plasma membrane and interacts with the cytoskeleton in vitro. PMID:11536654

  17. Distribution and Intrinsic Membrane Properties of Basal Forebrain GABAergic and Parvalbumin Neurons in the Mouse

    PubMed Central

    McKenna, James T.; Yang, Chun; Franciosi, Serena; Winston, Stuart; Abarr, Kathleen K.; Rigby, Matthew S.; Yanagawa, Yuchio; McCarley, Robert W.; Brown, Ritchie E.

    2013-01-01

    The basal forebrain (BF) strongly regulates cortical activation, sleep homeostasis, and attention. Many BF neurons involved in these processes are GABAergic, including a subpopulation of projection neurons containing the calcium-binding protein, parvalbumin (PV). However, technical difficulties in identification have prevented a precise mapping of the distribution of GABAergic and GABA/PV+ neurons in the mouse or a determination of their intrinsic membrane properties. Here we used mice expressing fluorescent proteins in GABAergic (GAD67-GFP knock-in mice) or PV+ neurons (PV-Tomato mice) to study these neurons. Immunohistochemical staining for GABA in GAD67-GFP mice confirmed that GFP selectively labeled BF GABAergic neurons. GFP+ neurons and fibers were distributed throughout the BF, with the highest density in the magnocellular preoptic area (MCPO). Immunohistochemistry for PV indicated that the majority of PV+ neurons in the BF were large (>20 μm) or medium-sized (15–20 μm) GFP+ neurons. Most medium and large-sized BF GFP+ neurons, including those retrogradely labeled from the neocortex, were fast-firing and spontaneously active in vitro. They exhibited prominent hyperpolarization-activated inward currents and subthreshold “spikelets,” suggestive of electrical coupling. PV+ neurons recorded in PV-Tomato mice had similar properties but had significantly narrower action potentials and a higher maximal firing frequency. Another population of smaller GFP+ neurons had properties similar to striatal projection neurons. The fast firing and electrical coupling of BF GABA/PV+ neurons, together with their projections to cortical interneurons and the thalamic reticular nucleus, suggest a strong and synchronous control of the neocortical fast rhythms typical of wakefulness and REM sleep. PMID:23254904

  18. Erythrocyte membrane properties in patients with essential hypertension.

    PubMed

    Kaczmarska, Magdalena; Fornal, Maria; Messerli, Franz H; Korecki, Jozef; Grodzicki, Tomasz; Burda, Kvetoslava

    2013-01-01

    In spite of the extensive research efforts that have been conducted over the last decades, it is still very difficult to point out genetic determinants or environmental conditions responsible for the development of essential hypertension. We searched for differences in the RBC membrane skeleton structure and O2 membrane permeability between RBCs from patients with both essential arterial hypertension and hypercholesterolemia, from patients having only hypercholesterolemia and from healthy donors. The topography of RBCs and the content of various hemoglobin forms were detected using atomic force microscopy and Mössbauer spectroscopy, respectively. We found that the membrane skeleton of RBCs from healthy donors displayed a well-known honeycomb pattern, whereas in patients with essential hypertension and/or hypercholesterolemia, who had never received anti-hypertensive therapy, it displayed a corncob pattern. Hypertensive RBCs had an oval shape and the average lateral to longitudinal diameter ratio for the changed cells (about 70%) did not exceed 0.80. We observed that after the incubation of RBCs under high nitrogen (low O2) pressure at room temperature and then their transfer into 85 K, a content of oxyHb (deoxyHbOH) already after 1 h reached a stable level of about 85 ± 3% (15 ± 3%) in hypertensives, whereas in healthy individuals it showed a decrease for deoxyHbOH and an increase for oxyHb, which stabilized at a level of about 81 ± 5% and 19 ± 5%, respectively, only after 9 h. Quantitative analysis of the Δ(oxyHb) change estimated as the difference between the oxyHb level measured after 9 and 2 h at 85 K under low N2 pressure (to slow down oxyHb formation) was significantly higher in normotensives than in hypertensive patients with or without hypercholesterolemia, 19.9 versus -4.2, p < 0.02. Our findings indicate an impaired oxygen release by Hb in RBCs of patients with hypertension under low oxygen pressure which if present in vivo may cause hypoxemia and

  19. Heterogeneity of Membrane Properties in Sympathetic Preganglionic Neurons of Neonatal Mice: Evidence of Four Subpopulations in the Intermediolateral Nucleus

    PubMed Central

    Zimmerman, Amanda

    2010-01-01

    Spinal cord sympathetic preganglionic neurons (SPNs) integrate activity from descending and sensory systems to determine the final central output of the sympathetic nervous system. The intermediolateral column (IML) has the highest number and density of SPNs and, within this region, SPN somas are found in distinct clusters within thoracic and upper lumbar spinal segments. Whereas SPNs exhibit a rostrocaudal gradient of end-target projections, individual clusters contain SPNs with diverse functional roles. Here we explored diversity in the electrophysiological properties observed in Hb9-eGFP–identified SPNs in the IML of neonatal mice. Overall, mouse SPN intrinsic membrane properties were comparable with those seen in other species. A wide range of values was obtained for all measured properties (up to a 10-fold difference), suggesting that IML neurons are highly differentiated. Using linear regression we found strong correlations between many cellular properties, including input resistance, rheobase, time constant, action potential shape, and degree of spike accommodation. The best predictor of cell function was rheobase, which correlated well with firing frequency–injected current (f–I) slopes as well as other passive and active membrane properties. The range in rheobase suggests that IML neurons have a recruitment order with stronger synaptic drives required for maximal recruitment. Using cluster analysis, we identified at least four subpopulations of SPNs, including one with a long time constant, low rheobase, and high f–I gain. We thus propose that the IML contains populations of neurons that are differentiable by their membrane properties and hypothesize they represent diverse functional classes. PMID:19923248

  20. Viscoelastic Properties of Extracellular Polymeric Substances Can Strongly Affect Their Washing Efficiency from Reverse Osmosis Membranes.

    PubMed

    Ferrando Chavez, Diana Lila; Nejidat, Ali; Herzberg, Moshe

    2016-09-01

    The role of the viscoelastic properties of biofouling layers in their removal from the membrane was studied. Model fouling layers of extracellular polymeric substances (EPS) originated from microbial biofilms of Pseudomonas aeruginosa PAO1 differentially expressing the Psl polysaccharide were used for controlled washing experiments of fouled RO membranes. In parallel, adsorption experiments and viscoelastic modeling of the EPS layers were conducted in a quartz crystal microbalance with dissipation (QCM-D). During the washing stage, as shear rate was elevated, significant differences in permeate flux recovery between the three different EPS layers were observed. According to the amount of organic carbon remained on the membrane after washing, the magnitude of Psl production provides elevated resistance of the EPS layer to shear stress. The highest flux recovery during the washing stage was observed for the EPS with no Psl. Psl was shown to elevate the layer's shear modulus and shear viscosity but had no effect on the EPS adhesion to the polyamide surface. We conclude that EPS retain on the membrane as a result of the layer viscoelastic properties. These results highlight an important relation between washing efficiency of fouling layers from membranes and their viscoelastic properties, in addition to their adhesion properties. PMID:27404109

  1. Nanomechanical properties of proteins and membranes depend on loading rate and electrostatic interactions.

    PubMed

    Medalsy, Izhar D; Müller, Daniel J

    2013-03-26

    Knowing the dynamic mechanical response of tissue, cells, membranes, proteins, nucleic acids, and carbohydrates to external perturbations is important to understand various biological and biotechnological problems. Atomic force microscopy (AFM)-based approaches are the most frequently used nanotechnologies to determine the mechanical properties of biological samples that range in size from microscopic to (sub)nanoscopic. However, the dynamic nature of biomechanical properties has barely been addressed by AFM imaging. In this work, we characterizethe viscoelastic properties of the native light-driven proton pump bacteriorhodopsin of the purple membrane of Halobacterium salinarum. Using force-distance curve (F-D)-based AFM we imaged purple membranes while force probing their mechanical response over a wide range of loading rates (from ∼0.5 to 100 μN/s). Our results show that the mechanical stiffness of protein and membrane increases with the loading rate up to a factor of 10 (from ∼0.3 to 3.2 N/m). In addition, the electrostatic repulsion between AFM tip and sample can alter the mechanical stiffness measured by AFM up to ∼60% (from ∼0.8 to 1.3 N/m).These findings indicate that the mechanical response of membranes and proteins and probably of other biomolecular systems should be determined at different loading rates to fully understand their properties. PMID:23442147

  2. Transport properties of proton-exchange membranes: Effect of supercritical-fluid processing and chemical functionality

    NASA Astrophysics Data System (ADS)

    Pulido Ayazo

    NafionRTM membranes commonly used in direct methanol fuel cells (DMFC), are tipically limited by high methanol permeability (also known as the cross-over limitation). These membranes have phase segregated sulfonated ionic domains in a perfluorinated backbone, which makes processing challenging and limited by phase equilibria considerations. This study used supercritical fluids (SCFs) as a processing alternative, since the gas-like mass transport properties of SCFs allow a better penetration into the membranes and the use of polar co-solvents influenced their morphology, fine-tuning the physical and transport properties in the membrane. Measurements of methanol permeability and proton conductivity were performed to the NafionRTM membranes processed with SCFs at 40ºC and 200 bar and the co-solvents as: acetone, tetrahydrofuran (THF), isopropyl alcohol, HPLC-grade water, acetic acid, cyclohexanone. The results obtained for the permeability data were of the order of 10 -8-10-9 cm2/s, two orders of magnitude lower than unprocessed Nafion. Proton conductivity results obtained using AC impedance electrochemical spectroscopy was between 0.02 and 0.09 S/cm, very similar to the unprocessed Nafion. SCF processing with ethanol as co-solvent reduced the methanol permeability by two orders of magnitude, while the proton conductivity was only reduced by 4%. XRD analysis made to the treated samples exhibited a decreasing pattern in the crystallinity, which affects the transport properties of the membrane. Also, SAXS profiles of the Nafion membranes processed were obtained with the goal of determining changes produced by the SCF processing in the hydrophilic domains of the polymer. With the goal of searching for new alternatives in proton exchange membranes (PEMs) triblock copolymer of poly(styrene-isobutylene-styrene) (SIBS) and poly(styrene-isobutylene-styrene) SEBS were studied. These sulfonated tri-block copolymers had lower methanol permeabilities, but also lower proton

  3. The Immunosuppressive Activity of Amniotic Membrane Mesenchymal Stem Cells on T Lymphocytes

    PubMed Central

    Alikarami, Fatemeh; Yari, Fatemeh; Amirizadeh, Naser; Nikougoftar, Mahin; Jalili, Mohammad Ali

    2015-01-01

    Background: Mesenchymal Stem Cells (MSCs) are isolated from different sources like placenta. The placenta and its membranes like Amniotic Membrane (AM) are readily available and easy to work with. There is only limited knowledge on the immunomodulatory properties of human Amniotic Membrane-derived Mesenchymal Stem Cells (hAM-MSCs). The aim of this study was to survey the suppressive activity of hAM-MSCs on T lymphocytes in vitro. Methods: Human AMs were obtained after caesarean section births from healthy women. After enzymatic digestion, cells were cultured and hAM-MSCs were obtained. In addition, human T lymphocytes were isolated and co-cultured with hAM-MSCs for 72 hr in the presence or absence of phytohemagglutinin (PHA). Subsequently, proliferation of T cells was analyzed using BrdU and subsequently flow cytometry technique. Besides, the production of IL-4 and IFN-γ was examined by ELISA method. Additionally, the expression of activation markers (CD38, HLA-DR) was studied on T lymphocytes by flow cytometry technique. Results: It was revealed that hAM-MSCs could significantly suppress the proliferation of T lymphocytes (p≤0.01) and significantly decrease the production of IFN-γ by T cells (p<0.05). hAM-MSCs also down regulated the expression of activation markers on the surface of T lymphocytes, CD38 and HLA-DR. The difference was significant between the case and control samples (p<0.05). All the comparisons were carried out between the case (Tcell+PHA+hAM-MSCs) and control (Tcell+PHA) groups. Conclusion: In conclusion, hAM-MSCs could inhibit the (mitogen-activated) T cells even in the absence of blood monocytes. Besides, hAM-MSCs-mediated inhibition of T lymphocytes was combined with down regulation of activation markers. PMID:26306147

  4. Membrane properties of Enchytraeus albidus originating from contrasting environments: a comparative analysis.

    PubMed

    Fisker, Karina Vincents; Bouvrais, Hélène; Overgaard, Johannes; Schöttner, Konrad; Ipsen, John H; Holmstrup, Martin

    2015-05-01

    Ectothermic animals adapted to different environmental temperatures are hypothesized to have biological membranes with different chemical and physical properties such that membrane properties are optimized for their particular thermal environments. To test this hypothesis we analyzed the composition of phospholipid fatty acids (PLFAs) in seven different populations of Enchytraeus albidus originating from different thermal environments. The seven populations differ markedly in origin (polar-temperate) and are also characterized by marked difference in cold tolerance. The dominant PLFAs of E. albidus were C20:5, C20:4 and C20:2 (53-61% of total PLFA) followed by C18:0, C20:1 and C22:2 (17-20% of total PLFA). As hypothesized the PLFA composition varied significantly between populations and molar percentage of several of the PLFAs (particularly C18:2) correlated with the lower lethal temperature (LT50) of the seven populations. Unsaturation ratio (UFA/SFA) and average PLFA chain length also correlated significantly with LT50, such that cold sensitive populations had a shorter chain length and a lower UFA/SFA compared to cold tolerant populations. Reconstituted membranes of the least and most cold tolerant populations were used to compare membranes' physical properties by fluorescence anisotropy and bending rigidity. Measurements of anisotropy did not show any overall difference between populations with different cold tolerance. This could be interpreted as if E. albidus populations have achieved a similar "optimal" fluidity of the membrane with a somewhat different PLFA composition. Our study suggests that membrane lipid composition could be important for the cold tolerance of E. albidus; however, these differences are not easily differentiated in the measurements of the membranes' physical properties. Other parameters such as accumulation of glucose for cryoprotection and energy supply may also be important components of enchytraeid freeze tolerance. PMID:25663468

  5. Zwitterionic Modifications for Enhancing the Antifouling Properties of Poly(vinylidene fluoride) Membranes.

    PubMed

    Venault, Antoine; Huang, Wen-Yu; Hsiao, Sheng-Wen; Chinnathambi, Arunachalam; Alharbi, Sulaiman Ali; Chen, Hong; Zheng, Jie; Chang, Yung

    2016-04-26

    The development of effective antibiofouling membranes is critical for many scientific interests and industrial applications. However, the existing available membranes often suffer from the lack of efficient, stable, and scalable antifouling modification strategy. Herein, we designed, synthesized, and characterized alternate copolymers of p(MAO-DMEA) (obtained by reaction between poly(maleic anhydride-alt-1-octadecene) and N,N-dimethylenediamine) and p(MAO-DMPA) (obtained by reaction between poly(maleic anhydride-alt-1-octadecene) and 3-(dimethylamino)-1-propylamine) of different carbon space length (CSL) using a ring-opening zwitterionization. We coated these copolymers on poly(vinylidene fluoride) (PVDF) membranes using a self-assembled anchoring method. Two important design parameters-the CSL of polymers and the coating density of polymers on membrane-were extensively examined for their effects on the antifouling performance of the modified membranes using a series of protein, cell, and bacterial assays. Both zwitterionic-modified membranes with different coating densities showed improved membrane hydrophilicity, increased resistance to protein, bacteria, blood cells, and platelet adsorption. However, while p(MAO-DMEA) with two CSLs and p(MAO-DMPA) with three CSLs only differ by one single carbon between the amino and ammonium groups, such subtle structural difference between the two polymers led to the fact that the membranes self-assembled with MAO-DMEA outperformed those modified with MAO-DMPA in all aspects of surface hydration, protein and bacteria resistance, and blood biocompatibility. This work provides an important structural-based design principle: a subtle change in the CSL of polymers affects the surface and antifouling properties of the membranes. It can help to achieve the design of more effective antifouling membranes for blood contacting applications. PMID:27044737

  6. Voltage-induced membrane displacement in patch pipettes activates mechanosensitive channels

    PubMed Central

    Gil, Ziv; Silberberg, Shai D.; Magleby, Karl L.

    1999-01-01

    The patch-clamp technique allows currents to be recorded through single ion channels in patches of cell membrane in the tips of glass pipettes. When recording, voltage is typically applied across the membrane patch to drive ions through open channels and to probe the voltage-sensitivity of channel activity. In this study, we used video microscopy and single-channel recording to show that prolonged depolarization of a membrane patch in borosilicate pipettes results in delayed slow displacement of the membrane into the pipette and that this displacement is associated with the activation of mechanosensitive (MS) channels in the same patch. The membrane displacement, ≈1 μm with each prolonged depolarization, occurs after variable delays ranging from tens of milliseconds to many seconds and is correlated in time with activation of MS channels. Increasing the voltage step shortens both the delay to membrane displacement and the delay to activation. Preventing depolarization-induced membrane displacement by applying positive pressure to the shank of the pipette or by coating the tips of the borosilicate pipettes with soft glass prevents the depolarization-induced activation of MS channels. The correlation between depolarization-induced membrane displacement and activation of MS channels indicates that the membrane displacement is associated with sufficient membrane tension to activate MS channels. Because membrane tension can modulate the activity of various ligand and voltage-activated ion channels as well as some transporters, an apparent voltage dependence of a channel or transporter in a membrane patch in a borosilicate pipette may result from voltage-induced tension rather than from direct modulation by voltage. PMID:10588750

  7. Preparation, characterization, biological activity, and transport study of polystyrene based calcium-barium phosphate composite membrane.

    PubMed

    Khan, Mohammad Mujahid Ali; Rafiuddin

    2013-10-01

    Calcium-barium phosphate (CBP) composite membrane with 25% polystyrene was prepared by co-precipitation method. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transformed infrared (FTIR), and Thermogravimetric analysis (TGA) were used to characterize the membrane. The membrane was found to be crystalline in nature with consistent arrangement of particles and no indication of visible cracks. The electrical potentials measured across the composite membrane in contact with univalent electrolytes (KCl, NaCl and LiCl), have been found to increase with decrease in concentrations. Thus the membrane was found to be cation-selective. Transport properties of developed membranes may be utilized for the efficient desalination of saline water and more importantly demineralization process. The antibacterial study of this composite membrane shows good results for killing the disease causing bacteria along with waste water treatment. PMID:23910337

  8. Enzymatically active high-flux selectively gas-permeable membranes

    DOEpatents

    Jiang, Ying-Bing; Cecchi, Joseph L.; Rempe, Susan; FU, Yaqin; Brinker, C. Jeffrey

    2016-01-26

    An ultra-thin, catalyzed liquid transport medium-based membrane structure fabricated with a porous supporting substrate may be used for separating an object species such as a carbon dioxide object species. Carbon dioxide flux through this membrane structures may be several orders of magnitude higher than traditional polymer membranes with a high selectivity to carbon dioxide. Other gases such as molecular oxygen, molecular hydrogen, and other species including non-gaseous species, for example ionic materials, may be separated using variations to the membrane discussed.

  9. Activation of a heat-stable cytolytic protein associated with the surface membrane of Naegleria fowleri.

    PubMed Central

    Lowrey, D M; McLaughlin, J

    1985-01-01

    Surface membrane-enriched fractions of Naegleria fowleri obtained after isopycnic centrifugation experiments contain a potent cytolytic activity as determined by hemolysis and 51Cr release assays. This surface membrane cytolysin was unaffected by a treatment at 75 degrees C for 30 min and accounted for 70 to 90% of cytolysis by whole-cell lysates of amoebae. This heat resistance as well as intimate membrane association distinguished the surface membrane cytolytic activity from a second heat-labile cytolytic activity which appears to be latent within lysosomes. The surface membrane cytolysin was found to be specifically activated by diluted samples of lysosomal fractions. The possible role of this surface membrane cytotoxin in the pathogenicity of N. fowleri is discussed. PMID:4055029

  10. Membrane properties and electrogenesis in the distal axons of small dorsal root ganglion neurons in vitro.

    PubMed

    Vasylyev, Dmytro V; Waxman, Stephen G

    2012-08-01

    Although it is generally thought that sensory transduction occurs at or close to peripheral nerve endings, with action potentials subsequently propagating along the axons of dorsal root ganglia (DRG) neurons toward the central nervous system, the small diameter of nociceptive axons and their endings have made it difficult to estimate their membrane properties and electrogenic characteristics. Even the resting potentials of nociceptive axons are unknown. In this study, we developed the capability to record directly with patch-clamp electrodes from the small-diameter distal axons of DRG neurons in vitro. We showed using current-clamp recordings that 1) these sensory axons have a resting potential of -60.2 ± 1 mV; 2) both tetrodotoxin (TTX)-sensitive (TTX-S) and TTX-resistant (TTX-R) Na(+) channels are present and available for activation at resting potential, at densities that can support action potential electrogenesis in these axons; 3) TTX-sensitive channels contribute to the amplification of small depolarizations that are subthreshold with respect to the action potential in these axons; 4) TTX-R channels can support the production of action potentials in these axons; and 5) these TTX-R channels can produce repetitive firing, even at depolarized membrane potentials where TTX-S channels are inactivated. Finally, using voltage-clamp recordings with an action potential as the command, we confirmed the presence of both TTX-S and TTX-R channels, which are activated sequentially during action potential in these axons. These results provide direct evidence for the presence of TTX-S and TTX-R Na(+) channels that are functionally available at resting potential and contribute to electrogenesis in small-diameter afferent axons. PMID:22572942

  11. The role of CD4 on mechanical properties of live cell membrane.

    PubMed

    Bui, Van-Chien; Nguyen, Thi-Huong

    2016-01-01

    Although much progress has been made in the characterization and identification of CD4 functions, its role in mechanical properties of cell membrane remains largely unknown. Here an atomic force microscopy (AFM) was used to investigate the roles of CD4 in the elasticity of the leukemic human Jurkat (clone E6-1) cell membranes. Analysis of the approach force curves with Hertz model for a completely elastic soft sample measured on the selected CD4+ and CD4- cells showed that CD4+ cell membrane was softer than CD4- one. To confirm that CD4 plays a role in altering cell elasticity, human embryonic kidney 293T cells were transiently transfected with wild type (wt) CD4 plasmid before being used in AFM nanoindentation experiments. The results also demonstrated CD4- membrane was stiffer than CD4+ one suggesting that CD4 integrated into plasma membrane and altered its mechanical properties. The study gives insights into the role of CD4 on cell membrane mechanical characteristics and might be helpful for development of cell biology and medicine. PMID:26362701

  12. Impact of lipid oxidization on biophysical properties of model cell membranes.

    PubMed

    Makky, Ali; Tanaka, Motomu

    2015-05-01

    The oxidization of glycerophospholipids in cell membranes due to aging and environmental stresses may cause a variety of pathological and physiological consequences. A variety of oxidized phospholipid products (OxPl) are produced by the chemical oxidization of unsaturated hydrocarbon chains, which would significantly change the physicochemical properties of cell membranes. In this work, we constructed cell membrane models in the absence and presence of two stable oxidized lipid products and investigated their impact on physical properties of supported membranes using quartz crystal microbalance with dissipation (QCM-D) and high-energy X-ray reflectivity (XRR). Our experimental findings suggest that the lipid oxidization up to 20 mol % leads to the rupture of vesicles right after the adsorption. Our XRR analysis unravels the membrane thinning and the decrease in the lateral ordering of lipids, which can be explained by the decrease in the lateral packing of hydrocarbon chains. Further studies on mechanics of membranes incorporating oxidized lipids can be attributed to the decrease in the bending rigidity and the increase in the permeability. PMID:25870900

  13. Structure changes and water filtration properties of electrospun polyamide nanofibre membranes.

    PubMed

    Daels, N; Harinck, L; Goethals, A; De Clerck, K; Van Hulle, S W H

    2016-01-01

    Nanofibre membranes are studied extensively in water treatment. Inappropriate storage, however, could alter their performance, e.g. regarding water filtration. This shows the need for investigating this effect in more detail so as to offer a solution for long-term behaviour and stability. In this study, polyamide nanofibre membranes were treated under different conditions, simulating the diverse storage conditions and to simulate their use in water filtration systems. Under all these different settings, nanofibre properties (scanning electron microscope pictures, dimensional changes, tensile strength) and water filtration performance (clean water permeability (CWP), bacterial removal) were investigated. The results demonstrate that, as soon as the dimensional change of a membrane is >2%, the CWP, tensile strength and bacterial removal significantly decrease. These dimensional changes occurred when the membrane became dry after it had been in contact with water. As such, it is important to keep the membrane either in dry or in wet conditions to store its unique properties. When heat-treated, the membrane had a higher tensile strength and kept its morphology and characteristics better during storage. PMID:27120647

  14. Physical chemistry and membrane properties of two phosphatidylinositol bisphosphate isomers†

    PubMed Central

    Wang, Yu-Hsiu; Radhakrishnan, Ravi; Janmey, Paul A.

    2015-01-01

    The most highly charged phospholipids, polyphosphoinositides, are often involved in signaling pathways that originate at cell-cell and cell-matrix contacts, and different isomers of polyphosphoinositides have distinct biological functions that cannot be explained by separate highly specific protein ligand binding sites [Lemmon, Nature Reviews Molecular and Cell Biology, 2008, 9 99–111]. PtdIns(3,5)P2 is a low abundance phosphoinositide localized to cytoplasmic-facing membrane surfaces, with relatively few known ligands, yet PtdIns(3,5)P2 plays a key role in controlling membrane trafficking events and cellular stress responses that cannot be duplicated by other phosphoinositides [Dove et al., Nature, 1997, 390, 187–192; Michell, FEBS Journal, 2013, 280, 6281–6294]. Here we show that PtdIns(3,5)P2 is structurally distinct from PtdIns(4,5)P2 and other more common phospholipids, with unique physical chemistry. Using multiscale molecular dynamics techniques on the quantum level, single molecule, and in bilayer settings, we found that the negative charge of PtdIns(3,5)P2 is spread over a larger area, compared to PtdIns(4,5)P2, leading to a decreased ability to bind divalent ions. Additionally, our results match well with experimental data characterizing the cluster forming potential of these isomers in the presence of Ca2+ [Wang et al., Journal of the American Chemical Society, 2012, 134, 3387–3395; van den Bogaart et al., Nature, 2011, 479, 552–555]. Our results demonstrate that the different cellular roles of PtdIns(4,5)P2 and PtdIns(3,5)P2 in vivo are not simply determined by their localization by enzymes that produce or degrade them, but also by their molecular size, ability to chelate ions, and the partial dehydration of those ions, which might affect the ability of PtdIns(3,5)P2 and PtdIns(4,5)P2 to form phosphoinositide-rich clusters in vitro and in vivo. PMID:25901568

  15. Physical chemistry and membrane properties of two phosphatidylinositol bisphosphate isomers.

    PubMed

    Slochower, David R; Wang, Yu-Hsiu; Radhakrishnan, Ravi; Janmey, Paul A

    2015-05-21

    The most highly charged phospholipids, polyphosphoinositides, are often involved in signaling pathways that originate at cell-cell and cell-matrix contacts, and different isomers of polyphosphoinositides have distinct biological functions that cannot be explained by separate highly specific protein ligand binding sites [Lemmon, Nat. Rev. Mol. Cell Biol., 2008, 9, 99-111]. PtdIns(3,5)P2 is a low abundance phosphoinositide localized to cytoplasmic-facing membrane surfaces, with relatively few known ligands, yet PtdIns(3,5)P2 plays a key role in controlling membrane trafficking events and cellular stress responses that cannot be duplicated by other phosphoinositides [Dove et al., Nature, 1997, 390, 187-192; Michell, FEBS J., 2013, 280, 6281-6294]. Here we show that PtdIns(3,5)P2 is structurally distinct from PtdIns(4,5)P2 and other more common phospholipids, with unique physical chemistry. Using multiscale molecular dynamics techniques on the quantum level, single molecule, and in bilayer settings, we found that the negative charge of PtdIns(3,5)P2 is spread over a larger area, compared to PtdIns(4,5)P2, leading to a decreased ability to bind divalent ions. Additionally, our results match well with experimental data characterizing the cluster forming potential of these isomers in the presence of Ca(2+) [Wang et al., J. Am. Chem. Soc., 2012, 134, 3387-3395; van den Bogaart et al., Nature, 2011, 479, 552-555]. Our results demonstrate that the different cellular roles of PtdIns(4,5)P2 and PtdIns(3,5)P2in vivo are not simply determined by their localization by enzymes that produce or degrade them, but also by their molecular size, ability to chelate ions, and the partial dehydration of those ions, which might affect the ability of PtdIns(3,5)P2 and PtdIns(4,5)P2 to form phosphoinositide-rich clusters in vitro and in vivo. PMID:25901568

  16. ULTRASTRUCTURE OF VEILLONELLA AND MORPHOLOGICAL CORRELATION OF AN OUTER MEMBRANE WITH PARTICLES ASSOCIATED WITH ENDOTOXIC ACTIVITY

    PubMed Central

    Bladen, Howard A.; Mergenhagen, Stephan E.

    1964-01-01

    Bladen, Howard A. (National Institute of Dental Research, Bethesda, Md.), and Stephan E. Mergenhagen. Ultrastructure of Veillonella and morphological correlation of an outer membrane with particles associated with endotoxic activity. J. Bacteriol. 88:1482–1492. 1964.—Normal, phenol-water extracted, and lysozyme-treated Veillonella cells were embedded in Vestopal W, sectioned, and examined by electron microscopy. Normal cells as well as the phenol-water extract (endotoxin) were examined by negative and positive contrast techniques. In thin sections of normal cells, three separate structural entities were observed surrounding the protoplasm, and were referred to as the outer membrane, the solid membrane, and the plasma membrane. The outer membrane was a membrane composed of two dense layers (30 A) separated by a less-dense layer (20 A), and followed a convoluted and continuous path around the cell. The solid membrane appeared as a taut, dense structure 100 to 500 A wide, and was separated from the outer membrane by up to several hundred Ångstroms. The plasma membrane was a unit-type membrane. After cells were treated with phenol-water, the outer membrane was absent, but the cells remained intact owing to the solid membrane. Observation of the phenol-water extract (endotoxin) revealed predominantly circular particles or discs which had approximately the same dimensions in height as the outer membrane had in width. Negatively stained whole cells showed similar structures on their surface. Lysozyme treatment of the cells did not affect the outer membrane; however, the solid membrane became diffuse and often disappeared, suggesting that the outer membrane and the solid membrane were separate structures. Images PMID:14234809

  17. Simulations of a Membrane-Anchored Peptide: Structure, Dynamics, and Influence on Bilayer Properties

    PubMed Central

    Jensen, Morten Ø.; Mouritsen, Ole G.; Peters, Günther H.

    2004-01-01

    A three-dimensional structure of a model decapeptide is obtained by performing molecular dynamics simulations of the peptide in explicit water. Interactions between an N-myristoylated form of the folded peptide anchored to dipalmitoylphosphatidylcholine fluid phase lipid membranes are studied at different applied surface tensions by molecular dynamics simulations. The lipid membrane environment influences the conformational space explored by the peptide. The overall secondary structure of the anchored peptide is found to deviate at times from its structure in aqueous solution through reversible conformational transitions. The peptide is, despite the anchor, highly mobile at the membrane surface with the peptide motion along the bilayer normal being integrated into the collective modes of the membrane. Peptide anchoring moderately alters the lateral compressibility of the bilayer by changing the equilibrium area of the membrane. Although membrane anchoring moderately affects the elastic properties of the bilayer, the model peptide studied here exhibits conformational flexibility and our results therefore suggest that peptide acylation is a feasible way to reinforce peptide-membrane interactions whereby, e.g., the lifetime of receptor-ligand interactions can be prolonged. PMID:15189854

  18. [Membrane surface fouling properties in MBRs for high-salinity wastewater treatment].

    PubMed

    Li, Bin; Wang, Zhi-Wei; An, Ying; Wu, Zhi-Chao

    2014-02-01

    The properties of membrane foulants in MBR treating high-salinity wastewater were studied. Results showed that the removal efficiency of organics and NH4(+) -N was stable and high-quality effluent was obtained after the operation time of 121 d; the ratio of VSS/ SS decreased and SVI declined at the same time, indicating that the inorganic content of sludge increased which might lead to more compact flocs and higher settling ability; SMP and EPS of the sludge were largely changed with a lower proportion of protein and a higher proportion of humic acid. Scanning electron microscope-energy diffusive X-ray analyzer (SEM-EDX) demonstrated that Na, Al, Mg, Ca, K, Fe, Ti, Cr, W, Si and Cl were the major inorganic elements in membrane foulants; Gel filtration chromatography (GFC) illustrated that there were organic matters with high molecular weight trapped by membrane and formed the membrane foulants; Fourier transform infrared (FTIR) spectroscopy and Excitation emission matrix (EEM) fluoresce spectroscopy discovered that carbohydrates, protein and humic acid were the main content of organics in membrane foulants.; quantitative analysis of membrane foulants showed that the amount of inorganic membrane foulants were significant when treating high-salinity wastewater. PMID:24812959

  19. Preparation and properties of SBS-g-DMAEMA copolymer membrane by ultraviolet radiation.

    PubMed

    Yang, J M; Jong, Y J; Hsu, K Y

    1997-05-01

    A styrene-butadiene-styrene triblock copolymer (SBS) membrane was prepared by solvent casting. Grafting of dimethyl amino ethyl methacrylate (DMAEMA) to this SBS membrane was subsequently conducted by ultraviolet radiation-induced graft copolymerization without degassing to obtain a SBS-g-DMAEMA copolymer membrane. The graft copolymer was characterized by infrared spectroscopy and scanning electron microscopy. The degree of grafting and the mechanical properties of SBS and SBS-g-DMAEMA were measured. Contact angle, water content, and protein absorption of fibrinogen and albumin experiments were also performed to evaluate the biocompatibility of SBS-g-DMAEMA graft copolymer membranes. It was found that the degree of grafting was related to the irradiation time, DMAEMA concentration, and temperature. The tensile strength of the SBS-g-DMAEMA membrane increased with an increase in the degree of grafting. By using Kaelble's equation and the contact angle data, the surface tension of SBS-g-DMAEMA was determined. It was found that with an increase in the degree of grafting, the surface tension and water content of SBS-g-DMAEMA membrane increased, whereas the contact angle decreased. The amount of absorption of albumin and fibrinogen decreased with an increase in amount of grafting. However, there was a minimum for the adsorption of proteins in the SBS-g-DMAEMA membrane. PMID:9135166

  20. Electrochemical performance and transport properties of a Nafion membrane in a hydrogen-bromine cell environment

    NASA Technical Reports Server (NTRS)

    Baldwin, Richard S.

