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1

A new membrane fractionation process based on the combination of hybrid membrane cells and differential diffusion of two solutes  

Microsoft Academic Search

A new membrane fractionation process based on the combination of hybrid membrane cells and differential diffusion of two solutes was studied by numerical methods. The hybrid membrane cell comprises semipermeable and fully-permeable membrane sub-sections. While the semi-permeable membranes are permeable to the solvent and impermeable to both solutes, the fully-permeable membranes are permeable to all components of the solution, including

S. I. S. Pinto; T. M. G. T. Rocha; J. M. Miranda; J. B. L. M. Campos

2009-01-01

2

STUDIES OF MEMBRANE FORMATION IN TETRAHYMENA PYRIFORMIS: II. Isolation and Lipid Analysis of Cell Fractions  

Microsoft Academic Search

A method has been devised to fractionate cells of Tetrahymena pyriformis, yielding pure or highly enriched preparations of cilia, cilia-associated soluble material, pellicles, mito- chondria, microsomes, and postmicrosomal supernatant .The method prevents the de- structive action of lipolytic enzymes commonly associated with this organism .Analysis of the membrane lipids of these fractions reveals significant differences in lipid composition . Most

YOSHINORI NOZAWA; GUY A. THOMPSON

1971-01-01

3

Metabolic Labeling and Membrane Fractionation for Comparative Proteomic Analysis of Arabidopsis thaliana Suspension Cell Cultures.  

PubMed

Plasma membrane microdomains are features based on the physical properties of the lipid and sterol environment and have particular roles in signaling processes. Extracting sterol-enriched membrane microdomains from plant cells for proteomic analysis is a difficult task mainly due to multiple preparation steps and sources for contaminations from other cellular compartments. The plasma membrane constitutes only about 5-20% of all the membranes in a plant cell, and therefore isolation of highly purified plasma membrane fraction is challenging. A frequently used method involves aqueous two-phase partitioning in polyethylene glycol and dextran, which yields plasma membrane vesicles with a purity of 95% (1). Sterol-rich membrane microdomains within the plasma membrane are insoluble upon treatment with cold nonionic detergents at alkaline pH. This detergent-resistant membrane fraction can be separated from the bulk plasma membrane by ultracentrifugation in a sucrose gradient (2). Subsequently, proteins can be extracted from the low density band of the sucrose gradient by methanol/chloroform precipitation. Extracted protein will then be trypsin digested, desalted and finally analyzed by LC-MS/MS. Our extraction protocol for sterol-rich microdomains is optimized for the preparation of clean detergent-resistant membrane fractions from Arabidopsis thaliana cell cultures. We use full metabolic labeling of Arabidopsis thaliana suspension cell cultures with K(15)NO3 as the only nitrogen source for quantitative comparative proteomic studies following biological treatment of interest (3). By mixing equal ratios of labeled and unlabeled cell cultures for joint protein extraction the influence of preparation steps on final quantitative result is kept at a minimum. Also loss of material during extraction will affect both control and treatment samples in the same way, and therefore the ratio of light and heave peptide will remain constant. In the proposed method either labeled or unlabeled cell culture undergoes a biological treatment, while the other serves as control (4). PMID:24121251

Szymanski, Witold G; Kierszniowska, Sylwia; Schulze, Waltraud X

2013-09-28

4

FURTHER CHARACTERIZATION OF PARTICULATE FRACTIONS FROM LYSED CELL ENVELOPES OF HALOBACTERIUM HALOBIUM AND ISOLATION OF GAS VACUOLE MEMBRANES  

Microsoft Academic Search

Lysates of cell envelopes from Halobacterium halobium have been separated into four fractions. A soluble, colorless fraction (I) containing protein, hexosamines, and no lipid is apparently derived from the cell wall. A red fraction (II), containing approximately 40 per cent lipid, 60 per cent protein, and a small amount of hexosamines consists of cell membrane disag- gregated into fragments of

WALTHER STOECKENIUS; WOLF H. KUNAU

1968-01-01

5

Surface labelling for human tumour KB cells. Iodination and fractionation of membrane glycoproteins.  

PubMed Central

1. Human tumour KB cells growing in suspension culture were labelled by lactoperoxidase-catalysed iodination. Several major radioactively labelled proteins were detected by poly-acrylamide-gel electrophoresis in sodium dodecyl sulphate. 2. After reduction with 2-mercaptoethanol the major radioactive electrophoretic bands migrated as substances with apparent molecular weights of about 90,000, 70,000, 60,000, 50,000 and 34,000 and corresponded closely to the positions at which the major glycosylated polypeptide subunits of KB-cell homogenates migrated during electrophoresis under the same conditions. 3. All the iodinated protein bands except one were present in purified preparations of KB plasma membranes. 4. Most of the 50,000-molecular-weight species, supposedly a surface protein component labelled during iodination of intact and viable KB cells by a non-penetrating enzyme reagent, appeared in a crude nuclear pellet during fractionation. 5. The glyco-protein nature of the major external iodinated species of KB cells was confirmed by adsorption chromatography of these substances, dissolved in low concentrations of Triton X-100, on a lectin-Sepharose column. Two major enzyme markers of the KB plasma membrane, 5'-nucleotidase and alkaline phosphatase were also found to be glycoproteins. 6. Enzyme-catalysed incorporation of radioactive iodine into a fraction of low molecular weight and soluble in chloroform-methanol mixtures also occurred during lactoperoxidase treatment of intact KB cells. The partial characterization of this fraction is briefly described. Images PLATE 2 PLATE 3 PLATE 1

Butters, T D; Hughes, R C

1975-01-01

6

Optimisation of the Factor VIII yield in mammalian cell cultures by reducing the membrane bound fraction.  

PubMed

In vivo, clotting Factor VIII (FVIII) circulates in plasma bound to von Willebrand factor (vWF), and the vWF:FVIII complex prevents binding of FVIII to phosphatidylserine (PS). Activation of FVIII by thrombin releases FVIII from vWF, and subsequently FVIII binds to PS exposed on activated platelets and forms the tenase complex together with clotting Factor IX. In vitro, during serum free production of recombinant FVIII (rFVIII), production cells also expose PS, and since vWF is not present to hinder interaction of secreted rFVIII with PS, rFVIII is partly associated with the cell membrane of the production cells. Recently, we showed that as much as 90% of secreted rFVIII is bound to transiently transfected production cells during serum free conditions. In this study, we investigated the effect of including vWF in the serum free medium, and demonstrate that addition of vWF results in release of active membrane bound rFVIII to the culture medium. Moreover, the attachment of rFVIII to cell membranes of un-transfected HEK293 cells was studied in the presence of compounds that competes for interactions between rFVIII and PS. Competitive assays between iodinated rFVIII (¹²?I-rFVIII) and annexin V or ortho-phospho-L-serine (OPLS) demonstrated that annexin V and OPLS were able to reduce the membrane bound fraction of rFVIII by 70% and 30%, respectively. Finally, adding OPLS to CHO cells stably expressing FVIII increased the yield by 50%. Using this new knowledge, the recovery of rFVIII could be increased considerably during serum free production of this therapeutic protein. PMID:21219947

Kolind, Mille Petersen; Nørby, Peder Lisby; Berchtold, Martin Werner; Johnsen, Laust Bruun

2011-01-08

7

PERSPECTIVE: Fractional order models of viscoelasticity as an alternative in the analysis of red blood cell (RBC) membrane mechanics  

NASA Astrophysics Data System (ADS)

New lumped-element models of red blood cell mechanics can be constructed using fractional order generalizations of springs and dashpots. Such 'spring-pots' exhibit a fractional order viscoelastic behavior that captures a wide spectrum of experimental results through power-law expressions in both the time and frequency domains. The system dynamics is fully described by linear fractional order differential equations derived from first order stress-strain relationships using the tools of fractional calculus. Changes in the composition or structure of the membrane are conveniently expressed in the fractional order of the model system. This approach provides a concise way to describe and quantify the biomechanical behavior of membranes, cells and tissues.

Craiem, Damian; Magin, Richard L.

2010-03-01

8

Fractional order models of viscoelasticity as an alternative in the analysis of red blood cell (RBC) membrane mechanics.  

PubMed

New lumped-element models of red blood cell mechanics can be constructed using fractional order generalizations of springs and dashpots. Such 'spring-pots' exhibit a fractional order viscoelastic behavior that captures a wide spectrum of experimental results through power-law expressions in both the time and frequency domains. The system dynamics is fully described by linear fractional order differential equations derived from first order stress-strain relationships using the tools of fractional calculus. Changes in the composition or structure of the membrane are conveniently expressed in the fractional order of the model system. This approach provides a concise way to describe and quantify the biomechanical behavior of membranes, cells and tissues. PMID:20090192

Craiem, Damian; Magin, Richard L

2010-01-20

9

Fractional order models of viscoelasticity as an alternative in the analysis of red blood cell (RBC) membrane mechanics  

PubMed Central

New lumped-element models of red blood cell mechanics can be constructed using fractional order generalizations of springs and dashpots. Such ‘spring-pots’ exhibit a fractional order viscoelastic behavior that captures a wide spectrum of experimental results through power-law expressions in both the time and frequency domains. The system dynamics is fully described by linear fractional order differential equations derived from first order stress–strain relationships using the tools of fractional calculus. Changes in the composition or structure of the membrane are conveniently expressed in the fractional order of the model system. This approach provides a concise way to describe and quantify the biomechanical behavior of membranes, cells and tissues.

Craiem, Damian; Magin, Richard L

2011-01-01

10

Binding of paroxetine to the serotonin transporter in membranes from different cells, subcellular fractions and species.  

PubMed

The binding of [(3)H]-paroxetine to membrane serotonin transporter (SERT) has been studied in membranes from different sources and subcellular fractions. From rat were membranes from venous blood platelets, brain total cortex, brain microsomes, brain crude and purified synaptosomes. Membranes were obtained from venous blood platelets from human volunteers and from brain cortex tissue from neurosurgery (cerebral lobectomies following craniocerebral injuries). The main finding was that the K (D) of paroxetine binding to the SERT was the same for platelet and nerve ending (synaptosomal) membranes. That parameter was significantly lower in membranes from brain microsomes and cortex total tissue. No species related difference was found, where comparison was possible, between human and rat tissue. The equality of K (D) of paroxetine binding to blood platelet membranes and to membranes from nerve endings appears to encourage the use of such membranes as a model for brain SERT. Binding at two different temperatures for several of the fractions suggests that paroxetine-SERT interaction is entropy-driven. PMID:18563559

Cupello, A; Albano, C; Gatta, E; Scarrone, S; Villa, E; Zona, G

2008-06-18

11

Terpenes in sponge cell membranes: Cell separation and membrane fractionation studies with the tropical marine sponge Amphimedon sp  

Microsoft Academic Search

The differing sponge and symbiotic microbial cell types in the tropical marine spongeAmphimedon sp. were fractionated according to density, investigated by electron microscopy, and analyzed by high-performance liquid\\u000a chromatography and nuclear magnetic resonance for the presence of the terpene metabolite diisocyanoadociane (1) and ?5,7-sterols (2–7). A sample of whole sponge was dissected into superficial ectosome and deeper choanosome. The superficial

Mary J. Garsona; Janice E. Thompsonb; Rundi M. Larsen; Christopher N. Battershill; Peter T. Murphy; Patricia R. Bergquist

1992-01-01

12

Tissue-culture fractionation. Zonal centrifugation of Lettr?e cells homogenized by glycerol-induced lysis: subfractionation of membranes in sucrose gradients.  

PubMed Central

1. Lettrée cells were grown intraperitoneally in MF-1 mice. 2. Cells that were loaded with glycerol were swollen in 0.1 M-sucrose and disrupted by Dounce homogenization. 3. Early-passage Lettrée cells were more easily disrupted than late-passage cells by this method, and the former produced larger fragments of plasma membrane. 4. The membranes were fractionated initially in sucrose gradients (on the basis of sedimentation rate) in a BXIV zonal rotor. 5. Fractions from this gradient were further resolved in isopycnic sucrose gradients. 6. Plasma-membrane and endoplasmic-reticulum fractions were recovered in good yield and high purity.

Graham, J M; Coffey, K H

1979-01-01

13

DNA swivel enzyme activity in a nuclear membrane fraction.  

PubMed

DNA swivel (nicking-rejoining) enzyme activity has been studied in various cell fractions of a human lymphoid cell line. Swivel activity is found only in chromatin and in a nuclear membrane fraction containing DNA and possessing endogenous DNA synthesizing activity. Twenty percent of the total swivel activity and less than one percent of the total DNA are in the membrane fraction. The swivel enzyme is more tightly bound to the membrane fraction than to the chromatin fraction. These observations suggest that the swivel enzyme may be a replication factor, specifically bound to replicating DNA in the membrane fraction. PMID:871320

Yoshida, S; Ungers, G; Rosenberg, B H

1977-01-01

14

A soft preparative method for membrane proteome analysis using frit inlet asymmetrical flow field-flow fractionation: application in a prostatic cancer cell line.  

PubMed

Membrane proteins participate in a number of important biological functions such as signal transduction, molecular transport, and cell-cell interactions. However, due to the nature of membrane proteins, the development of a preparative method that produces a sufficient yield of purified membrane proteins from the cell remains a challenge. In the present study, frit inlet asymmetrical flow field-flow fractionation (FI-AFlFFF) was employed to fractionate membrane fragments containing membrane proteins from free cytoplasmic proteins of prostatic cancer cell (DU145 cell) lysates. The isolated membrane proteins were then digested and analyzed by nanoflow liquid chromatography/tandem mass spectrometry (nLC-ESI-MS-MS). Since fractionation of the cell lysate mixtures containing membrane fragments and cytoplasmic proteins could be achieved based on the differences of their sizes in FI-AFlFFF, membrane fragments were partially isolated from the cytoplasmic proteins and collected. The performance of FI-AFlFFF for prefractionation of the membrane proteome was examined by comparing the number of membrane proteins that were identified with the number identified using an ultracentrifugation method. The application of FI-AFlFFF to membrane proteomics produced an increased yield of purified membrane proteins with fewer cytoplasmic proteins compared to a conventional ultracentrifugation method. PMID:19140673

Kang, Dukjin; Yoo, Jong Shin; Kim, Myeong Ok; Moon, Myeong Hee

2009-02-01

15

Kininogenase activity in plasma membranes and cell organelles from rabbit kidney cortex: Subcellular localization of renal kallikrein by free-flow electrophoresis and density-gradient fractionation  

Microsoft Academic Search

Kininogenase activity in plasma membranes and cell organelles from rabbit kidney cortex: Subcellular localization of renal kallikrein by free-flow electrophoresis and density-gradient fractionation. Subcellular fractions were prepared from a rabbit kidney cortex homogenate by density gradient and free-flow electrophoresis techniques. After enzymatic and morphologic characterization, we determined the kininogenase activity in the different fractions. This activity was present in those

Hans G Heidrich; Reinhard Geiger

1980-01-01

16

Subcellular fractionation of midgut cells of the sunn pest Eurygaster integriceps (Hemiptera: Scutelleridae): Enzyme markers of microvillar and perimicrovillar membranes  

Microsoft Academic Search

The subcellular distributions of six digestive and non-digestive enzymes (?-glucosidase, ?-glucosidase, alkaline phosphatase, acid phosphatase, aminopeptidase and lactate dehydrogenase) of Eurygaster integriceps have been studied. The subcellular distributions of acid phosphatase and ?-glucosidase are similar and the gradient ultracentrifugation profiles of these two enzymes overlap. Two partially membrane-bound enzymes, alkaline phosphatase and ?-glucosidase have similar distributions in differential centrifugation fractions,

M. Allahyari; A. R. Bandani; M. Habibi-Rezaei

2010-01-01

17

Antimicrobial properties of milkfat globule membrane fractions.  

PubMed

Milkfat globule membranes (MFGMs) were prepared from bovine cream according to standard procedures. These membranes and peptide hydrolysates, which were generated by proteolysis with immobilized digestive enzymes, were screened for antibacterial activity against Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica Typhimurium, Pseudomonas fluorescens, Bacillus cereus, Lactobacillus acidophilus, and Lactobacillus gasseri. Assays were first performed on beef heart infusion (BHI) plates spotted with test protein-peptide fractions and then seeded with lawns of indicator cells to monitor the zone of growth inhibition. Under these experimental conditions, MFGMs were most active against Salmonella Typhimurium and P. fluorescens. However, antibacterial activity was not seen after plating on Luria-Bertani (LB) medium. We determined that the antimicrobial effects observed on BHI plates were due to the generation of H2O2 by xanthine oxidase, a major protein constituent of the MFGMs, as a result of purine catalysis. This substrate is present in BHI but lacking in LB medium. Evaluation of purified xanthine oxidase alone resulted in analogous data trends. The growth of probiotic Lactobacillus strains were affected only marginally when grown on lactobacilli deMan Rogosa Sharpe plates, suggesting the decreased sensitivity of these bacteria to H2O2. In this study, several MFGM hydrolysates exhibited variable antibacterial activity against test food pathogens on agar plates prepared with M9 minimal media, and this variation was not attributable to xanthine oxidase enzymatic activity. The probiotic microorganisms were mostly resilient to these antibacterial fractions. Bovine MFGM fractions may represent an excellent resource material from which to generate native, naturally occurring biodefensive proteins and/or peptides. PMID:18236672

Clare, Debra A; Zheng, Zuoxing; Hassan, Hosni M; Swaisgood, Harold E; Catignani, George L

2008-01-01

18

Effects of cadmium and copper on peroxidase, NADH oxidase and IAA oxidase activities in cell wall, soluble and microsomal membrane fractions of pea roots.  

PubMed

Twelve-day-old seedlings of pea (Pisum sativum L.) that were treated for 4 days by 20 and 100 micromol/l Cd(NO3)2 or CuSO4 showed a growth reduction in all organs. From root protein extracts, the activities of guaiacol peroxidase (GPX; EC 1.11.1.7), ascorbate peroxidase (APX; EC 1.11.1.11), coniferyl alcohol peroxidase (CAPX), NADH oxidase, and indole-3-acetic acid (IAA) oxidase were measured in covalently--and ionically--[symbol: see text] bound cell wall, soluble, and microsomal membrane fractions. With the exception of 20 micromol/l Cu, metal treatments enhanced GPX activity in all fractions. Only IAA oxidase activity was metal-elevated in the covalently bound cell wall fraction, while the ionic one showed Cd stimulation for all assayed enzymic activities. These effects were not entirely observed in Cu-treated plants, since APX and IAA oxidase activities were only enhanced in this fraction. However, soluble extract showed stimulation of APX activity, while in the microsomal fraction metal exposure also increased the activities of CAPX and NADH oxidase. Differential responses of root cell fractions to the presence of cadmium and copper ions are discussed in regard to the contribution of their enzymic capacities in antioxidant, lignification, and auxin degradation pathways. Comparisons between metals and dose effects are also underlined. PMID:15602814

Chaoui, Abdelilah; Jarrar, Brahim; El Ferjani, Ezzedine

2004-11-01

19

A novel regulatory mechanism for trimeric GTP-binding proteins in the membrane and secretory granule fractions of human and rodent beta cells.  

PubMed Central

Recently we described roles for heterotrimeric and low-molecular-mass GTP-binding proteins in insulin release from normal rat islets. During these studies, we observed that a protein with an apparent molecular mass (37 kDa) similar to that of the beta subunit of trimeric GTP-binding proteins underwent phosphorylation in each of five classes of insulin-secreting cells. Incubation of the beta cell total membrane fraction or the isolated secretory granule fraction (but not the cytosolic fraction) with [gamma-32P]ATP or [gamma-32P]GTP resulted in the phosphorylation of this protein, which was selectively immunoprecipitated by an anti-serum directed against the common beta subunit of trimeric G-proteins. Disruption of the alpha beta gamma trimer (by pretreatment with either fluoroaluminate or guanosine 5'(-)[gamma-thio]triphosphate) prevented beta subunit phosphorylation. Based on differential sensitivities to pH, heat and the histidine-selective reagent diethyl pyrocarbonate (and reversal of the latter by hydroxylamine), the phosphorylated amino acid was presumptively identified as histidine. Incubation of pure beta subunit alone or in combination with the exogenous purified alpha subunit of transducin did not result in the phosphorylation of the beta subunit, but addition of the islet cell membrane fraction did support this event, suggesting that membrane localization (or a membrane-associated factor) is required for beta subunit phosphorylation. Incubation of phosphorylated beta subunit with G alpha.GDP accelerated the dephosphorylation of the beta subunit, accompanied by the formation of G alpha-GTP. Immunoblotting detected multiple alpha subunits (of Gi, G(o) and Gq) and at least one beta subunit in the secretory granule fraction of normal rat islets and insulinoma cells. These data describe a potential alternative mechanism for the activation of GTP-binding proteins in beta cells which contrasts with the classical receptor-agonist mechanism: G beta undergoes transient phosphorylation at a histidine residue by a GTP-specific protein kinase; this phosphate, in turn, may be transferred via a classical Ping-Pong mechanism to G alpha.GDP (inactive), yielding the active configuration G alpha.GTP in secretory granules (a strategic location to modulate exocytosis).

Kowluru, A; Seavey, S E; Rhodes, C J; Metz, S A

1996-01-01

20

MEMBRANES OF ANIMAL CELLS  

PubMed Central

Turnover studies of the surface membrane and of cell particulate matter of L cells in tissue culture in logarithmic and plateau phase of growth have been made. The rate of incorporation of isotope into these fractions and the rate of fall of specific activities of labeled L-cell fractions have been observed. The following interpretation of the data appears most likely although other interpretations are possible. Growing and nongrowing cells synthesize approximately similar amounts of surface membrane and particulate material. In the growing cell the material is incorporated with net increases in substance. There is relatively little turnover. In the nongrowing cell newly synthesized material is incorporated, but a corresponding amount of material is eliminated so that there is turnover without net increase of substance. Our results suggest that there is no gross differential turnover between the protein, lipid, and carbohydrate of the surface membrane under the conditions of our experiments. Metabolic inhibitors or omission of amino acids in the culture medium lead to a decrease in synthesis of surface membrane and cell particulates and cause an equivalent decrease in the rate of degradation of surface membrane and of particulates; therefore the synthetic and degradative aspects of turnover appear to be coupled. As cultures of nongrowing cells in suspension or on a glass surface age, their synthetic and turnover capacities diminish. Our results suggest that the cell may exist in a nongrowing state with a level of synthesis similar to that of a growing cell. It can exist in this state with a high level of turnover.

Warren, L.; Glick, M. C.

1968-01-01

21

Stimulation of Embryonic Rat Cells in Culture by a Protein Fraction Isolated from Fetal Calf Serum. 1 Electrophysiological Measurements at the Cell Surface Membranes.  

National Technical Information Service (NTIS)

Normal embryonic rat cells incubated in serum free medium accumulate in G sub 1 phase of the cell cycle. It is demonstrated that the surface membrane potential difference (PD) decreases immediately after changing serum free medium against culture medium c...

D. F. Huelser W. Frank

1972-01-01

22

Modulation of Hyaluronan Synthase Activity in Cellular Membrane Fractions*  

PubMed Central

Hyaluronan (HA), the only non-sulfated glycosaminoglycan, is involved in morphogenesis, wound healing, inflammation, angiogenesis, and cancer. In mammals, HA is synthesized by three homologous HA synthases, HAS1, HAS2, and HAS3, that polymerize the HA chain using UDP-glucuronic acid and UDP-N-acetylglucosamine as precursors. Since the amount of HA is critical in several pathophysiological conditions, we developed a non-radioactive assay for measuring the activity of HA synthases (HASs) in eukaryotic cells and addressed the question of HAS activity during intracellular protein trafficking. We prepared three cellular fractions: plasma membrane, cytosol (containing membrane proteins mainly from the endoplasmic reticulum and Golgi), and nuclei. After incubation with UDP-sugar precursors, newly synthesized HA was quantified by polyacrylamide gel electrophoresis of fluorophore-labeled saccharides and high performance liquid chromatography. This new method measured HAS activity not only in the plasma membrane fraction but also in the cytosolic membranes. This new technique was used to evaluate the effects of 4-methylumbeliferone, phorbol 12-myristate 13-acetate, interleukin 1?, platelet-derived growth factor BB, and tunicamycin on HAS activities. We found that HAS activity can be modulated by post-translational modification, such as phosphorylation and N-glycosylation. Interestingly, we detected a significant increase in HAS activity in the cytosolic membrane fraction after tunicamycin treatment. Since this compound is known to induce HA cable structures, this result links HAS activity alteration with the capability of the cell to promote HA cable formation.

Vigetti, Davide; Genasetti, Anna; Karousou, Evgenia; Viola, Manuela; Clerici, Moira; Bartolini, Barbara; Moretto, Paola; De Luca, Giancarlo; Hascall, Vincent C.; Passi, Alberto

2009-01-01

23

Detecting Microdomains in Intact Cell Membranes  

Microsoft Academic Search

Current models for cellular plasma membranes focus on spatial heterogeneity and how this heterogeneity relates to cell function. In particular, putative lipid raft membrane domains have been postulated to exist based in large part on the results that a significant fraction of the membrane is detergent insoluble and that molecules facilitating key membrane processes like signal transduction are often found

B. Christoffer Lagerholm; Gabriel E. Weinreb; Ken Jacobson; Nancy L. Thompson

2005-01-01

24

Composite fuel cell membranes  

Microsoft Academic Search

A bilayer or trilayer composite ion exchange membrane suitable for use in a fuel cell. The composite membrane has a high equivalent weight thick layer in order to provide sufficient strength and low equivalent weight surface layers for improved electrical performance in a fuel cell. In use, the composite membrane is provided with electrode surface layers. The composite membrane can

Keith R. Plowman; Timothy J. Rehg; Larry W. Davis; William P. Carl; Alan J. Cisar; Charles S. Eastland

1997-01-01

25

Composite fuel cell membranes  

Microsoft Academic Search

A bilayer or trilayer composite ion exchange membrane is described suitable for use in a fuel cell. The composite membrane has a high equivalent weight thick layer in order to provide sufficient strength and low equivalent weight surface layers for improved electrical performance in a fuel cell. In use, the composite membrane is provided with electrode surface layers. The composite

K. R. Plowman; T. J. Rehg; L. W. Davis; W. P. Carl; A. J. Cisar; C. S. Eastland

1997-01-01

26

Membrane fractionation of milk: state of the art and challenges  

Microsoft Academic Search

Separation of milk into well-defined fractions will lead to a more optimal use of milk components (milk fat, casein, serum proteins) and their functional properties. In principle, membrane separation technology is well capable of large-scale fractionation of milk. Membrane processes for the isolation of serum proteins from whey, and the reduction of bacteria and spores in skimmed milk have already

G. B. P. W. Brans; C. G. P. H. Schroën; R. G. M. van der Sman; R. M. Boom

2004-01-01

27

Composite fuel cell membranes  

DOEpatents

A bilayer or trilayer composite ion exchange membrane is described suitable for use in a fuel cell. The composite membrane has a high equivalent weight thick layer in order to provide sufficient strength and low equivalent weight surface layers for improved electrical performance in a fuel cell. In use, the composite membrane is provided with electrode surface layers. The composite membrane can be composed of a sulfonic fluoropolymer in both core and surface layers.

Plowman, K.R.; Rehg, T.J.; Davis, L.W.; Carl, W.P.; Cisar, A.J.; Eastland, C.S.

1997-08-05

28

Plasma cell membranes of the rat kidney  

Microsoft Academic Search

A fraction enriched with plasma cell membranes (PMF) was isolated from rat kidney homogenate by differential centrifugation. Before NaJ treatment electron micrographs of the preparation showed a membraneous fraction with only a small contamination of mitochondria. After treatment with NaJ the residual PMF exhibited a low microsomal glucose 6-phosphatase activity. Marker enzymes of other subcellular fractions were not detected. The

H. Ebel; N. G. Santo; K. Hierholzer

1971-01-01

29

Plant cell membranes  

SciTech Connect

The contents of this book are: Cells, Protoplasts, Vacuoles and Liposomes; Tonoplasts; Nuclei, Endolplasmic Reticulum, and Plasma Membrane; Peroxisomes; Plastids; Teneral Physical and Biochemical Methods; and Mitochondira.

Packer, L.; Douce, R.

1987-01-01

30

Gas phase fractionation method using porous ceramic membrane  

DOEpatents

Flaw-free porous ceramic membranes fabricated from metal sols and coated onto a porous support are advantageously used in gas phase fractionation methods. Mean pore diameters of less than 40 .ANG., preferably 5-20 .ANG. and most preferably about 15 .ANG., are permeable at lower pressures than existing membranes. Condensation of gases in small pores and non-Knudsen membrane transport mechanisms are employed to facilitate and increase membrane permeability and permselectivity.

Peterson, Reid A. (Madison, WI); Hill, Jr., Charles G. (Madison, WI); Anderson, Marc A. (Madison, WI)

1996-01-01

31

Electroporation of cell membranes.  

PubMed Central

Electric pulses of intensity in kilovolts per centimeter and of duration in microseconds to milliseconds cause a temporary loss of the semipermeability of cell membranes, thus leading to ion leakage, escape of metabolites, and increased uptake by cells of drugs, molecular probes, and DNA. A generally accepted term describing this phenomenon is "electroporation." Other effects of a high-intensity electric field on cell membranes include membrane fusions, bleb formation, cell lysis... etc. Electroporation and its related phenomena reflect the basic bioelectrochemistry of cell membranes and are thus important for the study of membrane structure and function. These phenomena also occur in such events as electric injury, electrocution, and cardiac procedures involving electric shocks. Electroporation has found applications in: (a) introduction of plasmids or foreign DNA into living cells for gene transfections, (b) fusion of cells to prepare heterokaryons, hybridoma, hybrid embryos... etc., (c) insertion of proteins into cell membranes, (d) improving drug delivery and hence effectiveness in chemotherapy of cancerous cells, (e) constructing animal model by fusing human cells with animal tissues, (f) activation of membrane transporters and enzymes, and (g) alteration of genetic expression in living cells. A brief review of mechanistic studies of electroporation is given.

Tsong, T Y

1991-01-01

32

Differential scanning calorimetry characterization of rabbit brain membrane fractions.  

PubMed

Various membrane fractions have been prepared from rabbit brain synaptosomes by centrifugation on discontinuous sucrose gradients after osmotic shock. These fractions were characterized by electron microscopy (E.M.), SDS-PAGE and GABA binding. The fractions were then studied by differential scanning calorimetry (DSC). The calorimetric results indicate that all the fractions studied show thermal transitions at around 60 degrees C which correspond to the "melting" of membrane structures. An additional transition at higher temperature (82 degrees C) seems to be associated with an enrichment in central myelin fragments. PMID:1809740

Cupello, A; Mancardi, G L; Candiano, G; Rialdi, G

1991-11-01

33

Heterogeneity of human red blood cell membrane: Co-existence of heavy and light membranes  

Microsoft Academic Search

The exact chemical composition of the red blood cell (RBC) membrane may vary depending on the methods used to isolate the membrane. We provide evidence here that RBC membrane can be fractionated by differential centrifugation and\\/or density gradient centrifugation into two distinct types, designated as ‘heavy membrane’ (HM) and ‘light membrane’ (LM). The amount of LM is twice that of

Salil K. Das; Shyamali Mukherjee

1999-01-01

34

Derivation of extracellular fluid volume fraction and equivalent dielectric constant of the cell membrane from dielectric properties of the human body. Part 2: A preliminary study for tracking the progression of surgical tissue injury  

Microsoft Academic Search

A study is conducted to determine whether the extracellular fluid (ECF) volume fraction and equivalent dielectric constant\\u000a of the cell membrane ?m, derived from the dielectric properties of the human body can track the progression of surgical tissue injury. Frequency-dependent\\u000a dielectric constants and electrical conductivities of body segments are obtained at surgical (trunk) and non-surgical sites\\u000a (arm and leg) from

T. Tatara; K. Tsuzaki

2000-01-01

35

Fractionation of olive mill wastewaters by membrane separation techniques.  

PubMed

This study aims to evaluate the potential of an integrated membrane system in the treatment of olive mill wastewaters (OMWs) to produce a purified fraction enriched in low molecular weight polyphenols, a concentrated fraction of organic substances and a water stream which can be reused in the extractive process of olive oil. In particular, a sequence of two ultrafiltration (UF) processes followed by a final nanofiltration (NF) step was investigated on laboratory scale operating in selected process parameters. The produced fractions were analyzed for their total content of polyphenols, total antioxidant activity (TAA), free low molecular weight polyphenols and total organic carbon (TOC). The performance of selected membranes in terms of productivity, fouling index and selectivity toward compounds of interest was also evaluated and discussed. An integrated membrane process was proposed to achieve high levels of purification of OMWs and a water fraction which can be discharged in aquatic systems or to be reused in the olive oil extraction process. PMID:23376489

Cassano, Alfredo; Conidi, Carmela; Giorno, Lidietta; Drioli, Enrico

2013-01-10

36

Inhibition of Adenosine Triphosphatase Activity from a Plasma Membrane Fraction of Acer pseudoplatanus Cells by 2,2,2-Trichloroethyl 3,4-Dichlorocarbanilate 12  

PubMed Central

2,2,2-Trichloroethyl 3,4-dichlorocarbanilate (SW26) is toxic for Acer pseudoplatanus cell cultures. It inhibited the cellular proton extrusion and depolarized the plasmalemma. In vitro, it inhibited the plasma membrane ATPase. SW 26 was also inhibitory to membrane ATPases of other origins—plant (maize shoot), fungus (Schizosaccharomyces pombe), and animal (dog kidney)—with about the same efficiency (7.5 micromolar < I50 < 22 micromolar). It did not inhibit the oligomycin-sensitive ATPase from purified plant mitochondria, nor molybdate-sensitive soluble phosphatases. SW26 was more specific for plasma membrane ATPases than diethylstilbestrol or vanadate. A Lineweaver-Burk plot analysis showed that inhibition kinetics were purely noncompetitive (Ki = 14.7 micromolar) below 20 micromolar. Above this concentration, the inhibition pattern was not consistent with Michaelis-Menten kinetics, and a Hill plot representation revealed a positive cooperativity.