    1987-01-01

    The overall energy conversion efficiency of a hydrogen-bromine energy storage system is highly dependent upon the characteristics and performance of the ion-exchange membrane utilized as a half-cell separator. The electrochemical performance and transport properties of a duPont Nafion membrane in an aqueous HBr-Br2 environment were investigated. Membrane conductivity data are presented as a function of HBr concentration and temperature for the determination of ohmic voltage losses across the membrane in an operational cell. Diffusion-controlled bromine permeation rates and permeabilities are presented as functions of solution composition and temperature. Relationships between the degree of membrane hydration and the membrane transport characteristics are discussed. The solution chemistry of an operational hydrogen-bromine cell undergoing charge from 45% HBr to 5% HBr is discussed, and, based upon the experimentally observed bromine permeation behavior, predicted cell coulombic losses due to bromine diffusion through the membrane are presented as a function of the cell state-of-charge.

  1. Composite Nafion/sulfonated zirconia membranes: effect of the filler surface properties on proton transport characteristics

    PubMed Central

    D’Epifanio, Alessandra; Navarra, Maria Assunta; Weise, F. Christoph; Mecheri, Barbara; Farrington, Jaime; Licoccia, Silvia; Greenbaum, Steve

    2009-01-01

    Due to their strong acidity and water affinity, sulfated zirconia nanoparticles were evaluated as inorganic additives in the formation of composite Nafion-based membranes. Two types of sulfated zirconia were obtained according to the preparation experimental conditions. Sulfated zirconia-doped Nafion membranes were prepared by a casting procedure. The properties of the composite membranes were compared with those of an unfilled Nafion membrane obtained by the same preparation method. The water uptake, measured at room temperature in a wide relative humidity range, was higher for the composite membranes, this confirming the hydrophilic nature of the selected additives. The membrane doped by zirconia particles having the highest sulphate group concentration showed the highest water diffusion coefficient in the whole range of temperature and relative humidity investigated due to the presence of SO42− providing extra acid sites for water diffusion. The proton diffusivity calculated from impedance spectroscopy measurements was compared with water self diffusion coefficients measured by NMR Spectroscopy. The difference between proton and water diffusivity became significant only at high humidification levels, highlighting the role of water in the intermolecular proton transfer mechanism. Finally, great improvements were found when using the composite membrane as electrolyte in a fuel cell working at very low relative humidity. PMID:20209115

  2. Simultaneously enhanced methanol barrier and proton conductive properties of phosphorylated titanate nanotubes embedded nanocomposite membranes

    NASA Astrophysics Data System (ADS)

    Wang, Jingtao; Zhao, Yuning; Hou, Weiqiang; Geng, Jiaqing; Xiao, Lulu; Wu, Hong; Jiang, Zhongyi

    The current study aims at simultaneously enhancing the methanol barrier and proton conductive properties of membranes for direct methanol fuel cell (DMFC) by embedding phosphorylated titanate nanotubes (PTNTs) into chitosan (CS) membrane. The enhancement is most probably due to the intrinsic interfacial interactions between PTNTs and CS chains, which are verified by the increased thermal stability and homogeneous dispersion of the fillers. The influence of PTNTs incorporation conditions including acid concentration and filler content upon the resulting nanocomposite membrane performance is extensively investigated. Compared with plain CS membrane, the presence of PTNTs within chitosan matrix will lead to denser chain packing, thus reduce free volume cavity size and fractional free volume (FFV) according to positron annihilation lifetime spectroscopy analysis. The reduced FFV and more tortuous pathway significantly suppress the methanol crossover through the membranes. Meanwhile, the presence of PTNTs constructs an uninterrupted channel for proton migration via functionalized P-OH groups and adsorbed water, and therefore improving the proton conductivity substantially. As a result, the nanocomposite membranes exhibit desirable comprehensive performance, which is about ten times higher than that of Nafion 117. We envisage that the current observations hint the encouraging application promises of such nanocomposite membranes in DMFC.

  3. Effects of glucose on cell viability and antioxidant and anti-inflammatory properties of phytochemicals and phytochemically modified membranes.

    PubMed

    Chang, Teng; Neelakandan, Chandrasekaran; DeFine, Linda; Alexander, Thomas; Kyu, Thein

    2014-10-16

    By virtue of antioxidant and anti-inflammable properties, plant-derived phytochemicals such as mangiferin and genistein have attracted considerable attention for functionalization of polymeric hemodialysis (HD) membranes via solution blending. In-vitro dihydrorhodamine (DHR) assay of the genistein-modified membranes revealed drastic reduction in the level of the reactive oxygen species (ROS). In contrast, mangiferin-modified HD membrane manifested the pro-oxidant activity. We suspected that such difference in ROS generation may be attributed to the glucose unit on the xanthone backbone of mangiferin. This hypothesis was confirmed by comparing the ROS levels of genistein versus genistin, and mangiferin versus xanthone and 3,4,5,6-tetrahydroxyxanthone. Phytochemicals without the glucose unit show better antioxidant property related to the glycosides. Anti-inflammatory property was further conducted by measuring the level of TNF-α in blood after contacting with the same selected phytochemicals. Of particular interest is that the glucose unit promotes the generation of TNF-α. PMID:25247624

  4. Tensile mechanical and creep properties of Descemet's membrane and lens capsule.

    PubMed

    Danielsen, Carl Christian

    2004-09-01

    Descemet's membrane (DM) and the lens capsule (LC) are two ocular basement membrane structures which in comparison with other basement membranes have exceptional thicknesses which increase with age. Both membranes are supposed to contain networks of type IV collagen and laminin linked together with nidogen/entactin and containing other glycoproteins and proteoglycans. DM is a unique basement membrane which in addition contains fine filaments of type VIII collagen arranged in a hexagonal lattice. The mechanical functions of the LC are in lens suspension and accommodation, and its mechanical properties, previously investigated, are of great interest from a surgical point of view. DM serves as an endothelial basement membrane. Otherwise, its physiological function is unknown but may be one of mechanical support, filtration, or fluid barrier. Data on the mechanical properties of DM or the supramolecular assembly of type VIII collagen are very scarce or absent. The aim of this study was to determine and compare the mechanical properties of the two ocular membranes in order to elucidate the properties of DM in the light of those of LC. The human eyes were from testamentary donors and rat, cow, and sow eyes were obtained from normal animals. The tensile mechanical properties were determined by a volume-strain procedure and creep properties by subjecting the membranes from the latter three species to a constant axial stress. In rat, cow, and sow, DM was less strained to obtain a fixed moderate stress value (0.5 MPa) and showed to be 3.4- to 5.2-fold stiffer and to attain 2.7- to 4.6-fold higher stress at a strain value of 0.10 when compared with LC. The maximal strain, stiffness and stress were found to be less than those of the LC. In humans, DM and LC showed very similar mechanical properties. The instantaneous creep of DM was found to be less than that of LC indicating a higher stiffness of DM in the axial direction. In conclusion, depending on the species, DM showed to

  5. Elastic properties and line tension of self-assembled bilayer membranes.

    PubMed

    Li, Jianfeng; Pastor, Kyle A; Shi, An-Chang; Schmid, Friederike; Zhou, Jiajia

    2013-07-01

    The elastic properties of a self-assembled bilayer membrane are studied using the self-consistent field theory, applied to a model system composed of flexible amphiphilic chains dissolved in hydrophilic polymeric solvents. Examining the free energy of bilayer membranes with different geometries allows us to calculate their bending modulus, Gaussian modulus, two fourth-order membrane moduli, and the line tension. The dependence of these parameters on the microscopic characteristics of the amphiphilic chain, characterized by the volume fraction of the hydrophilic component, is systematically studied. The theoretical predictions are compared with the results from a simple monolayer model, which approximates a bilayer membrane by two monolayers. The region of validity of the linear elasticity theory is analyzed by examining the higher-order contributions. PMID:23944501

  6. Elastic properties and line tension of self-assembled bilayer membranes

    NASA Astrophysics Data System (ADS)

    Li, Jianfeng; Pastor, Kyle A.; Shi, An-Chang; Schmid, Friederike; Zhou, Jiajia

    2013-07-01

    The elastic properties of a self-assembled bilayer membrane are studied using the self-consistent field theory, applied to a model system composed of flexible amphiphilic chains dissolved in hydrophilic polymeric solvents. Examining the free energy of bilayer membranes with different geometries allows us to calculate their bending modulus, Gaussian modulus, two fourth-order membrane moduli, and the line tension. The dependence of these parameters on the microscopic characteristics of the amphiphilic chain, characterized by the volume fraction of the hydrophilic component, is systematically studied. The theoretical predictions are compared with the results from a simple monolayer model, which approximates a bilayer membrane by two monolayers. The region of validity of the linear elasticity theory is analyzed by examining the higher-order contributions.

  7. Isolation of nano-meso scale detergent resistant membrane that has properties expected of lipid 'rafts'.

    PubMed

    Morris, Roger J; Jen, Angela; Warley, Alice

    2011-03-01

    This review assesses problems that confound attempts to isolate 'raft' domains from cell membranes, focusing in particular upon the isolation of detergent resistant membrane (DRM). Despite its widespread use, this technique is rightly viewed with skepticism by many membrane biochemists and biophysics for reasons that include the inability to isolate DRMs at 37°C, the temperature at which their lipids are supposed to be ordered and so exclude detergents. If solubilization is done in an ionic buffer that preserves the lamellar phase of the metastable inner leaflet lipids, DRMs can readily be isolated at 37°C, and these have many properties expected of lipid rafts. However, to date these DRMs have remained somewhat larger than current concepts of rafts. We describe an adaptation of this method that purifies nano-meso scale DRMs, and could be a significant step towards purifying the membrane of individual 'rafts'. PMID:21214574

  8. Structure-property relationships in flavour-barrier membranes with reduced high-temperature diffusivity

    SciTech Connect

    Heitfeld, Kevin A.; Schaefer, Dale W.

    2010-10-12

    Encapsulation is used to decrease the premature release of volatile flavour ingredients while offering protection against environmental damage such as oxidation, light-induced reactions, etc. Hydroxypropyl cellulose (HPC) is investigated here as a 'smart,' temperature responsive membrane for flavour encapsulation and delivery. Gel films were synthesized and characterized by diffusion and small-angle neutron and X-ray scattering techniques. Increasing temperature typically increases the diffusion rate across a membrane; HPC, however, can be tailored to give substantially improved elevated temperature properties. Scattering results indicate processing conditions have a significant impact on membrane morphology (micro phase separation). Under certain synthetic conditions, micro phase separation is mitigated and the membranes show temperature-independent diffusivity between 25 C and 60 C.

  9. Temporin L: antimicrobial, haemolytic and cytotoxic activities, and effects on membrane permeabilization in lipid vesicles.

    PubMed Central

    Rinaldi, Andrea C; Mangoni, Maria Luisa; Rufo, Anna; Luzi, Carla; Barra, Donatella; Zhao, Hongxia; Kinnunen, Paavo K J; Bozzi, Argante; Di Giulio, Antonio; Simmaco, Maurizio

    2002-01-01

    The temporins are a family of small, linear antibiotic peptides with intriguing biological properties. We investigated the antibacterial, haemolytic and cytotoxic activities of temporin L (FVQWFSKFLGRIL-NH2), isolated from the skin of the European red frog Rana temporaria. The peptide displayed the highest activity of temporins studied to date, against both human erythrocytes and bacterial and fungal strains. At variance with other known temporins, which are mainly active against Gram-positive bacteria, temporin L was also active against Gram-negative strains such as Pseudomonas aeruginosa A.T.C.C. 15692 and Escherichia coli D21 at concentrations comparable with those that are microbiocidal to Gram-positive bacteria. In addition, temporin L was cytotoxic to three different human tumour cell lines (Hut-78, K-562 and U-937), causing a necrosis-like cell death, although sensitivity to the peptide varied markedly with the specific cell line tested. A study of the interaction of temporin L with liposomes of different lipid compositions revealed that the peptide causes perturbation of bilayer integrity of both neutral and negatively charged membranes, as revealed by the release of a vesicle-encapsulated fluorescent marker, and that the action of the peptide is modulated to some extent by membrane lipid composition. In particular, the presence of negatively charged lipids in the model bilayer inhibits the lytic power of temporin L. We also show that the release of fluorescent markers caused by temporin L is size-dependent and that the peptide does not have a detergent-like effect on the membrane, suggesting that perturbation of bilayer organization takes place on a local scale, i.e. through the formation of pore-like openings. PMID:12133008

  10. Plant cell plasma membrane structure and properties under clinostatting

    NASA Astrophysics Data System (ADS)

    Polulakh, Yu. A.; Zhadko, S. I.; Klimchuk, D. A.; Baraboy, V. A.; Alpatov, A. N.; Sytnik, K. M.

    Structural-functional organization of plasma membrane of pea roots seedling was investigated by methods of chemiluminescence, fluorescence probes, chromatography and freeze-fracture studies under normal conditions and clinostatting. Phase character of lipid peroxidation intensity was fixed. The initial phase of this process is characterized by lipid peroxidation decreasing with its next induction. The primary changes depending on free-radical mechanisms of lipid peroxidation were excellently revealed by chemiluminescence. Plasmalemma microviscosity increased on the average of 15-20 % under microgravity at the initial stages of its phenomenon. There were major changes of phosphatidilcholine and phosphatidilethanolamine contents. The total quantity of phospholipids remained rather stable. Changes of phosphatide acid concentration point to degradation and phospholipids biosynthesis. There were increases of unsaturated fatty acids mainly at the expense of linoleic and linolenic acids and also a decrease of saturated fatty acid content at the expense of palmitic and stearic acids. Unsaturation index of fatty acids increased as well. On the whole fatty acid composition was variable in comparison with phospholipids. Probably it is one of mechanisms of maintaining of microviscosity within definite limits. Considerable structural changes in organization of plasmalemma protein-lipid complex were not revealed by the freeze-fracture studies.

  11. Differential effects of conjugated linoleic acid isomers on the biophysical and biochemical properties of model membranes

    PubMed Central

    Subbaiah, Papasani V.; Sircar, Debajit; Aizezi, Buzulagu; Mintzer, Evan

    2010-01-01

    Conjugated linoleic acids (CLA) are known to exert several isomer-specific biological effects, but their mechanisms of action are unclear. In order to determine whether the physicochemical effects of CLA on membranes play a role in their isomer-specific effects, we synthesized phosphatidylcholines (PCs) with 16:0 at sn-1 position and one of four CLA isomers (trans10 cis12 (A), trans9 trans11 (B), cis9 trans11 (C), and cis9 cis11 (D)) at sn-2, and determined their biophysical properties in monolayers and bilayers. The surface areas of the PCs with the two natural CLA (A and C) were similar at all pressures, but they differed significantly in presence of cholesterol, with PC-A condensing more than PC-C. Liposomes of PC-A similarly showed increased binding of cholesterol compared to PC-C liposomes. PC-A liposomes were less permeable to carboxyfluorescein compared to PC-C liposomes. The PC with two trans double bonds (B) showed the highest affinity to cholesterol and lowest permeability. The two natural CLA PCs (A and C) stimulated lecithin-cholesterol acyltransferase activity by 2-fold, whereas the unnatural CLA PCs (B and D) were inhibitory. These results suggest that the differences in the biophysical properties of CLA isomers A and C may partly contribute to the known differences in their biological effects. PMID:20004173

  12. Material properties of the Pt electrode deposited on nafion membrane by the impregnation-reduction method.

    PubMed

    Rashid, Muhammad; Jun, Tae-Sun; Kim, Yong Shin

    2013-05-01

    Platinum nanoparticles (Pt NPs) were chemically deposited on a Nafion polymer electrolyte membrane by the impregnation-reduction (I-R) procedure to prepare an active electrode for solid electrochemical sensors. Various analysis methods such as SEM, EDX, XRD and cyclic voltammogram (CV) measurements were employed in order to characterize microstructures and electrochemical properties of the Pt layer. At the conditions ([Pt(NH3)4Cl2] = 10 mM, [NaBH4] = 60 mM, 50 degrees C), the porous Pt thin-film, consisting of sphere-like particles formed by the agglomeration of primary polycrystalline Pt NPs with an average crystal size of 13-18 nm, was obtained and confirmed to have a large surface area (roughness factor = 267) and strong adhesion due to the formation of interfacial Pt-Nafion composites. The secondary globular particles were found to have an average diameter of 215 nm and irregular protuberances on the surface. Furthermore, this electrode exhibited well-resolved CV peaks for the hydrogen redox reactions in an acid solution, suggesting the existence of different adsorption sites and good electrochemical behaviors. Pt/Nafion electrodes were prepared under different conditions in [Pt(NH3)4Cl2], [NaBH4] and reaction temperature, and their material properties were discussed from the viewpoint of a Pt growth mechanism. PMID:23858916

  13. Deletion of the PDR16 gene influences the plasma membrane properties of the yeast Kluyveromyces lactis.

    PubMed

    Toth Hervay, Nora; Goffa, Eduard; Svrbicka, Alexandra; Simova, Zuzana; Griac, Peter; Jancikova, Iva; Gaskova, Dana; Morvova, Marcela; Sikurova, Libusa; Gbelska, Yvetta

    2015-04-01

    The plasma membrane is the first line of cell defense against changes in external environment, thus its integrity and functionality are of utmost importance. The plasma membrane properties depend on both its protein and lipid composition. The PDR16 gene is involved in the control of Kluyveromyces lactis susceptibility to drugs and alkali metal cations. It encodes the homologue of the major K. lactis phosphatidylinositol transfer protein Sec14p. Sec14p participates in protein secretion, regulation of lipid synthesis, and turnover in vivo. We report here that the plasma membrane of the Klpdr16Δ mutant is hyperpolarized and its fluidity is lower than that of the parental strain. In addition, protoplasts prepared from the Klpdr16Δ cells display decreased stability when subjected to hypo-osmotic conditions. These changes in membrane properties lead to an accumulation of radiolabeled fluconazole and lithium cations inside mutant cells. Our results point to the fact that the PDR16 gene of K. lactis (KlPDR16) influences the plasma membrane properties in K. lactis that lead to subsequent changes in susceptibility to a broad range of xenobiotics. PMID:25742422

  14. Detergent disruption of bacterial inner membranes and recovery of protein translocation activity

    SciTech Connect

    Cunningham, K.; Wickner, W.T. )

    1989-11-01

    Isolation of the integral membrane components of protein translocation requires methods for fractionation and functional reconstitution. The authors treated inner-membrane vesicles of Escherichia coli with mixtures of octyl {beta}-D-glucoside, phospholipids, and an integral membrane carrier protein under conditions that extract most of the membrane proteins into micellar solution. Upon dialysis, proteoliposomes were reconstituted that supported translocation of radiochemically pure ({sup 35}S)pro-OmpA (the precursor of outer membrane protein A). Translocation into these proteoliposomes required ATP hydrolysis and membrane proteins, indicating that the reaction is that of the inner membrane. The suspension of membranes in detergent was separated into supernatant and pellet fractions by ultracentrifugation. After reconstitution, translocation activity was observed in both fractions, but processing by leader peptidase of translocated pro-OmpA to OmpA was not detectable in the reconstituted pellet fraction. Processing activity was restored by addition of pure leader peptidase as long as this enzyme was added before detergent removal, indicating that the translocation activity is not associated with detergent-resistant membrane vesicles. These results show that protein translocation activity can be recovered from detergent-disrupted membrane vesicles, providing a first step towards the goal of isolating the solubilized components.

  15. Cholinesterase activity per unit surface area of conducting membranes.

    PubMed

    Brzin, M; Dettbarn, W D; Rosenberg, P; Nachmansohn, D

    1965-08-01

    According to theory, the action of acetylcholine (ACh) and ACh-esterase is essential for the permeability changes of excitable membranes during activity. It is, therefore, pertinent to know the activity of ACh-esterase per unit axonal surface area instead of per gram nerve, as it has been measured in the past. Such information has now been obtained with the newly developed microgasometric technique using a magnetic diver. (1) The cholinesterase (Ch-esterase) activity per mm(2) surface of sensory axons of the walking leg of lobster is 1.2 x 10(-3) microM/hr. (sigma = +/- 0.3 x 10(-3); SE = 0.17 x 10(-3)); the corresponding value for the motor axons isslightly higher: 1.93 x 10(-3) microM/hr. (sigma = +/- 0.41 x 10(-3); SE = +/- 0.14 x 10(-3)). Referred to gram nerve, the Ch-esterase activity of the sensory axons is much higher than that of the motor axons: 741 microM/hr. (sigma = +/- 73.5; SE = +/- 32.6) versus 111.6 microM/hr. (sigma = +/- 28.3; SE = +/- 10). (2) The enzyme activity in the small fibers of the stellar nerve of squid is 3.2 x 10(-4) microM/mm(2)/hr. (sigma = +/- 0.96 x 10(-4); SE = +/- 0.4 x 10(-4)). (3) The Ch-esterase activity per mm(2) surface of squid giant axon is 9.5 x 10(-5) microM/hr. (sigma = +/- 1.55 x 10(-5); SE = +/- 0.38 x 10(-5)). The value was obtained with small pieces of carefully cleaned axons after removal of the axoplasm and exposure to sonic disintegration. Without the latter treatment the figurewas 3.85 x 10(-5) microM/mm(2)/hr. (sigma = +/- 3.24 x 10(-5); SE = +/- 0.93 x 10(-5)). The experiments indicate the existence of permeability barriers in the cell wall surrounding part of the enzyme, since the substrate cannot reach all the enzyme even when small fragments of the cell wall are used without disintegration. (4) On the basis of the data obtained, some tentative approximations are made of the ratio of ACh released to Na ions entering the squid giant axon per cm(2) per impulse. PMID:5865929

  16. Pneumolysin Activates Macrophage Lysosomal Membrane Permeabilization and Executes Apoptosis by Distinct Mechanisms without Membrane Pore Formation

    PubMed Central

    Bewley, Martin A.; Naughton, Michael; Preston, Julie; Mitchell, Andrea; Holmes, Ashleigh; Marriott, Helen M.; Read, Robert C.; Mitchell, Timothy J.; Whyte, Moira K. B.

    2014-01-01

    ABSTRACT Intracellular killing of Streptococcus pneumoniae is complemented by induction of macrophage apoptosis. Here, we show that the toxin pneumolysin (PLY) contributes both to lysosomal/phagolysosomal membrane permeabilization (LMP), an upstream event programing susceptibility to apoptosis, and to apoptosis execution via a mitochondrial pathway, through distinct mechanisms. PLY is necessary but not sufficient for the maximal induction of LMP and apoptosis. PLY’s ability to induce both LMP and apoptosis is independent of its ability to form cytolytic pores and requires only the first three domains of PLY. LMP involves TLR (Toll-like receptor) but not NLRP3/ASC (nucleotide-binding oligomerization domain [Nod]-like receptor family, pyrin domain-containing protein 3/apoptosis-associated speck-like protein containing a caspase recruitment domain) signaling and is part of a PLY-dependent but phagocytosis-independent host response that includes the production of cytokines, including interleukin-1 beta (IL-1β). LMP involves progressive and selective permeability to 40-kDa but not to 250-kDa fluorescein isothiocyanate (FITC)-labeled dextran, as PLY accumulates in the cytoplasm. In contrast, the PLY-dependent execution of apoptosis requires phagocytosis and is part of a host response to intracellular bacteria that also includes NO generation. In cells challenged with PLY-deficient bacteria, reconstitution of LMP using the lysomotrophic detergent LeuLeuOMe favored cell necrosis whereas PLY reconstituted apoptosis. The results suggest that PLY contributes to macrophage activation and cytokine production but also engages LMP. Following bacterial phagocytosis, PLY triggers apoptosis and prevents macrophage necrosis as a component of a broad-based antimicrobial strategy. This illustrates how a key virulence factor can become the focus of a multilayered and coordinated innate response by macrophages, optimizing pathogen clearance and limiting inflammation. PMID:25293758

  17. CO2 Gas Transport Property of Sulfonated Poly(Arylenen Ether Sulfone) Copolymer Membrane.

    PubMed

    Lee, Hye Jin; Kim, Deuk Ju; Nam, Sang Yong

    2015-03-01

    The effect of functional groups such as sulfuric acid group and metal ions on the CO2 gas transport property of membranes was investigated. Sulfonated poly(arylene ether sulfone) (SPAES) was prepared by direct copolymerization with a non-sulfonated monomer and sulfonated monomer. The sulfonation degree of SPAES was controlled from 0 to 50%. Metal ions such as lithium and sodium were substituted for the protons of the -SO3H group. The thermal properties, microstructure of polymer chains, and the permeability and selectivity of membranes were evaluated. The solubility coefficient of CO2 gas increased with an increase in sulfonation degree. But the diffusivity was largely decreased and the CO2/N2 selectivity of the membrane substituted for metal ions was increased. PMID:26413703

  18. Probing conformational changes in lipoxygenases upon membrane binding: fine-tuning by the active site inhibitor ETYA.

    PubMed

    Di Venere, Almerinda; Nicolai, Eleonora; Ivanov, Igor; Dainese, Enrico; Adel, Susan; Angelucci, B C; Kuhn, Hartmut; Maccarrone, Mauro; Mei, Giampiero

    2014-01-01

    Lipoxygenases (LOXs) are lipid-peroxidizing enzymes that are involved in the metabolism of polyunsaturated fatty acids. Their biological activity includes a membrane binding process whose molecular details are not completely understood. The mechanism of enzyme-membrane interactions is thought to involve conformational changes at the level of the protein tertiary structure, and the extent of such alterations depends on the degree of structural flexibility of the different LOX isoforms. In this study, we have tested the resilience properties of a plant and a mammalian LOX, by using high pressure fluorescence measurements at different temperatures. The binding of LOXs to the lipid bilayer has been characterized using both large and giant unilamellar vesicles and electron transfer particles (inner mitochondrial membranes) as model membranes. The data indicate that the degree of LOXs' flexibility is strictly dependent on the two distinct N- and C-terminal domains that characterize the 3D structure of these enzymes. Furthermore, they demonstrate that increasing the rigidity of protein scaffolding by the presence of an active site ligand impairs the membrane binding ability of LOXs. These findings provide evidence that the amphitropic nature of LOXs is finely tuned by the interaction of the substrate with the residues of the active site, suggesting new strategies for the design of enzyme inhibitors. PMID:24012824

  19. Structure and properties of PVDF membrane with PES-C addition via thermally induced phase separation process

    NASA Astrophysics Data System (ADS)

    Wu, Lishun; Sun, Junfen

    2014-12-01

    Polyvinylidene fluoride (PVDF) membrane and PVDF membrane with phenolphthalein polyethersulfone (PES-C) addition were prepared via thermally induced phase separation (TIPS) method by using diphenyl carbonate (DPC) and dimethyl acetamide (DMAc) as mixed diluents. The effects of coagulation temperature and pre-evaporation time on structure and properties of membranes were studied. The changes of sewage flux in MBR and the attenuation coefficient of sewage flux were investigated. The resistance distributions of PVDF and PVDF/PES-C membranes were compared by resistance analysis. Membrane composition and structure were characterized by ATR-FTIR, TGA, SEM and AFM. The foulant on membranes was analyzed by FTIR. The contact angle of PVDF/PES-C membrane was lower than that of PVDF membrane. A thinner skin layer and a porous cellular support layer formed in PVDF/PES-C membrane and resulted in a higher porosity and pure water flux. The pure water flux and porosity of PVDF/PES-C membrane increased with rising coagulation temperature and decreased with extending pre-evaporation time. The flux attenuation coefficient, the cake layer resistance and internal fouling resistance of PVDF/PES-C membrane in MBR were smaller than those of PVDF membrane in MBR. The FTIR spectrum of foulant on membrane indicated that the foulant on PVDF/PES-C membrane was mostly composed of protein and polysaccharide, while the foulant on pure PVDF membrane included biopolymer clusters besides protein and polysaccharide.

  20. Circulating polymerase chain reaction chips utilizing multiple-membrane activation

    NASA Astrophysics Data System (ADS)

    Wang, Chih-Hao; Chen, Yi-Yu; Liao, Chia-Sheng; Hsieh, Tsung-Min; Luo, Ching-Hsing; Wu, Jiunn-Jong; Lee, Huei-Huang; Lee, Gwo-Bin

    2007-02-01

    This paper reports a new micromachined, circulating, polymerase chain reaction (PCR) chip for nucleic acid amplification. The PCR chip is comprised of a microthermal control module and a polydimethylsiloxane (PDMS)-based microfluidic control module. The microthermal control modules are formed with three individual heating and temperature-sensing sections, each modulating a specific set temperature for denaturation, annealing and extension processes, respectively. Micro-pneumatic valves and multiple-membrane activations are used to form the microfluidic control module to transport sample fluids through three reaction regions. Compared with other PCR chips, the new chip is more compact in size, requires less time for heating and cooling processes, and has the capability to randomly adjust time ratios and cycle numbers depending on the PCR process. Experimental results showed that detection genes for two pathogens, Streptococcus pyogenes (S. pyogenes, 777 bps) and Streptococcus pneumoniae (S. pneumoniae, 273 bps), can be successfully amplified using the new circulating PCR chip. The minimum number of thermal cycles to amplify the DNA-based S. pyogenes for slab gel electrophoresis is 20 cycles with an initial concentration of 42.5 pg µl-1. Experimental data also revealed that a high reproducibility up to 98% could be achieved if the initial template concentration of the S. pyogenes was higher than 4 pg µl-1. The preliminary results of the current paper were presented at the 19th IEEE International Conference on Micro Electro Mechanical Systems (IEEE MEMS 2006), Istanbul, Turkey, 22-26 January, 2006.

  1. Spectral properties and orientation of voltage-sensitive dyes in lipid membranes.

    PubMed

    Matson, Maria; Carlsson, Nils; Beke-Somfai, Tamás; Nordén, Bengt

    2012-07-24

    Voltage-sensitive dyes are frequently used for probing variations in the electric potential across cell membranes. The dyes respond by changing their spectral properties: measured as shifts of wavelength of absorption or emission maxima or as changes of absorption or fluorescence intensity. Although such probes have been studied and used for decades, the mechanism behind their voltage sensitivity is still obscure. We ask whether the voltage response is due to electrochromism as a result of direct field interaction on the chromophore or to solvatochromism, which is the focus of this study, as result of changed environment or molecular alignment in the membrane. The spectral properties of three styryl dyes, di-4-ANEPPS, di-8-ANEPPS, and RH421, were investigated in solvents of varying polarity and in model membranes using spectroscopy. Using quantum mechanical calculations, the spectral dependence of monomer and dimer ANEPPS on solvent properties was modeled. Also, the kinetics of binding to lipid membranes and the binding geometry of the probe molecules were found relevant to address. The spectral properties of all three probes were found to be highly sensitive to the local environment, and the probes are oriented nearly parallel with the membrane normal. Slow binding kinetics and scattering in absorption spectra indicate, especially for di-8-ANEPPS, involvement of aggregation. On the basis of the experimental spectra and time-dependent density functional theory calculations, we find that aggregate formation may contribute to the blue-shifts seen for the dyes in decanol and when bound to membrane models. In conclusion, solvatochromic and other intermolecular interactions effects also need to be included when considering electrochromic response voltage-sensitive dyes. PMID:22738247

  2. Optimization of membrane bioreactors by the addition of powdered activated carbon.

    PubMed

    Ng, Choon Aun; Sun, Darren; Bashir, Mohammed J K; Wai, Soon Han; Wong, Ling Yong; Nisar, Humaira; Wu, Bing; Fane, Anthony G

    2013-06-01

    It was found that with replenishment, powdered activated carbon (PAC) in the membrane bioreactor (MBR) would develop biologically activated carbon (BAC) which could enhance filtration performance of a conventional MBR. This paper addresses two issues (i) effect of PAC size on MBR (BAC) performance; and (ii) effect of sludge retention time (SRT) on the MBR performance with and without PAC. To interpret the trends, particle/floc size, concentration of mixed liquor suspended solid (MLSS), total organic carbon (TOC), short-term filtration properties and transmembrane pressure (TMP) versus time are measured. The results showed improved fouling control with fine, rather than coarse, PAC provided the flux did not exceed the deposition flux for the fine PAC. Without PAC, the longer SRT operation gave lower fouling at modest fluxes. With PAC addition, the shorter SRT gave better fouling control, possibly due to greater replenishment of the fresh PAC. PMID:23612160

  3. Isolation, Characterization and Biological Properties of Membrane Vesicles Produced by the Swine Pathogen Streptococcus suis

    PubMed Central

    Haas, Bruno; Grenier, Daniel

    2015-01-01

    Streptococcus suis, more particularly serotype 2, is a major swine pathogen and an emerging zoonotic agent worldwide that mainly causes meningitis, septicemia, endocarditis, and pneumonia. Although several potential virulence factors produced by S. suis have been identified in the last decade, the pathogenesis of S. suis infections is still not fully understood. In the present study, we showed that S. suis produces membrane vesicles (MVs) that range in diameter from 13 to 130 nm and that appear to be coated by capsular material. A proteomic analysis of the MVs revealed that they contain 46 proteins, 9 of which are considered as proven or suspected virulence factors. Biological assays confirmed that S. suis MVs possess active subtilisin-like protease (SspA) and DNase (SsnA). S. suis MVs degraded neutrophil extracellular traps, a property that may contribute to the ability of the bacterium to escape the host defense response. MVs also activated the nuclear factor-kappa B (NF-κB) signaling pathway in both monocytes and macrophages, inducing the secretion of pro-inflammatory cytokines, which may in turn contribute to increase the permeability of the blood brain barrier. The present study brought evidence that S. suis MVs may play a role as a virulence factor in the pathogenesis of S. suis infections, and given their composition be an excellent candidate for vaccine development. PMID:26110524

  4. Membrane Morphology Is Actively Transformed by Covalent Binding of the Protein Atg8 to PE-Lipids

    PubMed Central

    Knorr, Roland L.; Nakatogawa, Hitoshi; Ohsumi, Yoshinori; Lipowsky, Reinhard; Baumgart, Tobias; Dimova, Rumiana

    2014-01-01

    Autophagy is a cellular degradation pathway involving the shape transformation of lipid bilayers. During the onset of autophagy, the water-soluble protein Atg8 binds covalently to phosphatdylethanolamines (PEs) in the membrane in an ubiquitin-like reaction coupled to ATP hydrolysis. We reconstituted the Atg8 conjugation system in giant and nm-sized vesicles with a minimal set of enzymes and observed that formation of Atg8-PE on giant vesicles can cause substantial tubulation of membranes even in the absence of Atg12-Atg5-Atg16. Our findings show that ubiquitin-like processes can actively change properties of lipid membranes and that membrane crowding by proteins can be dynamically regulated in cells. Furthermore we provide evidence for curvature sorting of Atg8-PE. Curvature generation and sorting are directly linked to organelle shapes and, thus, to biological function. Our results suggest that a positive feedback exists between the ubiquitin-like reaction and the membrane curvature, which is important for dynamic shape changes of cell membranes, such as those involved in the formation of autophagosomes. PMID:25522362

  5. [Polypeptide and phospholipid composition of the Rickettsia prowazekii membrane and its immunogenic properties].

    PubMed

    Zezerov, E G; Loginov, V S; Berezneva, A S

    1985-06-01

    The composition of the cell membrane in R. prowazekii strain Breinl has been studied by the methods of electrophoresis in 7.5% polyacrylamide gel with 0.1% sodium dodecyl sulfate, iodination with Na125I in the presence of chloramine T or lactoperoxidase and the thin-layer chromatography of the common lipid fraction. Of six major polypeptides contained in whole rickettsial particles (3, 16, 26, 27, 28, 29), five polypeptides (3, 26, 27, 28, 29) making up 54% of all polypeptides of purified rickettsiae have been detected in membrane preparations obtained by either treatment. The molecular weights of these membrane polypeptides are, respectively, 133600, 34000, 29600, 21500 and 12400 daltons. The main membrane phospholipids are phosphatidylethanolamine (68.4%), phosphatidylglycerol (17.2%), phosphatidylcholine (5.1%) and cardiolipin (2.1%). The presence of cholesterol has also been established. The preparations of R. prowazekii membranes and individual membrane polypeptides are immunogenic and induce the formation of specific antibodies in white mice. The preparations of both membranes and surface polypeptide 3 (glycoprotein) have been found to possess a certain protective activity: the effect of the protection of white mice inoculated with R. prowazekii culture has proved to be 64%. PMID:3929506

  6. Overcoming foreign-body reaction through nanotopography: Biocompatibility and immunoisolation properties of a nanofibrous membrane.

    PubMed

    Wang, Kai; Hou, Wen-Da; Wang, Xi; Han, Chengsheng; Vuletic, Ivan; Su, Ni; Zhang, Wen-Xi; Ren, Qiu-Shi; Chen, Liangyi; Luo, Ying

    2016-09-01

    Implantable immunoisolation membranes need to possess superior biocompatibility to prohibit the fibrotic deposition that would reduce the nutrient supply and impair the viability/function of the encapsulated cells. Here, electrospun membranes based on thermoplastic polyurethane (TPU) were fabricated to contain microfibers (PU-micro) or nanofibers (PU-nano). The two types of membranes were compared in terms of their interaction with macrophage cells and the host tissues. It was found that the fibrous membranes of different topographies possess distinct material properties: PU-nano caused minimal macrophage responses in vitro and in vivo and induced only mild foreign body reactions compared to PU-micro membranes. A flat macroencapsulation device was fabricated using PU-nano membranes and its immunoisolation function investigated in subcutaneous transplantation models. The nanofibrous device demonstrated the capability to effectively shield the allografts from the immune attack of the host. Nanotopography may confer biocompatibility to materials and nanofibrous materials warrant further study for development of "invisible" immunoisolation devices for cell transplantation. PMID:27344368

  7. Thylakoid Membrane Maturation and PSII Activation Are Linked in Greening Synechocystis sp. PCC 6803 Cells1

    PubMed Central

    Barthel, Sandra; Bernát, Gábor; Seidel, Tobias; Rupprecht, Eva; Kahmann, Uwe; Schneider, Dirk

    2013-01-01

    Thylakoid membranes are typical and essential features of both chloroplasts and cyanobacteria. While they are crucial for phototrophic growth of cyanobacterial cells, biogenesis of thylakoid membranes is not well understood yet. Dark-grown Synechocystis sp. PCC 6803 cells contain only rudimentary thylakoid membranes but still a relatively high amount of phycobilisomes, inactive photosystem II and active photosystem I centers. After shifting dark-grown Synechocystis sp. PCC 6803 cells into the light, “greening” of Synechocystis sp. PCC 6803 cells, i.e. thylakoid membrane formation and recovery of photosynthetic electron transport reactions, was monitored. Complete restoration of a typical thylakoid membrane system was observed within 24 hours after an initial lag phase of 6 to 8 hours. Furthermore, activation of photosystem II complexes and restoration of a functional photosynthetic electron transport chain appears to be linked to the biogenesis of organized thylakoid membrane pairs. PMID:23922268

  8. Influence of microstructure and environment on nanoparticle membrane and superlattice mechanical properties

    NASA Astrophysics Data System (ADS)

    Salerno, K. Michael

    Assembly of nanoparticles (NPs) offers a means to tailor materials, incorporating unique nanoscale electro-optical behavior with controllable, responsive mechanical properties. Encoding NPs with organic ligands provides a way to simultaneously drive assembly and control assembly properties. Atomistic molecular dynamics simulations of alkanethiol-coated gold nanoparticles are used to examine how coating chemistry, temperature, and assembly history affect the properties of two-dimensional nanoparticle membranes and three-dimensional nanoparticle superlattices. Specifically, NPs were coated with dodecanethiol and octadecanethiol ligands with COOH or CH3 end groups and assembled into two-dimensional membranes at water vapor interface. Capping ligands with hydrogen-bond forming carboxyl groups rather than methyl groups more than doubles the membrane Young's modulus from 1.5 to 3.6 GPa. The orientational order of the coating oligomers indicates that ligands strongly bundle and orient within the membrane. This effect inhibits ligand interdigitation, decreasing stiffness. Ligand structure is also highly temperature dependent, causing membranes to lose mechanical stability at about 400K. We observe that the interface asymmetry leads to a measurable stress asymmetry. Due to buckling, stresses in 2D membranes are typically quite small, however 3D superlattices can reversibly reach pressures of 8 GPa. Simulations show that at these pressures the ligand-core bond can be an important failure point, and experiments show that core sintering occurs at high pressure, creating novel 3D and quasi-2D structures. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

  9. Structure/property relationships in polymer membranes for water purification and energy applications

    NASA Astrophysics Data System (ADS)

    Geise, Geoffrey

    Providing sustainable supplies of purified water and energy is a critical global challenge for the future, and polymer membranes will play a key role in addressing these clear and pressing global needs for water and energy. Polymer membrane-based processes dominate the desalination market, and polymer membranes are crucial components in several rapidly developing power generation and storage applications that rely on membranes to control rates of water and/or ion transport. Much remains unknown about the influence of polymer structure on intrinsic water and ion transport properties, and these relationships must be developed to design next generation polymer membrane materials. For desalination applications, polymers with simultaneously high water permeability and low salt permeability are desirable in order to prepare selective membranes that can efficiently desalinate water, and a tradeoff relationship between water/salt selectivity and water permeability suggests that attempts to prepare such materials should rely on approaches that do more than simply vary polymer free volume. One strategy is to functionalize hydrocarbon polymers with fixed charge groups that can ionize upon exposure to water, and the presence of charged groups in the polymer influences transport properties. Additionally, in many emerging energy applications, charged polymers are exposed to ions that are very different from sodium and chloride. Specific ion effects have been observed in charged polymers, and these effects must be understood to prepare charged polymers that will enable emerging energy technologies. This presentation discusses research aimed at further understanding fundamental structure/property relationships that govern water and ion transport in charged polymer films considered for desalination and electric potential field-driven applications that can help address global needs for clean water and energy.

  10. Facile surface glycosylation of PVDF microporous membrane via direct surface-initiated AGET ATRP and improvement of antifouling property and biocompatibility

    NASA Astrophysics Data System (ADS)

    Yuan, Jing; Meng, Jian-qiang; Kang, Yin-lin; Du, Qi-yun; Zhang, Yu-feng

    2012-01-01

    This paper describes a facile and novel approach for the surface glycosylation of poly(vinylidene difluoride) (PVDF) microporous membrane. A glycopolymer poly(D-gluconamidoethyl methacrylate) (PGAMA) was tethered onto the membrane surface via activators generated by electron transfer atom transfer radical polymerization (AGET ATRP) directly initiated from the PVDF surface. Chemical changes of membrane surface were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). It was revealed that PGAMA was successfully grafted onto the membrane surface and its grafting density can be modulated in a wide range up to 2.4 μmol/cm2. The effects of glycosylation on membrane morphology, flux and surface hydrophilicity were investigated. Field emission scanning electron microscopy (FESEM) results indicated shrinkage of the surface pore diameters and the growth of the glycopolymer layer on the membrane surface. The static water contact angle (WCA) of the membrane surface decreased from 110° to 30.4° with the increase of grafting density, indicating that the PGAMA grafts dramatically improved the surface hydrophilicity. The protein adsorption and platelets adhesion experiments indicated that the grafted PGAMA could effectively improve the membrane antifouling property and biocompatibility.

  11. Modification of trout sperm membranes associated with activation and cryopreservation. Implications for fertilizing potential.

    PubMed

    Purdy, P H; Barbosa, E A; Praamsma, C J; Schisler, G J

    2016-08-01

    We investigated the effects of two trout sperm activation solutions on sperm physiology and membrane organization prior to and following cryopreservation using flow cytometry and investigated their impact on in vitro fertility. Overall, frozen-thawed samples had greater phospholipid disorder when compared with fresh samples (high plasma membrane fluidity; P < 0.0001) and sperm activated with water also had high plasma membrane fluidity when compared to sperm activated with Lahnsteiner solution (LAS; P < 0.0001). Following cryopreservation water activated samples had membranes with greater membrane protein disorganization compared with LAS but the membrane protein organization of LAS samples was similar to samples prior to freezing (P < 0.0001). Post-thaw water activation resulted in significant increases in intracellular calcium compared to LAS (P < 0.002). In vitro fertility trials with frozen-thawed milt and LAS activation resulted in greater fertility (45%) compared to water activated samples (10%; P < 0.0001). Higher fertility rates correlated with lower intracellular calcium with water (R(2) = -0.9; P = 0.01) and LAS (R(2) = -0.85; P = 0.03) activation. Greater plasma membrane phospholipid (R(2) = -0.89; P = 0.02) and protein (R(2) = -0.84; P = 0.04) disorder correlated with lower water activation fertility rates. These membrane organization characteristics only approached significance with LAS activation in vitro fertility (P = 0.09, P = 0.06, respectively). Potentially the understanding of sperm membrane reorganizations and the physiology associated with activation following cryopreservation may enable users in a repository or hatchery setting to estimate the fertilizing potential of a sample and determine its value. PMID:27234987

  12. Age related changes in functions and physicochemical properties of rat jejunal brush border membrane after chronic ethanol administration.

    PubMed

    Lindi, C; Marciani, P; Omodeo-Sale, F

    1993-02-01

    1. We investigated the chronic effects of a 4 week treatment with ethanol on functions and physicochemical properties of BBM of young and adult rats (2 and 7 months old respectively). 2. In the ethanol treated groups the cholesterol/phospholipid and the protein/lipid ratios as well as the D-glucose uptake and lactase specific activity and Vmax were increased. In spite of a minor alcohol consumption the adult group was the more affected. 3. Membranes from the ethanol fed rats were less fluid and more tolerant to the in vitro addition of ethanol. PMID:8098680

  13. Effects of Lipid Composition and Solution Conditions on the Mechanical Properties of Membrane Vesicles

    PubMed Central

    Kato, Nobuhiko; Ishijima, Akihiko; Inaba, Takehiko; Nomura, Fumimasa; Takeda, Shuichi; Takiguchi, Kingo

    2015-01-01

    The mechanical properties of cell-sized giant unilamellar liposomes were studied by manipulating polystyrene beads encapsulated within the liposomes using double-beam laser tweezers. Mechanical forces were applied to the liposomes from within by moving the beads away from each other, which caused the liposomes to elongate. Subsequently, a tubular membrane projection was generated in the tip at either end of the liposome, or the bead moved out from the laser trap. The force required for liposome transformation reached maximum strength just before formation of the projection or the moving out of the bead. By employing this manipulation system, we investigated the effects of membrane lipid compositions and environment solutions on the mechanical properties. With increasing content of acidic phospholipids, such as phosphatidylglycerol or phosphatidic acid, a larger strength of force was required for the liposome transformation. Liposomes prepared with a synthetic dimyristoylphosphatidylcholine, which has uniform hydrocarbon chains, were transformed easily compared with liposomes prepared using natural phosphatidylcholine. Surprisingly, bovine serum albumin or fetuin (soluble proteins that do not bind to membranes) decreased liposomal membrane rigidity, whereas the same concentration of sucrose showed no particular effect. These results show that the mechanical properties of liposomes depend on their lipid composition and environment. PMID:25611306

  14. Thermal properties of phosphoric acid-doped polybenzimidazole membranes in water and methanol-water mixtures

    NASA Astrophysics Data System (ADS)

    Nores-Pondal, Federico J.; Buera, M. Pilar; Corti, Horacio R.

    The thermal properties of phosphoric acid-doped poly[2-2‧-(m-phenylene)-5-5‧ bi-benzimidazole] (PBI) and poly[2,5-benzimidazole] (ABPBI) membranes, ionomeric materials with promising properties to be used as electrolytes in direct methanol and in high temperature polymer electrolyte membrane (PEM) fuel cells, were studied by means of differential scanning calorimetry (DSC) technique in the temperature range from -145 °C to 200 °C. The DSC scans of samples equilibrated in water at different relative humidities (RH) and in liquid water-methanol mixtures were analyzed in relation to glass transition, water crystallization/melting and solvent desorption in different temperature regions. The thermal relaxation observed in the very low temperature region could be ascribed to the glass transition of the H 3PO 4-H 2O mixture confined in the polymeric matrix. After cooling the samples up to -145 °C, frozen water was detected in PBI and ABPBI at different RH, although at 100% RH less amount of water had crystallized than that observed in Nafion membranes under the same conditions. Even more important is the fact that the freezing degree of water is much lower in ABPBI membranes equilibrated in liquid water-methanol mixtures than that observed for PBI and, in a previous study, for Nafion. Thus, apart from other well known properties, acid-doped ABPBI emerges as an excellent ionomer for applications in direct methanol fuel cells working in cold environments.

  15. The Transport Properties of Activated Carbon Fibers

    DOE R&D Accomplishments Database

    di Vittorio, S. L.; Dresselhaus, M. S.; Endo, M.; Issi, J-P.; Piraux, L.

    1990-07-01

    The transport properties of activated isotropic pitch-based carbon fibers with surface area 1000 m{sup 2}/g have been investigated. We report preliminary results on the electrical conductivity, the magnetoresistance, the thermal conductivity and the thermopower of these fibers as a function of temperature. Comparisons are made to transport properties of other disordered carbons.

  16. The transport properties of activated carbon fibers

    SciTech Connect

    di Vittorio, S.L. . Dept. of Materials Science and Engineering); Dresselhaus, M.S. . Dept. of Electrical Engineering and Computer Science Massachusetts Inst. of Tech., Cambridge, MA . Dept. of Physics); Endo, M. . Dept. of Electrical Engineering); Issi, J-P.; Piraux, L.

    1990-07-01

    The transport properties of activated isotropic pitch-based carbon fibers with surface area 1000 m{sup 2}/g have been investigated. We report preliminary results on the electrical conductivity, the magnetoresistance, the thermal conductivity and the thermopower of these fibers as a function of temperature. Comparisons are made to transport properties of other disordered carbons. 19 refs., 4 figs.

  17. Zwitterionic polymer functionalization of polysulfone membrane with improved antifouling property and blood compatibility by combination of ATRP and click chemistry.

    PubMed

    Xiang, Tao; Lu, Ting; Xie, Yi; Zhao, Wei-Feng; Sun, Shu-Dong; Zhao, Chang-Sheng

    2016-08-01

    The chemical compositions are very important for designing blood-contacting membranes with good antifouling property and blood compatibility. In this study, we propose a method combining ATRP and click chemistry to introduce zwitterionic polymer of poly(sulfobetaine methacrylate) (PSBMA), negatively charged polymers of poly(sodium methacrylate) (PNaMAA) and/or poly(sodium p-styrene sulfonate) (PNaSS), to improve the antifouling property and blood compatibility of polysulfone (PSf) membranes. Attenuated total reflectance-Fourier transform infrared spectra, X-ray photoelectron spectroscopy and water contact angle results confirmed the successful grafting of the functional polymers. The antifouling property and blood compatibility of the modified membranes were systematically investigated. The zwitterionic polymer (PSBMA) grafted membranes showed good resistance to protein adsorption and bacterial adhesion; the negatively charged polymer (PNaSS or PNaMAA) grafted membranes showed improved blood compatibility, especially the anticoagulant property. Moreover, the PSBMA/PNaMAA modified membrane showed both antifouling property and anticoagulant property, and exhibited a synergistic effect in inhibiting blood coagulation. The functionalization of membrane surfaces by a combination of ATRP and click chemistry is demonstrated as an effective route to improve the antifouling property and blood compatibility of membranes in blood-contact. PMID:27039977

  18. Actomyosin dynamics drive local membrane component organization in an in vitro active composite layer.

    PubMed

    Köster, Darius Vasco; Husain, Kabir; Iljazi, Elda; Bhat, Abrar; Bieling, Peter; Mullins, R Dyche; Rao, Madan; Mayor, Satyajit

    2016-03-22

    The surface of a living cell provides a platform for receptor signaling, protein sorting, transport, and endocytosis, whose regulation requires the local control of membrane organization. Previous work has revealed a role for dynamic actomyosin in membrane protein and lipid organization, suggesting that the cell surface behaves as an active composite composed of a fluid bilayer and a thin film of active actomyosin. We reconstitute an analogous system in vitro that consists of a fluid lipid bilayer coupled via membrane-associated actin-binding proteins to dynamic actin filaments and myosin motors. Upon complete consumption of ATP, this system settles into distinct phases of actin organization, namely bundled filaments, linked apolar asters, and a lattice of polar asters. These depend on actin concentration, filament length, and actin/myosin ratio. During formation of the polar aster phase, advection of the self-organizing actomyosin network drives transient clustering of actin-associated membrane components. Regeneration of ATP supports a constitutively remodeling actomyosin state, which in turn drives active fluctuations of coupled membrane components, resembling those observed at the cell surface. In a multicomponent membrane bilayer, this remodeling actomyosin layer contributes to changes in the extent and dynamics of phase-segregating domains. These results show how local membrane composition can be driven by active processes arising from actomyosin, highlighting the fundamental basis of the active composite model of the cell surface, and indicate its relevance to the study of membrane organization. PMID:26929326

  19. Association dynamics and linear and nonlinear optical properties of an N-acetylaladanamide probe in a POPC membrane.

    PubMed

    Murugan, N Arul; Apostolov, Rossen; Rinkevicius, Zilvinas; Kongsted, Jacob; Lindahl, Erik; Ågren, Hans

    2013-09-11

    Along with the growing evidence that relates membrane abnormalities to various diseases, biological membranes have been acknowledged as targets for therapy. Any such abnormality in the membrane structure alters the membrane potential which in principle can be captured by measuring properties of specific optical probes. There exists by now many molecular probes with absorption and fluorescence properties that are sensitive to local membrane structure and to the membrane potential. To suggest new high-performance optical probes for membrane-potential imaging it is important to understand in detail the membrane-induced structural changes in the probe, the membrane association dynamics of the probe, and its membrane-specific optical properties. To contribute to this effort, we here study an optical probe, N-acetylaladanamide (NAAA), in the presence of a POPC lipid bilayer using a multiscale integrated approach to assess the probe structure, dynamics, and optical properties in its membrane-bound status and in water solvent. We find that the probe eventually assimilates into the membrane with a specific orientation where the hydrophobic part of the probe is buried inside the lipid bilayer, while the hydrophilic part is exposed to the water solvent. The computed absorption maximum is red-shifted when compared to the gas phase. The computations of the two-photon absorption and second harmonic generation cross sections of the NAAA probe in its membrane-bound state which is of its first kind in the literature suggest that this probe can be used for imaging the membrane potential using nonlinear optical microscopy. PMID:23951997

  20. Comparison of microbial communities of activated sludge and membrane biofilm in 10 full-scale membrane bioreactors.

    PubMed

    Jo, Sung Jun; Kwon, Hyeokpil; Jeong, So-Yeon; Lee, Chung-Hak; Kim, Tae Gwan

    2016-09-15

    Operation of membrane bioreactors (MBRs) for wastewater treatment is hampered by the membrane biofouling resulting from microbial activities. However, the knowledge of the microbial ecology of both biofilm and activated sludge in MBRs has not been sufficient. In this study, we scrutinized microbial communities of biofilm and activated sludge from 10 full-scale MBR plants. Overall, Flavobacterium, Dechloromonas and Nitrospira were abundant in order of abundance in biofilm, whereas Dechloromonas, Flavobacterium and Haliscomenobacter in activated sludge. Community structure was analyzed in either biofilm or activated sludge. Among MBRs, as expected, not only diversity of microbial community but also its composition was different from one another (p < 0.05). Between the biofilm and activated sludge, community composition made significant difference, but its diversity measures (i.e., alpha diversity, e.g., richness, diversity and evenness) did not (p > 0.05). Effects of ten environmental factors on community change were investigated using Spearman correlation. MLSS, HRT, F/M ratio and SADm explained the variation of microbial composition in the biofilm, whereas only MLSS did in the activated sludge. Microbial networks were constructed with the 10 environmental factors. The network results revealed that there were different topological characteristics between the biofilm and activated sludge networks, in which each of the 4 factors had different associations with microbial nodes. These results indicated that the different microbial associations were responsible for the variation of community composition between the biofilm and activated sludge. PMID:27262549

  1. In Vitro excitation of purified membrane fragments by cholinergic agonists : I. Pharmalogical properties of the excitable membrane fragments.

    PubMed

    Kasai, M; Changeux, J P

    1971-03-01

    Excitation of membrane fragments by cholinergic agonists is measuredin vitro by a filtration technique. Membrane fragments which contain high levels of the enzyme acetylcholinesterase and presumably originate from the innervated excitable faces of electroplax are first purified from homogenates of electric organ ofElectrophorus electricus by centrifugation in a sucrose gradient. Then the fragments, which make closed vesicles or microsacs, are equilibrated overnight with a medium containing(22)Na(+). After equilibration of the inside of the microsacs with the outside medium, the suspension is diluted into a nonradioactive medium. The(22)Na(+) content of the microsacs as a function of time is then followed by rapid filtration on Millipore filters. In the presence of cholinergic agonists, the time course of(22)Na(+) release changes: the rate of(22)Na(+) release increases. This increase is blocked byd-tubocurarine and is absent with microsacs derived from the non-innervated inexcitable membrane of the electroplax. The response to cholinergic agonists is thus followed on a completely cell-free system, in a well-defined environment. The dose-response curves to cholinergic agents obtainedin vitro agree, quantitatively, with the dose-response curves recordedin vivo by electrophysiological methods. In particular, the dose-response curve to agonists is sigmoid, the antagonism betweend-tubocurarine and carbamylcholine competitive, and the antagonism between tetracaine and carbamylcholine noncompetitive. The effects of two different affinity labeling reagents on the response to agonists and on the catalytic activity of acetylcholinesterase are followed in parallel on the same microsac preparation. The effects of dithiothreitol and of gramicidin A on the microsacs are studied and are found to be similar to those observedin vivo with the isolated electroplax. PMID:24173287

  2. Protonophore properties of hyperforin are essential for its pharmacological activity

    PubMed Central

    Sell, Thomas S.; Belkacemi, Thabet; Flockerzi, Veit; Beck, Andreas

    2014-01-01

    Hyperforin is a pharmacologically active component of the medicinal plant Hypericum perforatum (St. John's wort), recommended as a treatment for a range of ailments including mild to moderate depression. Part of its action has been attributed to TRPC6 channel activation. We found that hyperforin induces TRPC6-independent H+ currents in HEK-293 cells, cortical microglia, chromaffin cells and lipid bilayers. The latter demonstrates that hyperforin itself acts as a protonophore. The protonophore activity of hyperforin causes cytosolic acidification, which strongly depends on the holding potential, and which fuels the plasma membrane sodium-proton exchanger. Thereby the free intracellular sodium concentration increases and the neurotransmitter uptake by Na+ cotransport is inhibited. Additionally, hyperforin depletes and reduces loading of large dense core vesicles in chromaffin cells, which requires a pH gradient in order to accumulate monoamines. In summary the pharmacological actions of the “herbal Prozac” hyperforin are essentially determined by its protonophore properties shown here. PMID:25511254

  3. Human sensory neurons: Membrane properties and sensitization by inflammatory mediators

    PubMed Central

    Zhang, Jingming; Page, Guy; Ghetti, Andrea; Gereau, Robert W.

    2014-01-01

    Biological differences in sensory processing between human and model organisms may present significant obstacles to translational approaches in treating chronic pain. To better understand the physiology of human sensory neurons, we performed whole-cell patch-clamp recordings from 141 human dorsal root ganglion (hDRG) neurons from five young adult donors without chronic pain. Nearly all small diameter hDRG neurons (<50 μm) displayed an inflection on the descending slope of the action potential, a defining feature of rodent nociceptive neurons. A high proportion of hDRG neurons were responsive to the algogens allyl isothiocyanate (AITC) and ATP, as well as the pruritogens histamine and chloroquine. We show that a subset of hDRG neurons responded to the inflammatory compounds bradykinin and prostaglandin E2 with action potential discharge and show evidence of sensitization including lower rheobase. Compared to electrically-evoked action potentials, chemically-induced action potentials were triggered from less depolarized thresholds and showed distinct after-hyperpolarization kinetics. These data indicate that most small/medium hDRG neurons can be classified as nociceptors, that they respond directly to compounds that produce pain and itch, and can be activated and sensitized by inflammatory mediators. The use of hDRG neurons as preclinical vehicles for target validation is discussed. PMID:24973718

  4. Spatial distribution and activity of Na(+)/K(+)-ATPase in lipid bilayer membranes with phase boundaries.

    PubMed

    Bhatia, Tripta; Cornelius, Flemming; Brewer, Jonathan; Bagatolli, Luis A; Simonsen, Adam C; Ipsen, John H; Mouritsen, Ole G

    2016-06-01

    We have reconstituted functional Na(+)/K(+)-ATPase (NKA) into giant unilamellar vesicles (GUVs) of well-defined binary and ternary lipid composition including cholesterol. The activity of the membrane system can be turned on and off by ATP. The hydrolytic activity of NKA is found to depend on membrane phase, and the water relaxation in the membrane on the presence of NKA. By collapsing and fixating the GUVs onto a solid support and using high-resolution atomic-force microscopy (AFM) imaging we determine the protein orientation and spatial distribution at the single-molecule level and find that NKA is preferentially located at lo/ld interfaces in two-phase GUVs and homogeneously distributed in single-phase GUVs. When turned active, the membrane is found to unbind from the support suggesting that the protein function leads to softening of the membrane. PMID:26994932

  5. Focus on Extracellular Vesicles: Physiological Role and Signalling Properties of Extracellular Membrane Vesicles

    PubMed Central

    Iraci, Nunzio; Leonardi, Tommaso; Gessler, Florian; Vega, Beatriz; Pluchino, Stefano

    2016-01-01

    Extracellular vesicles (EVs) are a heterogeneous population of secreted membrane vesicles, with distinct biogenesis routes, biophysical properties and different functions both in physiological conditions and in disease. The release of EVs is a widespread biological process, which is conserved across species. In recent years, numerous studies have demonstrated that several bioactive molecules are trafficked with(in) EVs, such as microRNAs, mRNAs, proteins and lipids. The understanding of their final impact on the biology of specific target cells remains matter of intense debate in the field. Also, EVs have attracted great interest as potential novel cell-free therapeutics. Here we describe the proposed physiological and pathological functions of EVs, with a particular focus on their molecular content. Also, we discuss the advances in the knowledge of the mechanisms regulating the secretion of EV-associated molecules and the specific pathways activated upon interaction with the target cell, highlighting the role of EVs in the context of the immune system and as mediators of the intercellular signalling in the brain. PMID:26861302

  6. Cryomicroscopic determination of the membrane osmotic properties of human monocytes at subfreezing temperatures.

    PubMed

    McCaa, C; Diller, K R; Aggarwal, S J; Takahashi, T

    1991-08-01

    Monocytes were isolated from fresh whole human blood and resuspended in Hanks balanced salt solution; a portion of the cells was mixed with an equal volume of 2M dimethyl sulfoxide (DMSO) to form a 1 M solution. Microliter volumes of cell suspension were placed directly onto a computer-controlled cryostage and cooled to a predetermined subzero temperature. Ice was nucleated in the extracellular medium and a continuous video record was made of the subsequent osmotically induced volume changes of individual cells owing to exposure to the concentrated extracellular solutes. Selected micrographs emphasizing the initial transient data were digitized for computer analysis with an interactive boundary tracing algorithm to determine metric parameters of specific cells, and apparent volume changes were measured as a function of elapsed time after nucleation. The Kedem-Katchalsky-coupled transport equations were fit to the data using a network thermodynamic model implemented on a microcomputer to determine values for the permeability properties Lp, omega, and sigma. Experiments were performed over the temperature range from -7 degrees to -10 degrees C. Cells pre-equilibrated with DMSO had a lower Lp and a higher activation energy, delta E, than without additive, although the statistical significance of the difference could not be substantiated. It was found that the movement of DMSO across the plasma membrane in response to extracellular freezing was apparently so much smaller than the water flux that values for omega and sigma could not be determined from the data base. PMID:1935177

  7. Synthesis and characterization of polymer electrolyte membranes with controlled ion transport properties

    NASA Astrophysics Data System (ADS)

    Xu, Kui

    2011-12-01

    Ion-containing block copolymers hold promise as next-generation polymer electrolyte membrane (PEM) materials due to their capability to self-assemble into ordered nanostructures facilitating proton transport over a wide range of conditions. Ion-containing block copolymers, sulfonated poly(styrene- b-vinylidene fluoride-b-styrene), with varied degrees of sulfonation were synthesized. The synthetic strategy involved a new approach to chain-end functionalized poly(vinylidene fluoride) as a macro-initiator followed by atom transfer polymerization of styrene and sulfonation. Characterization of the polymers were extensively carried out by 1H and 19F nuclear magnetic resonance and Fouriertransform infrared spectroscopy, differential scanning calorimetry, and thermogravimetry analysis. Tapping mode atomic force microscopy and transmission electron microscopy were applied to study the phase separation and self-assembled morphology. Strong dependence of ion exchange capacity, water absorption, morphology and proton conductivity on the degree of sulfonation has been found. It has been observed that the conductivities of the block copolymers are considerably higher than the random copolymers of polystyrene and sulfonated polystyrene possessing similar ion exchange capacities. Copolymers of vinylidene fluoride and perfluoro(4-methyl-3,6-dioxane-7-ene) sulfonyl fluoride containing amino end-groups were synthesized for the first time. The prepared aminoterminated polymers underwent cross-linking reactions with 1,3,5-benzene triisocyanate to form proton conductive networks. The chain-end crosslinked fluoropolymer membranes exhibited excellent thermal, hydrolytic and oxidative stabilities. The ion exchange capacity, water uptake, the state of absorbed water, and transport properties of the membranes were found to be highly dependent upon the chemical composition of the copolymers. The cross-linked membranes showed extremely low methanol permeability, while maintaining high proton

  8. Tubular dense perovskite type membranes. Preparation, sealing, and oxygen permeation properties

    SciTech Connect

    Li, S.; Qi, H.; Xu, N.; Shi, J.

    1999-12-01

    Tubular dense perovskite type membranes were prepared by isostatic pressing and plastic extrusion. The resulting tubular La{sub 0.6}Sr{sub 0.4}Co{sub 0.2}Fe{sub 0.8}O{sub 3{minus}{delta}} perovskite type membrane prepared by plastic extrusion (designated as PE-LSCF) has a lower density and oxygen permeation flux compared with that prepared by isostatic pressing (designated as IP-LSCF). A ceramic binder developed by the research center provided reliable sealing for the tubular dense membrane at high temperature. The oxygen permeation flux increases with increasing temperature, and the value is about 0.13 cm{sup 3}/cm{sup 2} min (STP) at 1,123 K. The activation energy for oxygen permeation is 168 kJ/mol at the temperature range of 1,073--1,173. X-ray diffraction analysis for the membranes over 110 h of operation indicated that SrSO{sub 4}, CoSO{sub 4}, SrO, Co{sub 2}O{sub 3}, and La{sub 2}O{sub 3} were formed on the surfaces of the tubular membrane, especially for the tubular PE-LSCF membrane, because of interaction with trace SO{sub 2} in the air and the helium and segregation of surface elements.

  9. Dielectric elastomer laminates for active membrane pump applications

    NASA Astrophysics Data System (ADS)

    Pope, Kimberly; Tews, Alyson; Frecker, Mary I.; Mockensturm, Eric; Goulbourne, Nakhiah C.; Snyder, Alan J.

    2004-07-01

    Previous research has demonstrated promise for the use of dielectric elastomer (DE) films in diaphragm pump applications. Because the films tend to be quite thin, single layers operate at very low pressures. To make this technology suitable for practical applications, the films may be organized into laminates which will operate at increased pressures. Radially stretched circular diaphragms of two materials were tested: 3M VHB 4905 polyacrylate and spin-cast Nusil CF19-2186 silicone. The diaphragms were stacked, each layer sharing an electrode with the adjacent layer. The stack was mounted on a sealed chamber and energized at varied electric fields while regulated pressure was applied to the interior chamber, displacing the diaphragm. The pressure-volume properties of the stacks were recorded for each activation state.

  10. Characterization of charge properties of an ultrafiltration membrane modified by surface grafting of poly(allylamine) hydrochloride.