Blein, Jean-Pierre; de Cherade, Xavier; Bergon, Michel; Calmon, Jean-Pierre; Scalla, Rene

1986-01-01

37

Cell fractions and enzymatic activities of Ureaplasma urealyticum.  

PubMed Central

The localization of some enzymic activities in cell fractions of Ureaplasma urealyticum was studied. A quantitative evaluation of the effectiveness of several cell lysis procedures was obtained by using labeled membranes and sucrose density gradient centrifugation. Ultrasonic treatment was found to be the most effective procedure for lysing the cells, whereas digitonin and osmotic shock caused the lysis of only 70 and 50% of the cells, respectively. The localization of selected enzymes in Ureaplasma cells resembled that found in other Mycoplasma species. Adenosine triphosphatase, ribonuclease, deoxyribonuclease, and p-nitrophenylphosphatase activities were located exclusively in the membrane fraction, whereas urease and L-histidine ammonia-lyase were located in the cytoplasm.

Romano, N; La Licata, R

1978-01-01

38

Cell Membranes Tutorial  

NSDL National Science Digital Library

New from The Biology Project of the University of Arizona, this online tutorial "introduces the dynamic complexes of proteins, carbohydrates, and lipids that comprise cell membranes," and relates how membranes "are important for regulating ion and molecular traffic flow between cells." Each section of this Web site takes the form of a multiple choice question. Answer the question correctly, and a brief explanation of each answer choice will be displayed. Answer the question incorrectly, and a short but helpful tutorial with colorful diagrams will help get you on the right track. This would be an valuable Web site for students wishing to test themselves on cell membrane structure and function, but would not be especially useful for those new to the subject.

2002-01-01

39

Fuel cell membrane humidification  

DOEpatents

A polymer electrolyte membrane fuel cell assembly has an anode side and a cathode side separated by the membrane and generating electrical current by electrochemical reactions between a fuel gas and an oxidant. The anode side comprises a hydrophobic gas diffusion backing contacting one side of the membrane and having hydrophilic areas therein for providing liquid water directly to the one side of the membrane through the hydrophilic areas of the gas diffusion backing. In a preferred embodiment, the hydrophilic areas of the gas diffusion backing are formed by sewing a hydrophilic thread through the backing. Liquid water is distributed over the gas diffusion backing in distribution channels that are separate from the fuel distribution channels.

Wilson, Mahlon S. (Los Alamos, NM)

1999-01-01

40

Preparation and crossed immunoelectrophoretic analysis of cytoplasmic and outer membrane fractions from Neisseria gonorrhoeae.  

PubMed Central

Cell envelopes were obtained from lysates of Neisseria gonorrhoeae, colony type T1, prepared with lysozyme, ethylenediaminetetraacetate, and Brij 58. This preparation was separated into cytoplasmic (inner) and outer membrane fractions by equilibrium sucrose density gradient centrifugation. The former fraction was 10-fold enriched in L-lactate dehydrogenase activity with respect to the latter. On the basis of buoyant density in sucrose, polypeptide patterns in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and enzymatic activity, these preparations appear similar to cytoplasmic and outer membrane preparations from other gram-negative bacteria. The membrane preparations were analyzed by high-resolution crossed immunoelectrophoretic procedures. This technique permitted the identification of antigens originating from the structural components of the gonococcal cell. Among those found to be cytoplasmic membrane components was the fast-moving antigen which occurs widely in gram-negative bacteria. Images Fig. 2 Fig. 3 Fig. 4 Fig. 5

Collins, M L; Salton, M R

1980-01-01

41

Role of Menaquinones in Fe(III) Reduction by Membrane Fractions of Shewanella putrefaciens  

PubMed Central

Two Tn5-generated mutants of Shewanella putrefaciens with insertions in menD and menB were isolated and analyzed. Both mutants were deficient in the use of several terminal electron acceptors, including Fe(III). This deficiency was overcome by the addition of menaquinone (vitamin K2). Isolated membrane fractions from both mutants were unable to reduce Fe(III) in the absence of added menaquinone when formate was used as the electron donor. These results indicate that menaquinones are essential components for the reduction of Fe(III) by both whole cells and purified membrane fractions when formate or lactate is used as the electron donor.

Saffarini, Daad A.; Blumerman, Seth L.; Mansoorabadi, Karen J.

2002-01-01

42

Fractionation of multiwalled carbon nanotubes by cascade membrane microfiltration  

SciTech Connect

Multiwalled carbon nanotubes were purified and size-separated by a multistep microfiltration process through a sequence of track-etched polycarbonate membranes of various pore sizes in both dead-ended and cross-flow mode. For this cascade microfiltration, the electric arc derived raw multiwalled samples were suspended in an aqueous solution of sodium dodecyl sulfate in deionized water. By examining the deposits on the membrane surfaces and in the permeate suspensions with scanning electron microscopy and atomic force microscopy, the nanotube fractionation was confirmed and analyzed. These scanning techniques showed that the components of the crude sample, which included carbon nanotubes, polyhedral nanoparticles, and large aggregates, were separated from each other during the filtration. In addition, fractionation of the multiwalled carbon nanotubes according to length was possible.

Abatemarco, T.; Stickel, J.; Belfort, J.; Frank, B.P.; Ajayan, P.M.; Belfort, G. [Rensselaer Polytechnic Inst., Troy, NY (United States)

1999-05-06

43

Continuum modeling of cell membranes  

Microsoft Academic Search

In this paper, we develop a finite-deformation model for cell membranes with a view toward characterizing the local mechanical response of membranes in atomic force microscope (AFM) experiments. The membrane is modeled as a 2-D fluid continuum endowed with bending resistance. The general theory is used to obtain equations that describe axisymmetric equilibrium states. The membrane is assumed to enclose

Eveline Baesu; R. E. Rudd; J. Belak; M. McElfresh

2004-01-01

44

The cell membrane and receptors  

Microsoft Academic Search

The cell membrane, the plasmalemma, separates the intracellular fluid (ICF) from the surrounding extracellular fluid (ECF), and acts as an interface between the cell's environment and its contents. Because the ICF and ECF differ in composition, the cell membrane must act as a barrier; however, the metabolism of the cell requires the entry of raw materials and the exit of

James Waterhouse

2004-01-01

45

Albumin recovery enhancement in membrane plasma fractionation using pulsatile flow.  

PubMed

In therapeutic plasmapheresis using cascade filtration, it is important to maximize albumin recovery while rejecting as many gamma-globulins as possible. Several membrane fractionation techniques were investigated using fresh bovine and human plasma and cellulose acetate filters (PF 100, AKZO). In dead end mode the sieving coefficients were found to decrease as transmembrane pressure increased. This was due to membrane plugging during the course of filtration after about 20 minutes which lead to a rapid increase in transmembrane pressure. In single pass mode the albumin recovery factor generally remains around 40% since the permeate flux is much less than the inlet flow. When strong pulsations (4 to 6 Hz) were superposed on the inlet plasma flow in single pass mode, the albumin sieving coefficient remained at about 0.95 while the permeate flux was increased by 106%. As a result a recovery factor of more than 80% could be sustained for at least 90 minutes without membrane plugging. Therefore pulsatile flow plasma fractionation seems to be an interesting approach to combine continuous operation with high albumin recovery. PMID:2032751

Ding, L; Charcosset, C; Jaffrin, M Y

1991-01-01

46

Lateral Diffusion of Membrane Proteins at Cell Membrane  

Microsoft Academic Search

The cell membrane is an important organ of living cells, which has a complex structure influenced by the interaction between membrane proteins and cell membrane. On the basis of fluid motion and diffusion interaction, a simple model is proposed to evaluate quantitatively the effects of the protein size and membrane fluid velocity on the lateral diffusion of membrane proteins at

Lei Fan; Tian You Fan

2010-01-01

47

Lateral Diffusion of Membrane Proteins at Cell Membrane  

NASA Astrophysics Data System (ADS)

The cell membrane is an important organ of living cells, which has a complex structure influenced by the interaction between membrane proteins and cell membrane. On the basis of fluid motion and diffusion interaction, a simple model is proposed to evaluate quantitatively the effects of the protein size and membrane fluid velocity on the lateral diffusion of membrane proteins at the cell membrane. The study shows that the diffusion coefficient is a dominant factor on the lateral diffusion.

Fan, Lei; Fan, Tian You

48

Characterization of ATPases of apical membrane fractions from Locusta migratoria Malpighian tubules.  

PubMed

Apical and basal membrane fractions from Locusta Malpighian tubules were prepared and were characterized by marker enzyme analysis. The apical membranes contained an azide- and orthovanadate-insensitive ATPase activity that was inhibited by bafilomycin A1 (IC50 = 0.44 nM) and NEM (IC50 = 2.15 microM), and thus was characterized as putative V-type ATPase. The enzyme was stimulated by a variety of monovalent cations (Tris > K = Na > choline > Li = Rb) maximal stimulation occurring at 30-40 mM. It was also stimulated by a variety of monovalent anions (maximal activation 30-40 mM), but was strongly inhibited by nitrate and thiocyanate. SDS-PAGE separation of proteins present in the various membrane fractions was carried out. The apical membrane fraction alone contained a 28 kDa protein band that bound a monoclonal antibody specific for a 28 kDa peptide which was a component of the V-type ATPase from midgut of Manduca sexta and, in native gels, possessed ATPase activity which was also sensitive to both bafilomycin and NEM but not to azide or orthovanadate. Binding of the fluorescent monoclonal antibody was located at the apical boundary of the tubule cells. It was concluded that a V-type ATPase is present at the apical surface of Locusta Malpighian tubule cells and that it is involved in their secretory functioning. PMID:9684329

al-Fifi, Z I; Marshall, S L; Hyde, D; Anstee, J H; Bowler, K

1998-04-01

49

Membrane Compartmentation Is Required for Efficient T Cell Activation  

Microsoft Academic Search

The plasma membrane of mammalian cells contains detergent-resistant membrane rafts enriched in glycosphingolipids and cholesterol. Although several important signaling molecules have been found in such rafts, evidence documenting a functional role for their localization has been scarce. Using a fractionation scheme that preserves tyrosine phosphorylation, we show that T cell activation leads to a striking compartmentation in the rafts of

Ramnik Xavier; Todd Brennan; Qingqin Li; Christine McCormack; Brian Seed

1998-01-01

50

In vitro enzymatic reduction kinetics of mineral oxides by membrane fractions from Shewanella oneidensis MR-1  

NASA Astrophysics Data System (ADS)

This study documents the first example of in vitro solid-phase mineral oxide reduction by enzyme-containing membrane fractions. Previous in vitro studies have only reported the reduction of aqueous ions. Total membrane (TM) fractions from iron-grown cultures of Shewanella oneidensis MR-1 were isolated and shown to catalyze the reduction of goethite, hematite, birnessite, and ramsdellite/pyrolusite using formate. In contrast, nicotinamide adenine dinucleotide (NADH) and succinate cannot function as electron donors. The significant implications of observations related to this cell-free system are: (i) both iron and manganese mineral oxides are reduced by the TM fraction, but aqueous U(VI) is not; (ii) TM fractions from anaerobically grown, but not aerobically grown, cells can reduce the mineral oxides; (iii) electron shuttles and iron chelators are not needed for this in vitro reduction, documenting conclusively that reduction can occur by direct contact with the mineral oxide; (iv) electron shuttles and EDTA stimulate the in vitro Fe(III) reduction, documenting that exogenous molecules can enhance rates of enzymatic mineral reduction; and (v) multiple membrane components are involved in solid-phase oxide reduction. The membrane fractions, consisting of liposomes of cytoplasmic and outer membrane segments, contain at least 100 proteins including the enzyme that oxidizes formate, formate dehydrogenase. Mineral oxide reduction was inhibited by the addition of detergent Triton X-100, which solubilizes membranes and their associated proteins, consistent with the involvement of multiple electron carriers that are disrupted by detergent addition. In contrast, formate dehydrogenase activity was not inhibited by Triton X-100. The addition of anthraquinone-2,6-disulfonate (AQDS) and menaquinone-4 was unable to restore activity; however, menadione (MD) restored 33% of the activity. The addition of AQDS and MD to reactions without added detergent increased the rate of goethite reduction. The Michaelis Menten Km values of 71 ± 22 m2/L for hematite and 50 ± 16 m2/L for goethite were calculated as a function of surface area of the two insoluble minerals. Vmax was determined to be 123 ± 14 and 156 ± 13 nmol Fe(II)/min/mg of TM protein for hematite and goethite, respectively. These values are consistent with in vivo rates of reduction reported in the literature. These observations are consistent with our conclusion that the enzymatic reduction of mineral oxides is an effective probe that will allow elucidation of molecular chemistry of the membrane mineral interface where electron transfer occurs.

Ruebush, Shane S.; Icopini, Gary A.; Brantley, Susan L.; Tien, Ming

2006-01-01

51

Cryptococcus neoformans cryoultramicrotomy and vesicle fractionation reveals an intimate association between membrane lipids and glucuronxylomannan  

PubMed Central

Cryptococcus neoformans is an encapsulated pathogenic fungus. The cryptococcal capsule is composed of polysaccharides and is necessary for virulence. It has been previously reported that glucuronoxylomannan (GXM), the major capsular component, is synthesized in cytoplasmic compartments and transported to the extracellular space in vesicles, but knowledge on the organelles involved in polysaccharide synthesis and traffic is extremely limited. In this paper we report the GXM distribution in C. neoformans cells sectioned by cryoultramicrotomy and visualized by transmission electron microscopy (TEM) and polysaccharide immunogold staining. Cryosections of fungal cells showed high preservation of intracellular organelles and cell wall structure. Incubation of cryosections with an antibody to GXM revealed that cytoplasmic structures associated to vesicular compartments and reticular membranes are in close proximity to the polysaccharide. GXM was generally found in association with the membrane of intracellular compartments and within different layers of the cell wall. Analysis of extracellular fractions from cryptococcal supernatants by transmission electron microscopy in combination with serologic, chromatographic and spectroscopic methods revealed fractions containing GXM and lipids. These results indicate an intimate association of GXM and lipids in both intracellular and extracellular spaces consistent with polysaccharide synthesis and transport in membrane-associated structures.

Oliveira, Debora L.; Nimrichter, Leonardo; Miranda, Kildare; Frases, Susana; Faull, Kym F.; Casadevall, Arturo; Rodrigues, Marcio L.

2009-01-01

52

Transformation ofEscherichia coli withPlasmid Deoxyribonucleic Acid: Calcium-Induced Binding of Deoxyribonucleic AcidtoWholeCells andtoIsolated MembraneFractions  

Microsoft Academic Search

Plasmid deoxyribonucleic acid(DNA)was tightly boundtocellsofEscherichia coli at0°Cinthepresenceofdivalent cations. During incubation at42°C, 0.1to 1% ofthis DNA becameresistant todeoxyribonuclease. Deoxyribonuclease-re- sistant DNA binding andtheability toproduce transformants becamesaturated whentransformation mixtures contained 1to2ugofplasmid NTP16DNA and about 5x 10' viable cells. Underoptimumconditions, between 1and2molecule equivalents of3H-labeled NTP16DNA perviable cell becamedeoxyribonuclease resistant. Despite this, only0.1to1%ofviable cells becametransformed by saturating amountsoftheplasmid. Theresults suggest thattransport ofDNA acrosstheinner membraneisa

A. WESTON; M. G. M. BROWN; H. R. PERKINS; J. R. SAUNDERS

1981-01-01

53

Plasma membrane of the rat parotid gland: preparation and partial characterization of a fraction containing the secretory surface  

PubMed Central

A plasma membrane fraction from the rat parotid gland has been prepared by a procedure which selectively enriches for large membrane sheets. This fraction appears to have preserved several ultrastructural features of the acinar cell surface observed in situ. Regions of membrane resembling the acinar luminal border appear as compartments containing microvillar invaginations, bounded by elements of the junctional complex, and from which basolateral membranes extend beyond the junctional complex either to contact other apical compartments or to terminate as free ends. Several additional morphological features of the apical compartments suggest that they are primarily derived from the surface of acinar cells, rather than from the minority of other salivary gland cell types. Enzymatic activities characteristically associated with other cellular organelles are found at only low levels in the plasma membrane fraction. The fraction is highly enriched in two enzyme activities--K+ -dependent p-nitrophenyl phosphatase (K+ -NPPase, shown to be Na+/K+ adenosine triphosphatase; 20-fold) and gamma- glutamyl transpeptidase (GGTPase; 26-fold)--both known to mark plasma membranes in other tissues. These activities exhibit different patterns of recovery during fractionation, suggesting their distinct distributions among parotid cellular membranes. Secretion granule membranes also exhibit GGTPase, but no detectable K+ -NPPase. Since Na+/K+ adenosine triphosphatase and GGTPase, respectively, mark the basolateral and apical cellular surfaces in other epithelia, we hypothesize that these two enzymes mark distinct domains in the parotid plasmalemma, and that GGTPase, as the putative apical marker, may signify a compositional overlap between the two types of membranes which fuse during exocytosis.