    PubMed

    Dejeu, J; Lakard, B; Fievet, P; Lakard, S

    2009-05-01

    A polyethersulfone ultrafiltration membrane was functionalized by a cationic polyelectrolyte, the poly(allylamine) hydrochloride (PAH). The influence of the time of adsorption of PAH on the membrane charge properties was studied. Several characterization techniques were used to investigate the membrane modification. Tangential and transmembrane streaming potential measurements were conducted to characterize the outer and inner surfaces of the membrane, respectively. Both techniques indicated that the surface modification of the membrane was efficient. The charge of the outer surface was reversed (from negative values for the unmodified membrane to positive values for the modified membrane) and the charge of the inner surface was neutralized after adsorption of the cationic polyelectrolyte onto the pore walls. The modification of both the outer surface of the membrane and the pore walls was also put in evidence with membrane potential measurements. It was found that the charge of the PAH-modified membrane is affected by the time of immersion in PAH solution. Experimental data seem to show a fast modification of the membrane for the first 15 min; nevertheless, the modification was more pronounced after 24 h of PAH adsorption. Diffusion experiments carried out with unmodified and modified membranes for four salts (KCl, NaCl, MgCl, and CaCl(2)) showed a decrease in the salt permeability after functionalization of the membrane. The permeability decrease was greater for 2:1 salts than for 1:1 salts. This decrease was explained by electrostatic interactions. PMID:19215937

  11. New insights into membrane-active action in plasma membrane of fungal hyphae by the lipopeptide antibiotic bacillomycin L.

    PubMed

    Zhang, Bao; Dong, Chunjuan; Shang, Qingmao; Han, Yuzhu; Li, Pinglan

    2013-09-01

    Bacillomycin L, a natural iturinic lipopeptide produced by Bacillus amyloliquefaciens, is characterized by strong antifungal activities against a variety of agronomically important filamentous fungi including Rhizoctonia solani Kühn. Prior to this study, the role of membrane permeabilization in the antimicrobial activity of bacillomycin L against plant pathogenic fungi had not been investigated. To shed light on the mechanism of this antifungal activity, the permeabilization of R. solani hyphae by bacillomycin L was investigated and compared with that by amphotericin B, a polyene antibiotic which is thought to act primarily through membrane disruption. Our results derived from electron microscopy, various fluorescent techniques and gel retardation experiments revealed that the antifungal activity of bacillomycin L may be not solely a consequence of fungal membrane permeabilization, but related to the interaction of it with intracellular targets. Our findings provide more insights into the mode of action of bacillomycin L and other iturins, which could in turn help to develop new or improved antifungal formulations or result in novel strategies to prevent fungal spoilage. PMID:23756779

  12. Influence of activating hormones on human platelet membrane Ca/sup 2 +/-ATPase activity

    SciTech Connect

    Resink, T.J.; Dimitrov, D.; Stucki, S.; Buehler, F.R.

    1986-07-16

    Intact platelets were pretreated with hormones and thereafter membranes were prepared and Ca/sup 2 +/-ATPase activity determined. Thrombin decreased the V/sub max/ of Ca/sup 2 +/-ATPase after pretreatment of intact platelets. Platelet activating factor, vasopressin and ADP also decreased Ca/sup 2 +/-ATPase activity. 12-O-tetradecanoylphorbol-13-acetate (TPA) or A23187 or ionomycin alone had no effect, while the simultaneous pretreatment with TPA and Ca/sup 2 +/-ionophore decreased Ca/sup 2 +/-ATPase activity. cAMP elevating agents prostaglandin E/sub 1/ (PGE/sub 1/) and forskolin had no influence per se on Ca/sup 2 +/-ATPase, but antagonized the inhibitory effect of thrombin. The data suggest a close connection between phosphoinositide metabolism and the Ca/sup 2 +/-ATPase system.

  13. Functional, photochemically active, and chemically asymmetric membranes by interfacial polymerization of derivatized multifunctional prepolymers

    DOEpatents

    Lonsdale, Harold K.; Wamser, Carl C.

    1988-01-01

    The preparation of a novel class of thin film membranes by interfacial polymerization is disclosed, said membanes incorporating as part of their polymeric structure the functionality of monomeric or oligomeric precursors. Specific embodiments include porphyrin and phthalocyanime derivatives that are photochemically or electrochemically active, as well as chemically asymmetric membranes.

  14. One-way membrane trafficking of SOS in receptor-triggered Ras activation.

    PubMed

    Christensen, Sune M; Tu, Hsiung-Lin; Jun, Jesse E; Alvarez, Steven; Triplet, Meredith G; Iwig, Jeffrey S; Yadav, Kamlesh K; Bar-Sagi, Dafna; Roose, Jeroen P; Groves, Jay T

    2016-09-01

    SOS is a key activator of the small GTPase Ras. In cells, SOS-Ras signaling is thought to be initiated predominantly by membrane recruitment of SOS via the adaptor Grb2 and balanced by rapidly reversible Grb2-SOS binding kinetics. However, SOS has multiple protein and lipid interactions that provide linkage to the membrane. In reconstituted-membrane experiments, these Grb2-independent interactions were sufficient to retain human SOS on the membrane for many minutes, during which a single SOS molecule could processively activate thousands of Ras molecules. These observations raised questions concerning how receptors maintain control of SOS in cells and how membrane-recruited SOS is ultimately released. We addressed these questions in quantitative assays of reconstituted SOS-deficient chicken B-cell signaling systems combined with single-molecule measurements in supported membranes. These studies revealed an essentially one-way trafficking process in which membrane-recruited SOS remains trapped on the membrane and continuously activates Ras until being actively removed via endocytosis. PMID:27501536

  15. Active membrane transport and receptor proteins from bacteria.

    PubMed

    Saidijam, M; Bettaney, K E; Szakonyi, G; Psakis, G; Shibayama, K; Suzuki, S; Clough, J L; Blessie, V; Abu-Bakr, A; Baumberg, S; Meuller, J; Hoyle, C K; Palmer, S L; Butaye, P; Walravens, K; Patching, S G; O'reilly, J; Rutherford, N G; Bill, R M; Roper, D I; Phillips-Jones, M K; Henderson, P J F

    2005-08-01

    A general strategy for the expression of bacterial membrane transport and receptor genes in Escherichia coli is described. Expression is amplified so that the encoded proteins comprise 5-35% of E. coli inner membrane protein. Depending upon their topology, proteins are produced with RGSH6 or a Strep tag at the C-terminus. These enable purification in mg quantities for crystallization and NMR studies. Examples of one nutrient uptake and one multidrug extrusion protein from Helicobacter pylori are described. This strategy is successful for membrane proteins from H. pylori, E. coli, Enterococcus faecalis, Bacillus subtilis, Staphylococcus aureus, Microbacterium liquefaciens, Brucella abortus, Brucella melitensis, Campylobacter jejuni, Neisseria meningitides, Streptomyces coelicolor and Rhodobacter sphaeroides. PMID:16042616

  16. Novel Pendant Benzene Disulfonic Acid Blended SPPO Membranes for Alkali Recovery: Fabrication and Properties.

    PubMed

    Mondal, Abhishek N; Dai, Chunhua; Pan, Jiefeng; Zheng, Chunlei; Hossain, Md Masem; Khan, Muhammad Imran; Wu, Liang; Xu, Tongwen

    2015-07-29

    To reconcile the trade-off between separation performance and availability of desired material for cation exchange membranes (CEMs), we designed and successfully prepared a novel sulfonated aromatic backbone-based cation exchange precursor named sodium 4,4'-(((((3,3'-disulfo-[1,1'-biphenyl]-4,4'-diyl)bis(oxy)) bis(4,1-phenylene))bis(azanediyl))bis(methylene))bis(benzene-1,3-disulfonate) [DSBPB] from 4,4'-bis(4-aminophenoxy)-[1,1'-biphenyl]-3,3'-disulfonic acid [BAPBDS] by a three-step procedure that included sulfonation, Michael condensation followed by reduction. Prepared DSBPB was used to blend with sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) to get CEMs for alkali recovery via diffusion dialysis. Physiochemical properties and electrochemical performance of prepared membranes can be tuned by varying the dosage of DSBPB. All the thermo-mechanical properties like DMA and TGA were investigated along with water uptake (WR), ion exchange capacity (IEC), dimensional stability, etc. The effect of DSBPB was discussed in brief in connection with alkali recovery and ion conducting channels. The SPPO/DSBPB membranes possess both high water uptake as well as ion exchange capacity with high thermo-mechanical stability. At 25 °C the dialysis coefficients (UOH) appeared to be in the range of 0.0048-0.00814 m/h, whereas the separation factor (S) ranged from 12.61 to 36.88 when the membranes were tested for base recovery in Na2WO4/NaOH waste solution. Prepared membranes showed much improved DD performances compared to traditional SPPO membrane and possess the potentiality to be a promising candidate for alkali recovery via diffusion dialysis. PMID:26146932

  17. Lipid composition and sensitivity of Prototheca wickerhamii to membrane-active antimicrobial agents.

    PubMed Central

    Sud, I J; Feingold, D S

    1979-01-01

    The lipid composition of Prototheca wickerhamii ATCC 16529 is presented and discussed in relation to the unique susceptibility of the organism to drugs of three membrane-active antimicrobial classes: the polyenes, the polymyxins, and the imidazoles. The presence of ergosterol in the neutral lipid fraction of the membrane is likely responsible for the exquisite susceptibility to amphotericin B. The presence of a large quantity of free fatty acids in the membrane appears responsible for imidazole susceptibility. The membrane determinants of polymyxin B susceptibility are less well defined. PMID:518077

  18. Atomic layer deposition of SIO2 on porous alumina membranes: controlling the pore size and transport properties

    NASA Astrophysics Data System (ADS)

    Velleman, Leonora; Traini, Gerry; Evans, Peter J.; Atanacio, Armand; Shapter, Joe G.; Losic, Dusan

    2008-12-01

    Atomic layer deposition (ALD) of SiO2 onto nanoporous alumina (PA) membranes was investigated with the aim of adjusting the pore size and transport properties. PA membranes from commercial sources with a range of pore diameters (20 nm, 100 nm and 200 nm) were used and modified by atomic layer deposition using tris(tert-butoxy)silanol and water as the precursor couple. By adjusting the number of deposition cycles, the thickness of the conformal silica coating was controlled, reducing the effective pore diameter, and subsequently changing the transport properties of the PA membrane. Silica coated PA membranes with desired pore diameters from <5 nm to 100 nm were fabricated. In addition to the pore size, the transport properties and selectivity of fabricated silica coated PA membranes were controlled by chemical functionalisation using a silane with hydrophobic properties. Structural and chemical properties of modified membranes were studied by dynamic secondary ion mass spectrometry (DSIMS) and scanning electron microscopy (SEM). Spectrophotometric methods were used to evaluate the transport properties and selectivity of silica coated membranes by permeation studies of hydrophobic and hydrophilic organic molecules. The resultant silica/PA membranes with specific surface chemistry and controlled pore size are applicable for molecular separation, cell culture, bioreactors, biosensing and drug delivery.

  19. Sar1 GTPase Activity Is Regulated by Membrane Curvature*♦

    PubMed Central

    Hanna, Michael G.; Mela, Ioanna; Wang, Lei; Henderson, Robert M.; Chapman, Edwin R.; Edwardson, J. Michael; Audhya, Anjon

    2016-01-01

    The majority of biosynthetic secretory proteins initiate their journey through the endomembrane system from specific subdomains of the endoplasmic reticulum. At these locations, coated transport carriers are generated, with the Sar1 GTPase playing a critical role in membrane bending, recruitment of coat components, and nascent vesicle formation. How these events are appropriately coordinated remains poorly understood. Here, we demonstrate that Sar1 acts as the curvature-sensing component of the COPII coat complex and highlight the ability of Sar1 to bind more avidly to membranes of high curvature. Additionally, using an atomic force microscopy-based approach, we further show that the intrinsic GTPase activity of Sar1 is necessary for remodeling lipid bilayers. Consistent with this idea, Sar1-mediated membrane remodeling is dramatically accelerated in the presence of its guanine nucleotide-activating protein (GAP), Sec23-Sec24, and blocked upon addition of guanosine-5′-[(β,γ)-imido]triphosphate, a poorly hydrolysable analog of GTP. Our results also indicate that Sar1 GTPase activity is stimulated by membranes that exhibit elevated curvature, potentially enabling Sar1 membrane scission activity to be spatially restricted to highly bent membranes that are characteristic of a bud neck. Taken together, our data support a stepwise model in which the amino-terminal amphipathic helix of GTP-bound Sar1 stably penetrates the endoplasmic reticulum membrane, promoting local membrane deformation. As membrane bending increases, Sar1 membrane binding is elevated, ultimately culminating in GTP hydrolysis, which may destabilize the bilayer sufficiently to facilitate membrane fission. PMID:26546679

  20. Active endocannabinoids are secreted on extracellular membrane vesicles.

    PubMed

    Gabrielli, Martina; Battista, Natalia; Riganti, Loredana; Prada, Ilaria; Antonucci, Flavia; Cantone, Laura; Matteoli, Michela; Maccarrone, Mauro; Verderio, Claudia

    2015-02-01

    Endocannabinoids primarily influence neuronal synaptic communication within the nervous system. To exert their function, endocannabinoids need to travel across the intercellular space. However, how hydrophobic endocannabinoids cross cell membranes and move extracellularly remains an unresolved problem. Here, we show that endocannabinoids are secreted through extracellular membrane vesicles produced by microglial cells. We demonstrate that microglial extracellular vesicles carry on their surface N-arachidonoylethanolamine (AEA), which is able to stimulate type-1 cannabinoid receptors (CB1), and inhibit presynaptic transmission, in target GABAergic neurons. This is the first demonstration of a functional role of extracellular vesicular transport of endocannabinoids. PMID:25568329

  1. Silylated mesoporous silica membranes on polymeric hollow fiber supports: synthesis and permeation properties.

    PubMed

    Kim, Hyung-Ju; Brunelli, Nicholas A; Brown, Andrew J; Jang, Kwang-Suk; Kim, Wun-gwi; Rashidi, Fereshteh; Johnson, Justin R; Koros, William J; Jones, Christopher W; Nair, Sankar

    2014-10-22

    We report the synthesis and organic/water separation properties of mesoporous silica membranes, supported on low-cost and scalable polymeric (polyamide-imide) hollow fibers, and modified by trimethylsilylation with hexamethyldisilazane. Thin (∼1 μm) defect-free membranes are prepared, with high room-temperature gas permeances (e.g., 20,000 GPU for N2). The membrane morphology is characterized by multiple techniques, including SEM, TEM, XRD, and FT-ATR spectroscopy. Silylation leads to capping of the surface silanol groups in the mesopores with trimethylsilyl groups, and does not affect the integrity of the mesoporous silica structure and the underlying hollow fiber. The silylated membranes are evaluated for pervaporative separation of ethanol (EtOH), methylethyl ketone (MEK), ethyl acetate (EA), iso-butanol (i-BuOH), and n-butanol (n-BuOH) from their dilute (5 wt %) aqueous solutions. The membranes show separation factors in the range of 4-90 and high organic fluxes in the range of 0.18-2.15 kg m(-2) h(-1) at 303 K. The intrinsic selectivities (organic/water permeability ratios) of the silylated membranes at 303 K are 0.33 (EtOH/water), 0.5 (MEK/water), 0.25 (EA/water), 1.25 (i-BuOH/water), and 1.67 (n-BuOH/water) respectively, in comparison to 0.05, 0.015, 0.005, 0.08, and 0.14 for the unmodified membranes. The silylated membranes allow upgradation of water/organics feeds to permeate streams with considerably higher organics content. The selective and high-flux separation is attributed to both the organophilic nature of the modified mesopores and the large effective pore size. Comparison with other organics/water separation membranes reveals that the present membranes show promise due to high flux, use of scalable and low-cost supports, and good separation factors that can be further enhanced by tailoring the mesopore silylation chemistry. PMID:25255051

  2. Effects of vegetable oils on biochemical and biophysical properties of membrane retinal pigment epithelium cells.

    PubMed

    Said, Toihiri; Tremblay-Mercier, Jennifer; Berrougui, Hicham; Rat, Patrice; Khalil, Abdelouahed

    2013-10-01

    The aim of this study was to investigate the effect of vegetable oil enrichment of retinal pigment epithelial (RPE) cells on their biochemical and biophysical properties. For this, RPE cells were incubated with 4 different vegetables oils (olive oil, corn oil, argan oil, and camelina oil). The cytotoxicity of these vegetable oils was assessed in vivo on 8-week-old mice and in vitro by using the neutral red and YO-PRO-1 tests. Membrane fluidity was evaluated by fluorescence anisotropy using the fluorescent probe diphenylhexatriene, and membrane fatty acid composition was assessed by gas chromatography. None of the oils tested displayed cytotoxic effects. In vitro, omega-3 rich oils improved membrane fluidity by 47% compared with the control cells. The omega-3 PUFA content within membranes decreased by 38% to 55% when cells were incubated separately with olive oil, corn oil, or argan oil, and increased when cells were incubated with a mixture of those oils, or with camelina oil alone (50% and 103% increase, respectively). Our results show that the fatty acids in vegetable oil incorporate into retinal cells and increase the plasma membrane fluidity. PMID:24144052

  3. Fluorescence properties of the envelope membranes from spinach chloroplasts. Detection of protochlorophyllide.

    PubMed

    Pineau, B; Dubertret, G; Joyard, J; Douce, R

    1986-07-15

    At 77 K, under excitation at 440 nm, two major fluorescence emission peaks were observed in envelope membranes from spinach chloroplasts at 636 and 680 nm. A narrow range of wavelengths around 440 nm and a wider range of wavelengths between 390 and 440 nm, respectively, were responsible for excitation of the 636 and 680 nm fluorescence emissions which, in marked contrast with thylakoid fluorescence emission, were devoid of any exciting components between 460 and 500 nm. In acetonic extract of envelope membranes, two fluorescence emission peaks were observed at 635 and 675 nm. After extraction of the acetonic solution by nonpolar solvents (petroleum ether or hexane), the 675 nm fluorescence emission was partitioned between the polar and nonpolar phases whereas the 635 nm fluorescence emission was solely recovered in the polar phase. All together, the results obtained suggest that envelope membranes contain low amounts of pigments having the absorption and fluorescence spectroscopic properties, together with the behavior in polar/nonpolar solvents, of protochlorophyllide and chlorophyllide. In addition, modulation of the level of fluorescence at 636 and 680 nm could be obtained by addition of NADPH to envelope membranes under illumination. The presence of protochlorophyllide in chloroplast envelope membranes together with its possible photoconversion into chlorophyllide could have major implication for the understanding of chlorophyll biosynthesis in mature chloroplasts. PMID:3722197

  4. Uncoupling the Structure-Activity Relationships of β2 Adrenergic Receptor Ligands from Membrane Binding.

    PubMed

    Dickson, Callum J; Hornak, Viktor; Velez-Vega, Camilo; McKay, Daniel J J; Reilly, John; Sandham, David A; Shaw, Duncan; Fairhurst, Robin A; Charlton, Steven J; Sykes, David A; Pearlstein, Robert A; Duca, Jose S

    2016-06-23

    Ligand binding to membrane proteins may be significantly influenced by the interaction of ligands with the membrane. In particular, the microscopic ligand concentration within the membrane surface solvation layer may exceed that in bulk solvent, resulting in overestimation of the intrinsic protein-ligand binding contribution to the apparent/measured affinity. Using published binding data for a set of small molecules with the β2 adrenergic receptor, we demonstrate that deconvolution of membrane and protein binding contributions allows for improved structure-activity relationship analysis and structure-based drug design. Molecular dynamics simulations of ligand bound membrane protein complexes were used to validate binding poses, allowing analysis of key interactions and binding site solvation to develop structure-activity relationships of β2 ligand binding. The resulting relationships are consistent with intrinsic binding affinity (corrected for membrane interaction). The successful structure-based design of ligands targeting membrane proteins may require an assessment of membrane affinity to uncouple protein binding from membrane interactions. PMID:27239696

  5. Improved Methanol Barrier Property of Nafion Hybrid Membrane by Incorporating Nanofibrous Interlayer Self-Immobilized with High Level of Phosphotungstic Acid.

    PubMed

    Abouzari-lotf, Ebrahim; Nasef, Mohamed Mahmoud; Ghassemi, Hossein; Zakeri, Masoumeh; Ahmad, Arshad; Abdollahi, Yadollah

    2015-08-12

    High level of phosphotungstic acid (PWA) was self-immobilized on electrospun nylon nanofiberous sheet to fabricate highly selective methanol barrier layer for sandwich structured proton conducting membranes. Simple tuning for the assembly conditions of central layer and thickness of outer Nafion layers allowed obtaining different composite membranes with superior methanol barrier properties (namely, P=3.59×10(-8) cm2 s(-1)) coupled with proton conductivities reaching 58.6 mS cm(-1) at 30 °C. Comparable activation energy for proton transport and more than 20 times higher selectivity than Nafion 115 confirm the effectiveness of the central layer and resulting membranes for application in direct methanol fuel cells (DMFCs). When tested in DMFC single cell, the performance of hybrid membrane was far better than Nafion 115 especially at higher methanol concentrations. PMID:26196374

  6. Neomycin inhibits the phosphatidylinositol monophosphate and phosphatidylinositol bisphosphate stimulation of plasma membrane ATPase activity

    SciTech Connect

    Chen, Qiuyun; Boss, W.F. )

    1991-05-01

    The inositol phospholipids, phosphatidylinositol monophosphate (PIP) and phosphatidylinositol bisphosphate (PIP{sub 2}), have been shown to increase the vanadate-sensitive ATPase activity of plant plasma membranes. In this paper, the authors show the effect of various concentrations of phosphatidyinositol, PIP, and PIP{sub 2} on the plasma membrane vanadate-sensitive ATPase activity. PIP and PIP{sub 2} at concentrations at 10 nanomoles per 30 microgram membrane protein per milliliter of reaction mixture caused a twofold and 1.8-fold increase in the ATPase activity, respectively. The effect of these negatively charged phospholipids on the ATPase activity was inhibited by adding the positively charged aminoglycoside, neomycin. Neomycin did not affect the endogenous plasma membrane ATPase activity in the absence of exogenous lipids.

  7. Influence of polar and nonpolar carotenoids on structural and adhesive properties of model membranes.

    PubMed

    Augustynska, Dominika; Jemioła-Rzemińska, Małgorzata; Burda, Kvetoslava; Strzałka, Kazimierz

    2015-09-01

    Carotenoids, which are known primarily for their photoprotective and antioxidant properties, may also strongly influence the physical properties of membranes. The localization and orientation of these pigments in the lipid bilayer depends on their structure and is determined by their interactions with lipid molecules. This affects both phase behavior and the mechanical properties of membranes. Differential scanning calorimetry (DSC) and atomic force microscopy (AFM) allowed us to gain a direct insight into the differences between the interaction of the non-polar β-carotene and polar zeaxanthin embedded into DPPC liposomes. DSC results showed that zeaxanthin, having polar ionone rings, interacts more strongly with the membrane lipids than β-carotene. The decrease in molar heat capacity by a factor of 2 with a simultaneous broadening of the main phase transition (gel-to-liquid crystalline phase transition) as compared to the two other systems studied suggests some increased length of the coupled interactions between the polar xanthophyll and lipids. Long-distance interactions lead to the formation of larger clusters which may exhibit higher flexibility than small clusters when only short-distance interactions occur. AFM experiments show that adhesive forces are 2 and 10 times higher for DPPC membranes enriched in β-carotene and zeaxanthin, respectively, than those observed for an untreated system. Temperature dependent measurements of adhesion revealed that subphases can be formed in the gel lamellar state of DPPC bilayers. The presence of the non-polar carotenoid enhanced the effect and even a bifurcation of the substates was detected within a temperature range of 30.0-32.5°C prior to pretransition. It is the first time when the presence of subphases has been demonstrated. This knowledge can be helpful in better understanding the functioning of carotenoids in biological membranes. AFM seem to be a very unique and sensitive method for detecting such fine changes

  8. Membrane lipids regulate ganglioside GM2 catabolism and GM2 activator protein activity.

    PubMed

    Anheuser, Susi; Breiden, Bernadette; Schwarzmann, Günter; Sandhoff, Konrad

    2015-09-01

    Ganglioside GM2 is the major lysosomal storage compound of Tay-Sachs disease. It also accumulates in Niemann-Pick disease types A and B with primary storage of SM and with cholesterol in type C. Reconstitution of GM2 catabolism with β-hexosaminidase A and GM2 activator protein (GM2AP) at uncharged liposomal surfaces carrying GM2 as substrate generated only a physiologically irrelevant catabolic rate, even at pH 4.2. However, incorporation of anionic phospholipids into the GM2 carrying liposomes stimulated GM2 hydrolysis more than 10-fold, while the incorporation of plasma membrane stabilizing lipids (SM and cholesterol) generated a strong inhibition of GM2 hydrolysis, even in the presence of anionic phospholipids. Mobilization of membrane lipids by GM2AP was also inhibited in the presence of cholesterol or SM, as revealed by surface plasmon resonance studies. These lipids also reduced the interliposomal transfer rate of 2-NBD-GM1 by GM2AP, as observed in assays using Förster resonance energy transfer. Our data raise major concerns about the usage of recombinant His-tagged GM2AP compared with untagged protein. The former binds more strongly to anionic GM2-carrying liposomal surfaces, increases GM2 hydrolysis, and accelerates intermembrane transfer of 2-NBD-GM1, but does not mobilize membrane lipids. PMID:26175473

  9. Preparation of a novel positively charged nanofiltration composite membrane incorporated with silver nanoparticles for pharmaceuticals and personal care product rejection and antibacterial properties.

    PubMed

    Huang, Zhong-Hua; Yin, Yan-Na; Aikebaier, Gu-li-mi-la; Zhang, Yan

    2016-01-01

    A novel positively charged N-[(2-hydroxy-3-trimethylammonium)propyl] chloride chitosan (HTCC)-Ag/polyethersulfone (PES) composite nanofiltration membrane was easily prepared by coating the active layer, HTCC, onto PES as the support through epichlorohydrin as the cross-linking reagent and nano-Ag particles as the introduced inorganic components. Scanning election microscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and X-ray diffraction were employed to characterize the morphology of the resultant membranes, of which the molecular weight cut-off was about 941 Da. At 25 °C, the pure water permeability is 16.27 L/h·m(2)·MPa. Our results showed that the rejection of pharmaceuticals and personal care products (PPCPs) followed the sequence: atenolol > carbamazepine > ibuprofen, confirming that the membranes were positively charged. The antibacterial properties of the membranes were compared to elucidate the existence of Ag nanoparticles which help to improve antibacterial activity against Gram-negative Escherichia coli (DH5α, Rosetta) and Gram-positive Bacillus subtilis. The inhibition zone diameters of HTCC-Ag/PES membranes towards E. coli DH5α, E. coli Rosetta and Bacillus subtilis were 17.77, 16.18, and 15.44 mm, respectively. It was found that HTCC-Ag/PES membrane has a better antibacterial activity against E. coli than against Bacillus subtilis, especially for E. coli DH5α. PMID:27120646

  10. Erythrocyte membrane modifying agents and the inhibition of Plasmodium falciparum growth: structure-activity relationships for betulinic acid analogues.

    PubMed

    Ziegler, Hanne L; Franzyk, Henrik; Sairafianpour, Majid; Tabatabai, Mehrnoush; Tehrani, Mahboubeh D; Bagherzadeh, Karim; Hägerstrand, Henry; Staerk, Dan; Jaroszewski, Jerzy W

    2004-01-01

    The natural triterpene betulinic acid and its analogues (betulinic aldehyde, lupeol, betulin, methyl betulinate and betulinic acid amide) caused concentration-dependent alterations of erythrocyte membrane shape towards stomatocytes or echinocytes according to their hydrogen bonding properties. Thus, the analogues with a functional group having a capacity of donating a hydrogen bond (COOH, CH(2)OH, CONH(2)) caused formation of echinocytes, whereas those lacking this ability (CH(3), CHO, COOCH(3)) induced formation of stomatocytes. Both kinds of erythrocyte alterations were prohibitive with respect to Plasmodium falciparum invasion and growth; all compounds were inhibitory with IC(50) values in the range 7-28 microM, and the growth inhibition correlated well with the extent of membrane curvature changes assessed by transmission electron microscopy. Erythrocytes pre-loaded with betulinic acid or its analogues and extensively washed in order to remove excess of the chemicals could not serve as hosts for P. falciparum parasites. Betulinic acid and congeners can be responsible for in vitro antiplasmodial activity of plant extracts, as shown for Zataria multiflora Boiss. (Labiatae) and Zizyphus vulgaris Lam. (Rhamnaceae). The activity is evidently due to the incorporation of the compounds into the lipid bilayer of erythrocytes, and may be caused by modifications of cholesterol-rich membrane rafts, recently shown to play an important role in parasite vacuolization. The established link between erythrocyte membrane modifications and antiplasmodial activity may provide a novel target for potential antimalarial drugs. PMID:14697777

  11. Role of liquid membrane phenomenon in the anti-bacterial activity of Cefuroxime Sodium

    PubMed Central

    Nagesh, C.; Shankaraiah, M. M.; Venkatesh, J. S.; Setty, S. Ramachandra

    2010-01-01

    The role of liquid membrane phenomenon has been studied in the anti bacterial activity of cephalosporins i.e. Cefuroxime sodium. In our earlier publication [1] it was reported that hydraulic permeability data obtained to demonstrate the existence of liquid membrane in series with supporting membrane generated by Cefuroxime sodium. Transport of selected permeants (glucose, PABA, glycine, and ions like Mg++, NH4+, PO4-, Ca++, Na+, K+ and Cl-) through liquid membrane generated by Cefuroxime sodium in series with supporting membrane has been studied. The results indicated that the liquid membrane generated by Cefuroxime sodium inhibit the transport of various essential bio-molecules and permeants in to the cell. This modification in permeability of different permeants in the presence of the liquid membranes is likely to play significant role in the biological actions of Cefuroxime sodium. The anti-bacterial activity of Cefuroxime sodium further confirmed that the generation of liquid membrane by Cefuroxime sodium is also contributing for the antibacterial activity of them. PMID:24825969

  12. Correlation of Daptomycin Bactericidal Activity and Membrane Depolarization in Staphylococcus aureus

    PubMed Central

    Silverman, Jared A.; Perlmutter, Nancy G.; Shapiro, Howard M.

    2003-01-01

    The objective of this study was to further elucidate the role of membrane potential in the mechanism of action of daptomycin, a novel lipopeptide antibiotic. Membrane depolarization was measured by both fluorimetric and flow cytometric assays. Adding daptomycin (5 μg/ml) to Staphylococcus aureus gradually dissipated membrane potential. In both assays, cell viability was reduced by >99% and membrane potential was reduced by >90% within 30 min of adding daptomycin. Cell viability decreased in parallel with changes in membrane potential, demonstrating a temporal correlation between bactericidal activity and membrane depolarization. Decreases in viability and potential also showed a dose-dependent correlation. Depolarization is indicative of ion movement across the cytoplasmic membrane. Fluorescent probes were used to demonstrate Ca2+-dependent, daptomycin-triggered potassium release from S. aureus. Potassium release was also correlated with bactericidal activity. This study demonstrates a clear correlation between dissipation of membrane potential and the bactericidal activity of daptomycin. A multistep model for daptomycin's mechanism of action is proposed. PMID:12878516

  13. Plasma Membrane ATPase Activity following Reversible and Irreversible Freezing Injury 1

    PubMed Central

    Iswari, S.; Palta, Jiwan P.

    1989-01-01

    Plasma membrane ATPase has been proposed as a site of functional alteration during early stages of freezing injury. To test this, plasma membrane was purified from Solanum leaflets by a single step partitioning of microsomes in a dextran-polyethylene glycol two phase system. Addition of lysolecithin in the ATPase assay produced up to 10-fold increase in ATPase activity. ATPase activity was specific for ATP with a Km around 0.4 millimolar. Presence of the ATPase enzyme was identified by immunoblotting with oat ATPase antibodies. Using the phase partitioning method, plasma membrane was isolated from Solanum commersonii leaflets which had four different degrees of freezing damage, namely, slight (reversible), partial (partially reversible), substantial and total (irreversible). With slight (reversible) damage the plasma membrane ATPase specific activity increased 1.5- to 2-fold and its Km was decreased by about 3-fold, whereas the specific activity of cytochrome c reductase and cytochrome c oxidase in the microsomes were not different from the control. However, with substantial (lethal, irreversible) damage, there was a loss of membrane protein, decrease in plasma membrane ATPase specific activity and decrease in Km, while cytochrome c oxidase and cytochrome c reductase were unaffected. These results support the hypothesis that plasma membrane ATPase is altered by slight freeze-thaw stress. Images Figure 1 Figure 2 PMID:16666856

  14. Tetraspanins regulate the protrusive activities of cell membrane

    SciTech Connect

    Bari, Rafijul; Guo, Qiusha; Zhongnan Hospital, Wuhan University, Wuhan ; Xia, Bing; Zhang, Yanhui H.; Giesert, Eldon E.; Levy, Shoshana; Zheng, Jie J.; Zhang, Xin A.

    2011-12-02

    Highlights: Black-Right-Pointing-Pointer Tetraspanins regulate microvillus formation. Black-Right-Pointing-Pointer Tetraspanin CD81 promotes microvillus formation. Black-Right-Pointing-Pointer Tetraspanin CD82 inhibits microvillus formation. Black-Right-Pointing-Pointer Based on this study, we extrapolated a general cellular mechanism for tetraspanins. Black-Right-Pointing-Pointer Tetraspanins engage various functions by regulating membrane protrusion morphogenesis. -- Abstract: Tetraspanins have gained increased attention due to their functional versatility. But the universal cellular mechanism that governs such versatility remains unknown. Herein we present the evidence that tetraspanins CD81 and CD82 regulate the formation and/or development of cell membrane protrusions. We analyzed the ultrastructure of the cells in which a tetraspanin is either overexpressed or ablated using transmission electron microscopy. The numbers of microvilli on the cell surface were counted, and the radii of microvillar tips and the lengths of microvilli were measured. We found that tetraspanin CD81 promotes the microvillus formation and/or extension while tetraspanin CD82 inhibits these events. In addition, CD81 enhances the outward bending of the plasma membrane while CD82 inhibits it. We also found that CD81 and CD82 proteins are localized at microvilli using immunofluorescence. CD82 regulates microvillus morphogenesis likely by altering the plasma membrane curvature and/or the cortical actin cytoskeletal organization. We predict that membrane protrusions embody a common morphological phenotype and cellular mechanism for, at least some if not all, tetraspanins. The differential effects of tetraspanins on microvilli likely lead to the functional diversification of tetraspanins and appear to correlate with their functional propensity.

  15. Killing of Staphylococci by θ-Defensins Involves Membrane Impairment and Activation of Autolytic Enzymes

    PubMed Central

    Wilmes, Miriam; Stockem, Marina; Bierbaum, Gabriele; Schlag, Martin; Götz, Friedrich; Tran, Dat Q.; Schaal, Justin B.; Ouellette, André J.; Selsted, Michael E.; Sahl, Hans-Georg

    2014-01-01

    θ-Defensins are cyclic antimicrobial peptides expressed in leukocytes of Old world monkeys. To get insight into their antibacterial mode of action, we studied the activity of RTDs (rhesus macaque θ-defensins) against staphylococci. We found that in contrast to other defensins, RTDs do not interfere with peptidoglycan biosynthesis, but rather induce bacterial lysis in staphylococci by interaction with the bacterial membrane and/or release of cell wall lytic enzymes. Potassium efflux experiments and membrane potential measurements revealed that the membrane impairment by RTDs strongly depends on the energization of the membrane. In addition, RTD treatment caused the release of Atl-derived cell wall lytic enzymes probably by interaction with membrane-bound lipoteichoic acid. Thus, the premature and uncontrolled activity of these enzymes contributes strongly to the overall killing by θ-defensins. Interestingly, a similar mode of action has been described for Pep5, an antimicrobial peptide of bacterial origin. PMID:25632351

  16. Immobilization and activity assay of cytochrome P450 on patterned lipid membranes

    SciTech Connect

    Ueda, Yoshihiro; Morigaki, Kenichi . E-mail: morigaki-kenichi@aist.go.jp; Tatsu, Yoshiro; Yumoto, Noboru; Imaishi, Hiromasa . E-mail: himaish@kobe-u.ac.jp

    2007-04-20

    We report on a methodology for immobilizing cytochrome P450 on the surface of micropatterned lipid bilayer membranes and measuring the enzymatic activity. The patterned bilayer comprised a matrix of polymeric lipid bilayers and embedded fluid lipid bilayers. The polymeric lipid bilayer domains act as a barrier to confine fluid lipid bilayers in defined areas and as a framework to stabilize embedded membranes. The fluid bilayer domains, on the other hand, can contain lipid compositions that facilitate the fusion between lipid membranes, and are intended to be used as the binding agent of microsomes containing rat CYP1A1. By optimizing the membrane compositions of the fluid bilayers, we could selectively immobilize microsomal membranes on these domains. The enzymatic activity was significantly higher on lipid bilayer substrates compared with direct adsorption on glass. Furthermore, competitive assay experiment between two fluorogenic substrates demonstrated the feasibility of bioassays based on immobilized P450s.

  17. Immobilization and activity assay of cytochrome P450 on patterned lipid membranes.

    PubMed

    Ueda, Yoshihiro; Morigaki, Kenichi; Tatsu, Yoshiro; Yumoto, Noboru; Imaishi, Hiromasa

    2007-04-20

    We report on a methodology for immobilizing cytochrome P450 on the surface of micropatterned lipid bilayer membranes and measuring the enzymatic activity. The patterned bilayer comprised a matrix of polymeric lipid bilayers and embedded fluid lipid bilayers. The polymeric lipid bilayer domains act as a barrier to confine fluid lipid bilayers in defined areas and as a framework to stabilize embedded membranes. The fluid bilayer domains, on the other hand, can contain lipid compositions that facilitate the fusion between lipid membranes, and are intended to be used as the binding agent of microsomes containing rat CYP1A1. By optimizing the membrane compositions of the fluid bilayers, we could selectively immobilize microsomal membranes on these domains. The enzymatic activity was significantly higher on lipid bilayer substrates compared with direct adsorption on glass. Furthermore, competitive assay experiment between two fluorogenic substrates demonstrated the feasibility of bioassays based on immobilized P450s. PMID:17335776

  18. Activated pathways for the directed insertion of patterned nanoparticles into polymer membranes.

    PubMed

    Ting, Christina L; Frischknecht, Amalie L

    2013-10-28

    We combine the string method with self-consistent field theory to compute the most probable transition pathway, i.e. the minimum free energy path, for the insertion of Janus and protein-like nanoparticles into a polymer membrane bilayer. The method makes no assumptions in the reaction coordinate and overcomes the long timescales challenge associated with simulating rare events. Our study suggests that one approach to building functional polymer–nanoparticle composite membranes with oriented nanoparticles is through electrostatic interactions. In particular, hydrophobic Janus nanoparticles with an asymmetric charge distribution can be made to directionally insert into charged membranes. This process is kinetically driven, and involves overcoming a thermally surmountable activation barrier, which requires favorable interactions between the nanoparticle and the hydrophilic block of the membrane. In contrast, the insertion of protein-like nanoparticles with alternating hydrophilic–hydrophobic–hydrophilic domains into polymer membranes does not occur as a thermally activated event. PMID:26029770

  19. Formation and Properties of Membrane-Ordered Domains by Phytoceramide: Role of Sphingoid Base Hydroxylation.

    PubMed

    Marquês, Joaquim T; Cordeiro, André M; Viana, Ana S; Herrmann, Andreas; Marinho, H Susana; de Almeida, Rodrigo F M

    2015-09-01

    Phytoceramide is the backbone of major sphingolipids in fungi and plants and is essential in several tissues of animal organisms, such as human skin. Its sphingoid base, phytosphingosine, differs from that usually found in mammals by the addition of a hydroxyl group to the 4-ene, which may be a crucial factor for the different properties of membrane microdomains among those organisms and tissues. Recently, sphingolipid hydroxylation in animal cells emerged as a key feature in several physiopathological processes. Hence, the study of the biophysical properties of phytosphingolipids is also relevant in that context since it helps us to understand the effects of sphingolipid hydroxylation. In this work, binary mixtures of N-stearoyl-phytoceramide (PhyCer) with palmitoyloleoylphosphatidylcholine (POPC) were studied. Steady-state and time-resolved fluorescence of membrane probes, X-ray diffraction, atomic force microscopy, and confocal microscopy were employed. As for other saturated ceramides, highly rigid gel domains start to form with just ∼5 mol % PhyCer at 24 °C. However, PhyCer gel-enriched domains in coexistence with POPC-enriched fluid present additional complexity since their properties (maximal order, shape, and thickness) change at specific POPC/PhyCer molar ratios, suggesting the formation of highly stable stoichiometric complexes with their own properties, distinct from both POPC and PhyCer. A POPC/PhyCer binary phase diagram, supported by the different experimental approaches employed, is proposed with complexes of 3:1 and 1:2 stoichiometries which are stable at least from ∼15 to ∼55 °C. Thus, it provides mechanisms for the in vivo formation of sphingolipid-enriched gel domains that may account for stable membrane compartments and diffusion barriers in eukaryotic cell membranes. PMID:26262576

  20. Preparation and properties of co-reticulated invertase supported by an ultrafiltration membrane.

    PubMed Central

    Cantarella, M; Gianfreda, L; Palescandolo, R; Scardi, V

    1977-01-01

    Yeast invertase was co-reticulated with glutaraldehyde to bovine serum albumin to give a soluble bound enzyme that was immobilized as a tightly adhering layer on the active surface of an ultrafiltration membrane. The Michaelis constant and stability of this immobilized-enzyme system are compared with those of the enzyme either in the native form or immobilized as a dynamically formed gel layer on an ultrafiltration membrane, as previously described by us [Drioli, Gianfreda, Palescandolo & Scardi (1975) Biotechnol, Bioeng, 17, 1365-1367]. PMID:588266

  1. Preparation and properties of co-reticulated invertase supported by an ultrafiltration membrane.

    PubMed

    Cantarella, M; Gianfreda, L; Palescandolo, R; Scardi, V

    1977-10-01

    Yeast invertase was co-reticulated with glutaraldehyde to bovine serum albumin to give a soluble bound enzyme that was immobilized as a tightly adhering layer on the active surface of an ultrafiltration membrane. The Michaelis constant and stability of this immobilized-enzyme system are compared with those of the enzyme either in the native form or immobilized as a dynamically formed gel layer on an ultrafiltration membrane, as previously described by us [Drioli, Gianfreda, Palescandolo & Scardi (1975) Biotechnol, Bioeng, 17, 1365-1367]. PMID:588266

  2. Modification of trout sperm membranes associated with activation and cryopreservation. Implications for fertilizing potential

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Abstract We investigated the effects of two trout sperm activation solutions on sperm physiology and membrane organization prior to and following cryopreservation using flow cytometry and investigated their impact on in vitro fertility. Cryopreservation caused greater phospholipid disorder (high pl...

  3. Influence of active layer and support layer surface structures on organic fouling propensity of thin-film composite forward osmosis membranes.

    PubMed

    Lu, Xinglin; Arias Chavez, Laura H; Romero-Vargas Castrillón, Santiago; Ma, Jun; Elimelech, Menachem

    2015-02-01

    In this study, we investigate the influence of surface structure on the fouling propensity of thin-film composite (TFC) forward osmosis (FO) membranes. Specifically, we compare membranes fabricated through identical procedures except for the use of different solvents (dimethylformamide, DMF and N-methyl-2-pyrrolidinone, NMP) during phase separation. FO fouling experiments were carried out with a feed solution containing a model organic foulant. The TFC membranes fabricated using NMP (NMP-TFC) had significantly less flux decline (7.47 ± 0.15%) when compared to the membranes fabricated using DMF (DMF-TFC, 12.70 ± 2.62% flux decline). Water flux was also more easily recovered through physical cleaning for the NMP-TFC membrane. To determine the fundamental cause of these differences in fouling propensity, the active and support layers of the membranes were extensively characterized for physical and chemical characteristics relevant to fouling behavior. Polyamide surface roughness was found to dominate all other investigated factors in determining the fouling propensities of our membranes relative to each other. The high roughness polyamide surface of the DMF-TFC membrane was also rich in larger leaf-like structures, whereas the lower roughness NMP-TFC membrane polyamide layer contained more nodular and smaller features. The support layers of the two membrane types were also characterized for their morphological properties, and the relation between support layer surface structure and polyamide active layer formation was discussed. Taken together, our findings indicate that support layer structure has a significant impact on the fouling propensity of the active layer, and this impact should be considered in the design of support layer structures for TFC membranes. PMID:25564877

  4. Effects of porogen and cross-linking agents on improved properties of silica-supported macroporous chitosan membranes for enzyme immobilization.

    PubMed

    Yang, Wen-Yi; Thirumavalavan, Munusamy; Lee, Jiunn-Fwu

    2015-04-01

    A series of silica-supported macroporous chitosan membranes (CM15, CM20, and CM25) was prepared by varying the ratio of 70-230-μm-sized silica particles. These synthesized membranes were further cross-linked using different cross-linking agents for covalent immobilization of biological macromolecules especially enzymes and in this study, Bovine serum albumin and laccase. Effects of silica particle and cross-linking agents on their flow rates, surface properties, and chemical and biological properties were explored. Pore size of as-synthesized membranes was 0.1192, 0.1268, and 0.1623 μm, respectively, for CM15, CM20, and CM25. The effect of various parameters such as temperature and pH on the relative activity of both free and immobilized enzymes was studied in details. The relative enzyme activity upon immobilization was greatly enhanced several folds of its original activity. The stability of enzymes over a range of temperature and pH was significantly improved by immobilization. The optimum temperature and pH were determined to be 50 °C and pH 3, respectively, for both the free and the immobilized enzymes. The immobilized enzyme possessed good operational stability and reusability properties that support its potentiality for practical applications. Among three membranes, CM25 is confirmed to be efficient candidate due to its improved characteristics. PMID:25432857

  5. Drug-induced reactive oxygen species (ROS) rely on cell membrane properties to exert anticancer effects

    PubMed Central

    Molavian, Hamid R.; Goldman, Aaron; Phipps, Colin J.; Kohandel, Mohammad; Wouters, Bradly G.; Sengupta, Shiladitya; Sivaloganathan, Sivabal

    2016-01-01

    Pharmacological concentrations of small molecule natural products, such as ascorbic acid, have exhibited distinct cell killing outcomes between cancer and normal cells whereby cancer cells undergo apoptosis or necrosis while normal cells are not adversely affected. Here, we develop a mathematical model for ascorbic acid that can be utilized as a tool to understand the dynamics of reactive oxygen species (ROS) induced cell death. We determine that not only do endogenous antioxidants such as catalase contribute to ROS-induced cell death, but also cell membrane properties play a critical role in the efficacy of ROS as a cytotoxic mechanism against cancer cells vs. normal cells. Using in vitro assays with breast cancer cells, we have confirmed that cell membrane properties are essential for ROS, in the form of hydrogen peroxide (H2O2), to induce cell death. Interestingly, we did not observe any correlation between intracellular H2O2 and cell survival, suggesting that cell death by H2O2 is triggered by interaction with the cell membrane and not necessarily due to intracellular levels of H2O2. These findings provide a putative mechanistic explanation for the efficacy and selectivity of therapies such as ascorbic acid that rely on ROS-induced cell death for their anti-tumor properties. PMID:27278439

  6. Bicelles and Other Membrane Mimics: Comparison of Structure, Properties, and Dynamics from MD Simulations.

    PubMed

    Vestergaard, Mikkel; Kraft, Johan F; Vosegaard, Thomas; Thøgersen, Lea; Schiøtt, Birgit

    2015-12-31

    The increased interest in studying membrane proteins has led to the development of new membrane mimics such as bicelles and nanodiscs. However, only limited knowledge is available of how these membrane mimics are affected by embedded proteins and how well they mimic a lipid bilayer. Herein, we present molecular dynamics simulations to elucidate structural and dynamic properties of small bicelles and compare them to a large alignable bicelle, a small nanodisc, and a lipid bilayer. Properties such as lipid packing and properties related to embedding both an α-helical peptide and a transmembrane protein are investigated. The small bicelles are found to be very dynamic and mainly assume a prolate shape substantiating that small bicelles cannot be regarded as well-defined disclike structures. However, addition of a peptide results in an increased tendency to form disc-shaped bicelles. The small bicelles and the nanodiscs show increased peptide solvation and difference in peptide orientation compared to embedding in a bilayer. The large bicelle imitated a bilayer well with respect to both curvature and peptide solvation, although peripheral binding of short tailed lipids to the embedded proteins is observed, which could hinder ligand binding or multimer formation. PMID:26610232

  7. Drug-induced reactive oxygen species (ROS) rely on cell membrane properties to exert anticancer effects.

    PubMed

    Molavian, Hamid R; Goldman, Aaron; Phipps, Colin J; Kohandel, Mohammad; Wouters, Bradly G; Sengupta, Shiladitya; Sivaloganathan, Sivabal

    2016-01-01

    Pharmacological concentrations of small molecule natural products, such as ascorbic acid, have exhibited distinct cell killing outcomes between cancer and normal cells whereby cancer cells undergo apoptosis or necrosis while normal cells are not adversely affected. Here, we develop a mathematical model for ascorbic acid that can be utilized as a tool to understand the dynamics of reactive oxygen species (ROS) induced cell death. We determine that not only do endogenous antioxidants such as catalase contribute to ROS-induced cell death, but also cell membrane properties play a critical role in the efficacy of ROS as a cytotoxic mechanism against cancer cells vs. normal cells. Using in vitro assays with breast cancer cells, we have confirmed that cell membrane properties are essential for ROS, in the form of hydrogen peroxide (H2O2), to induce cell death. Interestingly, we did not observe any correlation between intracellular H2O2 and cell survival, suggesting that cell death by H2O2 is triggered by interaction with the cell membrane and not necessarily due to intracellular levels of H2O2. These findings provide a putative mechanistic explanation for the efficacy and selectivity of therapies such as ascorbic acid that rely on ROS-induced cell death for their anti-tumor properties. PMID:27278439

  8. Gβ1γ2 activates phospholipase A2-dependent Golgi membrane tubule formation

    PubMed Central

    Bechler, Marie E.; Brown, William J.

    2014-01-01

    Heterotrimeric G proteins transduce the ligand binding of transmembrane G protein coupled receptors into a variety of intracellular signaling pathways. Recently, heterotrimeric Gβγ subunit signaling at the Golgi complex has been shown to regulate the formation of vesicular transport carriers that deliver cargo from the Golgi to the plasma membrane. In addition to vesicles, membrane tubules have also been shown to mediate export from the Golgi complex, which requires the activity of cytoplasmic phospholipase A2 (PLA2) enzyme activity. Through the use of an in vitro reconstitution assay with isolated Golgi complexes, we provide evidence that Gβ1γ2 signaling also stimulates Golgi membrane tubule formation. In addition, we show that an inhibitor of Gβγ activation of PLA2 enzymes inhibits in vitro Golgi membrane tubule formation. Additionally, purified Gβγ protein stimulates membrane tubules in the presence of low (sub-threshold) cytosol concentrations. Importantly, this Gβγ stimulation of Golgi membrane tubule formation was inhibited by treatment with the PLA2 antagonist ONO-RS-082. These studies indicate that Gβ1γ2 signaling activates PLA2 enzymes required for Golgi membrane tubule formation, thus establishing a new layer of regulation for this process. PMID:25019068

  9. cBid, Bax and Bcl-xL exhibit opposite membrane remodeling activities

    PubMed Central

    Bleicken, S; Hofhaus, G; Ugarte-Uribe, B; Schröder, R; García-Sáez, A J

    2016-01-01

    The proteins of the Bcl-2 family have a crucial role in mitochondrial outer membrane permeabilization during apoptosis and in the regulation of mitochondrial dynamics. Current models consider that Bax forms toroidal pores at mitochondria that are responsible for the release of cytochrome c, whereas Bcl-xL inhibits pore formation. However, how Bcl-2 proteins regulate mitochondrial fission and fusion remains poorly understood. By using a systematic analysis at the single vesicle level, we found that cBid, Bax and Bcl-xL are able to remodel membranes in different ways. cBid and Bax induced a reduction in vesicle size likely related to membrane tethering, budding and fission, besides membrane permeabilization. Moreover, they are preferentially located at highly curved membranes. In contrast, Bcl-xL not only counterbalanced pore formation but also membrane budding and fission. Our findings support a mechanism of action by which cBid and Bax induce or stabilize highly curved membranes including non-lamellar structures. This molecular activity reduces the energy for membrane remodeling, which is a necessary step in toroidal pore formation, as well as membrane fission and fusion, and provides a common mechanism that links the two main functions of Bcl-2 proteins. PMID:26913610

  10. cBid, Bax and Bcl-xL exhibit opposite membrane remodeling activities.

    PubMed

    Bleicken, S; Hofhaus, G; Ugarte-Uribe, B; Schröder, R; García-Sáez, A J

    2016-01-01

    The proteins of the Bcl-2 family have a crucial role in mitochondrial outer membrane permeabilization during apoptosis and in the regulation of mitochondrial dynamics. Current models consider that Bax forms toroidal pores at mitochondria that are responsible for the release of cytochrome c, whereas Bcl-xL inhibits pore formation. However, how Bcl-2 proteins regulate mitochondrial fission and fusion remains poorly understood. By using a systematic analysis at the single vesicle level, we found that cBid, Bax and Bcl-xL are able to remodel membranes in different ways. cBid and Bax induced a reduction in vesicle size likely related to membrane tethering, budding and fission, besides membrane permeabilization. Moreover, they are preferentially located at highly curved membranes. In contrast, Bcl-xL not only counterbalanced pore formation but also membrane budding and fission. Our findings support a mechanism of action by which cBid and Bax induce or stabilize highly curved membranes including non-lamellar structures. This molecular activity reduces the energy for membrane remodeling, which is a necessary step in toroidal pore formation, as well as membrane fission and fusion, and provides a common mechanism that links the two main functions of Bcl-2 proteins. PMID:26913610

  11. Daptomycin exerts rapid bactericidal activity against Bacillus anthracis without disrupting membrane integrity

    PubMed Central

    Xing, Yu-hua; Wang, Wei; Dai, Su-qin; Liu, Ti-yan; Tan, Jun-jie; Qu, Guo-long; Li, Yu-xia; Ling, Yan; Liu, Gang; Fu, Xue-qi; Chen, Hui-peng

    2014-01-01

    Aim: To examine whether the novel cyclic lipopeptide antibiotic daptomycin could be used to treat anthrax and to study the mechanisms underlying its bactericidal action against Bacillus anthracis. Methods: Spore-forming B anthracis AP422 was tested. MIC values of antibiotics were determined. Cell membrane potential was measured using flow cytometric assays with membrane potential-sensitive fluorescent dyes. Cell membrane integrity was detected using To-Pro-3 iodide staining and transmission electron microscopy. K+ efflux and Na+ influx were measured using the fluorescent probes PBFI and SBFI-AM, respectively. Results: Daptomycin exhibited rapid bactericidal activity against vegetative B anthracis with a MIC value of 0.78 μg/mL, which was comparable to those of ciprofloxacin and penicillin G. Furthermore, daptomycin prevented the germinated spores from growing into vegetative bacteria. Daptomycin concentration-dependently dissipated the membrane potential of B anthracis and caused K+ efflux and Na+ influx without disrupting membrane integrity. In contrast, both ciprofloxacin and penicillin G did not change the membrane potential of vegetative bacteria or spores. Penicillin G disrupted membrane integrity of B anthracis, whereas ciprofloxacin had no such effect. Conclusion: Daptomycin exerts rapid bactericidal action against B anthracis via reducing membrane potential without disrupting membrane integrity. This antibiotic can be used as an alternate therapy for B anthracis infections. PMID:24362329

  12. Deuterated detergents for structural and functional studies of membrane proteins: Properties, chemical synthesis and applications.

    PubMed

    Hiruma-Shimizu, Kazumi; Shimizu, Hiroki; Thompson, Gary S; Kalverda, Arnout P; Patching, Simon G

    2015-01-01

    Detergents are amphiphilic compounds that have crucial roles in the extraction, purification and stabilization of integral membrane proteins and in experimental studies of their structure and function. One technique that is highly dependent on detergents for solubilization of membrane proteins is solution-state NMR spectroscopy, where detergent micelles often serve as the best membrane mimetic for achieving particle sizes that tumble fast enough to produce high-resolution and high-sensitivity spectra, although not necessarily the best mimetic for a biomembrane. For achieving the best quality NMR spectra, detergents with partial or complete deuteration can be used, which eliminate interfering proton signals coming from the detergent itself and also eliminate potential proton relaxation pathways and strong dipole-dipole interactions that contribute line broadening effects. Deuterated detergents have also been used to solubilize membrane proteins for other experimental techniques including small angle neutron scattering and single-crystal neutron diffraction and for studying membrane proteins immobilized on gold electrodes. This is a review of the properties, chemical synthesis and applications of detergents that are currently commercially available and/or that have been synthesized with partial or complete deuteration. Specifically, the detergents are sodium dodecyl sulphate (SDS), lauryldimethylamine-oxide (LDAO), n-octyl-β-D-glucoside (β-OG), n-dodecyl-β-D-maltoside (DDM) and fos-cholines including dodecylphosphocholine (DPC). The review also considers effects of deuteration, detergent screening and guidelines for detergent selection. Although deuterated detergents are relatively expensive and not always commercially available due to challenges associated with their chemical synthesis, they will continue to play important roles in structural and functional studies of membrane proteins, especially using solution-state NMR. PMID:26906947

  13. Dissociation of membrane binding and lytic activities of the lymphocyte pore-forming protein (perforin).

    PubMed

    Young, J D; Damiano, A; DiNome, M A; Leong, L G; Cohn, Z A

    1987-05-01

    Granules isolated from CTL and NK cells contain a cytolytic pore-forming protein (PFP/perforin). At low temperatures (on ice), PFP binds to erythrocyte membranes without producing hemolysis. Hemolysis occurs when the PFP-bound erythrocytes are warmed up to 37 degrees C, which defines a temperature-dependent, lytic (pore-formation) step distinct from the membrane-binding event. Ca2+ and neutral pH are required for both membrane binding and pore formation by PFP. Serum, LDL, HDL, and heparin inhibit the hemolytic activity of PFP by blocking its binding to lipid membranes. Lysis by PFP that has bound to erythrocyte membranes is no longer susceptible to the effect of these inhibitors. The hemolytic activities associated with intact granules and solubilized PFP show different requirements for Ca2+ and pH, indicating that cytolysis produced by isolated granules may involve an additional step, possibly fusion of granules with membranes. It is suggested that three distinct Ca2+- and pH-dependent events may be involved during cell killing by CTL and NK cells: fusion of cytoplasmic granules of effector cells with their plasma membrane, releasing PFP from cells; binding of the released PFP to target membranes; and insertion of monomers and the subsequent formation of lytic pores in the target membrane. The serum-mediated inhibition of membrane binding by PFP could prevent the accidental injury of bystander cells by cell-released PFP, but would allow cytolysis to proceed to completion once PFP has bound to the target membrane. PMID:3494808

  14. Designing a biocidal reverse osmosis membrane coating: Synthesis and biofouling properties

    SciTech Connect

    Hibbs, Michael R.; McGrath, Lucas K.; Kang, Seoktae; Adout, Atar; Altman, Susan J.; Elimelech, Menachem; Cornelius, Chris J.

    2015-12-04

    In this study, a biocidal coating was developed in order to reduce biofouling on a reverse osmosis (RO) membrane using a quaternary ammonium (QA) functionalized polymer. The synthesis of a series of polysulfone (PS) ionomers with QA groups is described, and a method for spraying these QA ionomers as an alcoholic solution, which dried into water insoluble coatings. Contact angle and streaming potential were used to analyze the coating's hydrophilicity and surface charge. Both PS-QA1 and the commercial RO membrane had an apparent contact angle of 68° that increased to 126° for PS-QA12 corresponding to alkyl chain length. A negatively charged particle-probe was used to measure coated and uncoated RO membrane interaction forces. Measured interaction forces correlated strongly with the length of alkyl chains or hydrophobicity of the coated surfaces. Uncoated RO membranes and ones coated with PS-QA were exposed to suspensions of Escherichia coli cells. All four PS-QA coatings showed significant biotoxicity and killed 100% of the E. coli cells, but uncoated RO membranes had metabolically active biofilms. However, coatings tested in a RO crossflow system showed a flux reduction that is attributed to mass transfer resistance due to excessively thick films.

  15. Designing a biocidal reverse osmosis membrane coating: Synthesis and biofouling properties

    DOE PAGESBeta

    Hibbs, Michael R.; McGrath, Lucas K.; Kang, Seoktae; Adout, Atar; Altman, Susan J.; Elimelech, Menachem; Cornelius, Chris J.

    2015-12-04

    In this study, a biocidal coating was developed in order to reduce biofouling on a reverse osmosis (RO) membrane using a quaternary ammonium (QA) functionalized polymer. The synthesis of a series of polysulfone (PS) ionomers with QA groups is described, and a method for spraying these QA ionomers as an alcoholic solution, which dried into water insoluble coatings. Contact angle and streaming potential were used to analyze the coating's hydrophilicity and surface charge. Both PS-QA1 and the commercial RO membrane had an apparent contact angle of 68° that increased to 126° for PS-QA12 corresponding to alkyl chain length. A negativelymore » charged particle-probe was used to measure coated and uncoated RO membrane interaction forces. Measured interaction forces correlated strongly with the length of alkyl chains or hydrophobicity of the coated surfaces. Uncoated RO membranes and ones coated with PS-QA were exposed to suspensions of Escherichia coli cells. All four PS-QA coatings showed significant biotoxicity and killed 100% of the E. coli cells, but uncoated RO membranes had metabolically active biofilms. However, coatings tested in a RO crossflow system showed a flux reduction that is attributed to mass transfer resistance due to excessively thick films.« less

  16. Enzymatic Oxidation of Cholesterol: Properties and Functional Effects of Cholestenone in Cell Membranes

    PubMed Central

    Neuvonen, Maarit; Manna, Moutusi; Mokkila, Sini; Javanainen, Matti; Rog, Tomasz; Liu, Zheng; Bittman, Robert; Vattulainen, Ilpo; Ikonen, Elina

    2014-01-01

    Bacterial cholesterol oxidase is commonly used as an experimental tool to reduce cellular cholesterol content. That the treatment also generates the poorly degradable metabolite 4-cholesten-3-one (cholestenone) has received less attention. Here, we investigated the membrane partitioning of cholestenone using simulations and cell biological experiments and assessed the functional effects of cholestenone in human cells. Atomistic simulations predicted that cholestenone reduces membrane order, undergoes faster flip-flop and desorbs more readily from membranes than cholesterol. In primary human fibroblasts, cholestenone was released from membranes to physiological extracellular acceptors more avidly than cholesterol, but without acceptors it remained in cells over a day. To address the functional effects of cholestenone, we studied fibroblast migration during wound healing. When cells were either cholesterol oxidase treated or part of cellular cholesterol was exchanged for cholestenone with cyclodextrin, cell migration during 22 h was markedly inhibited. Instead, when a similar fraction of cholesterol was removed using cyclodextrin, cells replenished their cholesterol content in 3 h and migrated similarly to control cells. Thus, cholesterol oxidation produces long-term functional effects in cells and these are in part due to the generated membrane active cholestenone. PMID:25157633

  17. Aqueous solution behaviour and membrane disruptive activity of pH-responsive PEGylated pseudo-peptides and their intracellular distribution.

    PubMed

    Chen, Rongjun; Yue, Zhilian; Eccleston, Mark E; Slater, Nigel K H

    2008-11-01

    The effect of PEGylation on the aqueous solution properties and cell membrane disruptive activity of a pH-responsive pseudo-peptide, poly(l-lysine iso-phthalamide), has been investigated by dynamic light scattering, haemolysis and lactate dehydrogenase (LDH) assays. Intracellular trafficking of the polymers has been examined using confocal and fluorescence microscopy. With increasing degree of PEGylation, the modified polymers can form stabilised compact structures with reduced mean hydrodynamic diameters. Poly(l-lysine iso-phthalamide) with a low degree of PEGylation (17.4 wt%) retained pH-dependent solution behaviour and showed enhanced kinetic membrane disruptive activity compared to the parent polymer. It facilitated trafficking of endocytosed materials into the cytoplasm of HeLa cells. At levels of PEGylation in excess of 25.6 wt%, the modified polymers displayed a single particle size distribution unresponsive to pH, as well as a decrease in cell membrane lytic ability. The mechanism involved in membrane destabilisation was also investigated, and the potential applications of these modified polymers in drug delivery were discussed. PMID:18708250

  18. The Ultrastructures and Mechanical Properties of the Descement's Membrane in Fuchs Endothelial Corneal Dystrophy.

    PubMed

    Xia, Dan; Zhang, Shuai; Nielsen, Esben; Ivarsen, Anders Ramløv; Liang, Chunyong; Li, Qiang; Thomsen, Karen; Hjortdal, Jesper Østergaard; Dong, Mingdong

    2016-01-01

    Fuchs endothelial corneal dystrophy (FECD), is the most common corneal endothelial dystrophy, and contributes up to 50% of all corneal transplantations performed in developed countries. FECD develops in Descemet's membrane (DM) and possibly alters the mechanical properties and internal structures in this basal lamina. In this work, the morphology and mechanical properties of FECD-DMs are studied by transmission electron microscopy (TEM) and quantitative dynamic atomic force microscopy (QD-AFM) at nano scale. Pathological wide-space collagens that are typical of FECD display different mechanical properties in that they are softer than the remaining tissue both for dehydrated- and fully hydrated samples. Additionally, the hydration level has major influence on the mechanical properties. These findings could help to further understand the structural changes in FECD, and possibly be useful for further characterization of the disease, the diagnosis and assessment or even pathologic analysis. PMID:26980551

  19. The Ultrastructures and Mechanical Properties of the Descement’s Membrane in Fuchs Endothelial Corneal Dystrophy

    PubMed Central

    Xia, Dan; Zhang, Shuai; Nielsen, Esben; Ivarsen, Anders Ramløv; Liang, Chunyong; Li, Qiang; Thomsen, Karen; Hjortdal, Jesper Østergaard; Dong, Mingdong

    2016-01-01

    Fuchs endothelial corneal dystrophy (FECD), is the most common corneal endothelial dystrophy, and contributes up to 50% of all corneal transplantations performed in developed countries. FECD develops in Descemet’s membrane (DM) and possibly alters the mechanical properties and internal structures in this basal lamina. In this work, the morphology and mechanical properties of FECD-DMs are studied by transmission electron microscopy (TEM) and quantitative dynamic atomic force microscopy (QD-AFM) at nano scale. Pathological wide-space collagens that are typical of FECD display different mechanical properties in that they are softer than the remaining tissue both for dehydrated- and fully hydrated samples. Additionally, the hydration level has major influence on the mechanical properties. These findings could help to further understand the structural changes in FECD, and possibly be useful for further characterization of the disease, the diagnosis and assessment or even pathologic analysis. PMID:26980551

  20. Structure and Properties of a Semi-crystalline Cationic Polymer for Anion Exchange Membranes

    NASA Astrophysics Data System (ADS)

    Beyer, Frederick; Price, Samuel; Savage, Alice; Ren, Xiaoming; Insane Membranes Collaboration

    Nafion has long been studied in order to understand its combination of good mechanical properties, chemical resistance, and excellent charge transport characteristics. In the past decade, uncertainty regarding the morphological behavior of Nafion has largely been resolved, allowing researchers to mimic and improve on the structure of this material. In this presentation, work to incorporate key characteristics of Nafion into a model cation-containing polymer will be described. In these new materials, semi-crystalline atactic poly(norbornene) is used to introduce good mechanical properties to anion-exchange membranes, analogous to the PTFE crystallites in Nafion. The ether linkages between the charged species and backbone are also utilized to place the cationic species (trimethylamine) in our materials into a mechanically soft environment. The resulting polymer shows some characteristics that are similar to those of Nafion. In this presentation, the synthesis, alkaline stability, mechanical properties, morphological behavior and charge transport properties will all be described.