1982-01-01

54

Foam Fractionation of Major Cell Components.  

National Technical Information Service (NTIS)

A study of foam fractionation as a separation technique was undertaken to determine distribution coefficients for various major cell components. Surface tension measurements were made to determine the solute concentration ranges within which separation by...

S. C. Loftus J. C. Yeung D. R. Christman

1977-01-01

55

Kallikrein and Renin in the Membrane Fractions of the Rat Kidney.  

National Technical Information Service (NTIS)

Plasma membrane (PM) and endoplasmic reticulum (ER) enriched fractions were isolated from the homogenized rat kidney. Transmission electron micrographs of PM showed empty vesicles but no granules present in the fraction. Kallikrein activity was detected i...

K. Nishimura P. E. Ward E. G. Erdos

1980-01-01

56

Disorders of red cell membrane.  

PubMed

Studies during the last three decades have enabled the development of detailed molecular insights into the structural basis of altered function in various inherited red cell membrane disorders. This review highlights our current understanding of molecular and mechanistic insights into various inherited red cell membrane disorders involving either altered membrane structural organization (hereditary spherocytosis, hereditary elliptocytosis and hereditary ovalocytosis) or altered membrane transport function (hereditary stomatocytosis). The molecular basis for the vast majority of cases of hereditary spherocytosis, elliptocytosis and ovalocytosis have been fully defined while little progress has been made in defining the molecular basis for hereditary stomatocytosis. Mutations in a number of distinct genes account for hereditary spherocytosis and elliptocytosis, while a single genetic defect accounts for all cases of hereditary ovalocytosis. Based on these molecular insights, a comprehensive understanding of the structural basis for altered membrane function has been developed. Loss of vertical linkage between membrane skeleton and lipid bilayer leads to membrane loss in hereditary spherocytosis, while weakening of lateral linkages between skeletal proteins leads to membrane fragmentation and surface area loss in hereditary elliptocytosis. Importantly, the severity of anaemia in both these disorders is directly related to extent of membrane surface area loss. Splenectomy results in amelioration of anaemia. PMID:18341630

An, Xiuli; Mohandas, Narla

2008-03-12

57

The Molecules of the Cell Membrane.  

ERIC Educational Resources Information Center

|Cell membrane molecules form a simple, two-dimensional liquid controlling what enters and leaves the cell. Discusses cell membrane molecular architecture, plasma membranes, epithelial cells, cycles of endocytosis and exocytosis, and other topics. Indicates that some cells internalize, then recycle, membrane area equivalent to their entire surface…

Bretscher, Mark S.

1985-01-01

58

High-Speed Pectic Enzyme Fractionation by Immobilised Metal Ion Affinity Membranes  

Microsoft Academic Search

Immobilised metal ion affinity polysulphone hollow-fibre membranes with a high capacity for protein adsorption were prepared and their application for commercial pectic enzyme fractionation was studied. The pass-through fraction containing pectin lyase (PL) is useful for fruit-juice clarification without methanol production on account of pectin-esterase (PE) being retained by the IDA-Cu2+ membrane.

SILVIA ANDREA CAMPERI; Mariano Grasselli; Osvaldo Cascone

59

High-speed pectic enzyme fractionation by immobilised metal ion affinity membranes  

Microsoft Academic Search

Immobilised metal ion affinity polysulfone hollow-fibre membranes, with a high capacity for protein adsorption, were prepared and their utilisation for commercial pectic enzyme fractionation was studied. The pass-through fraction containing pectinlyase is useful for fruit-juice clarification without methanol production on account of pectinesterase being retained by the IDA-Cu2+ membrane.

Silvia Andrea Camperi; Mariano Grasselli; Osvaldo Cascone

2000-01-01

60

Determination of membrane pore size distribution using the fractional rejection of nonionic and charged macromolecules  

Microsoft Academic Search

The objective of this study was to develop a new measurement technique for the determination of pore size distributions (PSDs) of polymeric and ceramic membranes, including NF, UF, and MF membranes. The proposed method uses the fractional rejection (FR) concept of a solute in membrane pores. Experimental measurements were conducted using a high performance liquid chromatography (HPLC) equipped with size

Sangyoup Lee; Gary Amy; Seung-Kwang Hong; Seung-Hyeon Moon; Duck-Hee Lee; Jaeweon Cho

2002-01-01

61

Membrane fractions active in poliovirus RNA replication contain VPg precursor polypeptides  

SciTech Connect

The poliovirus specific polypeptide P3-9 is of special interest for studies of viral RNA replication because it contains a hydrophobic region and, separated by only seven amino acids from that region, the amino acid sequence of the genome-linked protein VPg. Membraneous complexes of poliovirus-infected HeLa cells that contain poliovirus RNA replicating proteins have been analyzed for the presence of P3-9 by immunoprecipitation. Incubation of a membrane fraction rich in P3-9 with proteinase leaves the C-terminal 69 amino acids of P3-9 intact, an observation suggesting that this portion is protected by its association with the cellular membrane. These studies have also revealed two hitherto undescribed viral polypeptides consisting of amino acid sequences of the P2 andf P3 regions of the polyprotein. Sequence analysis by stepwise Edman degradation show that these proteins are 3b/9 (M/sub r/77,000) and X/9 (M/sub r/50,000). 3b/9 and X/9 are membrane bound and are turned over rapidly and may be direct precursors to proteins P2-X and P3-9 of the RNA replication complex. P2-X, a polypeptide void of hydrophobic amino acid sequences but also found associated with membranes, is rapidly degraded when the membraneous complex is treated with trypsin. It is speculated that P2-X is associated with membranes by its affinity to the N-terminus of P3-9.

Takegami, T.; Semler, B.L.; Anderson, C.W.; Wimmer, E.

1983-01-01

62

Pervaporation membranes in direct methanol fuel cells  

Microsoft Academic Search

The membranes in direct methanol fuel cells must both conduct protons and serve as a barrier for methanol. Nafion, the most common fuel cell membrane, is an excellent conductor but a poor barrier. Polyvinyl alcohol pervaporation membranes are good methanol barriers but poor conductors. These and most other pervaporation membranes offer no significant advantages over Nafion in methanol fuel cell

Bryan S. Pivovar; Yuxin Wang; E. L. Cussler

1999-01-01

63

Analyzing Subcellular mRNA Localization via Cell Fractionation  

PubMed Central

Summary The partitioning of secretory and membrane protein-encoding mRNAs to the endoplasmic reticulum (ER), and their translation on ER-associated ribosomes, governs access to the secretory/exocytic pathways of the cell. As mRNAs encoding secretory and membrane proteins comprise approximately 30% of the transcriptome, the localization of mRNAs to the ER represents an extraordinarily prominent, ubiquitous, and yet poorly understood RNA localization phenomenon. The partitioning of mRNAs to the ER is generally thought to be achieved by the signal recognition particle (SRP) pathway. In this pathway, mRNA localization to the ER is determined by the translation product – translation yields an N-terminal signal sequence or topogenic signal that is recognized by the SRP and the resulting mRNA-ribosome-SRP complex is then recruited to the ER membrane. Recent studies have demonstrated that mRNAs can be localized to the ER via a signal sequence and/or translation-independent pathway(s) and that discrete sets of cytosolic protein-encoding mRNAs are enriched on the ER membrane, though they lack an encoded signal sequence. These key findings reopen investigations into the mechanism(s) that govern mRNA localization to the ER. In this contribution, we describe two independent methods that can be utilized to study this important and poorly understood aspect of eukaryotic cell biology. These methods comprise two independent means of fractionating tissue culture cells to yield free/cytosolic polyribosomes and ER membrane-bound polyribosomes. Detailed methods for the fractionation and characterization of the two polyribosome pools are provided.

Jagannathan, Sujatha; Nwosu, Christine; Nicchitta, Christopher V.

2013-01-01

64

Dielectric Breakdown of Cell Membranes  

PubMed Central

With human and bovine red blood cells and Escherichia coli B, dielectric breakdown of cell membranes could be demonstrated using a Coulter Counter (AEG-Telefunken, Ulm, West Germany) with a hydrodynamic focusing orifice. In making measurements of the size distributions of red blood cells and bacteria versus increasing electric field strength and plotting the pulse heights versus the electric field strength, a sharp bend in the otherwise linear curve is observed due to the dielectric breakdown of the membranes. Solution of Laplace's equation for the electric field generated yields a value of about 1.6 V for the membrane potential at which dielectric breakdown occurs with modal volumes of red blood cells and bacteria. The same value is also calculated for red blood cells by applying the capacitor spring model of Crowley (1973. Biophys. J. 13:711). The corresponding electric field strength generated in the membrane at breakdown is of the order of 4 · 106 V/cm and, therefore, comparable with the breakdown voltages for bilayers of most oils. The critical detector voltage for breakdown depends on the volume of the cells. The volume-dependence predicted by Laplace theory with the assumption that the potential generated across the membrane is independent of volume, could be verified experimentally. Due to dielectric breakdown the red blood cells lose hemoglobin completely. This phenomenon was used to study dielectric breakdown of red blood cells in a homogeneous electric field between two flat platinum electrodes. The electric field was applied by discharging a high voltage storage capacitor via a spark gap. The calculated value of the membrane potential generated to produce dielectric breakdown in the homogeneous field is of the same order as found by means of the Coulter Counter. This indicates that mechanical rupture of the red blood cells by the hydrodynamic forces in the orifice of the Coulter Counter could also be excluded as a hemolysing mechanism. The detector voltage (or the electric field strength in the orifice) depends on the membrane composition (or the intrinsic membrane potential) as revealed by measuring the critical voltage in E. coli B harvested from the logarithmic and stationary growth phases. The critical detector voltage increased by about 30% for a given volume on reaching the stationary growth phase.

Zimmermann, U.; Pilwat, G.; Riemann, F.

1974-01-01

65

Dielectric breakdown of cell membranes.  

PubMed

With human and bovine red blood cells and Escherichia coli B, dielectric breakdown of cell membranes could be demonstrated using a Coulter Counter (AEG-Telefunken, Ulm, West Germany) with a hydrodynamic focusing orifice. In making measurements of the size distributions of red blood cells and bacteria versus increasing electric field strength and plotting the pulse heights versus the electric field strength, a sharp bend in the otherwise linear curve is observed due to the dielectric breakdown of the membranes. Solution of Laplace's equation for the electric field generated yields a value of about 1.6 V for the membrane potential at which dielectric breakdown occurs with modal volumes of red blood cells and bacteria. The same value is also calculated for red blood cells by applying the capacitor spring model of Crowley (1973. Biophys. J. 13:711). The corresponding electric field strength generated in the membrane at breakdown is of the order of 4 . 10(6) V/cm and, therefore, comparable with the breakdown voltages for bilayers of most oils. The critical detector voltage for breakdown depends on the volume of the cells. The volume-dependence predicted by Laplace theory with the assumption that the potential generated across the membrane is independent of volume, could be verified experimentally. Due to dielectric breakdown the red blood cells lose hemoglobin completely. This phenomenon was used to study dielectric breakdown of red blood cells in a homogeneous electric field between two flat platinum electrodes. The electric field was applied by discharging a high voltage storage capacitor via a spark gap. The calculated value of the membrane potential generated to produce dielectric breakdown in the homogeneous field is of the same order as found by means of the Coulter Counter. This indicates that mechanical rupture of the red blood cells by the hydrodynamic forces in the orifice of the Coulter Counter could also be excluded as a hemolysing mechanism. The detector voltage (or the electric field strength in the orifice) depends on the membrane composition (or the intrinsic membrane potential) as revealed by measuring the critical voltage in E. coli B harvested from the logarithmic and stationary growth phases. The critical detector voltage increased by about 30% for a given volume on reaching the stationary growth phase. PMID:4611517

Zimmermann, U; Pilwat, G; Riemann, F

1974-11-01

66

Characterization and quantitation of concanavalin A binding by plasma membrane enriched fractions from soybean root  

SciTech Connect

The binding of concanavalin A (Con A) to soybean root membranes in plasma membrane enriched fractions (recovered from the 34/45% interface of simplified discontinuous sucrose density gradients) was studied using a radiochemical assay employing tritated (/sup 3/H)-Con A. The effect of lectin concentration, time, and membrane protein concentration on the specific binding of /sup 3/H-Con A by the membranes was evaluated. Kinetic analyses showed that Con A will react with membranes in that fraction in a characteristic and predictable manner. The parameters for an optimal and standard binding assay were established. Maximal binding occurred with Con A concentrations in the range of 8 to 16% of the total membrane protein with incubation times greater than 40 min at 22 C. Approximately 10/sup 15/ molecules of /sup 3/H-Con A were bound per microgram of membrane protein at saturation. Binding was reversible. Greater than 92% of the total Con A bound at saturation was released by addition of ..cap alpha..-methyl mannoside. A major peak of /sup 3/H-Con A binding was also observed in fractions recovered from the 25/30% interface of a complex discontinuous sucrose density gradient when membranes were isolated in the absence of Mg/sup 2 +/. When high Mg/sup 2 +/ was present in the isolation and gradient media, the peak was shifted to a fraction recovered from the 34/38% sucrose interface. These results suggest that Con A binding sites are also present on membranes of the endoplasmic reticulum. The amount of Con A bound by endoplasmic reticulum membranes was at least twice the amount bound by membranes in plasma membrane enriched fractions when binding was compared on a per unit membrane protein basis. In contrast, mitochondrial inner membranes, which equilibrate at the same density as plasma membranes, had little ability to bind the lectin.

Berkowitz, R.L.; Travis, R.L.

1981-11-01

67

Effect of aniracetam on phosphatidylinositol transfer protein alpha in cytosolic and plasma membrane fractions of astrocytes subjected to simulated ischemia in vitro.  

PubMed

Brain ischemia affects phosphoinositide metabolism and the level of lipid-derived second messengers. Phosphatidylinositol transfer proteins (PI-PTs) are responsible for the transport of phosphatidylinositol (PI) and other phospholipids through membranes. Isoform of PI-TPs (PI-TPalpha) is an essential component in ensuring substrate supply for phospholipase C (PLC). The current study was conducted to examine potential effect of aniracetam on PI-TPalpha expression and to characterize the PI-TPalpha isoform distribution between membrane and cytosol fractions of astrocytes exposed to simulated ischemia in vitro. After 8 h period of ischemia, the level of PI-TPalpha was significantly higher in cytosol (by about 28%) as well as in membrane fraction (by about 80%) in comparison with control. We have found that aniracetam treatment of astrocytes in normoxia significantly increased the level of PI-TPalpha in membrane fraction with a maximal effect at 0.1 microM concentration of aniracetam (by about 195% of control). In membrane fractions of ischemic cells, aniracetam increased PI-TPalpha expression in a concentration-dependent manner. In ischemic cells, aniracetam (10 microM) has elevated PI-TPalpha expression up to 155% and 428% in cytosolic and membrane fractions in comparison with ischemic untreated cells, respectively. The study has shown that aniracetam significantly activates PI-TPalpha in cell membrane fraction and this effect might be connected with previously described activation of MAP kinase cascade. PMID:16227651

Gabryel, Bozena; Chalimoniuk, Ma?gorzata; Ma?ecki, Andrzej; Strosznajder, Joanna B

68

Wrinkled Membrane Morphology of Biological Cell  

NASA Astrophysics Data System (ADS)

Membranes of many biological cells possess a wrinkled surface topology that, in some instance, serves as a reservoir for providing large surface area and membrane expansion during osmotic swelling. We consider and model the development of the wrinkled morphology to result from buckling instabilities which occur during the membrane growth. In particular, we examine the wrinkled membrane morphology of white blood cell experimentally and numerically. Our results show that the deformation mismatch between the membrane and the cytoskeleton during membrane growth triggers buckling of the membrane. This behavior of the wrinkled topology enables expansion of the cell during swelling and reveals interesting details on the role of the membrane topology.