  1. Effect of Chlorotriphenyl Derivatives of Sn and Pb upon Biophysical Properties of Membranes

    PubMed Central

    Man, Dariusz; Podolak, Marian; Engel, Grzegorz; Boniewska, Ewa

    2009-01-01

    Biophysical activity of two twin organometallic compounds Triphenyltin chloride (TPhT) and Triphenyllead chloride (TPhL) in their interreaction with model membranes, as well as with yeast cells Saccharomyces cerevisiae, was investigated. Four measurement methods were used in the experiments: two physical methods (spin probes method and the electric method); two biological methods (minimal inhibitory concentration /MIC/ and yeast survival test). It has been found that the activity of TPhT in interaction with model membranes and yeast cells is distinctly greater than that of TPhL. The activity manifests itself by considerable increase in the fluidity of the middle part of liposome bilayer, change in the polarization direction of the transmembrane voltage of filters impregnated with lauric acid, and in complete inhibition of growth of yeast cells at the concentration of 5 μg/mL. PMID:19606258

  2. Estimating the magnitude of near-membrane PDE4 activity in living cells.

    PubMed

    Xin, Wenkuan; Feinstein, Wei P; Britain, Andrea L; Ochoa, Cristhiaan D; Zhu, Bing; Richter, Wito; Leavesley, Silas J; Rich, Thomas C

    2015-09-15

    Recent studies have demonstrated that functionally discrete pools of phosphodiesterase (PDE) activity regulate distinct cellular functions. While the importance of localized pools of enzyme activity has become apparent, few studies have estimated enzyme activity within discrete subcellular compartments. Here we present an approach to estimate near-membrane PDE activity. First, total PDE activity is measured using traditional PDE activity assays. Second, known cAMP concentrations are dialyzed into single cells and the spatial spread of cAMP is monitored using cyclic nucleotide-gated channels. Third, mathematical models are used to estimate the spatial distribution of PDE activity within cells. Using this three-tiered approach, we observed two pharmacologically distinct pools of PDE activity, a rolipram-sensitive pool and an 8-methoxymethyl IBMX (8MM-IBMX)-sensitive pool. We observed that the rolipram-sensitive PDE (PDE4) was primarily responsible for cAMP hydrolysis near the plasma membrane. Finally, we observed that PDE4 was capable of blunting cAMP levels near the plasma membrane even when 100 μM cAMP were introduced into the cell via a patch pipette. Two compartment models predict that PDE activity near the plasma membrane, near cyclic nucleotide-gated channels, was significantly lower than total cellular PDE activity and that a slow spatial spread of cAMP allowed PDE activity to effectively hydrolyze near-membrane cAMP. These results imply that cAMP levels near the plasma membrane are distinct from those in other subcellular compartments; PDE activity is not uniform within cells; and localized pools of AC and PDE activities are responsible for controlling cAMP levels within distinct subcellular compartments. PMID:26201952

  3. Model of red blood cell membrane skeleton: electrical and mechanical properties.

    PubMed

    Kozlov, M M; Markin, V S

    1987-12-21

    A theoretical membrane skeleton model of erythrocyte has been developed and successfully applied to interpret electrical and mechanical properties of the red blood cell spectrin-actin network. The model is based on the structure of the membrane skeleton that is comprised of unit cells each containing an actin protofilament and shooting forth a few spectrin heterodimers. The loose ends of the heterodimers of adjacent cells can form bonds with each other giving rise to an integrated network. The number of bonds depends on the temperature. The bond length being excessive (2.6 times the distance between the centers of adjacent cells), the bonds are flexible, and can thus be regarded as entropy springs. The advanced model has been employed to calculate the shear modulus of the membrane skeleton as well as to establish its temperature dependence. In a wide range of temperatures mu(T) is a decreasing function well fitting the experimental data. The relationship between the membrane bilayer-free size of the skeleton and the ionic strength of the solution has been derived to appear in good agreement with the results obtained previously. Experimental data combined with the advanced theory yield the average number of heterodimers per unit cell, m0, as equal to ca. 5; the spectrin heterodimer charge has been estimated. PMID:3455470

  4. Photoinduced charge transfer properties of bolaamphiphile membrane-gramicidrin diad composites

    NASA Astrophysics Data System (ADS)

    Thompson, David H.; Kim, Jong-Mok; Di Meglio, Ciro

    1993-04-01

    Ether-linked bolaform amphiphiles (Langmuir 1992 8, 637; J. Am. Chem. Soc. 1992, 9035) and novel gramicidin-porphyrin `diads' (MRS Symposium Series, Vol. 277, 1992, 93) have been synthesized. Protocols for vectorial insertion of the derivatized gramicidins into bolaform lipid vesicles have been developed and the photochemical behavior of these proteinaceous composite membranes probed in the presence of electron donors and acceptors. Photoinduced electron transfer properties of the gramicidin-porphyrin conjugates were compared in TRIS- buffered dihexadecyl-phosphate bilayer (DHP) and bolaform monolayer membrane vesicles containing dithiothreitol as sacrificial donor and methyl viologen as electron acceptor on both the inner and outer vesicle surfaces. Although the rates of methyl viologen photoreduction varied depending on the mode of diad orientation within DHP bilayer membranes, photoreduction rates were not orientation- dependent in bolaform membrane vesicles containing the gramicidin-porphyrin diad. The relevance of these results on vectorial electron transfer processes in lamellar systems and the design of integrated charge transfer components is discussed.

  5. Ultem®/ZIF-8 mixed matrix membranes for gas separation: Transport and physical properties

    DOE PAGESBeta

    Eiras, Daniel; Labreche, Ying; Pessan, Luiz Antonio

    2016-02-19

    Mixed matrix membranes are promising options for improving gas separation processes. Zeolitic imidazolate frameworks (ZIFs) have a porous structure similar to conventional zeolites, being capable in principle of separating gases based on their differences in kinetic diameter while offering the advantage of having a partial organic character. This partial organic nature improves the compatibility between the sieve and the polymer, and a combination of the mentioned characteristics makes these hybrid materials interesting for the preparation of mixed matrix gas separation membranes. In this context the present work reports the preparation of Ultem®/ZIF-8 mixed matrix membranes and their permeabilities to puremore » CO2, N2 and CH4 gases. A significant increase in permeability with increase in CO2/N2 selectivity was observed for the mixed matrix systems as compared to the properties of the neat Ultem®. Sorption results allowed to speculate that the ZIF-8 framework is not completely stable dimensionally, what influences the separation process by allowing gases with higher kinetic diameter than its nominal aperture to be sorbed and to diffuse through the crystal. Lastly, sorption and diffusion selectivities indicate that the higher separation performance of the mixed matrix membranes is governed by the diffusion process associated with the influence of gas molecule´s geometry.« less

  6. Opposite effect of membrane raft perturbation on transport activity of KCC2 and NKCC1.

    PubMed

    Hartmann, Anna-Maria; Blaesse, Peter; Kranz, Thorsten; Wenz, Meike; Schindler, Jens; Kaila, Kai; Friauf, Eckhard; Nothwang, Hans Gerd

    2009-10-01

    In the majority of neurons, the intracellular Cl(-) concentration is set by the activity of the Na(+)-K(+)-2Cl(-) cotransporter (NKCC1) and the K(+)-Cl(-) cotransporter (KCC2). Here, we investigated the cotransporters' functional dependence on membrane rafts. In the mature rat brain, NKCC1 was mainly insoluble in Brij 58 and co-distributed with the membrane raft marker flotillin-1 in sucrose density flotation experiments. In contrast, KCC2 was found in the insoluble fraction as well as in the soluble fraction, where it co-distributed with the non-raft marker transferrin receptor. Both KCC2 populations displayed a mature glycosylation pattern. Disrupting membrane rafts with methyl-beta-cyclodextrin (MbetaCD) increased the solubility of KCC2, yet had no effect on NKCC1. In human embryonic kidney-293 cells, KCC2 was strongly activated by a combined treatment with MbetaCD and sphingomyelinase, while NKCC1 was inhibited. These data indicate that membrane rafts render KCC2 inactive and NKCC1 active. In agreement with this, inactive KCC2 of the perinatal rat brainstem largely partitioned into membrane rafts. In addition, the exposure of the transporters to MbetaCD and sphingomyelinase showed that the two transporters differentially interact with the membrane rafts. Taken together, membrane raft association appears to represent a mechanism for co-ordinated regulation of chloride transporter function. PMID:19686239

  7. Fusion-Triggered Switching of Enzymatic Activity on an Artificial Cell Membrane

    PubMed Central

    Mukai, Masaru; Sasaki, Yoshihiro; Kikuchi, Jun-ichi

    2012-01-01

    A nanosensory membrane device was constructed for detecting liposome fusion through changes in an enzymatic activity. Inspired by a biological signal transduction system, the device design involved functionalized liposomal membranes prepared by self-assembly of the following molecular components: a synthetic peptide lipid and a phospholipid as matrix membrane components, a Schiff's base of pyridoxal 5′-phosphate with phosphatidylethanolamine as a thermo-responsive artificial receptor, NADH-dependent L-lactate dehydrogenase as a signal amplifier, and Cu2+ ion as a signal mediator between the receptor and enzyme. The enzymatic activity of the membrane device was adjustable by changing the matrix lipid composition, reflecting the thermotropic phase transition behavior of the lipid membranes, which in turn controlled receptor binding affinity toward the enzyme-inhibiting mediator species. When an effective fusogen anionic polymer was added to these cationic liposomes, membrane fusion occurred, and the functionalized liposomal membranes responded with changes in enzymatic activity, thus serving as an effective nanosensory device for liposome fusion detection. PMID:22778625

  8. Probing the effect of elevated cholesterol on the mechanical properties of membrane-cytoskeleton by optical tweezers

    NASA Astrophysics Data System (ADS)

    Rajkumar, Arun S.; Muley, Ajit; Chatterjee, Suvro; Jaffar Ali, B. M.

    2010-08-01

    The composition of the cell membrane and the surrounding physiological factors determine the nature and dynamics of membrane-cytoskeleton coupling. Mechanical strength of a cell is mainly derived from such coupling. In this article, we investigate the effect of extra cellular cholesterol on the membrane-cytoskelaton connectivity of single cell endothelium and consequent remodeling of its mechanical properties. Using optical tweezers as a force probe, we have measured membrane stiffness (km), membrane microviscosity (ηeff ) and the two-dimensional shear modulus (G'(f)) as a function of extracellular cholesterol in the range of 0.1mM to 6mM. We find that membrane stiffness and shear modulus are dependent on cholesterol-induced membrane-cytoskeletal organization. Further, by disrupting the membranecytoskeletal connectivity with Cytochalasin D, an actin delpolymerizing molecule, we recover pure membrane behaviour devoid of any cytoskeleton attachment. However, behaviour of ηeff was found to be unaffected by disruption of membrane-cytoskeleton organization. We infer that cholesterol is playing a distinct role in modulating membrane organization and membrane-cytoskeleton connectivity independently. We further discuss implications of our approach in characterizing cellular mechanics.

  9. A procedure for the rapid isolation from rat liver of plasma membrane vesicles exhibiting Ca2+-transport and Ca2+-ATPase activities.

    PubMed Central

    Epping, R J; Bygrave, F L

    1984-01-01

    A technique is described for the isolation of a plasma membrane-enriched preparation from a rat liver post-mitochondrial fraction by using discontinuous Percoll density-gradient centrifugation. The procedure is simple, of high reproducibility and yield and requires a total isolation time of only 90 min. The preparation consists almost exclusively of membrane vesicles and is enriched approx. 26-fold in plasma membrane-localized enzymes with minor contamination (less than 10%) with membranes derived mainly from the endoplasmic reticulum and Golgi apparatus. Approx. 20% of the fraction comprises tightly-sealed vesicles in the inverted orientation which are capable of accumulating calcium ions and exhibiting vanadate-insensitive Ca2+-ATPase activity. The properties of these activities, including insensitivity to vanadate, oxalate, and to p-chloromercuribenzoate as well as a lack of requirement for added Mg2+, contrast markedly with the reported properties of Ca2+ transport by the endoplasmic reticulum isolated from rat liver. The technique may have wide application in the study of plasma membrane-associated activities in rat liver, particularly in relation to sinusoidal membrane surface-related events. Images Fig. 2. PMID:6239615

  10. Characterization of a secretase activity which releases angiotensin-converting enzyme from the membrane.

    PubMed Central

    Oppong, S Y; Hooper, N M

    1993-01-01

    Angiotensin-converting enzyme (ACE; EC 3.4.1.15.1) exists in both membrane-bound and soluble forms. Phase separation in Triton X-114 and a competitive e.l.i.s.a. have been employed to characterize the activity which post-translationally converts the amphipathic, membrane-bound form of ACE in pig kidney microvilli into a hydrophilic, soluble form. This secretase activity was enriched to a similar extent as other microvillar membrane proteins, was tightly membrane-associated, being resistant to extensive washing of the microvillar membranes with 0.5 M NaCl, and displayed a pH optimum of 8.4. The ACE secretase was not affected by inhibitors of serine-, thiol- or aspartic-proteases, nor by reducing agents or alpha 2-macroglobulin. The metal chelators, EDTA and 1,10-phenanthroline, inhibited the secretase activity, with, in the case of EDTA, an inhibitor concentration of 2.5 mM causing 50% inhibition. In contrast, EGTA inhibited the secretase by a maximum of 15% at a concentration of 10 mM. The inhibition of EDTA was reactivated substantially (83%) by Mg2+ ions, and partially (34% and 29%) by Zn2+ and Mn2+ ions respectively. This EDTA-sensitive secretase activity was also present in microsomal membranes prepared from pig lung and testis, and from human lung and placenta, but was absent from human kidney and human and pig intestinal brush-border membranes. The form of ACE released from the microvillar membrane by the secretase co-migrated on SDS/PAGE with ACE purified from pig plasma, thus the action and location of the secretase would be consistent with it possibly having a role in the post-translational proteolytic cleavage of membrane-bound ACE to generate the soluble form found in blood, amniotic fluid, seminal plasma and other body fluids. Images Figure 4 PMID:8389141

  11. Sodium pump molecular activity and membrane lipid composition in two disparate ectotherms, and comparison with endotherms.

    PubMed

    Turner, Nigel; Hulbert, A J; Else, Paul L

    2005-02-01

    Previous research has shown that the lower sodium pump molecular activity observed in tissues of ectotherms compared to endotherms, is largely related to the lower levels of polyunsaturates and higher levels of monounsaturates found in the cell membranes of ectotherms. Marine-based ectotherms, however, have very polyunsaturated membranes, and in the current study, we measured molecular activity and membrane lipid composition in tissues of two disparate ectothermic species, the octopus (Octopus vulgaris) and the bearded dragon lizard (Pogona vitticeps), to determine whether the high level of membrane polyunsaturation generally observed in marine-based ectotherms is associated with an increased sodium pump molecular activity relative to other ectotherms. Phospholipids from all tissues of the octopus were highly polyunsaturated and contained high concentrations of the omega-3 polyunsaturate, docosahexaenoic acid (22:6 (n-3)). In contrast, phospholipids from bearded dragon tissues contained higher proportions of monounsaturates and lower proportions of polyunsaturates. Sodium pump molecular activity was only moderately elevated in tissues of the octopus compared to the bearded dragon, despite the much greater level of polyunsaturation in octopus membranes. When the current data were combined with data for the ectothermic cane toad, a significant (P = 0.003) correlation was observed between sodium pump molecular activity and the content of 22:6 (n-3) in the surrounding membrane. These results are discussed in relation to recent work which shows a similar relationship in endotherms. PMID:15726386

  12. Comparative catalytic activity of PET track-etched membranes with embedded silver and gold nanotubes

    NASA Astrophysics Data System (ADS)

    Mashentseva, Anastassiya; Borgekov, Daryn; Kislitsin, Sergey; Zdorovets, Maxim; Migunova, Anastassiya

    2015-12-01

    Irradiated by heavy ions nanoporous polyethylene terephthalate track-etched membranes (PET TeMs) after +15Kr84 ions bombardment (1.75 MeV/nucl with the ion fluency of 1 × 109 cm-2) and sequential etching was applied in this research as a template for development of composites with catalytically enriched properties. A highly ordered silver and gold nanotubes arrays were embedded in 100 nm pores of PET TeMs via electroless deposition technique at 4 °C during 1 h. All "as-prepared" composites were examined for catalytic activity using reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by sodium borohydride as a common reaction to test metallic nanostructures catalysts. The effect of temperature on the catalytic activity was investigated in range of 292-313 K and activation energy were calculated. Kapp of Ag/PET composites linearly increase with an increase of the temperature thus normal Arrhenius behavior have been seen and the activation energy was calculated to be 42.13 kJ/mol. Au/PET composites exhibit not only more powerful catalytic activity but also non-linear dependence of rate constant from temperature. Kapp increased with increasing temperature throughout the 292-308 K temperature range; the reaction had an activation energy 65.32 kJ/mol. In range 311-313 K rate constant dramatically decreased and the apparent activation energy at this temperature rang was -91.44 kJ/mol due some structural changes, i.e. agglomeration of Au nanoparticles on the surface of composite.

  13. Testing the limits of rational design by engineering pH sensitivity into membrane-active peptides.

    PubMed

    Wiedman, Gregory; Wimley, William C; Hristova, Kalina

    2015-04-01

    In this work, we sought to rationally design membrane-active peptides that are triggered by low pH to form macromolecular-sized pores in lipid bilayers. Such peptides could have broad utility in biotechnology and in nanomedicine as cancer therapeutics or drug delivery vehicles that promote release of macromolecules from endosomes. Our approach to rational design was to combine the properties of a pH-independent peptide, MelP5, which forms large pores allowing passage of macromolecules, with the properties of two pH-dependent membrane-active peptides, pHlip and GALA. We created two hybrid sequences, MelP5_Δ4 and MelP5_Δ6, by using the distribution of acidic residues on pHlip and GALA as a guide to insert acidic amino acids into the amphipathic helix of MelP5. We show that the new peptides bind to lipid bilayers and acquire secondary structure in a pH-dependent manner. The peptides also destabilize bilayers in a pH-dependent manner, such that lipid vesicles release the small molecules ANTS/DPX at low pH only. Thus, we were successful in designing pH-triggered pore-forming peptides. However, no macromolecular release was observed under any conditions. Therefore, we abolished the unique macromolecular poration properties of MelP5 by introducing pH sensitivity into its sequence. We conclude that the properties of pHlip, GALA, and MelP5 are additive, but only partially so. We propose that this lack of additivity is a limitation in the rational design of novel membrane-active peptides, and that high-throughput approaches to discovery will be critical for continued progress in the field. PMID:25572997

  14. Preparation and Properties of Polysulfone-poly(ethylene glycol) graft copolymer membrane.

    PubMed

    Woo, Seung-Moon; Kim, Deuk-Ju; Nam, Sang-Yong

    2014-10-01

    In this study, Graft copolymers composed of PSf backbones and PEG side chains were synthesized to prepare gas separation membranes with enhancing permeability and selectivity on carbon dioxide separation. PSf-g-PEG copolymers were synthesized by two steps, chloromethylation and graft reactions. Grafted PEG segment of PSf was controlled by molecular weight of PEG. Thermal properties of prepared mebrane were studied by TGA and DSC. T(g) of the copolymers was decreased with increasing of molecular weight of PEG. Hydrophilicity of PSf-g-PEG copolymer membrane was measured using contact angle method, and PEG grafted polymers showed lower contact angles due to higher hydrophilicity. Gas permeation properties of CO2 and N2 gases through the membranes were measured using time-lag method. The permeability of CO2 was enhanced with PEG moiety contents and increasing of number of PEG segment. The selectivity of CO2/N2 was increased with introducing of PEG due to higher solubility with CO2 gas. PMID:25942870

  15. Molecular simulations of the effects of phospholipid and cholesterol peroxidation on lipid membrane properties.

    PubMed

    Neto, Antenor J P; Cordeiro, Rodrigo M

    2016-09-01

    Non-enzymatic lipid peroxidation may change biomembrane structure and function. Here, we employed molecular dynamics simulations to study the effects of either phospholipid or cholesterol peroxidation individually, as well as the combined peroxidation of both components. When lipids were peroxidized, the generated OOH groups migrated to the membrane surface and engaged in H-bonds with each other and the phospholipid carbonyl ester groups. It caused the sn-2 acyl chains of phospholipid hydroperoxides to bend and the whole sterol backbone of cholesterol hydroperoxides to tilt. When phospholipids were kept intact, peroxidation of the sterol backbone led to a partial degradation of its condensing and ordering properties, independently of the position and isomerism of the OOH substitution. However, even in massively peroxidized membranes in which all phospholipids and cholesterol were peroxidized, the condensing and ordering properties of the sterol backbone were still significant. The possible implications for the formation of membrane lateral domains were discussed. Cholesterol peroxyl radicals were also investigated and we found that the OO groups did not migrate to the headgroups region. PMID:27349733

  16. Phospholipid-cationic lipid interactions: influences on membrane and vesicle properties.

    PubMed

    Campbell, R B; Balasubramanian, S V; Straubinger, R M

    2001-05-01

    Liposomes composed of synthetic dialkyl cationic lipids and zwitterionic phospholipids such as dioleoylphosphatidylethanolamine have been studied extensively as vehicles for gene delivery, but the broader potentials of these cationic liposomes for drug delivery have not. An understanding of phospholipid-cationic lipid interactions is essential for rational development of this potential. We evaluated the effect of the cationic lipid DOTAP (N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium) on liposome physical properties such as size and membrane domain structure. DSC (differential scanning calorimetry) showed progressive decrease and broadening of the phase transition temperature of dipalmitoylphosphatidylcholine (DPPC) with increasing fraction of DOTAP, in the range of 0.4-20 mol%. Laurdan (6-dodecanolyldimethylamino-naphthalene), a fluorescent probe of membrane domain structure, showed that DOTAP and DPPC remained miscible at all ratios tested. DOTAP reduced the size of spontaneously-forming PC-containing liposomes, regardless of the acyl chain length and degree of saturation. The anionic lipid DOPG (dioleoylphosphatidylglycerol) had similar effects on DPPC membrane fluidity and size. However, DOTAP/DOPC (50/50) vesicles were taken up avidly by OVCAR-3 human ovarian tumor cells, in contrast to DOPG/DOPC (50/50) liposomes. Overall, DOTAP exerts potent effects on bilayer physical properties, and may provide advantages for drug delivery. PMID:11334622

  17. Investigation of the pore structure and morphology of cellulose acetate membranes using small-angle neutron scattering. 1: Cellulose acetate active layer membranes

    SciTech Connect

    Kulkarni, S.; Krause, S. ); Wignall, G.D. . Solid State Div.); Hammouda, B. . Center for High Resolution Neutron Scattering)

    1994-11-07

    The structure of ultrathin cellulose acetate membranes, known as active layer membranes, has been investigated using small-angle neutron scattering. These membranes are known to have structural and functional similarity to the surface or skin layer in commercial reverse-osmosis (RO) membranes and hence are useful model systems for understanding the structure of the RO membrane skin layer. Active layer membranes were studied after swelling them with either D[sub 2]O or CD[sub 3]OD. The results in both cases clearly indicated the presence of very small (10--20 [angstrom]) porous structures in the membrane. The presence of such pores has been a subject of long-standing controversy in this area. The data were analyzed using a modified Debye-Bueche analysis and the resultant membrane structure was seen to agree well with structural information from electron microscopic studies. Finally, a possible explanation for the differences in scattering observed between the D[sub 2]O swollen membranes and the CD[sub 3]OD swollen membranes has been presented.

  18. Properties of poly(ethylene terephthalate) track membranes with a polymer layer obtained by plasma polymerization of pyrrole vapors

    NASA Astrophysics Data System (ADS)

    Kravets, L.; Dmitriev, S.; Lizunov, N.; Satulu, V.; Mitu, B.; Dinescu, G.

    2010-03-01

    The structure and the charge transport properties of poly(ethylene terephthalate) track membrane modified by pyrrole plasma were studied. It was found that polymer deposition on the surface of a track membrane via plasma polymerization of pyrrole results in the creation of composite nanomembranes that, in the case of the formation of a semipermeable layer, possess asymmetric conductivity in electrolyte solutions - a rectification effect similar to that of a p-n junction in semiconductors. It is caused by presence in the membranes of two layers with different functional groups and also by the pore geometry. Such membranes can be used to create chemical and biochemical sensors.

  19. Membrane permeability and the loss of germination factor from Neurospora crassa at low water activities

    NASA Technical Reports Server (NTRS)

    Charlang, G.; Horowitz, N. H.

    1974-01-01

    Neurospora crassa conidia incubating in buffer at low water activities release a germination-essential component as well as 260-nm absorbing and ninhydrin-positive materials, regardless of whether an electrolyte or nonelectrolyte is used to reduce water activity. Chloroform and antibiotics known to increase cell-membrane permeability have a similar effect. This suggests that membrane damage occurs in media of low water activity and that an increase in permeability is responsible for the release of cellular components. The damage caused in media of low water activity is nonlethal in most cases, and the conidia recover when transferred to nutrient medium.

  20. The antifungal activity and membrane-disruptive action of dioscin extracted from Dioscorea nipponica.

    PubMed

    Cho, Jaeyong; Choi, Hyemin; Lee, Juneyoung; Kim, Mi-Sun; Sohn, Ho-Yong; Lee, Dong Gun

    2013-03-01

    Dioscin is a kind of steroidal saponin isolated from the root bark of wild yam Dioscorea nipponica. We investigated the antifungal effect of dioscin against different fungal strains and its antifungal mechanism(s) in Candida albicans cells. Using the propidium iodide assay and calcein-leakage measurement, we confirmed that dioscin caused fungal membrane damage. Furthermore, we evaluated the ability of dioscin to disrupt the plasma membrane potential, using 3,3'-dipropylthiadicarbocyanine iodide [DiSC(3)(5)] and bis-(1,3-dibarbituric acid)-trimethine oxanol [DiBAC(4)(3)]. Cells stained with the dyes had a significant increase in fluorescent intensity after exposure to dioscin, indicating that dioscin has an effect on the membrane potential. To visualize the effect of dioscin on the cell membrane, we synthesized rhodamine-labeled giant unilamellar vesicles (GUVs) mimicking the outer leaflet of the plasma membrane of C. albicans. As seen in the result, the membrane disruptive action of dioscin caused morphological change and rhodamine leakage of the GUVs. In three-dimensional contour-plot analysis using flow cytometry, we observed a decrease in cell size, which is in agreement with our result from the GUV assay. These results suggest that dioscin exerts a considerable antifungal activity by disrupting the structure in membrane after invading into the fungal membrane, resulting in fungal cell death. PMID:23262192

  1. Powder Activated Carbon Pretreatment of a Microfiltration Membrane for the Treatment of Surface Water

    PubMed Central

    Song, Yali; Dong, Bingzhi; Gao, Naiyun; Ma, Xiaoyan

    2015-01-01

    This study focused on the effect of powder activated carbon (PAC) adsorption on microfiltration (MF) membrane performance. The results showed that PAC pretreatment offered high organic matter removal rates for both dissolved organic carbon (DOC) and ultraviolet absorbance at 254 nm (UV254) during 10–200 mg/L PAC dosage. The removal efficiencies of organic matter by MF membrane filtration decreased with the increase of organic matter removal rate by PAC adsorption. PAC mainly removed organic matter of about 3 kDa molecular weight (MW). MF membrane maintained more than 5 kDa MW organic matter on the membrane after PAC adsorption. The results of membrane filtration indicated that PAC pretreatment slightly promoted membrane flux, regardless of PAC dosage. It seems that the organic matter fouling membrane was concentrated in more than 3 kDa MW. PAC removed markedly less than 3 kDa MW organic matter and had less effect on more than 3 kDa organic matter. Thus, PAC cannot reduce membrane fouling. PMID:26378552

  2. Membrane-Active Sequences within gp41 Membrane Proximal External Region (MPER) Modulate MPER-Containing Peptidyl Fusion Inhibitor Activity and the Biosynthesis of HIV-1 Structural Proteins

    PubMed Central

    Zhang, Si Min; Jejcic, Alenka; Tam, James P.; Vahlne, Anders

    2015-01-01

    The membrane proximal external region (MPER) is a highly conserved membrane-active region located at the juxtamembrane positions within class I viral fusion glycoproteins and essential for membrane fusion events during viral entry. The MPER in the human immunodeficiency virus type I (HIV-1) envelope protein (Env) interacts with the lipid bilayers through a cluster of tryptophan (Trp) residues and a C-terminal cholesterol-interacting motif. The inclusion of the MPER N-terminal sequence contributes to the membrane reactivity and anti-viral efficacy of the first two anti-HIV peptidyl fusion inhibitors T20 and T1249. As a type I transmembrane protein, Env also interacts with the cellular membranes during its biosynthesis and trafficking. Here we investigated the roles of MPER membrane-active sequences during both viral entry and assembly, specifically, their roles in the design of peptidyl fusion inhibitors and the biosynthesis of viral structural proteins. We found that elimination of the membrane-active elements in MPER peptides, namely, penta Trp→alanine (Ala) substitutions and the disruption of the C-terminal cholesterol-interacting motif through deletion inhibited the anti-viral effect against the pseudotyped HIV-1. Furthermore, as compared to C-terminal dimerization, N-terminal dimerization of MPER peptides and N-terminal extension with five helix-forming residues enhanced their anti-viral efficacy substantially. The secondary structure study revealed that the penta-Trp→Ala substitutions also increased the helical content in the MPER sequence, which prompted us to study the biological relevance of such mutations in pre-fusion Env. We observed that Ala mutations of Trp664, Trp668 and Trp670 in MPER moderately lowered the intracellular and intraviral contents of Env while significantly elevating the content of another viral structural protein, p55/Gag and its derivative p24/capsid. The data suggest a role of the gp41 MPER in the membrane-reactive events during

  3. The role of spontaneous lipid curvature in the interaction of interfacially active peptides with membranes.

    PubMed

    Koller, Daniel; Lohner, Karl

    2014-09-01

    Research on antimicrobial peptides is in part driven by urgent medical needs such as the steady increase in pathogens being resistant to antibiotics. Despite the wealth of information compelling structure-function relationships are still scarce and thus the interfacial activity model has been proposed to bridge this gap. This model also applies to other interfacially active (membrane active) peptides such as cytolytic, cell penetrating or antitumor peptides. One parameter that is strongly linked to interfacial activity is the spontaneous lipid curvature, which is experimentally directly accessible. We discuss different parameters such as H-bonding, electrostatic repulsion, changes in monolayer surface area and lateral pressure that affect induction of membrane curvature, but also vice versa how membrane curvature triggers peptide response. In addition, the impact of membrane lipid composition on the formation of curved membrane structures and its relevance for diverse mode of action of interfacially active peptides and in turn biological activity are described. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova. PMID:24853655

  4. Phosphatidylinositol kinase is activated in membranes derived from cells treated with epidermal growth factor.

    PubMed Central

    Walker, D H; Pike, L J

    1987-01-01

    The ability of epidermal growth factor (EGF) to stimulate phosphatidylinositol (PtdIns) kinase activity in A431 cells was examined. The incorporation of 32P from [gamma-32P]ATP into PtdIns by A431 membranes was increased in membranes prepared from cells that had been pretreated with EGF. Demonstration of a stimulation of the PtdIns kinase activity by EGF required the use of subconfluent cultures and was dependent on the inclusion of protease inhibitors in the buffers used to prepare the membranes. Stimulation of the PtdIns kinase activity was rapid. The activation peaked 2 min after the addition of EGF and declined slowly thereafter. Half-maximal stimulation of the PtdIns kinase occurred at 7 nM EGF. Kinetic analyses of the reaction indicated that treatment of the cells with EGF resulted in a decrease in the Km for PtdIns with no change in the Vmax. The kinetic parameters for the utilization of ATP were unchanged in the EGF-treated membranes compared to the control membranes. Pretreatment of the cells with the phorbol ester phorbol 12-myristate 13-acetate blocked the ability of EGF to stimulate PtdIns kinase activity. These findings demonstrate that a PtdIns kinase activity in A431 cells is regulated by EGF and provide a good system for examining the mechanism by which EGF stimulates the activity of this intracellular enzyme. PMID:2823265

  5. Regulation of membrane associated protein kinase C activity by guanine nucleotide in rabbit peritoneal neutrophils

    SciTech Connect

    Huang, C.K.; Devanney, J.F.

    1986-03-05

    Addition of phorbol myristate acetate (PMA) (0.1 ..mu..g/ml) or guanosine-5'-0-(3-thiotriphosphate) (GTP..gamma..S) (10..mu..M) to the membrane fraction from rabbit peritoneal neutrophils results in an increase of phosphorylation of several membrane proteins. To test whether membrane associated protein kinase C is involved in the activation, histone is added to the membrane as a substrate for protein kinase C. Phosphorylation of histone is determined by counting the gel pieces containing histone IIIS after separation from other membrane components by SDS-gel electrophoresis. In the presence of CaC12 (20 ..mu..M), GTP..gamma..S (10 ..mu..M) or PMA (0.1 ..mu..g/ml) stimulates the phosphorylation of histone IIIS (40% to 70% increase). To achieve this effect calcium is required for GTP..gamma..S but not for PMA. The effect of GTP..gamma..S but not PMA is inhibited in membranes obtained from cells pretreated with pertussis toxin. Membrane protein kinase C is solubilized with Triton X-100 (1%) and then applied to a DEAE-52 cellulose column chromatography. Two peaks of protein kinase C activity are observed. Peak one is eluted at 40 mM NaCl, peak two is eluted at 140 mM NaCl. The activity of peak one is stimulated with phosphatidylserine (PS) and PMA but not with PS and calcium. The activity of peak two is stimulated with either PS and PMA or PS and calcium. The results suggest that GTP binding protein is involved in the activation of membrane associated protein kinase C and the kinase may exist in two forms, calcium sensitive and calcium insensitive.

  6. Nanostructure and Properties of Sulfonated Polyarylenethioethersulfone Copolymers as Proton Exchange Fuel Cell Membranes

    SciTech Connect

    Yoonessi,M.; Bai, Z.; Dang, T.

    2007-01-01

    A systematic investigation of properties and nanostructure of sulfonated polyarylenethioethersulfone (SPTES) copolymer proton exchange membranes for fuel cell applications has been presented. SPTES copolymers are high temperature resistant (250 C), and form tough films with excellent proton conductivity up to 170 {+-} 5 mS/cm (SPTES 70 @ 85 C, 85%RH). Small angle X-ray scattering of hydrated SPTES 70 revealed the presence of local water domains (diameter {approx}5 nm) within the copolymer. The high proton conductivity of the membranes is attributed to the formation of these ionic aggregates containing water molecules, which facilitate proton transfer. AFM studies of SPTES 70 as a function of humidity (25-65%RH) showed an increase in hydrophilic domains with increasing humidity at 22 C.

  7. Effect of substrate mechanical properties on T cell activation

    NASA Astrophysics Data System (ADS)

    Hui, King; Upadhyaya, Arpita

    2013-03-01

    T cell activation is a key process in cell-mediated immunity, and engagement of T cell receptors by peptides on antigen presenting cells leads to activation of signaling cascades as well as cytoskeletal reorganization and large scale membrane deformations. While significant advances have been made in understanding the biochemical signaling pathways, the effects imposed by the physical environment and the role of mechanical forces on cell activation are not well understood. In this study, we have used anti-CD3 coated elastic polyacrylamide gels as stimulatory substrates to enable the spreading of Jurkat T cells and the measurement of cellular traction forces. We have investigated the effect of substrate stiffness on the dynamics of T cell spreading and cellular force generation. We found that T cells display more active and sustained edge dynamics on softer gels and that they exert increased traction stresses with increasing gel stiffness. A dynamic actin cytoskeleton was required to maintain the forces generated during activation, as inferred from small molecule inhibition experiments. Our results indicate an important role for physical properties of the antigen presenting cell as well as cytoskeleton-driven forces in signaling activation.

  8. Activity of immobilised rat hepatic microsomal CYP2E1 using alumina membrane as a support.

    PubMed

    Tanvir, Shazia; Morandat, Sandrine; Frederic, Nadaud; Adenier, Hervé; Pulvin, Sylviane

    2009-11-30

    Porous alumina membranes are attractive materials for the construction of biosensors and also have utility for the production of immobilised enzyme bioreactors. Microsomes from rat liver were adsorbed onto alumina membrane activated by silane. Microsomal membranes were pumped through the channels where they became immobilised by binding to amine groups on the surface of the alumina membrane. In an effort to gain a quantitative understanding of the effects of microsomal film growth on enzyme activity, we compared the para-nitrophenol (pNP) hydroxylase activity of the microsomes by varying the amount of microsomes fixed in alumina microchannels. The alumina membrane was placed in a fluidic device at a fast flow that afforded short residence time (seconds) to obtain transformation of pNP to 4-nitrocatechol (pNC), which was detected by LC-MS/MS. This enabled the use of this bioreactor where CYP2E1 activity is low and tissue sources are limiting. The microsomes, successfully immobilised on the alumina membranes, were used to produce stable biocatalytic reactors that can be used repeatedly over a period of 2 months. PMID:19703600

  9. G-1-activated membrane estrogen receptors mediate increased contractility of the human myometrium.

    PubMed

    Maiti, K; Paul, J W; Read, M; Chan, E C; Riley, S C; Nahar, P; Smith, R

    2011-06-01

    Estrogens are key mediators of increased uterine contractility at labor. We sought to determine whether membrane-associated estrogen receptors, such as the recently described seven-transmembrane receptor G protein-coupled receptor 30 (GPR30), mediated some of this effect. Using human myometrium obtained at term cesarean section before or after the onset of labor, we demonstrated the presence of GPR30 mRNA and protein using quantitative RT-PCR and Western blotting. GPR30 receptor was localized to the cell membrane and often colocalized with calveolin-1. Using the specific estrogen membrane receptor agonist G-1 and myometrial explants, we showed that membrane receptor activation led to phosphorylation of MAPK and the actin-modifying small heat shock protein 27. Using myometrial strips incubated with G-1 or vehicle we demonstrated that estrogen membrane receptor activation increased the myometrial contractile response to oxytocin. These data suggest that activation of the plasma membrane estrogen receptor GPR30 likely participates in the physiology of the human myometrium during pregnancy and identifies it as a potential target to modify uterine activity. PMID:21427217

  10. Activation of Endothelial Nitric Oxide (eNOS) Occurs through Different Membrane Domains in Endothelial Cells

    PubMed Central

    Tran, Jason; Magenau, Astrid; Rodriguez, Macarena; Rentero, Carles; Royo, Teresa; Enrich, Carlos; Thomas, Shane R.; Grewal, Thomas; Gaus, Katharina

    2016-01-01

    Endothelial cells respond to a large range of stimuli including circulating lipoproteins, growth factors and changes in haemodynamic mechanical forces to regulate the activity of endothelial nitric oxide synthase (eNOS) and maintain blood pressure. While many signalling pathways have been mapped, the identities of membrane domains through which these signals are transmitted are less well characterized. Here, we manipulated bovine aortic endothelial cells (BAEC) with cholesterol and the oxysterol 7-ketocholesterol (7KC). Using a range of microscopy techniques including confocal, 2-photon, super-resolution and electron microscopy, we found that sterol enrichment had differential effects on eNOS and caveolin-1 (Cav1) colocalisation, membrane order of the plasma membrane, caveolae numbers and Cav1 clustering. We found a correlation between cholesterol-induced condensation of the plasma membrane and enhanced high density lipoprotein (HDL)-induced eNOS activity and phosphorylation suggesting that cholesterol domains, but not individual caveolae, mediate HDL stimulation of eNOS. Vascular endothelial growth factor (VEGF)-induced and shear stress-induced eNOS activity was relatively independent of membrane order and may be predominantly controlled by the number of caveolae on the cell surface. Taken together, our data suggest that signals that activate and phosphorylate eNOS are transmitted through distinct membrane domains in endothelial cells. PMID:26977592

  11. Structural basis for activation, assembly and membrane binding of ESCRT-III Snf7 filaments

    PubMed Central

    Tang, Shaogeng; Henne, W Mike; Borbat, Peter P; Buchkovich, Nicholas J; Freed, Jack H; Mao, Yuxin; Fromme, J Christopher; Emr, Scott D

    2015-01-01

    The endosomal sorting complexes required for transport (ESCRTs) constitute hetero-oligomeric machines that catalyze multiple topologically similar membrane-remodeling processes. Although ESCRT-III subunits polymerize into spirals, how individual ESCRT-III subunits are activated and assembled together into a membrane-deforming filament remains unknown. Here, we determine X-ray crystal structures of the most abundant ESCRT-III subunit Snf7 in its active conformation. Using pulsed dipolar electron spin resonance spectroscopy (PDS), we show that Snf7 activation requires a prominent conformational rearrangement to expose protein-membrane and protein-protein interfaces. This promotes the assembly of Snf7 arrays with ~30 Å periodicity into a membrane-sculpting filament. Using a combination of biochemical and genetic approaches, both in vitro and in vivo, we demonstrate that mutations on these protein interfaces halt Snf7 assembly and block ESCRT function. The architecture of the activated and membrane-bound Snf7 polymer provides crucial insights into the spatially unique ESCRT-III-mediated membrane remodeling. DOI: http://dx.doi.org/10.7554/eLife.12548.001 PMID:26670543

  12. Effects of chemical sanitization using NaOH on the properties of polysulfone and polyethersulfone ultrafiltration membranes.

    PubMed

    Teella, Achyuta; Zydney, Andrew L; Zhou, Hongyi; Olsen, Cathryn; Robinson, Craig

    2015-01-01

    Membranes used in bioprocessing applications are typically sanitized before use to insure aseptic operation. However, there is almost no information in the literature on the effects of this preuse sanitization step on the properties of the membrane. Experiments were performed with commercially available hollow fiber polysulfone (PSf) and polyethersulfone (PES) membranes with different nominal molecular weight cutoffs. Data were obtained for the membrane hydraulic permeability, dextran retention coefficients, zeta potential (surface charge), and extent of protein adsorption both before and after sanitization with 0.5 N NaOH at 45°C for 30 min. Changes in chemical composition were examined using ATR-FT-IR and XPS. Sanitization caused a large increase in the net negative charge for all membranes. There was a small reduction in hydraulic permeability and a significant increase in dextran retention for the polyethersulfone membranes, consistent with a reduction in the effective pore size. Spectroscopic analyses suggest that this change is likely due to the base-catalyzed hydrolysis of the lactam ring in polyvinylpyrrolidone (PVP) that is typically is used as a wetting/pore-forming agent in PSf and PES membranes. Preuse sanitization also appeared to have a small effect on protein adsorption, although the extent of adsorption was quite low for both the virgin and sanitized membranes. The observed changes in membrane properties could have a significant impact on the ultrafiltration performance, demonstrating the importance of standardizing the sanitization procedures even in process development and scale-down validation studies. PMID:25367682

  13. Nonlinear Dielectric Spectroscopy as an Indirect Probe of Metabolic Activity in Thylakoid Membrane

    PubMed Central

    Fang, Jie; Palanisami, Akilan; Rajapakshe, Kimal; Widger, William R.; Miller, John H.

    2011-01-01

    Nonlinear dielectric spectroscopy (NDS) is a non-invasive probe of cellular metabolic activity with potential application in the development of whole-cell biosensors. However, the mechanism of NDS interaction with metabolic membrane proteins is poorly understood, partly due to the inherent complexity of single cell organisms. Here we use the light-activated electron transport chain of spinach thylakoid membrane as a model system to study how NDS interacts with metabolic activity. We find protein modification, as opposed to membrane pump activity, to be the dominant source of NDS signal change in this system. Potential mechanisms for such protein modifications include reactive oxygen species generation and light-activated phosphorylation. PMID:25586698

  14. Permeability and electrical properties of planar lipid membranes from thylakoid lipids.

    PubMed Central

    Fuks, B; Homblé, F

    1994-01-01

    Electrical measurements were carried out on planar lipid membranes from thylakoid lipids. The specific capacitance of membranes formed from decane-containing monogalactosyldiacylglycerol (MGDG), which accounts for 57% of the total lipid content of thylakoids, showed that it adopted a bilayer structure. Solvent-free bilayers of MGDG were not formed, with very rare exceptions, indicating that decane is required to stabilize the planar conformation. However, this cone-shaped lipid produces bilayer structures in combination with other cylindrical thylakoid lipids even in the absence of organic solvent. We compared the properties of solvent-free and decane-containing bilayers from MGDG, soybean lecithin, and the quaternary mixture of lipids similar to that found in vivo. The conductance of decane-MGDG was 26 times higher than that of decane-lecithin. The flux through the decane-lecithin bilayer was found to be slightly dependent on pH, whereas the decane-MGDG membrane was not. The specific conductance of bilayers formed from the quaternary mixture of lipids was 5 to 10 times larger than lecithin (with alkane or not). Further experiments with bilayers made in the presence of a KCl gradient showed that decane-MGDG, decane-MGDG/DGDG/SQDG/PG, and solvent-free MGDG/DGDG/SQDG/PG were cation-selective. The permeability coefficient for potassium ranged from 4.9 to 8.3 x 10(-11) cm s-1. The permeability coefficient for protons in galactolipids, however, was determined to be about six orders of magnitude higher than the value for potassium ions. The HCl permeation mechanism through the lipid membranes was determined from diffusion potentials measured in HCl gradients. Our results suggest that HCl was not transported as neutral molecules. The data is discussed with regard to the function of galactolipids in the ion transport through thylakoid membranes. PMID:8061192

  15. Functional properties of the major outer membrane protein in Stenotrophomonas maltophilia.

    PubMed

    Chen, Yih-Yuan; Wu, Han-Chiang; Lin, Juey-Wen; Weng, Shu-Fen

    2015-08-01

    Stenotrophomonas maltophilia is an opportunistic pathogen that is closely associated with high morbidity and mortality in debilitated and immunocompromised individuals. Therefore, to investigate the pathogenesis mechanism is urgently required. However, there are very few studies to evaluate the functional properties of outer membrane protein, which may contribute to the pathogenesis in S. maltophilia. In this study, three abundant proteins in the outer membrane fraction of S. maltophilia were identified by liquid chromatography-tandem mass spectrometry as OmpW1, MopB, and a hypothetical protein. MopB, a member of the OmpA family, was firstly chosen for functional investigation in this study because many OmpA-family proteins are known to be involved in pathogenesis and offer potential as vaccines. Membrane fractionation analyses demonstrated that MopB was indeed the most abundant outer membrane protein (OMP) in S. maltophilia. For functional studies, the mopB mutant of S. maltophilia (SmMopB) was constructed by insertional mutation. MopB deficiency resulted in a change in the protein composition of OMPs and altered the architecture of the outer membrane. The SmMopB strain exhibited reduced cytotoxicity toward L929 fibroblasts and was more sensitive to numerous stresses, including human serum, sodium dodecyl sulfate, and hydrogen peroxide compared with wildtype S. maltophilia. These results suggest that MopB may be a good candidate for the design of vaccines or anti-MopB drugs for controlling serious nosocomial infections of multidrug-resistant S. maltophilia, especially in immunosuppressed patients. PMID:26224456

  16. Characterisation of Conformational and Ligand Binding Properties of Membrane Proteins Using Synchrotron Radiation Circular Dichroism (SRCD).

    PubMed

    Hussain, Rohanah; Siligardi, Giuliano

    2016-01-01

    Membrane proteins are notoriously difficult to crystallise for use in X-ray crystallographic structural determination, or too complex for NMR structural studies. Circular dichroism (CD) is a fast and relatively easy spectroscopic technique to study protein conformational behaviour in solution. The advantage of synchrotron radiation circular dichroism (SRCD) measured with synchrotron beamlines compared to the CD from benchtop instruments is the extended spectral far-UV region that increases the accuracy of secondary structure estimations, in particular under high ionic strength conditions. Membrane proteins are often available in small quantities, and for this SRCD measured at the Diamond B23 beamline has successfully facilitated molecular recognition studies. This was done by probing the local tertiary structure of aromatic amino acid residues upon addition of chiral or non-chiral ligands using long pathlength cells (1-5 cm) of small volume capacity (70 μl-350 μl). In this chapter we describe the use of SRCD to qualitatively and quantitatively screen ligand binding interactions (exemplified by Sbma, Ace1 and FsrC proteins); to distinguish between functionally similar drugs that exhibit different mechanisms of action towards membrane proteins (exemplified by FsrC); and to identify suitable detergent conditions to observe membrane protein-ligand interactions using stabilised proteins (exemplified by inositol transporters) as well as the stability of membrane proteins (exemplified by GalP, Ace1). The importance of the in solution characterisation of the conformational behaviour and ligand binding properties of proteins in both far- andnear-UV regions and the use of high-throughput CD (HT-CD) using 96- and 384-well multiplates to study the folding effects in various protein crystallisation buffers are also discussed. PMID:27553234

  17. Comparison of the Mechanical Properties of Early Leukocyte- and Platelet-Rich Fibrin versus PRGF/Endoret Membranes

    PubMed Central

    Khorshidi, Hooman; Raoofi, Saeed; Bagheri, Rafat; Banihashemi, Hodasadat

    2016-01-01

    Objectives. The mechanical properties of membranes are important factors in the success of treatment and clinical handling. The goal of this study was to compare the mechanical properties of early leukocyte- and platelet-rich fibrin (L-PRF) versus PRGF/Endoret membrane. Materials and Methods. In this experimental study, membranes were obtained from 10 healthy male volunteers. After obtaining 20 cc venous blood from each volunteer, 10 cc was used to prepare early L-PRF (group 1) and the rest was used to get a membrane by PRGF-Endoret system (group 2). Tensile loads were applied to specimens using universal testing machine. Tensile strength, stiffness, and toughness of the two groups of membranes were calculated and compared by paired t-test. Results. The mean tensile strength and toughness were higher in group 1 with a significant difference (P < 0.05). The mean stiffness in group 1 was also higher but not statistically significant (P > 0.05). Conclusions. The results showed that early L-PRF membranes had stronger mechanical properties than membranes produced by PRGF-Endoret system. Early L-PRF membranes might have easier clinical handling and could be a more proper scaffold in periodontal regenerative procedures. The real results of the current L-PRF should be in fact much higher than what is reported here. PMID:26880919

  18. Membrane processes for removal of pharmaceutically active compounds (PhACs) from water and wastewaters.

    PubMed

    Taheran, Mehrdad; Brar, Satinder K; Verma, M; Surampalli, R Y; Zhang, T C; Valero, J R

    2016-03-15

    Pharmaceutically active compounds (PhACs), which find their way easily into the water sources, are emerging as a major concern for drinking water quality and aquatic species. Therefore, their removal from water sources is a priority from environmental point of view. During the past decade, different methods including membrane separation, adsorption systems and chemical transformation have been evaluated for removal of these compounds. This paper reviews different aspects of PhAC removal by using membrane separation processes, as they have been conventionally known to show high potential in the production of superior quality drinking and industrial water. In brief, osmosis membranes can efficiently remove almost all PhACs though its operational cost is relatively high and nanofiltration (NF) membranes are highly influenced by electrostatic and hydrophobic interaction. Moreover, the efficiency of membrane bioreactors (MBRs) is difficult to predict due to the complex interaction of compounds with microorganisms. To improve the performance and robustness of membrane technology, it is suggested to combine membranes with other systems, such as activated carbon and enzymatic degradation. PMID:26789358

  19. Properties of follicle-stimulating-hormone receptor in cell membranes of bovine testis.

    PubMed Central

    Cheng, K W

    1975-01-01

    A simple method for preparing plasma membranes from bovine testes is described. Bovine testicular receptor has a high affinity and specificity for 125I-labelled human FSH (follicle-stimulating hormone). The specific binding of 125I-labelled human FSH to the plasma membranes is a saturable process with respect to the amounts of receptor protein and FSH added. The association and dissociation of 125I-labelled human FSH are time- and temperature-dependent, and the binding of labelled human FSH to bovine testicular receptor is strong and not readily reversible. Scatchard [Ann. N.Y. Acad. Sci. (1949) 51, 660-672] analysis indicates a dissociation constant, Kd, of 9.8 X10(-11)M, and 5.9 X 10(-14)mol of binding sites/mg of membrane protein. The testicular membrane receptor is heat-labile. Preheating at 40 degrees C for 15 min destroyed 30% of the binding activity. Specific binding is pH-dependent, with an optimum between pH 7.0 and 7.5. Brief exposure to extremes of pH caused irreversible damage to the receptors. The ionic strength of the incubation medium markedly affects the association of 125I-labelled human FSH with its testicular receptor. Various cations at concentrations of 0.1M inhibit almost completely the binding of 125I-labelled human FSH. Nuclectides and steroid hormones at concentrations of 1mM and 5mu/ml respectively have no effect on the binding of FSH to its receptor. Incubation of membranes with and chymotrypsin resulted in an almost complete loss of binding activity, suggesting that protein moieties are essential for the binding of 125I-labelled human FSH. Binding of 125I-labelled human FSH to bovine testicular receptor does not result in destruction or degradation of the hormone. PMID:242318

  20. Development of a novel microperfusion chamber for determination of cell membrane transport properties.

    PubMed Central

    Gao, D Y; Benson, C T; Liu, C; McGrath, J J; Critser, E S; Critser, J K

    1996-01-01

    A novel microperfusion chamber was developed to measure kinetic cell volume changes under various extracellular conditions and to quantitatively determine cell membrane transport properties. This device eliminates modeling ambiguities and limitations inherent in the use of the microdiffusion chamber and the micropipette perfusion technique, both of which have been previously validated and are closely related optical technologies using light microscopy and image analysis. The resultant simplicity should prove to be especially valuable for study of the coupled transport of water and permeating solutes through cell membranes. Using the microperfusion chamber, water and dimethylsulfoxide (DMSO) permeability coefficients of mouse oocytes as well as the water permeability coefficient of golden hamster pancreatic islet cells were determined. In these experiments, the individual cells were held in the chamber and perfused at 22 degrees C with hyperosmotic media, with or without DMSO (1.5 M). The cell volume change was videotaped and quantified by image analysis. Based on the experimental data and irreversible thermodynamics theory for the coupled mass transfer across the cell membrane, the water permeability coefficient of the oocytes was determined to be 0.47 micron. min-1. atm-1 in the absence of DMSO and 0.65 microns. min-1. atm-1 in the presence of DMSO. The DMSO permeability coefficient of the oocyte membrane and associated membrane reflection coefficient to DMSO were determined to be 0.23 and 0.85 micron/s, respectively. These values are consistent with those determined using the micropipette perfusion and microdiffusion chamber techniques. The water permeability coefficient of the golden hamster pancreatic islet cells was determined to be 0.27 microns. min-1. atm-1, which agrees well with a value previously determined using an electronic sizing (Coulter counter) technique. The use of the microperfusion chamber has the following major advantages: 1) This method

  1. Influence of low-power laser radiation on the activity of some membraneous and mitochondrial enzymes of hepatocytes in rats

    NASA Astrophysics Data System (ADS)

    Cieslar, Grzegorz; Adamek, Mariusz; Sieron, Aleksander; Kaminski, Marcin

    1995-01-01

    It was observed in some experiments that visible laser radiation activates the enzymatic function of mitochondria, while infrared laser radiation affects the enzymatic activity of cellular membranes. The aim of the study was to estimate the activity of some membranous as well as mitochondrial enzymes of hepatocytes in rats irradiated with infrared laser. Experimental material consisted of 38 Wistar rats divided into 2 groups -- a studied group exposed to infrared laser radiation and a control group, in which no irradiation was made. A semiconductive infrared laser (wavelength -- 904 nm, mean power -- 8.9 mW) was used. The clean-shaven skin of the right infracostal region of animals was irradiated 5 minutes daily for 15 consecutive days. After finishing the experiment in the preparations from obtained segments of the left liver lobe, the enzymatic activity of succinate dehydrogenase (SDH, EC 1.3.99.1), lactic dehydrogenase (LDH, EC 1.1.1.27), Mg2+ dependent ATP-ase (ATP-ase Mg2+, EC 3.1.3.2.) and acid phosphatase (AcP, EC 3.6.1.8.) was estimated with the use of histochemical methods. In the case of SDH and LDH the increase of enzymatic activity was observed in all 3 zones of liver cluster, especially in male rats. In the case of ATP-ase Mg2+ and AcP the increase of enzymatic activity in biliary canaliculi of hepatocytes in all zones of the liver cluster was observed. On the basis of the obtained results it was proved that infrared laser radiation activates significantly the enzymatic activity of most of the analyzed enzymes, which means that it affects not only properties of biological membranes but also activates the oxidoreductive processes of organism, as it has been observed for visible laser radiation. On the basis of the spectrum of energetic levels in macromolecules (Jablonski's diagram) the mechanisms of availed results are discussed both for enzymes possessing and not possessing chromatophores.

  2. Controlled release and antibacterial activity of tetracycline hydrochloride-loaded bacterial cellulose composite membranes.

    PubMed

    Shao, Wei; Liu, Hui; Wang, Shuxia; Wu, Jimin; Huang, Min; Min, Huihua; Liu, Xiufeng

    2016-07-10

    Bacterial cellulose (BC) is widely used in biomedical applications. In this study, we prepared an antibiotic drug tetracycline hydrochloride (TCH)-loaded bacterial cellulose (BC) composite membranes, and evaluated the drug release, antibacterial activity and biocompatibility. The structure and morphology of the fabricated BC-TCH composite membranes were characterized using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The TCH release results show that the incorporation of BC matrix to load TCH is able to control the release. In vitro antibacterial assay demonstrate that the developed BC-TCH composites displayed excellent antibacterial activity solely associated with the loaded TCH drug. More importantly, the BC-TCH composite membranes display good biocompatibility. These characteristics of BC-TCH composite membranes indicate that they may successfully serve as wound dressings and other medical biomaterials. PMID:27106158

  3. Effects of Boron on Proton Transport and Membrane Properties of Sunflower (Helianthus annuus L.) Cell Microsomes.

    PubMed Central

    Ferrol, N.; Belver, A.; Roldan, M.; Rodriguez-Rosales, M. P.; Donaire, J. P.

    1993-01-01

    Boron deficiency and toxicity inhibit ATP-dependent H+ pumping and vanadate-sensitive ATPase activity in sunflower roots and cell suspensions. The effects of boron on H+ pumping and on passive H+ conductance, as well as on fluorescence anisotropy in KI-washed microsomes isolated from sunflower (Helianthus annuus L. cv Enano) cell suspensions, have been investigated. Boron deficiency reduced the total and vanadate-sensitive ATPase activities as well as the vanadate-sensitive ATP-dependent H+ pumping without affecting the amount of antigenic ATPase protein as measured by immunoblotting with an Arabidopsis thaliana plasma membrane anti-H+-ATPase polyclonal antibody. Kinetic studies revealed that boron deficiency reduced Vmax of vanadate-sensitive ATPase activity with little change in the apparent Km for Mg2+-ATP. Proton leakage was greater in microsomal vesicles isolated from cells grown without boron and incubated in reaction medium without added boron, and this effect was reversed by addition of boron to the reaction medium. Fluorescence anisotropy indicated that diphenyl hexatriene and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene probes were immobilized to a greater extent in microsomes from cells grown without boron than in those from cells grown with 100 [mu]M H3BO3. The apparent decrease of membrane fluidity in microsomes from cells grown without boron was reversed by the addition of boron to the reaction medium. Taken together these data suggest that inhibition of H+ gradient formation in microsomes from sunflower cells grown in the absence of boron could be due to the combined effects of reduced H+-ATPase activity and increased passive conductance across the membrane, possibly resulting from increased membrane rigidity. PMID:12231978

  4. Luminol electrochemiluminescence for the analysis of active cholesterol at the plasma membrane in single mammalian cells.

    PubMed

    Ma, Guangzhong; Zhou, Junyu; Tian, Chunxiu; Jiang, Dechen; Fang, Danjun; Chen, Hongyuan

    2013-04-16

    A luminol electrochemiluminescence assay was reported to analyze active cholesterol at the plasma membrane in single mammalian cells. The cellular membrane cholesterol was activated by the exposure of the cells to low ionic strength buffer or the inhibition of intracellular acyl-coA/cholesterol acyltransferase (ACAT). The active membrane cholesterol was reacted with cholesterol oxidase in the solution to generate a peak concentration of hydrogen peroxide on the electrode surface, which induced a measurable luminol electrochemiluminescence. Further treatment of the active cells with mevastatin decreased the active membrane cholesterol resulting in a drop in luminance. No change in the intracellular calcium was observed in the presence of luminol and voltage, which indicated that our analysis process might not interrupt the intracellular cholesterol trafficking. Single cell analysis was performed by placing a pinhole below the electrode so that only one cell was exposed to the photomultiplier tube (PMT). Twelve single cells were analyzed individually, and a large deviation on luminance ratio observed exhibited the cell heterogeneity on the active membrane cholesterol. The smaller deviation on ACAT/HMGCoA inhibited cells than ACAT inhibited cells suggested different inhibition efficiency for sandoz 58035 and mevastatin. The new information obtained from single cell analysis might provide a new insight on the study of intracellular cholesterol trafficking. PMID:23527944

  5. Fast serial analysis of active cholesterol at the plasma membrane in single cells.

    PubMed

    Tian, Chunxiu; Zhou, Junyu; Wu, Zeng-Qiang; Fang, Danjun; Jiang, Dechen

    2014-01-01

    Previously, our group has utilized the luminol electrochemiluminescence to analyze the active cholesterol at the plasma membrane in single cells by the exposure of one cell to a photomultiplier tube (PMT) through a pinhole. In this paper, fast analysis of active cholesterol at the plasma membrane in single cells was achieved by a multimicroelectrode array without the pinhole. Single cells were directly located on the microelectrodes using cell-sized microwell traps. A cycle of voltage was applied on the microelectrodes sequentially to induce a peak of luminescence from each microelectrode for the serial measurement of active membrane cholesterol. A minimal time of 1.60 s was determined for the analysis of one cell. The simulation and the experimental data exhibited a semisteady-state distribution of hydrogen peroxide on the microelectrode after the reaction of cholesterol oxidase with the membrane cholesterol, which supported the relative accuracy of the serial analysis. An eight-microelectrode array was demonstrated to analyze eight single cells in 22 s serially, including the channel switching time. The results from 64 single cells either activated by low ion strength buffer or the inhibition of intracellular acyl-coA/cholesterol acyltransferase (ACAT) revealed that most of the cells analyzed had the similar active membrane cholesterol, while few cells had more active cholesterol resulting in the cellular heterogeneity. The fast single-cell analysis platform developed will be potentially useful for the analysis of more molecules in single cells using proper oxidases. PMID:24328095

  6. Preparation and characterization of modified nano-porous PVDF membrane with high antifouling property using UV photo-grafting

    NASA Astrophysics Data System (ADS)

    Rahimpour, A.; Madaeni, S. S.; Zereshki, S.; Mansourpanah, Y.

    2009-05-01

    In this study, the poly(vinylidene fluoride) (PVDF) membrane was prepared via immersion precipitation technique and modified by UV photo-grafting of hydrophilic monomers on the top membrane surface. Acrylic acid (AA) and 2-hydroxyethylmethacrylate (HEMA) as acrylic monomers and 2,4-phenylenediamine (PDA) and ethylene diamine (EDA) as amino monomers were used at different concentrations to modify the membrane and improve the hydrophilicity with less fouling tendency. Moreover the presence of benzophenon as photo-initiator for grafting the hydrophilic monomers onto PVDF membrane surface was elucidated. The virgin and modified PVDF membranes were characterized by contact angle, ATR-FTIR, SEM and cross-flow filtration. The contact angle measurements demonstrated that the hydrophilicities of the membranes were significantly enhanced by UV photo-grafting of hydrophilic monomers onto the membrane surface. The ATR-FTIR confirmed the occurrence of modification on PVDF membrane by UV photo-grafting. The pure water flux of membranes was declined by UV photo-grafting but the milk water permeation and protein rejection were slightly improved. Moreover the antifouling properties and flux recovery of PVDF membrane were improved by UV photo-grafting of hydrophilic monomers.

  7. CVD synthesis and gas permeation properties of thin palladium/alumina membranes

    SciTech Connect

    Xomeritakis, G.; Lin, Y.S.

    1998-01-01

    Thin (0.5--5-{micro}m) palladium (Pd) membranes were prepared inside pores or on the surface of mesoporous (pore size 4--6 nm), sol-gel-derived {gamma}-Al{sub 2}O{sub 3} supports by the chemical vapor deposition (CVD) method using palladium acetylacetonate and palladium chloride (together with hydrogen) as Pd precursors. When Pd is deposited in the form of metal plugs inside pores of {gamma}-Al{sub 2}O{sub 3}, He permeance of the composite membranes increases exponentially with temperature, indicating activated diffusion through the microporous metal deposit defects, while only modest permselectivity for H{sub 2} is observed. When Pd is deposited in the form of a metal film on the surface of {gamma}-Al{sub 2}O{sub 3}, He permeance is governed by Knudsen-viscous flow through meso/macroporous metal film defects. The H{sub 2} permeance of different palladium membranes prepared by CVD appears to increase with palladium crystal grain size. The highest H{sub 2} permeance and H{sub 2}:He permselectivity for membranes prepared in this study are about 1.0--2.0 {times} 10{sup {minus}7} mol/m {center_dot} s {center_dot} Pa and 200--300 at 300 C, respectively.

  8. Effect of partial or complete elimination of light-harvesting complexes on the surface electric properties and the functions of cyanobacterial photosynthetic membranes.

    PubMed

    Dobrikova, Anelia G; Domonkos, Ildikó; Sözer, Özge; Laczkó-Dobos, Hajnalka; Kis, Mihály; Párducz, Árpád; Gombos, Zoltán; Apostolova, Emilia L

    2013-02-01

    Influence of the modification of the cyanobacterial light-harvesting complex [i.e. phycobilisomes (PBS)] on the surface electric properties and the functions of photosynthetic membranes was investigated. We used four PBS mutant strains of Synechocystis sp. PCC6803 as follows: PAL (PBS-less), CK (phycocyanin-less), BE (PSII-PBS-less) and PSI-less/apcE(-) (PSI-less with detached PBS). Modifications of the PBS content lead to changes in the cell morphology and surface electric properties of the thylakoid membranes as well as in their functions, such as photosynthetic oxygen-evolving activity, P700 kinetics and energy transfer between the pigment-protein complexes. Data reveal that the complete elimination of PBS in the PAL mutant causes a slight decrease in the electric dipole moments of the thylakoid membranes, whereas significant perturbations of the surface charges were registered in the membranes without assembled PBS-PSII macrocomplex (BE mutant) or PSI complex (PSI-less mutant). These observations correlate with the detected alterations in the membrane structural organization. Using a polarographic oxygen rate electrode, we showed that the ratio of the fast to the slow oxygen-evolving PSII centers depends on the partial or complete elimination of light-harvesting complexes, as the slow operating PSII centers dominate in the PBS-less mutant and in the mutant with detached PBS. PMID:22582961

  9. Specificity and mechanism of action of alpha-helical membrane-active peptides interacting with model and biological membranes by single-molecule force spectroscopy

    PubMed Central

    Sun, Shiyu; Zhao, Guangxu; Huang, Yibing; Cai, Mingjun; Shan, Yuping; Wang, Hongda; Chen, Yuxin

    2016-01-01

    In this study, to systematically investigate the targeting specificity of membrane-active peptides on different types of cell membranes, we evaluated the effects of peptides on different large unilamellar vesicles mimicking prokaryotic, normal eukaryotic, and cancer cell membranes by single-molecule force spectroscopy and spectrum technology. We revealed that cationic membrane-active peptides can exclusively target negatively charged prokaryotic and cancer cell model membranes rather than normal eukaryotic cell model membranes. Using Acholeplasma laidlawii, 3T3-L1, and HeLa cells to represent prokaryotic cells, normal eukaryotic cells, and cancer cells in atomic force microscopy experiments, respectively, we further studied that the single-molecule targeting interaction between peptides and biological membranes. Antimicrobial and anticancer activities of peptides exhibited strong correlations with the interaction probability determined by single-molecule force spectroscopy, which illustrates strong correlations of peptide biological activities and peptide hydrophobicity and charge. Peptide specificity significantly depends on the lipid compositions of different cell membranes, which validates the de novo design of peptide therapeutics against bacteria and cancers. PMID:27363513

  10. Specificity and mechanism of action of alpha-helical membrane-active peptides interacting with model and biological membranes by single-molecule force spectroscopy.