Wang, Lifeng; Castro, Carlos; Boyce, Mary

2010-03-01

69

Membrane proteins of dense lysosomes from Chinese hamster ovary cells  

SciTech Connect

In this work membrane proteins from lysosomes were studied in order to gain more information on the biogenesis and intracellular sorting of this class of membrane proteins. Membrane proteins were isolated from a purified population of lysosomes. These proteins were then examined for various co- and post-translational modifications which could serve as potential intracellular sorting signals. Biochemical analysis using marker enzymatic activities detected no plasma membrane, Golgi, endoplasmic reticulum, peroxisomes, mitochondria, or cytosol. Analysis after incorporation of ({sup 3}H)thymidine or ({sup 3}H)uridine detected no nuclei or ribosomes. A fraction containing integral membrane proteins was obtained from the dense lysosomes by extraction with Triton X-114. Twenty-three polypeptides which incorporated both ({sup 35}S)methionine and ({sup 3}H)leucine were detected by SDS PAGE in this membrane fraction, and ranged in molecular weight from 30-130 kDa. After incorporation by cells of various radioactive metabolic precursors, the membrane fraction from dense lysosomes was examined and was found to be enriched in mannose, galactose, fucose, palmitate, myristate, and sulfate, but was depleted in phosphate. The membrane fraction from dense lysosomes was then analyzed by SDS PAGE to determine the apparent molecular weights of modified polypepties.

Chance, S.C.

1987-01-01

70

Elasticities and stabilities: lipid membranes vs cell membranes  

Microsoft Academic Search

A cell membrane can be simply regarded as composite material consisting of lipid bilayer, membrane cytoskeleton beneath lipid bilayer, and proteins embedded in lipid bilayer and linked with membrane cytoskeleton if one only concerns its mechanical properties. In this Chapter, above all, the authors give a brief introduction to some important work on mechanical properties of lipid bilayers following Helfrich's

Z. C. Tu; R. An; Z. C. Ou-Yang

2005-01-01

71

Physical membrane displacement: Reconstitution in a cell-free system and relationship to cell growth +  

Microsoft Academic Search

Summary Physical membrane displacement is a process common to all forms of vesicle budding as well as cell enlargement and pleomorphic shape changes. Cell-free reconstitution of membrane budding has been achieved with transitional endoplasmic reticulum fractions from both plants and animals where 50 to 70 nm transition vesicles have been observed to bud from the part-rough, part-smooth membrane elements that

D. J. Morré

1994-01-01

72

In vitro enzymatic reduction kinetics of mineral oxides by membrane fractions from Shewanella oneidensis MR1  

Microsoft Academic Search

This study documents the first example of in vitro solid-phase mineral oxide reduction by enzyme-containing membrane fractions. Previous in vitro studies have only reported the reduction of aqueous ions. Total membrane (TM) fractions from iron-grown cultures of Shewanella oneidensis MR-1 were isolated and shown to catalyze the reduction of goethite, hematite, birnessite, and ramsdellite\\/pyrolusite using formate. In contrast, nicotinamide adenine

Shane S. Ruebush; Gary A. Icopini; Susan L. Brantley; Ming Tien

2006-01-01

73

Characteristics of different fractions of microbial flocs and their role in membrane fouling.  

PubMed

Characteristics of different fractions (small flocs vs. large flocs) of sludge flocs from a submerged anaerobic membrane bioreactor treating thermomechanical pulping (TMP) whitewater were determined using various analytic techniques, including extraction and chemical analysis of extracellular polymeric substances (EPS), particle size analyzer, and polymer chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE). The results showed that the fraction of smaller flocs contained a higher level of bound EPS and had a higher fractal dimension as compared to the fraction of larger flocs. PCR-DGGE analysis indicated that there were significant differences in microbial community between the fraction of smaller flocs and large flocs. The microbial community of the smaller flocs was similar to that of the sludge cake layers, indicating the pioneering role of the microbial community in smaller flocs in membrane fouling. These findings provide a new insight in the difference of membrane fouling potential between smaller flocs and larger flocs fraction. PMID:21252429

Lin, H J; Gao, W J; Leung, K T; Liao, B Q

2011-01-01

74

Alginate block fractions and their effects on membrane fouling.  

PubMed

Alginate has been commonly used as a model foulant in studies of membrane organic fouling. As a complex polymer, alginate is composed of two different monomers, namely M ((1 ? 4) linked ?-D-mannopyranuronic acid) and G ((1 ? 4) linked ?-L-gulopyranuronic acid) which are randomly arranged into MG-, MM- and GG-blocks. So far, little information is available about fouling propensity of each block in microfiltration. In this study, microfiltration experiments were conducted respectively with MG-, MM- and GG-blocks separated from alginate under defined conditions. Results showed the severest fouling in the filtration of MG-block, and the least flux decline in the filtration of MM-block. The initial pore blocking was found to be responsible for the fouling observed in MG-block filtration, while the cake layer formed on membrane surface during the MM-block filtration could serve as a pre-filter that prevented membrane from further pore blocking. In order to look into fouling mechanisms, the effects of transparent exopolymeric particles (TEP) on membrane fouling were also studied. TEP were found to form through aggregation or cross-link of alginate blocks. As TEP were bigger than original alginate blocks, they could facilitate the formation of cake layer on membrane surface. It was observed that more TEP were produced from MM-blocks than from MG-blocks in solutions. This in turn explained why cake resistance was dominant in the filtration of MM-blocks as compared to MG-blocks. The analysis by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory further revealed that MM-blocks had lowest cohesive interaction energy among all three alginate blocks, which favoured aggregation of MM-blocks, and ultimately leading to the formation of more TEP. This study provided insights into the roles of different alginate blocks in development of membrane fouling, and suggested that the membrane fouling would be related to molecular structure of alginate. PMID:24070866

Meng, Shujuan; Liu, Yu

2013-09-10

75

Reliability of membrane test cell measurements  

Microsoft Academic Search

Membrane test cells are extensively used for quality assurance, screening tests and in many research projects. However, many practitioners will agree that test cell results may vary considerably and their accuracy can be inadequate for scale-up to larger membrane units. The reliability of test cells is, besides other factors, influenced by small-scale variations of membrane material properties. The performance of

T. Schipolowski; A. Je?owska; G. Wozny

2006-01-01

76

Water-soluble proteins of the human red cell membrane  

Microsoft Academic Search

Summary Procedures were developed for preparation of red cell membranes almost free of hemoglobin but with minimal loss of membrane proteins. Two water-soluble protein fractions are described, each constituting about 25% of the ghost protein. The first is ionically bonded and can be solubilized in water rapidly at pH 7.0 and more slowly at higher ionic strength solutions, with a

J. Th. Hoogeveen; R. Juliano; J. Coleman; A. Rothstein

1970-01-01

77

Phospholipids and acyl groups of subcellular membrane fractions from human intracranial tumors  

Microsoft Academic Search

The phospholipids from subcellular fractions of human intracranial tumors were examined. For comparison, mi- crosomes were isolated from a fetal human brain and from the gray matter of adult human brains. The subcellular membranes of tumors had a higher protein-to-phospholipid ratio than the normal brain membranes. The microsomes from tumors had a lower proportion of diacylglycerophosphorylethanolamine and higher proportions of

G. Y. Sun; B. S. Leung

2009-01-01

78

Cell sorting by one gravity SPLITT fractionation.  

PubMed

The need for innovative separative techniques suitable for the fractionation of biomaterials prompted this investigation into the performance of the gravitational split-flow thin channel (G-SPLITT) system as a cell sorter. The rigorous mathematical description of the separation mechanism allows achievement of fast separation of several million myeloma cells from healthy splenocytes using flow conditions calculated from theory. Separation in G-SPLITT is based on differences in sedimentation rate. For accurate prediction of the optimal working conditions, this parameter was directly measured by cell tracking velocimetry rather than relying on a measure of diameter (by Multisizer) and an assumed density for each cell population. We also discuss the influence of different flow conditions on the effectiveness of separation. PMID:16097771

Benincasa, Maria-Anna; Moore, Lee R; Williams, P Stephen; Poptic, Earl; Carpino, Francesca; Zborowski, Maciej

2005-08-15

79

Membrane degradation mechanisms in polymer electrolyte membrane fuel cells  

NASA Astrophysics Data System (ADS)

Membrane degradation and failure is one of the most important factors limiting the lifetime of polymer electrolyte membrane fuel cells (PEMFCs). Increasing the membrane life by developing degradation mitigation strategies in the cell or developing a new membrane with improved life requires a detailed understanding of the membrane degradation mechanism during operation in a PEMFC. An in-situ and nondestructive technique, which relies on the measurement of the membrane degradation rate in a fuel cell, was used to study the chemical/electrochemical mode of membrane degradation. NafionRTM membrane was used for the degradation study and fluoride emission rate (FER) as measured from the fuel cell effluent water analysis was used as a quantitative indicator of the membrane degradation rate. The degradation mechanism was studied by a detailed investigation of the effect of reactants, catalyst properties (location, potential, catalyst type, interaction with O2 and H2O), cell current, membrane thickness, NafionRTM counterion, and direction of water movement on the membrane degradation rate. Based on the experimental findings it is shown that commonly known membrane degradation mechanisms involving formation of active oxygen species from H 2O2 decomposition or the direct formation of active oxygen species in the oxygen reduction reaction are not the dominating membrane degradation mechanisms in PEMFCs. It is proposed that molecular H2 and O 2 react on the surface of Pt catalyst to form the membrane degrading species. Depending upon the catalyst location the source of H2 or O2 or both is from the reactant crossover through the membrane. The reaction mechanism is chemical in nature and depends upon the catalyst surface properties and the relative concentrations of H2 and O 2 at the catalyst. The membrane degradation rate also depends on the residence time of the species in the membrane and the reaction volume i.e. the membrane thickness. Thus, the membrane degradation may not be limited only to the polymer surface in contact with Pt catalyst. The sulfonic acid groups in the NafionRTM side chain are key to the mechanism by which the radical species attack the polymer.

Mittal, Vishal Onkarmal

80

The proteomics of plant cell membranes  

Microsoft Academic Search

Membrane proteins are involved in many different functions depending on their location in the cell. Characterization of the membrane proteome can bring new insights to the function of different plant membrane systems and the subcellular compartments where the proteins are found. Plant membrane pro- teomics can also provide valuable information about plant-specific biological processes. Despite recent ad- vances in the

Setsuko Komatsu; Hirosato Konishi; Makoto Hashimoto

2010-01-01

81

Development of a novel adsorptive membrane chromatographic method for the fractionation of polyphenols from bilberry.  

PubMed

A novel membrane chromatographic method with a membrane adsorber (Sartobind S) has been developed on the laboratory scale that allows a fractionation of bilberry (Vaccinium myrtillus) constituents into the following three groups of polyphenols: anthocyanins, copigments, and polymers. By using this methodology, a pure anthocyanin fraction free of other copigments and polymeric phenols can be obtained. Using this approach, it provides fractions allowing a more thorough testing of the biological effects of the individual groups of bilberry polyphenols as well as the study of possible synergistic effects between these different groups of bioactive constituents from bilberry. PMID:22309451

Juadjur, Andreas; Winterhalter, Peter

2012-02-28

82

Fractions!  

NSDL National Science Digital Library

Practice all of the activities to help you learn fractions! Go through all five levels of Fractions Review Activities Practice Naming Fractions Do you remember how to do Fraction Sets? Play these games when you have finished the top three activities: Cross the River Pizza Party Fractions Rescue Island Adding Subtracting Fractions SPLAT Mrs. Anderson's Fraction Games Action Fraction Soccer Shootout Fraction Multiplication Soccer Shootout Fraction Division Dirt Bike Fractions Comparisons ...

Lerdahl, Miss

2011-02-01

83

Fractionation of carrier ampholytes in multicompartment electrolyzers with isoelectric membranes.  

PubMed

Multicompartment electrolyzers with isoelectric membranes can be successfully utilized for the preparation of carrier ampholytes of narrow pH ranges from commercially available wider pH intervals. An example is given on the preparation of a 0.6 pH unit (pH 6.7-7.3) range from a standard pH 6-8 interval. A 10% Ampholine solution is focused in an electrolyzer equipped with the following isoelectric membranes: pI 6.0, 6.7, 7.3 and 8.0. The narrow pH 6.7-7.3 cut can be efficiently utilized for base-line separation and quantitation of hemoglobin A from its glycated form, Hb A1c. This analysis is important for the screening and follow up of diabetic patients. The advantage of multicompartment electrolyzers are: (i) precision in the preparation of narrow pH cuts, due to the presence of membranes with defined pI values; (ii) ability to perform in both small- and large-scale operations and (iii) absence of contaminants leaching from granulated supports, as typical of some previous techniques. PMID:8586068

Bossi, A; Righetti, P G

1995-10-01

84

Elasticities and stabilities: lipid membranes vs cell membranes  

Microsoft Academic Search

A cell membrane can be simply regarded as composite material consisting of\\u000alipid bilayer, membrane cytoskeleton beneath lipid bilayer, and proteins\\u000aembedded in lipid bilayer and linked with membrane cytoskeleton if one only\\u000aconcerns its mechanical properties. In this Chapter, above all, the authors\\u000agive a brief introduction to some important work on mechanical properties of\\u000alipid bilayers following Helfrich's

Z. C. Tu; R. An; Z. C. Ou-Yang

2005-01-01

85

Preparation and properties of thyroid cell membranes  

Microsoft Academic Search

Summary Calf and human thyroids have been disrupted by nitrogen microcavitation, and the thyroid membranes prepared by repeated centrifugation in low ionic strength buffers. Two classes of membranes were prepared by centrifugation on a discontinuous gradient of ficoll. A lighter fraction was comprised of somewhat larger vesicles; they were higher in Na+-K+-activated ATPase, phosphodiesterase, and 5'-nucleotidase than was the heavier

John B. Stanbury; Janice V. Wicken; Mary Ann Lafferty

1969-01-01

86

Adhesive specificity of juvenile rat and chicken liver cells and membranes.  

PubMed Central

Liver cells, isolated from either juvenile rats or chickens by a collagenase perfusion technique, reaggregated when maintained in suspension. The cells exhibited marked adhesive specificity; when suspensions contained both cell types, the aggregates consisted primarily of either rat or chicken cells. Adhesive specificity was also observed with plasma membrane fractions isolated from rat liver homogenates, and with comparable fractions from chicken liver. These membranes stimulated aggregation of the homologous but not the heterologous cell type. Other membrane fractions had little or no effect on the aggregation of the homologous cell type. These and other properties of the liver cell and membrane preparations suggest that biochemical studies on cell-cell recognition and adhesion can most effectively be conducted with cells from juvenile and adult animals. Images

Obrink, B; Kuhlenschmidt, M S; Roseman, S

1977-01-01

87

Cell Plasma Membranes and Phase Transitions  

Microsoft Academic Search

Cell plasma membrane phaseplays a large role in membrane trafficking and signaling. The rolethat membrane phase plays in cell\\u000a function, current hypothesesconcerning the size and time duration of the phase transitions, andthe role in disease are discussed.

Mark M. Banaszak Holl

88

Biogenesis of the red cell membrane and cytoskeletal proteins during erythropoiesis in vitro  

Microsoft Academic Search

Purified erythroid progenitor cells (CFU-E) were used to study in vitro the production of the proteins present in the plasma membrane and the membrane skeleton. At different stages of erythropoiesis incorporation of (³⁵S)methionine was measured and membranes were isolated. Whereas incorporation in the total protein mass of the cells increased during erythropoiesis, the labeling of the membrane protein fraction decreased.

W. Nijhof; P. K. Wierenga

1988-01-01

89

In Vitro Stimulation of Human Peripheral Blood Lymphocytes by Soluble and Membrane Fractions of Renografin-Purified Typhus Group Rickettsiae  

PubMed Central

Cell-free extracts of disrupted Renografin-purified Rickettsia typhi and R. prowazekii were evaluated as antigens in lymphocyte transformation assays for cell-mediated immunity to typhus group rickettsiae in 19 individuals with and 9 without histories of exposure to these organisms. Exposure consisted of clinical disease, vaccination with epidemic typhus vaccine, or occupational exposure to these agents. Both the soluble and membrane fractions of disrupted purified rickettsiae were used, and transformation of peripheral blood lymphocytes (PBL) was determined in microcultures by incorporation of [3]thymidine. Of the antigen concentrations tested (1 to 400 ?g/ml), 10?g/ml appeared to be the most satisfactory. At this concentration, PBL transformation was highly reproducible and correlated well with donor exposure and the presence of enzyme-linked immunosorbent assay anti-typhus group immunoglobulin G. At higher concentrations, PBL from both exposed and control donors often responded to a lipopolysaccharide-like component present in these preparations. Specific transformation responses to rickettsial fractions were detected in several individuals decades after infection or vaccination, indicating that both fractions contained antigens associated with persisting cell-mediated immunity in humans. Generally, stimulation indexes with the soluble fraction were slightly greater than those obtained with corresponding concentrations of the membrane preparation, and in three individuals transformation was observed only with the soluble fraction. PBL transformation to soluble fractions also appeared to have some species specificity, since PBL from individuals with documented R. typhi infections were more responsive to the homologous soluble preparation than to the soluble fraction of R. prowazekii. PBL transformation also correlated well with homologous but only poorly with heterologous enzyme-linked immunosorbent assay immunoglobulin G titers.

Bourgeois, A. Louis; Dasch, Gregory A.; Strong, Douglas M.

1980-01-01

90

Junctional membrane uncoupling. Permeability transformations at a cell membrane junction.  

PubMed

The permeability of the membrane surfaces where cells are in contact (junctional membranes) in Chironomus salivary glands depends on Ca(++) and Mg(++). When the concentration of these ions at the junctional membranes is raised sufficiently, these normally highly permeable membranes seal off; their permeability falls one to three orders, as they approach the nonjunctional membranes in conductance. This permeability transformation is achieved in three ways: (a) by iontophoresis of Ca(++) into the cell; (b) by entry of Ca(++) and/or Mg(++) from the extracellular fluid into the cell through leaks in the cell surface membrane (e.g., injury); or (c) by entry of these ions through leaks arising, probably primarily in the perijunctional insulation, due to trypsin digestion, anisotonicity, alkalinity, or chelation. Ca(++) and Mg(++) appear to have three roles in the junctional coupling processes: (a) in the permeability of the junctional membranes; (b) in the permeability of the perijunctional insulation; and (c) a role long known- in the mechanical stability of the cell junction. The two latter roles may well be closely interdependent, but the first is clearly independent of the others. PMID:6050971

Loewenstein, W R; Nakas, M; Socolar, S J

1967-08-01

91

Tracking microdomain dynamics in cell membranes  

PubMed Central

Studies of the diffusion of proteins and lipids in the plasma membrane of cells have long pointed to the presence of membrane domains. A major challenge in the field of membrane biology has been to characterize the various cellular structures and mechanisms that impede free diffusion in cell membranes and determine the consequences that membrane compartmentalization has on cellular biology. In this review, we will provide a brief summary of the classes of domains that have been characterized to date, focusing on recent efforts to identify the properties of lipid rafts in cells through measurements of protein and lipid diffusion.

Day, Charles A.; Kenworthy, Anne K.

2009-01-01

92

Purification of Torpedo californica post-synaptic membranes and fractionation of their constituent proteins.  

PubMed Central

A rapid methof for preparation of membrane fractions highly enriched in nicotinic acetylcholine receptor from Torpedo californica electroplax is described. The major step in this purification involves sucrose-density-gradient centrifugation in a reorienting rotor. Further purification of these membranes can be achieved by selective extraction of proteins by use of alkaline pH or by treatment with solutions of lithium di-idosalicylate. The alkali-treated membranes retain functional characteristics of the untreated membranes and in addition contain essentially only the four polypeptides (mol.wts. 40000, 50000, 60000 and 65000) characteristic of the receptor purified by affinity chromatography. Dissolution of the purified membranes or of the alkali-treated purified membranes in sodium cholate solution followed by sucrose-density-gradient centrifugation in the same detergent solution yields solubilized receptor preparations comparable with the most highly purified protein obtained by affinity-chromatographic procedures. Images Fig. 1. Fig. 2. Fig. 3. Fig. 5. Fig. 7. PLATE 1

Elliott, J; Blanchard, S G; Wu, W; Miller, J; Strader, C D; Hartig, P; Moore, H P; Racs, J; Raftery, M A

1980-01-01

93

Red blood cell membrane defects.  

PubMed

We present an overview of the currently known molecular basis of red cell membrane disorders. A detailed discussion of the structure of the red cell membrane and the pathophysiology and clinical aspects of its disorders is reported. Generally speaking, hereditary spherocytosis (HS) results from a loss of erythrocyte surface area. The mutations of most cases of HS are located in the following genes: ANK1, SPTB, SLC4A1, EPB42 and SPTA1, which encode for ankyrin, spectrin beta-chain, the anion exchanger 1 (band 3), protein 4.2 and spectrin alpha-chain, respectively. Hereditary elliptocytosis (HE) reflects a diminished elasticity of the skeleton. Its aggravated form, hereditary pyropoikilocytosis (HPP), implies that the skeleton undergoes further destabilization. The mutations responsible for HE and HPP, lie in the SPTA1 and SPTB gene, and in the EPB41 gene encoding protein 4.1. Allele alpha LELY is a common polymorphic allele, which plays the role of an aggravating factor when it occurs in trans of an elliptocytogenic allele of the SPTA1 gene. Southeast Asian ovalocytosis derives from a change in band 3. The genetic disorders of membrane permeability to monovalent cations required a positional cloning approach. In this respect, channelopathies represent a new frontier in the field. Dehydrated hereditary stomatocytosis (DHS) was shown to belong to a pleiotropic syndrome: DHS + fetal edema + pseudohyperkalemia, which maps 16q23-24. Splenectomy is strictly contraindicated in DHS and another disease of the same class, overhydrated hereditary stomatocytosis, because it increases the risk of thromboembolic accidents. PMID:14692233

Iolascon, Achille; Perrotta, Silverio; Stewart, Gordon W

2003-03-01

94

A Markovian approach to prostate cell survival under fractionated radiotherapy  

NASA Astrophysics Data System (ADS)

In this work, the survival of clonogenic PC-3 and DU-145 prostate cell lines exposed to conventional fractionated radiotherapy are modeled using an iterated birth-death Markov process. The model consists of a birth-death Markov process where the states in the chain represent the number of surviving clonogenic cells, and are separated by radiation fractions in which the survival of tumor cells immediately following a fraction is described by the linear-quadratic model. The stochastic behavior of the cell population between fractions is described by a birth-death Markov process, which determines the number of cells present for the subsequent fraction. Results show that for an initial clonogen population of 109 cells to reach zero at 2 Gy/fraction, 44 fractions must be delivered to DU-145 prostate cells, and 19 fractions to PC-3 prostate cells. At 2.75 Gy/fraction, 27 fractions must be delivered to DU-145 prostate cells and 13 fractions to PC-3 prostate cells for treatment termination. An advantage of the proposed model is that it can be used to simulate constant as well as variable radiation intervals and dosages. Model construction, validation, results, and applications are discussed.

Castelino, Robin; Falou, Omar; Rodrigues, Matthew; El Kaffas, Ahmed; Galiano, Eduardo

2011-03-01

95

A vacuolar-type proton pump in a vesicle fraction enriched with potassium transporting plasma membranes from tobacco hornworm midgut  

SciTech Connect

Mg-ATP dependent electrogenic proton transport, monitored with fluorescent acridine orange, 9-aminoacridine, and oxonol V, was investigated in a fraction enriched with potassium transporting goblet cell apical membranes of Manduca sexta larval midgut. Proton transport and the ATPase activity from the goblet cell apical membrane exhibited similar substrate specificity and inhibitor sensitivity. ATP and GTP were far better substrates than UTP, CTP, ADP, and AMP. Azide and vanadate did not inhibit proton transport, whereas 100 microM N,N'-dicyclohexylcarbodiimide and 30 microM N-ethylmaleimide were inhibitors. The pH gradient generated by ATP and limiting its hydrolysis was 2-3 pH units. Unlike the ATPase activity, proton transport was not stimulated by KCl. In the presence of 20 mM KCl, a proton gradient could not be developed or was dissipated. Monovalent cations counteracted the proton gradient in an order of efficacy like that for stimulation of the membrane-bound ATPase activity: K+ = Rb+ much greater than Li+ greater than Na+ greater than choline (chloride salts). Like proton transport, the generation of an ATP dependent and azide- and vanadate-insensitive membrane potential (vesicle interior positive) was prevented largely by 100 microM N,N'-dicyclohexylcarbodiimide and 30 microM N-ethylmaleimide. Unlike proton transport, the membrane potential was not affected by 20 mM KCl. In the presence of 150 mM choline chloride, the generation of a membrane potential was suppressed, whereas the pH gradient increased 40%, indicating an anion conductance in the vesicle membrane. Altogether, the results led to the following new hypothesis of electrogenic potassium transport in the lepidopteran midgut. A vacuolar-type electrogenic ATPase pumps protons across the apical membrane of the goblet cell, thus energizing electroneutral proton/potassium antiport. The result is a net active and electrogenic potassium flux.

Wieczorek, H.; Weerth, S.; Schindlbeck, M.; Klein, U.

1989-07-05

96

Membrane lipids and cell death: an overview  

Microsoft Academic Search

In this article we overview major aspects of membrane lipids in the complex area of cell death, comprising apoptosis and various forms of programmed cell death. We have focused here on glycerophospholipids, the major components of cellular membranes. In particular, we present a detailed appraisal of mitochondrial lipids that attract increasing interest in the field of cell death, while the

Ileana M. Cristea; Mauro Degli Esposti

2004-01-01

97

Vesicle Trafficking and Cell Surface Membrane Patchiness  

Microsoft Academic Search

Membrane proteins and lipids often appear to be distributed in patches on the cell surface. These patches are often assumed to be membrane domains, arising from specific molecular associations. However, a computer simulation (Gheber and Edidin, 1999) shows that membrane patchiness may result from a combination of vesicle trafficking and dynamic barriers to lateral mobility. The simulation predicts that the

Qing Tang; Michael Edidin

2001-01-01

98

Resistance of cell membranes to different detergents  

Microsoft Academic Search

Partial resistance of cell membranes to solubilization with mild detergents and the analysis of isolated detergent-resistant membranes (DRMs) have been used operationally to define membrane domains. Given the multitude of detergents used for this purpose, we sought to investigate whether extraction with different detergents might reflect the same underlying principle of domain formation. We therefore compared the protein and lipid

Sebastian Schuck; Masanori Honsho; Kim Ekroos; Andrej Shevchenko; Kai Simons

2003-01-01

99

High electrical field effects on cell membranes  

Microsoft Academic Search

Electrical charging of lipid membranes causes electroporation with sharp membrane conductance increases. Several recent observations, especially at very high field strength, are not compatible with the simple electroporation picture. Here we present several relevant experiments on cell electrical responses to very high external voltages. We hypothesize that, not only are aqueous pores created within the lipid membranes, but that nanoscale

U. Pliquett; R. P. Joshi; V. Sridhara; K. H. Schoenbach

2007-01-01

100

Advanced composite polymer electrolyte fuel cell membranes  

Microsoft Academic Search

A new type of reinforced composite perfluorinated polymer electrolyte membrane, GORE-SELECT(trademark) (W.L. Gore & Assoc.), is characterized and tested for fuel cell applications. Very thin membranes (5-20 microns thick) are available. The combination of reinforcement and thinness provides high membrane, conductances (80 S\\/cm(exp 2) for a 12-micron thick membrane at 25 degrees C) and improved water distribution in the operating

Mahlon S. Wilson; Thomas A. Zawodzinski; Shimshon Gottesfeld; Jeffrey A. Kolde; Bamdad Bahar

1995-01-01

101

Development of ionomer membranes for fuel cells  

Microsoft Academic Search

In this contribution an overview is given about the state-of-the-art at the membrane development for proton-conductive polymer (composite) membranes for the application membrane fuel cells, focusing on the membrane developments in this field performed at ICVT.For preparation of the polymers, processes have been developed for sulfonated arylene main-chain polymers as well as for arylene main-chain polymers containing basic N-containing groups,

Jochen A. Kerres

2001-01-01

102

Advanced composite polymer electrolyte fuel cell membranes  

SciTech Connect

A new type of reinforced composite perfluorinated polymer electrolyte membrane, GORE-SELECT{trademark} (W.L. Gore & Assoc.), is characterized and tested for fuel cell applications. Very thin membranes (5-20 {mu}m thick) are available. The combination of reinforcement and thinness provides high membrane, conductances (80 S/cm{sup 2} for a 12 {mu}m thick membrane at 25{degrees}C) and improved water distribution in the operating fuel cell without sacrificing longevity or durability. In contrast to nonreinforced perfluorinated membranes, the x-y dimensions of the GORE-SELECT membranes are relatively unaffected by the hydration state. This feature may be important from the viewpoints of membrane/electrode interface stability and fuel cell manufacturability.

Wilson, M.S.; Zawodzinski, T.A.; Gottesfeld, S.; Kolde, J.A.; Bahar, B.

1995-09-01

103

Interaction of Sickle Cell Hemoglobin with Erythrocyte Membranes  

NASA Astrophysics Data System (ADS)

The interactions of hemoglobin S with the erythrocyte membrane were compared with the corresponding interactions of hemoglobin A by measuring in both steady-state and kinetic experiments the quenching of the fluorescence of a probe embedded in erythrocyte membranes. Whereas hemoglobin A could be dissociated from membranes, a fraction of hemoglobin S was irreversibly bound even in the oxy state. Deoxyhemoglobin S interacted much more strongly with erythrocyte membranes than did deoxyhemoglobin A: a portion of the deoxyhemoglobin S was irreversibly bound, and the reversibly bound fraction of hemoglobin S dissociated more slowly than did deoxyhemoglobin A. It is suggested that the binding of deoxyhemoglobin S is a two-step reaction in which the first step involves electrostatic interaction with band III erythrocyte membrane protein and the second step involves a hydrophobic interaction with membrane lipids. The latter reaction reflects the greater hydrophobicity of hemoglobin S. The unique interaction of hemoglobin S with erythrocyte membranes may be important in the formation of irreversibly sickled cells.

Shaklai, N.; Sharma, V. S.; Ranney, H. M.

1981-01-01

104

Membrane glycoproteins of differentiating skeletal muscle cells  

SciTech Connect

The composition of N-linked glycoprotein oligosaccharides was studied in myoblasts and myotubes of the C2 muscle cell line. Oligosaccharides were radioactively labelled for 15 hr with (TH) mannose and plasma membranes isolated. Ten glycopeptides were detected by SDS-PAGE and fluorography. The extent of labelling was 4-6 fold greater in myoblasts vs myotubes. A glycopeptide of Mr > 100,000 was found exclusively in myoblast membranes. Lectin chromatography revealed that the proportion of tri-, tetranntenary, biantennary and high mannose chains was similar throughout differentiation. The high mannose chain fraction was devoid of hybrid chains. The major high mannose chain contained nine mannose residues. The higher level of glycopeptide labelling in myoblasts vs myotubes corresponded to a 5-fold greater rate of protein synthesis. Pulse-chase experiments were used to follow the synthesis of the Dol-oligosaccharides. Myoblasts and myotubes labelled equivalently the glucosylated tetradecasaccharide but myoblasts labelled the smaller intermediates 3-4 greater than myotubes. Myoblasts also exhibited a 2-3 fold higher Dol-P dependent glycosyl transferase activity for chain elongation and Dol-sugar synthesis. Together these results show that the degree of protein synthesis and level of Dol-P are contributing factors in the higher capacity of myoblasts to produce N-glycoproteins compared to myotubes.

Miller, K.R.; Remy, C.N.; Smith, P.B.

1987-05-01

105

Enhancement of synaptic vesicle attachment to the plasma membrane fraction by copper  

Microsoft Academic Search

Synaptic vesicles from rat brain were labeled with125I, and the association of the vesicles with other subcellular components of brain was examined using a centrifugation assay. Copper at micromolar concentrations enhances the binding of the vesicles to the synaptic membrane as well as other fractions. Magnesium, Ca2+, and calmodulin with Ca2+ are ineffective. There is virtually no binding of synaptic

Wayne Hoss; Michele Formaniak

1980-01-01

106

Proton Exchange Membranes for Fuel Cells  

SciTech Connect

Proton exchange membrane, also known as polymer electrolyte membrane, fuel cells (PEMFCs) offer the promise of efficient conversion of chemical energy of fuel, such as hydrogen or methanol, into electricity with minimal pollution. Their widespread use to power zero-emission automobiles as part of a hydrogen economy can contribute to enhanced energy security and reduction in greenhouse gas emissions. However, the commercial viability of PEMFC technology is hindered by high cost associated with the membrane electrode assembly (MEA) and poor membrane durability under prolonged operation at elevated temperature. Membranes for automotive fuel cell applications need to perform well over a period comparable to the life of an automotive engine and under heavy load cycling including start-stop cycling under sub-freezing conditions. The combination of elevated temperature, changes in humidity levels, physical stresses and harsh chemical environment contribute to membrane degradation. Perfluorinated sulfonic acid (PFSA)-based membranes, such as Nafion®, have been the mainstay of PEMFC technology. Their limitations, in terms of cost and poor conductivity at low hydration, have led to continuing research into membranes that have good proton conductivity at elevated temperatures above 120 °C and under low humidity conditions. Such membranes have the potential to avoid catalyst poisoning, simplify fuel cell design and reduce the cost of fuel cells. Hydrocarbon-based membranes are being developed as alternatives to PFSA membranes, but concerns about chemical and mechanical stability and durability remain. Novel anhydrous membranes based on polymer gels infused with protic ionic liquids have also been recently proposed, but considerable fundamental research is needed to understand proton transport in novel membranes and evaluate durability under fuel cell operating conditions. In order to advance this promising technology, it is essential to rationally design the next generation of PEMs based on an understanding of chemistry, membrane morphology and proton transport obtained from experiment, theory and computer simulation.