    PubMed

    Sun, Shiyu; Zhao, Guangxu; Huang, Yibing; Cai, Mingjun; Shan, Yuping; Wang, Hongda; Chen, Yuxin

    2016-01-01

    In this study, to systematically investigate the targeting specificity of membrane-active peptides on different types of cell membranes, we evaluated the effects of peptides on different large unilamellar vesicles mimicking prokaryotic, normal eukaryotic, and cancer cell membranes by single-molecule force spectroscopy and spectrum technology. We revealed that cationic membrane-active peptides can exclusively target negatively charged prokaryotic and cancer cell model membranes rather than normal eukaryotic cell model membranes. Using Acholeplasma laidlawii, 3T3-L1, and HeLa cells to represent prokaryotic cells, normal eukaryotic cells, and cancer cells in atomic force microscopy experiments, respectively, we further studied that the single-molecule targeting interaction between peptides and biological membranes. Antimicrobial and anticancer activities of peptides exhibited strong correlations with the interaction probability determined by single-molecule force spectroscopy, which illustrates strong correlations of peptide biological activities and peptide hydrophobicity and charge. Peptide specificity significantly depends on the lipid compositions of different cell membranes, which validates the de novo design of peptide therapeutics against bacteria and cancers. PMID:27363513

  11. Efficient energy transmission and amplification in the cochlea relies on frequency-dependent material properties of the tectorial membrane

    NASA Astrophysics Data System (ADS)

    Jones, Gareth P.; Lukashkina, Victoria A.; Russell, Ian J.; Elliott, Stephen J.; Lukashkin, Andrei N.

    2015-12-01

    The remarkable sensitivity, frequency selectivity, and dynamic range of the mammalian cochlea relies on longitudinal transmission of minuscule amounts of energy as passive, pressure-driven, basilar membrane (BM) traveling waves which are actively amplified at frequency-specific locations. Transmission of passive waves through viscous tissue situated in a viscous media is not an easy task. Here we describe mechanical properties of the tectorial membrane (TM) which facilitate this transmission. From mechanical measurements of isolated segments of the TM, we discovered that the stiffness of the TM is reduced when it is mechanically stimulated at physiologically relevant magnitudes and at frequencies below their frequency place in the cochlea. The reduction in stiffness functionally uncouples the TM from the organ of Corti, thereby minimizing energy losses during passive traveling wave propagation. Stiffening and decreased viscosity of the TM at high stimulus frequencies can potentially facilitate active amplification, especially in the high-frequency, basal turn, where energy loss due to internal friction within the TM is less than in the apex. This prediction is confirmed by neural recordings from several frequency regions of the cochlea.

  12. Detergent-free domain isolated from Xenopus egg plasma membrane with properties similar to those of detergent-resistant membranes.

    PubMed

    Luria, Ayala; Vegelyte-Avery, Vaida; Stith, Brad; Tsvetkova, Nelly M; Wolkers, Willem F; Crowe, John H; Tablin, Fern; Nuccitelli, Richard

    2002-11-01

    Microdomains known as "rafts" have been isolated from many cell types as detergent-resistant membranes (DRMs) and are enriched in sphingolipids and cholesterol. However, there has been considerable controversy over whether such domains are found in native membranes or are artificially generated by the purification procedure. This controversy is based at least in part on the fact that raft membranes were first detected following detergent extraction in the cold. We isolated two plasma membrane fractions, without detergent treatment, using a discontinuous sucrose density gradient. One fraction was designated "light" and the other "heavy." These fractions were compared with DRMs, which were isolated in the presence of 1% Triton X-100. We found that Xenopus DRMs are enriched with sphingomyelin and cholesterol and exhibit a phase state similar to the liquid-ordered phase. Comparison of DRM complexes with the light and heavy plasma membrane fractions revealed some physical and biochemical similarities between the light fraction of the plasma membrane and the DRM complexes, based on (1) the phosphatidylcholine/sphingomyelin ratio and (2) the protein composition visualized on a two-dimensional gel. These two fractions are also quite similar in their thermotropic phase behavior, and their high levels of ganglioside GM1. We conclude that the light membrane fraction isolated in a detergent-free environment has many of the characteristics normally associated with DRMs. PMID:12403620

  13. Improved antibacterial activity of nanofiltration polysulfone membranes modified with silver nanoparticles.

    PubMed

    Andrade, Patricia Fernanda; de Faria, Andreia Fonseca; Oliveira, Silvana Ruella; Arruda, Marco Aurélio Zezzi; Gonçalves, Maria do Carmo

    2015-09-15

    Polysulfone membranes (PSf) containing silver nanoparticles were prepared by the wet phase-inversion process. Silver nanoparticles (AgNP) were dispersed into the polymer matrix using two different methodologies. In the first one, the AgNP were synthesized and further dispersed into the polymer solution (ex situ process). In the second method, the formation of the AgNP was performed in situ. The AgNP crystalline structure in the PSf membranes was confirmed by X-ray diffraction. Field emission scanning electron microscopy images showed that the addition of AgNP in PSf membranes caused no significant changes to the finger-like morphology. When the ex situ methodology was applied, 45 nm average size AgNP were uniformly distributed in the internal pores of the membranes. However, when the AgNP were formed through the in situ process, the AgNP were uniformly and preferentially distributed on the top and bottom surfaces of the membrane. In the last case, the AgNP showed cubic morphology when present in the bottom and top surfaces, however, when inside the membrane their morphology was spherical. The cubic-like nanoparticles displayed a 38 nm average edge length. The silver ion released from the membrane during water filtration was measured using inductively coupled plasma mass spectrometry, which showed a silver leaching of approximately 2 μg L(-1). The nanocomposite membranes prepared by the in situ method exhibited a better antibacterial activity, in comparison to those prepared by ex situ, and also a decrease in 90% Escherichia coli adhered cells compared to the pristine PSf membranes. In conclusion, the in situ procedure can be considered a feasible, simple, and reproducible methodology to prepare anti-biofouling polysulfone membranes containing AgNP. PMID:26099831

  14. Tuning Liposome Membrane Permeability by Competitive Peptide Dimerization and Partitioning-Folding Interactions Regulated by Proteolytic Activity

    PubMed Central

    Lim, Seng Koon; Sandén, Camilla; Selegård, Robert; Liedberg, Bo; Aili, Daniel

    2016-01-01

    Membrane active peptides are of large interest for development of drug delivery vehicles and therapeutics for treatment of multiple drug resistant infections. Lack of specificity can be detrimental and finding routes to tune specificity and activity of membrane active peptides is vital for improving their therapeutic efficacy and minimize harmful side effects. We describe a de novo designed membrane active peptide that partition into lipid membranes only when specifically and covalently anchored to the membrane, resulting in pore-formation. Dimerization with a complementary peptide efficiently inhibits formation of pores. The effect can be regulated by proteolytic digestion of the inhibitory peptide by the matrix metalloproteinase MMP-7, an enzyme upregulated in many malignant tumors. This system thus provides a precise and specific route for tuning the permeability of lipid membranes and a novel strategy for development of recognition based membrane active peptides and indirect enzymatically controlled release of liposomal cargo. PMID:26892926

  15. Tuning Liposome Membrane Permeability by Competitive Peptide Dimerization and Partitioning-Folding Interactions Regulated by Proteolytic Activity.

    PubMed

    Lim, Seng Koon; Sandén, Camilla; Selegård, Robert; Liedberg, Bo; Aili, Daniel

    2016-01-01

    Membrane active peptides are of large interest for development of drug delivery vehicles and therapeutics for treatment of multiple drug resistant infections. Lack of specificity can be detrimental and finding routes to tune specificity and activity of membrane active peptides is vital for improving their therapeutic efficacy and minimize harmful side effects. We describe a de novo designed membrane active peptide that partition into lipid membranes only when specifically and covalently anchored to the membrane, resulting in pore-formation. Dimerization with a complementary peptide efficiently inhibits formation of pores. The effect can be regulated by proteolytic digestion of the inhibitory peptide by the matrix metalloproteinase MMP-7, an enzyme upregulated in many malignant tumors. This system thus provides a precise and specific route for tuning the permeability of lipid membranes and a novel strategy for development of recognition based membrane active peptides and indirect enzymatically controlled release of liposomal cargo. PMID:26892926

  16. Tuning Liposome Membrane Permeability by Competitive Peptide Dimerization and Partitioning-Folding Interactions Regulated by Proteolytic Activity

    NASA Astrophysics Data System (ADS)

    Lim, Seng Koon; Sandén, Camilla; Selegård, Robert; Liedberg, Bo; Aili, Daniel

    2016-02-01

    Membrane active peptides are of large interest for development of drug delivery vehicles and therapeutics for treatment of multiple drug resistant infections. Lack of specificity can be detrimental and finding routes to tune specificity and activity of membrane active peptides is vital for improving their therapeutic efficacy and minimize harmful side effects. We describe a de novo designed membrane active peptide that partition into lipid membranes only when specifically and covalently anchored to the membrane, resulting in pore-formation. Dimerization with a complementary peptide efficiently inhibits formation of pores. The effect can be regulated by proteolytic digestion of the inhibitory peptide by the matrix metalloproteinase MMP-7, an enzyme upregulated in many malignant tumors. This system thus provides a precise and specific route for tuning the permeability of lipid membranes and a novel strategy for development of recognition based membrane active peptides and indirect enzymatically controlled release of liposomal cargo.

  17. Golgi membrane fission requires the CtBP1-S/BARS-induced activation of lysophosphatidic acid acyltransferase δ.

    PubMed

    Pagliuso, Alessandro; Valente, Carmen; Giordano, Lucia Laura; Filograna, Angela; Li, Guiling; Circolo, Diego; Turacchio, Gabriele; Marzullo, Vincenzo Manuel; Mandrich, Luigi; Zhukovsky, Mikhail A; Formiggini, Fabio; Polishchuk, Roman S; Corda, Daniela; Luini, Alberto

    2016-01-01

    Membrane fission is an essential cellular process by which continuous membranes split into separate parts. We have previously identified CtBP1-S/BARS (BARS) as a key component of a protein complex that is required for fission of several endomembranes, including basolateral post-Golgi transport carriers. Assembly of this complex occurs at the Golgi apparatus, where BARS binds to the phosphoinositide kinase PI4KIIIβ through a 14-3-3γ dimer, as well as to ARF and the PKD and PAK kinases. We now report that, when incorporated into this complex, BARS binds to and activates a trans-Golgi lysophosphatidic acid (LPA) acyltransferase type δ (LPAATδ) that converts LPA into phosphatidic acid (PA); and that this reaction is essential for fission of the carriers. LPA and PA have unique biophysical properties, and their interconversion might facilitate the fission process either directly or indirectly (via recruitment of proteins that bind to PA, including BARS itself). PMID:27401954

  18. Golgi membrane fission requires the CtBP1-S/BARS-induced activation of lysophosphatidic acid acyltransferase δ

    PubMed Central

    Pagliuso, Alessandro; Valente, Carmen; Giordano, Lucia Laura; Filograna, Angela; Li, Guiling; Circolo, Diego; Turacchio, Gabriele; Marzullo, Vincenzo Manuel; Mandrich, Luigi; Zhukovsky, Mikhail A.; Formiggini, Fabio; Polishchuk, Roman S.; Corda, Daniela; Luini, Alberto

    2016-01-01

    Membrane fission is an essential cellular process by which continuous membranes split into separate parts. We have previously identified CtBP1-S/BARS (BARS) as a key component of a protein complex that is required for fission of several endomembranes, including basolateral post-Golgi transport carriers. Assembly of this complex occurs at the Golgi apparatus, where BARS binds to the phosphoinositide kinase PI4KIIIβ through a 14-3-3γ dimer, as well as to ARF and the PKD and PAK kinases. We now report that, when incorporated into this complex, BARS binds to and activates a trans-Golgi lysophosphatidic acid (LPA) acyltransferase type δ (LPAATδ) that converts LPA into phosphatidic acid (PA); and that this reaction is essential for fission of the carriers. LPA and PA have unique biophysical properties, and their interconversion might facilitate the fission process either directly or indirectly (via recruitment of proteins that bind to PA, including BARS itself). PMID:27401954

  19. Composition, structure and mechanical properties define performance of pulmonary surfactant membranes and films.

    PubMed

    Parra, Elisa; Pérez-Gil, Jesús

    2015-01-01

    The respiratory surface in the mammalian lung is stabilized by pulmonary surfactant, a membrane-based system composed of multiple lipids and specific proteins, the primary function of which is to minimize the surface tension at the alveolar air-liquid interface, optimizing the mechanics of breathing and avoiding alveolar collapse, especially at the end of expiration. The goal of the present review is to summarize current knowledge regarding the structure, lipid-protein interactions and mechanical features of surfactant membranes and films and how these properties correlate with surfactant biological function inside the lungs. Surfactant mechanical properties can be severely compromised by different agents, which lead to surfactant inhibition and ultimately contributes to the development of pulmonary disorders and pathologies in newborns, children and adults. A detailed comprehension of the unique mechanical and rheological properties of surfactant layers is crucial for the diagnostics and treatment of lung diseases, either by analyzing the contribution of surfactant impairment to the pathophysiology or by improving the formulations in surfactant replacement therapies. Finally, a short review is also included on the most relevant experimental techniques currently employed to evaluate lung surfactant mechanics, rheology, and inhibition and reactivation processes. PMID:25260665

  20. Sphingomyelinase D Activity in Model Membranes: Structural Effects of in situ Generation of Ceramide-1-Phosphate

    PubMed Central

    Stock, Roberto P.; Brewer, Jonathan; Wagner, Kerstin; Ramos-Cerrillo, Blanca; Duelund, Lars; Jernshøj, Kit Drescher; Olsen, Lars Folke; Bagatolli, Luis A.

    2012-01-01

    The toxicity of Loxosceles spider venom has been attributed to a rare enzyme, sphingomyelinase D, which transforms sphingomyelin to ceramide-1-phosphate. The bases of its inflammatory and dermonecrotic activity, however, remain unclear. In this work the effects of ceramide-1-phosphate on model membranes were studied both by in situ generation of this lipid using a recombinant sphingomyelinase D from the spider Loxosceles laeta and by pre-mixing it with sphingomyelin and cholesterol. The systems of choice were large unilamellar vesicles for bulk studies (enzyme kinetics, fluorescence spectroscopy and dynamic light scattering) and giant unilamellar vesicles for fluorescence microscopy examination using a variety of fluorescent probes. The influence of membrane lateral structure on the kinetics of enzyme activity and the consequences of enzyme activity on the structure of target membranes containing sphingomyelin were examined. The findings indicate that: 1) ceramide-1-phosphate (particularly lauroyl ceramide-1-phosphate) can be incorporated into sphingomyelin bilayers in a concentration-dependent manner and generates coexistence of liquid disordered/solid ordered domains, 2) the activity of sphingomyelinase D is clearly influenced by the supramolecular organization of its substrate in membranes and, 3) in situ ceramide-1-phosphate generation by enzymatic activity profoundly alters the lateral structure and morphology of the target membranes. PMID:22558302

  1. Aryl-alkyl-lysines: Membrane-Active Small Molecules Active against Murine Model of Burn Infection.

    PubMed

    Ghosh, Chandradhish; Manjunath, Goutham B; Konai, Mohini M; Uppu, Divakara S S M; Paramanandham, Krishnamoorthy; Shome, Bibek R; Ravikumar, Raju; Haldar, Jayanta

    2016-02-12

    Infections caused by drug-resistant Gram-negative pathogens continue to be significant contributors to human morbidity. The recent advent of New Delhi metallo-β-lactamase-1 (blaNDM-1) producing pathogens, against which few drugs remain active, has aggravated the problem even further. This paper shows that aryl-alkyl-lysines, membrane-active small molecules, are effective in treating infections caused by Gram-negative pathogens. One of the compounds of the study was effective in killing planktonic cells as well as dispersing biofilms of Gram-negative pathogens. The compound was extremely effective in disrupting preformed biofilms and did not select resistant bacteria in multiple passages. The compound retained activity in different physiological conditions and did not induce any toxic effect in female Balb/c mice until concentrations of 17.5 mg/kg. In a murine model of Acinetobacter baumannii burn infection, the compound was able to bring the bacterial burden down significantly upon topical application for 7 days. PMID:27624962

  2. Phosphatidylserine Decarboxylase 1 (Psd1) Promotes Mitochondrial Fusion by Regulating the Biophysical Properties of the Mitochondrial Membrane and Alternative Topogenesis of Mitochondrial Genome Maintenance Protein 1 (Mgm1)*

    PubMed Central

    Chan, Eliana Y. L.; McQuibban, G. Angus

    2012-01-01

    Non–bilayer-forming lipids such as cardiolipin, phosphatidic acid, and phosphatidylethanolamine (PE) are proposed to generate negative membrane curvature, promoting membrane fusion. However, the mechanism by which lipids regulate mitochondrial fusion remains poorly understood. Here, we show that mitochondrial-localized Psd1, the key yeast enzyme that synthesizes PE, is required for proper mitochondrial morphology and fusion. Yeast cells lacking Psd1 exhibit fragmented and aggregated mitochondria with impaired mitochondrial fusion during mating. More importantly, we demonstrate that a reduction in PE reduces the rate of lipid mixing during fusion of liposomes with lipid compositions reflecting the mitochondrial membrane. This suggests that the mitochondrial fusion defect in the Δpsd1 strain could be due to the altered biophysical properties of the mitochondrial membrane, resulting in reduced fusion kinetics. The Δpsd1 strain also has impaired mitochondrial activity such as oxidative phosphorylation and reduced mitochondrial ATP levels which are due to a reduction in mitochondrial PE. The loss of Psd1 also impairs the biogenesis of s-Mgm1, a protein essential for mitochondrial fusion, further exacerbating the mitochondrial fusion defect of the Δpsd1 strain. Increasing s-Mgm1 levels in Δpsd1 cells markedly reduced mitochondrial aggregation. Our results demonstrate that mitochondrial PE regulates mitochondrial fusion by regulating the biophysical properties of the mitochondrial membrane and by enhancing the biogenesis of s-Mgm1. While several proteins are required to orchestrate the intricate process of membrane fusion, we propose that specific phospholipids of the mitochondrial membrane promote fusion by enhancing lipid mixing kinetics and by regulating the action of profusion proteins. PMID:23045528

  3. Correlation of microstructure and thermo-mechanical properties of a novel hydrogen transport membrane

    NASA Astrophysics Data System (ADS)

    Zhang, Yongjun

    A key part of the FutureGen concept is to support the production of hydrogen to fuel a "hydrogen economy," with the use of clean burning hydrogen in power-producing fuel cells, as well as for use as a transportation fuel. One of the key technical barriers to FutureGen deployment is reliable and efficient hydrogen separation technology. Most Hydrogen Transport Membrane (HTM) research currently focuses on separation technology and hydrogen flux characterization. No significant work has been performed on thermo-mechanical properties of HTMs. The objective of the thesis is to understand the structure-property correlation of HTM and to characterize (1) thermo mechanical properties under different reducing environments and thermal cycles (thermal shock), and (2) evaluate the stability of the novel HTM material. A novel HTM cermet bulk sample was characterized for its physical and mechanical properties at both room temperature and at elevated temperature up to 1000°C. Micro-structural properties and residual stresses were evaluated in order to understand the changing mechanism of the microstructure and its effects on the mechanical properties of materials. A correlation of the microstructural and thermo mechanical properties of the HTM system was established for both HTM and the substrate material. Mechanical properties of both selected structural ceramics and the novel HTM cermet bulk sample are affected mainly by porosity and microstructural features, such as grain size and pore size-distribution. The Young's Modulus (E-value) is positively correlated to the flexural strength for materials with similar crystallographic structure. However, for different crystallographic materials, physical properties are independent of mechanical properties. Microstructural properties, particularly, grain size and crystallographic structure, and thermodynamic properties are the main factors affecting the mechanical properties at both room and high temperatures. The HTM cermet behaves

  4. New insight into influence of mechanical stirring on membrane fouling of membrane bioreactor: Mixed liquor properties and hydrodynamic conditions.

    PubMed

    Qi, Chao; Wang, Jinnan; Lin, Yaohua

    2016-07-01

    Although membrane bioreactor is widely used in wastewater treatment, the problem of membrane fouling remains to be resolved. This paper focused on the influence of mechanical stirring on membrane fouling. Ammonium removal decreased with viscous bulking when stirring rates slowed down. Trans-membrane pressure increased more rapidly when the stirring rate decreased. The resistance of the gel layer increased significantly under low stirring rates, which indicated that the fouling rates of MBR in different stages were attributed to gel layer variation. The proportion of small particles increased when stirring rates slowed down. Furthermore, 16S rRNA gene amplicon sequencing showed that Proteobacteria and Actinobacteria were dominant in the mixed liquor. The relative abundance of Actinobacteria increased from 41% to 50% in the entire experiment. The computational fluid dynamics model was used to simulate the fluid flow characteristics. The model indicated velocities and directions of the fluid flow changes with different stirring rates. PMID:27058400

  5. Cognition Is Cool: Can Hemispheric Activation Be Assessed by Tympanic Membrane Thermometry?

    ERIC Educational Resources Information Center

    Cherbuin, Nicolas; Brinkman, Cobie

    2004-01-01

    Hemispheric activation during cognitive tasks using functional magnetic resonance imaging (fMRI) can be difficult to interpret, uncomfortable, and is not widely available. This study investigated whether tympanic membrane thermometry could be used as a broad measure of hemispheric activation. Infrared probes measured ear temperature continuously…

  6. [Effect of powdered activated carbon on the sludge mixed liquor characteristics and membrane fouling of MBR].

    PubMed

    Li, Shao-Feng; Gao, Yuan

    2011-02-01

    Effect of dosing powder activated carbon (PAC) on the characteristics of the sludge mixed liquor in membrane bioreactor (MBR) was investigated by parallel tests. And the reason that PAC mitigated membrane fouling was also explored. The results showed that PAC could decrease mixture viscosity and increase sludge particle size, which led to less trans-membrane pressure developing. Extracellular polymer substances (EPS) content, sludge specific resistance and cake layer resistance (R(c)) had a good correlation. Adding PAC could decrease EPS concentration, sludge specific resistance and then slow down the increase of R(c), which mitigated membrane fouling. Membrane pore blocking resistance (R(p)) increased exponentially with increasing of the soluble microbial products (SMP) concentration in the supernatant. Dosing PAC reduced the SMP concentration and slowed down the growth rate of R(p), which was helpful to mitigating membrane fouling. R(c) and R(p) increased along with the operation of MBRs and R(c)/R(f) (26.32% -63.16%) was always greater than R(p)/R(f) (7.89% -35.32%) which suggested the R(c) was the main factor in membrane fouling. Moreover, it was also found that controlling of dosing PAC on R(c) was better than it on R(p). PMID:21528575

  7. Comparing graphene, carbon nanotubes, and superfine powdered activated carbon as adsorptive coating materials for microfiltration membranes.

    PubMed

    Ellerie, Jaclyn R; Apul, Onur G; Karanfil, Tanju; Ladner, David A

    2013-10-15

    Multi-walled carbon nanotubes (MWCNTs), nano-graphene platelets (NGPs), and superfine powdered activated carbon (S-PAC) were comparatively evaluated for their applicability as adsorptive coatings on microfiltration membranes. The objective was to determine which materials were capable of contaminant removal while causing minimal flux reduction. Methylene blue and atrazine were the model contaminants. When applied as membrane coatings, MWCNTs had minimal retention capabilities for the model contaminants, and S-PAC had the fastest removal. The membrane coating approach was also compared with a stirred vessel configuration, in which the adsorbent was added to a stirred flask preceding the membrane cell. Direct application of the adsorbent to the membrane constituted a greater initial reduction in permeate concentrations of the model contaminants than with the stirred flask setup. All adsorbents except S-PAC showed flux reductions less than 5% after application as thin-layer membrane coatings, and flux recovery after membrane backwashing was greater than 90% for all materials and masses tested. PMID:23911830

  8. The preparation and immunosuppressive properties of equine antihuman thymocyte membrane immunoglobulin G.

    PubMed

    Diethelm, A G; Chambers, L; Sachs, G; Balch, C M; Phillips, S J; Thiry, C

    1979-02-01

    Human thymocytes separated by a Ficoll gradient produced a cell population that was 99% pure thymocytes and free of platelets, leukocytes, and epithelial cells. These cells, disrupted by a nitrogen bomb, produced a membrane-ribosome antigen fraction confirmed by enzyme analysis. Equine antithymocyte membrane-immunoglobulin G (ATM-IgC) prepared against this antigen in four of five horses contained immunosuppressive properties capable of prolonging monkey skin allograft survival longer than 21 days. No adverse effects were noted by the intramuscular and intravenous administration of this antisera to primates, and autopsy examination showed marked depletion of paracortical lymphocytes in the spleen and mesenteric lymph nodes. A moderate thrombocytopenia occurred during a 4 hour intravenous administration of ATM-IgG to primates with a marked decrease in the peripheral lymphocyte count. The deposition of ATM-IgG upon monkey glomerular basement membrane could not be demonstrated by immunofluorescent techniques. The specificity of this globulin to contain anti-T-cell antibody was confirmed by an immunofluorescent assay in that ATM-IgG reacted with both human thymocytes and peripheral blood thymus-dependent cells, but was nonreactive when tested against a panel of human cells free of thymus-dependent antigens. PMID:105416

  9. Study of fluid and transport properties of porous anodic aluminum membranes by dynamic atomic force microscopy.

    PubMed

    Wu, Chu; Leese, Hannah S; Mattia, Davide; Dagastine, Raymond R; Chan, Derek Y C; Tabor, Rico F

    2013-07-16

    Recent work on carbon nanotubes (CNT) has focused on their potential application in water treatment as a result of their predicted and observed enhanced flow rates. Recent work on the lesser-known porous anodic alumina membranes (PAAMs) has also shown flow enhancement, albeit at only a fraction of what has been observed in CNTs. Despite their potential applications, little research has been conducted on PAAMs' hydrodynamic properties, and in this Article we present experimental results and theoretical models that explore the fluid flow behavior around and through these membranes. The experiments were conducted using an atomic force microscope (AFM) that pushed a solid silica particle against PAAMs that were characterized with different pore diameters. Furthermore, the PAAMs were classified as either closed or open, with the latter allowing fluid to pass through. The theoretical model developed to describe the experimental data incorporates Derjaguin-Landau-Verwey-Overbeek (DLVO) effects, cantilever drag, and hydrodynamic forces. By using the slip boundary condition for the hydrodynamic forces, we were able to fit the model to experimental findings and also demonstrate that the difference between closed and open PAAMs was negligible. The slip lengths did not correspond to any physical feature of the PAAMs, but our model does provide a simple yet effective means of describing the hydrodynamics for not only PAAMs but for membranes in general. PMID:23750974

  10. Temporal variations of membrane foulants in the process of using flat-sheet membrane for simultaneous thickening and digestion of waste activated sludge.

    PubMed

    Wu, Zhichao; Zhu, Xuefeng; Wang, Zhiwei

    2011-07-01

    Membrane foulants were extracted at different operation time in simultaneous sludge thickening and digestion reactors using flat-sheet membranes. Temporal variations of foulants were analyzed by three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy, gel filtration chromatography (GFC), particle size distribution (PSD) and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy. Results showed that during the first 4days fouling was mainly assigned to internal membrane foulants (IMFs), and afterwards external membrane foulants (EMFs) increased dramatically. EEM analysis showed that both IMFs and EMFs changed during the operation. Cluster analysis demonstrated that the characteristics of IMFs were relatively similar; however, both quantity and properties of EMFs were changed. GFC analysis showed that EMFs contained more molecules with large molecular weight compared to IMFs. PSD analysis illuminated that particle size of EMFs gradually increased and was larger than that of IMFs. ATR-FTIR analysis indicated that the foulants on membranes consisted of polysaccharides and proteins. PMID:21555218

  11. Effects of the membrane action of tetralin on the functional and structural properties of artificial and bacterial membranes.

    PubMed Central

    Sikkema, J; Poolman, B; Konings, W N; de Bont, J A

    1992-01-01

    Tetralin is toxic to bacterial cells at concentrations below 100 mumol/liter. To assess the inhibitory action of tetralin on bacterial membranes, a membrane model system, consisting of proteoliposomes in which beef heart cytochrome c oxidase was reconstituted as the proton motive force-generating mechanism, and several gram-positive and gram-negative bacteria were studied. Because of its hydrophobicity, tetralin partitioned into lipid membranes preferentially (lipid/buffer partition coefficient of tetralin is approximately 1,100). The excessive accumulation of tetralin caused expansion of the membrane and impairment of different membrane functions. Studies with proteoliposomes and intact cells indicated that tetralin makes the membrane permeable for ions (protons) and inhibits the respiratory enzymes, which leads to a partial dissipation of the pH gradient and electrical potential. The effect of tetralin on the components of the proton motive force as well as disruption of protein-lipid interaction(s) could lead to impairment of various metabolic functions and to low growth rates. The data offer an explanation for the difficulty in isolating and cultivating microorganisms in media containing tetralin or other lipophilic compounds. PMID:1314806

  12. Impact of Embedded Endocannabinoids and Their Oxygenation by Lipoxygenase on Membrane Properties

    PubMed Central

    2012-01-01

    N-Arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol are the best characterized endocannabinoids. Their biological activity is subjected to metabolic control whereby a dynamic equilibrium among biosynthetic, catabolic, and oxidative pathways drives their intracellular concentrations. In particular, lipoxygenases can generate hydroperoxy derivatives of endocannabinoids, endowed with distinct activities within cells. The in vivo interaction between lipoxygenases and endocannabinoids is likely to occur within cell membranes; thus, we sought to ascertain whether a prototypical enzyme like soybean (Glycine max) 15-lipoxygenase-1 is able to oxygenate endocannabinoids embedded in synthetic vesicles and how these substances could affect the binding ability of the enzyme to different lipid bilayers. We show that (i) embedded endocannabinoids increase membrane fluidity; (ii) 15-lipoxygenase-1 preferentially binds to endocannabinoid-containing bilayers; and that (iii) 15-lipoxygenase-1 oxidizes embedded endocannabinoids and thus reduces fluidity and local hydration of membrane lipids. Together, the present findings reveal further complexity in the regulation of endocannabinoid signaling within the central nervous system, disclosing novel control by oxidative pathways. PMID:22860207

  13. [Purification and properties of membrane-bound methane hydroxylase from Methylococcus capsulatus (strain M)].

    PubMed

    Gvozdev, R I; Tukhvatullin, I A; Tumanova, L V

    2008-01-01

    Membrane fraction of Methylococcus capsulatus (strain M) were treated with [14C]acetylene, an affinity label binding to the active center of membrane-bound methane monooxygenase (MMO). High-purity particulate form of methane hydroxylase (pMH) was obtained by ion exchange and hydrophobic chromatography. According to SDS-PAGE data, the enzyme contained three polypeptides with molecular weights of 47 (alpha), 27 (beta), and 25 (gamma) kDa in the ratio 1:1:1. The radiolabel was contained in the beta-subunit of pMH. The protein contained 1 or 2 atoms of nonheme iron and 2-4 atoms of copper per a minimum molecular weight of 99 kDa. This protein did not oxidize methane or propylene in the presence of NADH but was able to oxidize low quantities of methane in the presence of duroquinol. It was established that methanol dehydrogenase (MD) and NADH oxidoreductase (NADH-OR) are peripheral membrane proteins. Possible causes of low activity of high-purity methane hydroxylase are discussed. PMID:18946992

  14. Side Chain Hydrophobicity Modulates Therapeutic Activity and Membrane Selectivity of Antimicrobial Peptide Mastoparan-X

    PubMed Central

    Gjetting, Torben; Andresen, Thomas L.

    2014-01-01

    The discovery of new anti-infective compounds is stagnating and multi-resistant bacteria continue to emerge, threatening to end the “antibiotic era”. Antimicrobial peptides (AMPs) and lipo-peptides such as daptomycin offer themselves as a new potential class of antibiotics; however, further optimization is needed if AMPs are to find broad use as antibiotics. In the present work, eight analogues of mastoparan-X (MPX) were investigated, having side chain modifications in position 1, 8 and 14 to modulate peptide hydrophobicity. The self-association properties of the peptides were characterized, and the peptide-membrane interactions in model membranes were compared with the bactericidal and haemolytic properties. Alanine substitution at position 1 and 14 resulted in higher target selectivity (red blood cells versus bacteria), but also decreased bactericidal potency. For these analogues, the gain in target selectivity correlated to biophysical parameters showing an increased effective charge and reduction in the partitioning coefficient for membrane insertion. Introduction of an unnatural amino acid, with an octyl side chain by amino acid substitution, at positions 1, 8 and 14 resulted in increased bactericidal potency at the expense of radically reduced membrane target selectivity. Overall, optimized membrane selectivity or bactericidal potency was achieved by changes in side chain hydrophobicity of MPX. However, enhanced potency was achieved at the expense of selectivity and vice versa in all cases. PMID:24621994

  15. Characterization of a Membrane-active Peptide from the Bordetella pertussis CyaA Toxin*

    PubMed Central

    Subrini, Orso; Sotomayor-Pérez, Ana-Cristina; Hessel, Audrey; Spiaczka-Karst, Johanna; Selwa, Edithe; Sapay, Nicolas; Veneziano, Rémi; Pansieri, Jonathan; Chopineau, Joel; Ladant, Daniel; Chenal, Alexandre

    2013-01-01

    Bordetella pertussis, the pathogenic bacteria responsible for whooping cough, secretes several virulence factors, among which is the adenylate cyclase toxin (CyaA) that plays a crucial role in the early stages of human respiratory tract colonization. CyaA invades target cells by translocating its catalytic domain directly across the plasma membrane and overproduces cAMP, leading to cell death. The molecular process leading to the translocation of the catalytic domain remains largely unknown. We have previously shown that the catalytic domain per se, AC384, encompassing residues 1–384 of CyaA, did not interact with lipid bilayer, whereas a longer polypeptide, AC489, spanning residues 1–489, binds to membranes and permeabilizes vesicles. Moreover, deletion of residues 375–485 within CyaA abrogated the translocation of the catalytic domain into target cells. Here, we further identified within this region a peptidic segment that exhibits membrane interaction properties. A synthetic peptide, P454, corresponding to this sequence (residues 454–485 of CyaA) was characterized by various biophysical approaches. We found that P454 (i) binds to membranes containing anionic lipids, (ii) adopts an α-helical structure oriented in plane with respect to the lipid bilayer, and (iii) permeabilizes vesicles. We propose that the region encompassing the helix 454–485 of CyaA may insert into target cell membrane and induce a local destabilization of the lipid bilayer, thus favoring the translocation of the catalytic domain across the plasma membrane. PMID:24064217

  16. Quantitative structure-activity relationship (QSAR) analysis of surfactants influencing attachment of a Mycobacterium sp. to cellulose acetate and aromatic polyamide reverse osmosis membranes.

    PubMed

    Campbell, P; Sriniva