Devanathan, Ramaswami

2010-11-01

107

Localization of the membrane-associated CTP:phosphocholine cytidylyltransferase in Chinese hamster ovary cells with an altered membrane composition.  

PubMed

The subcellular localization of the membrane-associated CTP:phosphocholine cytidylyltransferase was determined in Chinese hamster ovary cells in which the phospholipid composition had been altered by growth in the presence of N-methylethanolamine or treatment with phospholipase C. Cell homogenates were fractionated on Percoll density gradients, and marker enzyme activities were used to determine the location of the cellular membrane fractions. The peak of cytidylyltransferase activity occurred in the gradient at a density intermediate to that of the peaks of endoplasmic reticulum and plasma membrane markers. The profile of cytidylyltransferase activity most closely resembled that of the Golgi membrane marker; however, upon sucrose gradient centrifugation, the profile of the Golgi apparatus was very different from that of cytidylyltransferase. Differential centrifugation suggested a nuclear membrane association of the enzyme. Cytidylyltransferase was associated with a membrane fraction that sedimented when subjected to very low speed centrifugation (65 x g, 5 min). From Percoll gradient fractions, nuclei were identified by microscopy, and they migrated with cytidylyltransferase activity. The data are consistent with a localization of cytidylyltransferase in the nuclear membrane. PMID:2547775

Morand, J N; Kent, C

1989-08-15

108

Lipid microdomains in cell surface membranes  

Microsoft Academic Search

Lipid microdomains within cell membranes are detected by a variety of experimental techniques, each of which characterizes microdomains on a different time and spatial scale. The sum of the data on lipid microdomains has yet to be integrated into a single model of cell membrane structure. Indeed, one highlight of the past year is a new analysis of experimental results

Michael Edidin

1997-01-01

109

Interaction of Defensins with Model Cell Membranes  

NASA Astrophysics Data System (ADS)

Antimicrobial peptides (AMPs) comprise a key component of innate immunity for a wide range of multicellular organisms. For many AMPs, activity comes from their ability to selectively disrupt and lyse bacterial cell membranes. There are a number of proposed models for this action, but the detailed molecular mechanism of selective membrane permeation remains unclear. Theta defensins are circularized peptides with a high degree of selectivity. We investigate the interaction of model bacterial and eukaryotic cell membranes with theta defensins RTD-1, BTD-7, and compare them to protegrin PG-1, a prototypical AMP, using synchrotron small angle x-ray scattering (SAXS). The relationship between membrane composition and peptide induced changes in membrane curvature and topology is examined. By comparing the membrane phase behavior induced by these different peptides we will discuss the importance of amino acid composition and placement on membrane rearrangement.

Sanders, Lori K.; Schmidt, Nathan W.; Yang, Lihua; Mishra, Abhijit; Gordon, Vernita D.; Selsted, Michael E.; Wong, Gerard C. L.

2009-03-01

110

Cytochemical Properties of Osteoblast Cell Membrane Domains.  

National Technical Information Service (NTIS)

The interactions of osteoblasts with one another and with the extracellular milieu are of vital importance for cell function. These interactions are mediated by cell membrane-associated components. In the present work, we studied the distribution of sever...

L. P. Watson Y. H. Kang M. C. Falk

1989-01-01

111

Isolation of plasma membranes from cultured glioma cells and application to evaluation of membrane sphingomyelin turnover  

SciTech Connect

A rapid and reliable method for the isolation of plasma membranes and microsomes of high purity and yield from cultured glioma cells is described. The procedure involves disruption by N2 cavitation, preliminary separation by centrifugation in Tricine buffer, and final separation on a gradient formed from 40% Percoll at pH 9.3. Enzyme and chemical markers indicated greater than 60% yield with six- to eightfold enrichment for plasma membranes and greater than 25% yield with three- to fourfold enrichment for a microsomal fraction consisting mainly of endoplasmic reticulum. The final fractions were obtained with high reproducibility in less than 1 h from the time of cell harvesting. Application of this procedure to human fibroblasts in culture is assessed. The isolation procedure was applied to investigations of synthesis and turnover of sphingomyelin and phosphatidylcholine in plasma membranes of glioma cells following incubation for 4-24 h with (methyl-/sup 3/H)choline. These studies indicated that radioactivity from phosphatidylcholine synthesized in microsomes from exogenous choline may serve as a precursor of the head-group of sphingomyelin accumulating in the plasma membrane.

Cook, H.W.; Palmer, F.B.; Byers, D.M.; Spence, M.W.

1988-11-01

112

Cytosolic factors in bovine neutrophil oxidase activation. Partial purification and demonstration of translocation to a membrane fraction  

SciTech Connect

The O{sub 2}{sup {center dot}{minus}}-generating oxidase of bovine neutrophils is activated in a cell-free system consisting of a particulate fraction enriched in plasma membrane and containing the dormant oxidase, a high-speed supernatant from neutrophil homogenate (cytosol), Mg ions, GTP{gamma}S, and arachidonic acid. The cytosolic components participating in the activation of the membrane-bound oxidase have been investigated. These components were resolved into several active peaks by Q Sepharose chromatography. Partial purification of two active fractions containing a limited number of proteins of 65, 56, 53, and 45 kDa was achieved by gel filtration of cytosol on Ultrogel AcA44, followed by chromatography on hydroxylapatite and Mono Q. The specific oxidase-activating potency of these partially purified fractions was 6-8-fold higher than that of crude cytosol. These data indicate that oxidase activation requires more than one cytosolic component to be activated. To check whether translocation of cytosolic proteins to the membrane occurred concomitantly with oxidase activation, use was made of radiolabeled cytosolic proteins. Cytosol was treated with phenyl({sup 14}C)isothiocyanate (({sup 14}C)PITC). Translocation was studied under conditions in which production of O{sub 2}{sup {center dot}{minus}} was largely modulated by varying the amount of arachidonic acid added to the cell-free system. Maximal oxidase activation with optimal concentration of arachidonic acid resulted in the selective translocation of labeled cytosolic proteins of 65, 53, 45, and 17 kDa to the membrane.

Doussiere, J.; Pilloud, M.C.; Vignais, P.V. (Centre d'Etudes Nucleaires, Grenoble (France))

1990-03-06

113

Solubilization and Partial Purification of the Adenosine Triphosphatase from a Corn Root Plasma Membrane Fraction  

PubMed Central

The K+-stimulated ATPase was partially purified from a plasma membrane fraction from corn roots (WF9 × Mo 17) by solubilization with 30 millimolar octyl-?-d-glucopyranoside followed by precipitation with dilute ammonium sulfate. The specific activity of the enzyme was increased about five times by this procedure. The molecular weight of the detergent-extracted ATPase complex was estimated to be at least 500,000 daltons by chromatography on a Bio-Gel A-5m column. Negative staining electron microscopy indicated that the detergent-extracted material consisted of amorphous particles, while the ammonium sulfate precipitate was composed of uniform vesicles with an average diameter of 100 nanometers. The protein composition of the ammonium sulfate precipitate was significantly different from that of the plasma membrane fraction when compared by sodium dodecyl sulfate gel electrophoresis. The characteristics of the partially purified ATPase resembled those of the plasma membrane associated enzyme. The ATPase required Mg2+, was further stimulated by K+, was almost completely inhibited by 0.1 millimolar diethylstilbestrol, and was not affected by 5.0 micrograms per milliliter oligomycin. Although the detergents sodium cholate, deoxycholate, Triton X-100 and Lubrol WX also solubilized some membrane protein, none solubilized the K+-stimulated ATPase activity. Low concentrations of each detergent, including octyl-?-d-glucopyranoside, activated the ATPase and higher concentrations inactivated the enzyme. These results suggest that the plasma membrane ATPase is a large, integral membrane protein or protein complex that requires lipids to maintain its activity. Images

Dupont, Frances M.; Leonard, Robert T.

1980-01-01

114

Purified Vesicles of Tobacco Cell Vacuolar and Plasma Membranes Exhibit Dramatically Different Water Permeability and Water Channel Activity  

Microsoft Academic Search

The vacuolar membrane or tonoplast (TP) and the plasma membrane (PM) of tobacco suspension cells were purified by free-flow electrophoresis (FFE) and aqueous two-phase partitioning, with enrichment factors from a crude microsomal fraction of >= 4- to 5-fold and reduced contamination by other cellular membranes. For each purified fraction, the mean apparent diameter of membrane vesicles was determined by freeze-fracture

Christophe Maurel; Frederique Tacnet; Josette Guclu; Jean Guern; Pierre Ripoche

1997-01-01

115

Binding of vinblastine and estramustine to isolated plasma membrane fractions from human prostate and prostatic tumors  

Microsoft Academic Search

The binding of vinblastine (VLB) and estramustine (EM) to plasma membranes isolated from human prostate, prostatic tumors as well as from Dunning rat prostatic AT-1 tumors was studied. In addition, the uptake of these drugs in AT-1 tumor cells in culture was examined. Binding of VLB was six-fold lower than that of EM in membrane preparations from all three sources.

Satish Batra; Irené Larsson

1996-01-01

116

Imaging of membrane systems and membrane traffic in living cells.  

PubMed

Eukaryotic cells are composed of an intricate system of internal membranes that are organized into different compartments--including the endoplasmic reticulum (ER), the nuclear envelope, the Golgi complex (GC), lysosomes, endosomes, caveolae, mitochondria, and peroxisomes--that perform specialized tasks within the cell. The localization and dynamics of intracellular compartments are now being studied in living cells because of the availability of green fluorescent protein (GFP)-fusion proteins and recent advances in fluorescent microscope imaging systems. Results using these techniques are revealing how intracellular compartments maintain their steady-state organization and distributions, how they undergo growth and division, and how they transfer protein and lipid components between themselves through the formation and trafficking of membrane transport intermediates. This article describes methods using GFP-fusion proteins to visualize the behavior of organelles and to track membrane-bound transport intermediates moving between them. Practical issues related to the construction and expression of GFP-fusion proteins are discussed first. These are essential for optimizing the brightness and expression levels of GFP-fusion proteins so that intracellular membrane-bound structures containing these fusion proteins can be readily visualized. Next, techniques for performing time-lapse imaging using a confocal laser-scanning microscope (CLSM) are detailed, including the use of photobleaching to highlight organelles and transport intermediates. Methods for the acquisition and analysis of data are then discussed. Finally, commonly used and exciting new approaches for perturbing membrane traffic are outlined. PMID:22046036

Snapp, Erik Lee; Lajoie, Patrick

2011-11-01

117

Reduction of Soluble and Insoluble Iron Forms by Membrane Fractions of Shewanella oneidensis Grown under Aerobic and Anaerobic Conditions  

Microsoft Academic Search

The effect of iron substrates and growth conditions on in vitro dissimilatory iron reduction by membrane fractions of Shewanella oneidensis MR-1 was characterized. Membrane fractions were separated by sucrose density gradients from cultures grown with O2, fumarate, and aqueous ferric citrate as the terminal electron acceptor. Marker enzyme assays and two-dimensional gel electrophoresis demonstrated the high degree of separation between

Shane S. Ruebush; Susan L. Brantley; Ming Tien

2006-01-01

118

Fractional occurrence of defects in membranes and mechanically driven interleaflet phospholipid transport  

NASA Astrophysics Data System (ADS)

The picture of biological membranes as uniform, homogeneous bileaflet structures has been revised in recent times due to the growing recognition that these structures can undergo significant fluctuations both in local curvature and in thickness. In particular, evidence has been obtained that a temporary, localized disordering of the lipid bilayer structure (defects) may serve as a principal pathway for movement of lipid molecules from one leaflet of the membrane to the other. How frequently these defects occur and how long they remain open are important unresolved questions. In this report, we calculate the rate of molecular transport through a transient defect in the membrane and compare this result to measurements of the net transbilayer flux of lipid molecules measured in an experiment in which the lipid flux is driven by differences between the mechanical stress in the two leaflets of the membrane bilayer. Based on this comparison, we estimate the frequency of defect occurrence in the membrane. The occurrence of defects is rare: the probability of finding a defect in 1.0 ?m2 of a lecithin membrane is estimated to be ~6.0×10-6. Based on this fractional occurrence of defects, the free energy of defect formation is estimated to be ~1.0×10-19 J. The calculations provide support for a model in which interleaflet transport in membranes is accelerated by mechanically driven lipid flow.

Raphael, Robert M.; Waugh, Richard E.; Svetina, Saša.; Žekš, Boštjan

2001-11-01

119

Heterogeneity of renal brush border membrane (BBM) fractions isolated by differential and density gradient centrifugation  

SciTech Connect

To differentiate BBM from proximal convoluted tubules (PCT) and from pars recta (PR), the authors isolated separately membrane fractions from superficial cortex (SC-tissue) and from juxtamedullary cortex plus outer stripe of red medulla (JM-tissue) by centrifugation in Percoll gradient. BBM separated on Percoll gradient into the higher density zone (zone A), and lower density zone (zone B). The zone B from SC-tissue membranes showed a peak with high activity of alkaline phosphatase (AP) and maltase but low activities of ..gamma..-glutamyl transferase (GGT) and leucineaminopeptidase (LAP). Membranes from JM-tissue separated into a major peak in zone A, with very high activities of GGT and LAP, markers for PR, along with lesser activity of AP. In addition, zone B showed a small peak of AP and very slight shoulder of GGT and LAP. In membranes from both SC-tissue and JM-tissue, either zone A or zone B, they found concentrative uptake of both /sup 32/Pi and L-(/sup 3/H)-proline in the presence of Na/sup +/-gradient. They suggest, based on distribution of BBM marker enzymes, that membrane fraction in zone B from SC-tissue contains BBM vesicles predominantly from PCT of outer cortical nephrons. Further, BBM vesicles from JM-tissue in zone A are predominantly from PR segments and in zone B from PCT of deep nephrons.

Gapstur, S.M.; Yusufi, A.N.K.; Ginkinger, K.; Szczepanska-Konkel, M.; Dousa, T.P.

1986-03-01

120

Red cell membrane: past, present, and future  

PubMed Central

As a result of natural selection driven by severe forms of malaria, 1 in 6 humans in the world, more than 1 billion people, are affected by red cell abnormalities, making them the most common of the inherited disorders. The non-nucleated red cell is unique among human cell type in that the plasma membrane, its only structural component, accounts for all of its diverse antigenic, transport, and mechanical characteristics. Our current concept of the red cell membrane envisions it as a composite structure in which a membrane envelope composed of cholesterol and phospholipids is secured to an elastic network of skeletal proteins via transmembrane proteins. Structural and functional characterization of the many constituents of the red cell membrane, in conjunction with biophysical and physiologic studies, has led to detailed description of the way in which the remarkable mechanical properties and other important characteristics of the red cells arise, and of the manner in which they fail in disease states. Current studies in this very active and exciting field are continuing to produce new and unexpected revelations on the function of the red cell membrane and thus of the cell in health and disease, and shed new light on membrane function in other diverse cell types.

Gallagher, Patrick G.

2008-01-01

121

Natural organic matter (NOM) fouling of ultrafiltration membranes: fractionation of NOM in surface water and characterisation by LC-OCD  

Microsoft Academic Search

Natural organic matter (NOM) plays a significant role in fouling of ultrafiltration membranes in drinking water treatment processes. The aim of this study was to obtain a better understanding of the interactions between the fractional components of NOM and a hydrophilic PES\\/PVP hollow fiber ultrafiltration membrane (150–200 kDa). NOM was fractionated into hydrophobic, transphilic and hydrophilic acid fractions according to

Maria D. Kennedy; Hyoung K. Chun; Victor A. Quintanilla Yangalia; Bas G. J. Heijman; Jan C. Schippers

2005-01-01

122

Plasma membrane associated membranes (PAM) from Jurkat cells contain STIM1 protein  

Microsoft Academic Search

A proper cooperation between the plasma membrane, the endoplasmic reticulum and the mitochondria seems to be essential for numerous cellular processes involved in Ca2+ signalling and maintenance of Ca2+ homeostasis. A presence of microsomal and mitochondrial proteins together with those characteristic for the plasma membrane in the fraction of the plasma membrane associated membranes (PAM) indicates a formation of stabile

Katarzyna Kozie?; Magdalena Lebiedzinska; Gyorgy Szabadkai; Marta Onopiuk; Wojciech Brutkowski; Katarzyna Wierzbicka; Grzegorz Wilczy?ski; Paolo Pinton; Jerzy Duszy?ski; Krzysztof Zab?ocki; Mariusz R. Wieckowski

2009-01-01

123

Lamin B Content in Chromatin Fractions after Purification of Nuclear Matrix from Cells of Different Types  

Microsoft Academic Search

We analyzed the content of lamin B, one of the main proteins of the nuclear membrane, in different chromatin fractions obtained\\u000a during purification of the nuclear matrix from different cell types. Depending on cell type and nuclear matrix preparation\\u000a technique, lamin B was found in different not associated with matrix chromatin compartments. This effect was observed after\\u000a chromatin extraction with

M. A. Lapshina; I. I. Parkhomenko; R. I. Papina; A. A. Terentiev

2008-01-01

124

Microscale isoelectric fractionation using immobilized pH-specific membranes for multi-dimensional analysis.  

SciTech Connect

We report on advancements of our microscale isoelectric fractionation ({mu}IEFr) methodology for fast on-chip separation and concentration of proteins based on their isoelectric points (pI). We establish that proteins can be fractionated depending on posttranslational modifications into different pH specific bins, from where they can be efficiently transferred to downstream membranes for additional processing and analysis. This technology can enable on-chip multidimensional glycoproteomics analysis, as a new approach to expedite biomarker identification and verification.

Mai, Junyu; Sommer, Gregory Jon; Hatch, Anson V.

2010-10-01

125

Sickle cell membranes and oxidative damage.  

PubMed Central

Sickle erythrocytes and their membranes are susceptible to endogenous free-radical-mediated oxidative damage which correlates with the proportion of irreversibly sickled cells. The suppression of incubation-induced oxidative stress by antioxidants, free radical scavengers and an iron chelator suggest that oxidation products of membrane-bound haemoglobin contribute towards the pathology of the disease.

Rice-Evans, C; Omorphos, S C; Baysal, E

1986-01-01

126

Proton Exchange Membranes for Fuel Cells  

Microsoft Academic Search

Proton exchange membrane, also known as polymer electrolyte membrane, fuel cells (PEMFCs) offer the promise of efficient conversion of chemical energy of fuel, such as hydrogen or methanol, into electricity with minimal pollution. Their widespread use to power zero-emission automobiles as part of a hydrogen economy can contribute to enhanced energy security and reduction in greenhouse gas emissions. However, the

Devanathan

2010-01-01

127

A multi-dimensional approach for fractionating proteins using charged membranes.  

PubMed

In an effort to increase selectivity among proteins with crossflow ultrafiltration, we offer and demonstrate a comprehensive approach to fractionate proteins of similar molecular weight and relatively close pI values. This multidimensional approach involves optimizing membrane charge type and density together with operating conditions such as precise control of pH, ionic strength, and transmembrane pressure for reduced membrane fouling. Each filtration experiment was performed in cross-flow configuration for ?20?min, allowing fast screening for optimal separation as determined by maximum selectivity, ?, and purity, P. Using our comprehensive approach for fractionating mixtures RNase A-lysozyme and BSA-hemoglobin, we obtained values of ??=?9.1, P?=?95.7%, and ??=?6.5, P?=?62.1%, respectively. PMID:23296474

Sorci, Mirco; Gu, Minghao; Heldt, Caryn L; Grafeld, Elizabeth; Belfort, Georges

2013-02-09

128

A membrane bending model of outer hair cell electromotility.  

PubMed Central

We propose a new mechanism for outer hair cell electromotility based on electrically induced localized changes in the curvature of the plasma membrane (flexoelectricity). Electromechanical coupling in the cell's lateral wall is modeled in terms of linear constitutive equations for a flexoelectric membrane and then extended to nonlinear coupling based on the Langevin function. The Langevin function, which describes the fraction of dipoles aligned with an applied electric field, is shown to be capable of predicting the electromotility voltage displacement function. We calculate the electrical and mechanical contributions to the force balance and show that the model is consistent with experimentally measured values for electromechanical properties. The model rationalizes several experimental observations associated with outer hair cell electromotility and provides for constant surface area of the plasma membrane. The model accounts for the isometric force generated by the cell and explains the observation that the disruption of spectrin by diamide reduces force generation in the cell. We discuss the relation of this mechanism to other proposed models of outer hair cell electromotility. Our analysis suggests that rotation of membrane dipoles and the accompanying mechanical deformation may be the molecular mechanism of electromotility.

Raphael, R M; Popel, A S; Brownell, W E

2000-01-01

129

On the Interactions of Lipids and Proteins in the Red Blood Cell Membrane  

Microsoft Academic Search

The effects of temperature and of the action of a purified phospholipase C enzyme preparation on human red blood cell membranes has been investigated by chemical analyses, circular dichroism, and proton magnetic resonance measurements. The results indicate that a substantial fraction of the phospholipids and the proteins of the membranes can change structure independently of one another, suggesting a mosaic

Michael Glaser; Henry Simpkins; S. J. Singer; Michael Sheetz; Sunney I. Chan

1970-01-01

130

Role of Menaquinones in Fe(III) Reduction by Membrane Fractions of Shewanella putrefaciens  

Microsoft Academic Search

Two Tn5-generated mutants of Shewanella putrefaciens with insertions in menD and menB were isolated and analyzed. Both mutants were deficient in the use of several terminal electron acceptors, including Fe(III). This deficiency was overcome by the addition of menaquinone (vitamin K2). Isolated membrane fractions from both mutants were unable to reduce Fe(III) in the absence of added menaquinone when formate

Daad A. Saffarini; Seth L. Blumerman; Karen J. Mansoorabadi

2002-01-01

131

Characterization of a Partially Purified Adenosine Triphosphatase from a Corn Root Plasma Membrane Fraction 1  

PubMed Central

The (K+,Mg2+)-ATPase was partially purified from a plasma membrane fraction from corn roots (WF9 × Mol7) and stored in liquid N2 without loss of activity. Specific activity was increased 4-fold over that of the plasma membrane fraction. ATPase activity resembled that of the plasma membrane fraction with certain alterations in cation sensitivity. The enzyme required a divalent cation for activity (Co2+ > Mg2+ > Mn2+ > Zn2+ > Ca2+) when assayed at 3 millimolar ATP and 3 millimolar divalent cation at pH 6.3. When assayed in the presence of 3 millimolar Mg2+, the enzyme was further activated by monovalent cations (K+, NH4+, Rb+ ? Na+, Cs+, Li+). The pH optima were 6.5 and 6.3 in the absence and presence of 50 millimolar KCl, respectively. The enzyme showed simple Michaelis-Menten kinetics for the substrate ATP-Mg, with a Km of 1.3 millimolar in the absence and 0.7 millimolar in the presence of 50 millimolar KCl. Stimulation by K+ approached simple Michaelis-Menten kinetics, with a Km of approximately 4 millimolar KCl. ATPase activity was inhibited by sodium orthovanadate. Half-maximal inhibition was at 150 and 35 micromolar in the absence and presence of 50 millimolar KCl. The enzyme required the substrate ATP. The rate of hydrolysis of other substrates, except UDP, IDP, and GDP, was less than 20% of ATP hydrolysis. Nucleoside diphosphatase activity was less than 30% of ATPase activity, was not inhibited by vanadate, was not stimulated by K+, and preferred Mn2+ to Mg2+. The results demonstrate that the (K+,Mg2+)-ATPase can be clearly distinguished from nonspecific phosphohydrolase and nucleoside diphosphatase activities of plasma membrane fractions prepared from corn roots.

Dupont, Frances M.; Burke, Linda L.; Spanswick, Roger M.

1981-01-01

132

Membrane elastic properties and cell function.  

PubMed

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

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

2013-07-03

133

Activity of Plasma Membrane H + ATPase in Coleoptile Cells during Development of Maize Seedlings  

Microsoft Academic Search

Hydrolytic activities of the H+-ATPase were compared for plasma membrane fractions isolated from coleoptile cells of 3-, 4-, and 5-day-old etiolated maize seedlings. The membrane preparations obtained by differential centrifugation were additionally purified in the gradient of sucrose density and in the polyethylene glycol-dextran system. The highest level of ATP-hydrolyzing activity was observed in the plasmalemma fraction obtained from 4-day-old

E. L. Rudashevskaya; A. A. Kirpichnikova; M. F. Shishova

2005-01-01

134

Bacteria sorting by field-flow fractionation. Application to whole-cell Escherichia coil vaccine strains.  

PubMed

Sorting and quantification of deactivated bacteria is an important way of quality control for whole-cell bacterial vaccines. In general, surface features of deactivated bacteria used for whole-cell bacterial vaccines affect the immunoresponse to bacteria-associated antigens. Enumeration of bacteria is also an important process development parameter for these vaccines. Field-flow fractionation (FFF) was previously applied to the separation of bacteria. For the first time, FFF is used for sorting bacteria strains of the same species on the basis of differences in bacterial membrane characteristics. Two FFF techniques, gravitational FFF (GrFFF) and asymmetrical flow FFF (AsFIFFF), are shown to be able to fractionate, distinguish, and quantify different deactivated Escherichia coli strains used for vaccines. E. coli can differ in the presence of fimbriae on the bacterial membrane. Fimbriae affect E. coli pathology and thus the use of E. coli for vaccines. GrFFF and AsFIFFF are able to fractionate fimbriated/ nonfimbriated cells in mixtures of different strains. While GrFFF is characterized by low cost and simplicity, As-FIFFF shows a higher performance in size fractionation with a high-speed separation. Coupled, on-line UV/visible turbidimetry yields the relative numbers of fractionated cells and sample recovery. Scanning electron microscopy and quasi-elastic light scattering are employed as uncorrelated techniques for size and morphology analysis of the E. coli strains. PMID:12380810

Reschiglian, Pierluigi; Zattoni, Andrea; Roda, Barbara; Casolari, Sonia; Moon, Myeong Hee; Lee, Jisun; Jung, Jaehong; Rodmalm, Kåre; Cenacchi, Giovanna

2002-10-01

135

Organelle-free cytoplasmic volume fraction of rabbit retinal Müller (glial) cells.  

PubMed

Retinal Müller (glial) cells are thought to act as "cables" carrying spatial buffering K+ currents from the sites of neuronal release into the reservoir of the vitrous body. In order to calculate the amplitude of such currents it is necessary to know the intracellular volume fraction which is able to carry these currents. Thus, this organelle-free volume fraction was measured in transmission electron microscopic photograms of rabbit Müller cells. This volume fraction was found to vary between 0.7 and more than 0.9 in various retinal layers except at the "external limiting membrane" where it was reduced to 0.24 by the accumulation of mitochondria. In enzymatically isolated cells all values are slightly increased by cell swelling. PMID:2607130

Reichenbach, A

1989-01-01

136

Specific binding of a fungal glucan phytoalexin elicitor to membrane fractions from soybean Glycine max  

SciTech Connect

Treatment of soybean tissues with elicitors results in the production of phytoalexins, one of a number of inducible plant defense reactions against microbial infections. The present study uses a ..beta..-1,3-(/sup 3/H) glucan elicitor fraction from Phytophthora megasperma f.sp. glycinea, a fungal pathogen of soybean, to identify putative elicitor targets in soybean tissues. Use of the radiolabeled elicitor disclosed saturable high-affinity elicitor binding site(s) in membrane fractions of soybean roots. Highest binding activity is associated with a plasma membrane-enriched fraction. The apparent K/sub d/ value for ..beta..-glucan elicitor binding is approx. = 0.2 x 10/sup -6/ M and the maximum number of binding sites is 0.5 pmol per mg of protein. Competition studies the (/sup 3/H)glucan elicitor and a number of polysaccharides demonstrate that only polysaccharides of a branched ..beta..-glucan type effectively displace the radiolabeled ligand from membrane binding. Differential displacing activity of the glucans on P. megasperma elicitor binding corresponds closely to their respective ability to elicit phytoalexin production in a cotyledon bioassay.

Schmidt, W.E.; Ebel, J.

1987-06-01

137

[Cell membrane changes and skin diseases].  

PubMed

Biological membranes are laminar bilayers of lipoids with thermolabile biophysical properties. Changing temperatures not only result in altered polarity and permeability of the membranes, but also in changes of the various membrane receptors (e.g. histamine and beta-adrenergic receptors) and the cell makers. In healthy persons, lower temperatures (25 degrees) lead to elevated suppressor properties, and the T4 ratio is below 1.0. At 37 and 41 degrees C, there is a growing number of helper cells, and the T4/T8 ratio becomes normal again. In psoriatic patients, the number of helper cells does not change with the temperature. We also found some evidence for changes of the cell membranes in atopic dermatitis and chronic urticaria. PMID:2907212

Rácz, I

1988-10-15

138

Alternate Fuel Cell Membranes for Energy Independence  

SciTech Connect

The overall objective of this project was the development and evaluation of novel hydrocarbon fuel cell (FC) membranes that possess high temperature performance and long term chemical/mechanical durability in proton exchange membrane (PEM) fuel cells (FC). The major research theme was synthesis of aromatic hydrocarbon polymers of the poly(arylene ether sulfone) (PAES) type containing sulfonic acid groups tethered to the backbone via perfluorinated alkylene linkages and in some cases also directly attached to the phenylene groups along the backbone. Other research themes were the use of nitrogen-based heterocyclics instead of acid groups for proton conduction, which provides high temperature, low relative humidity membranes with high mechanical/thermal/chemical stability and pendant moieties that exhibit high proton conductivities in the absence of water, and synthesis of block copolymers consisting of a proton conducting block coupled to poly(perfluorinated propylene oxide) (PFPO) blocks. Accomplishments of the project were as follows: 1) establishment of a vertically integrated program of synthesis, characterization, and evaluation of FC membranes, 2) establishment of benchmark membrane performance data based on Nafion for comparison to experimental membrane performance, 3) development of a new perfluoroalkyl sulfonate monomer, N,N-diisopropylethylammonium 2,2-bis(p-hydroxyphenyl) pentafluoropropanesulfonate (HPPS), 4) synthesis of random and block copolymer membranes from HPPS, 5) synthesis of block copolymer membranes containing high-acid-concentration hydrophilic blocks consisting of HPPS and 3,3'-disulfonate-4,4'-dichlorodiphenylsulfone (sDCDPS), 6) development of synthetic routes to aromatic polymer backbones containing pendent 1H-1,2,3-triazole moieties, 7) development of coupling strategies to create phase-separated block copolymers between hydrophilic sulfonated prepolymers and commodity polymers such as PFPO, 8) establishment of basic performance properties of experimental membranes, 9) fabrication and FC performance testing of membrane electrode assemblies (MEA) from experimental membranes, and 10) measurement of ex situ and in situ membrane durability of experimental membranes. Although none of the experimental hydrocarbon membranes that issued from the project displayed proton conductivities that met DOE requirements, the project contributed to our basic understanding of membrane structure-property relationships in a number of key respects. An important finding of the benchmark studies is that physical degradation associated with humidity and temperature variations in the FC tend to open new fuel crossover pathways and act synergistically with chemical degradation to accelerate overall membrane degradation. Thus, for long term membrane survival and efficient fuel utilization, membranes must withstand internal stresses due to humidity and temperature changes. In this respect, rigid aromatic hydrocarbon fuel cell membranes, e.g. PAES, offer an advantage over un-modified Nafion membranes. The benchmark studies also showed that broadband dielectric spectroscopy is a potentially powerful tool in assessing shifts in the fundamental macromolecular dynamics caused by Nafion chemical degradation, and thus, this technique is of relevance in interrogating proton exchange membrane durability in fuel cells and macromolecular dynamics as coupled to proton migration, which is of fundamental relevance in proton exchange membranes in fuel cells. A key finding from the hydrocarbon membrane synthesis effort was that rigid aromatic polymers containing isolated ion exchange groups tethered tightly to the backbone (short tether), such as HPPS, provide excellent mechanical and durability properties but do not provide sufficient conductivity, in either random or block configuration, when used as the sole ion exchange monomer. However, we continue to hypothesize that longer tethers, and tethered groups spaced more closely within the hydrophilic chain elements of the polymer, will yield highly conductive materials with excellent mech

Storey, Robson, F.; Mauritz, Kenneth, A.; Patton, Derek, L.; Savin, Daniel, A.

2012-12-18

139

Top down proteomics of human membrane proteins from enriched mitochondrial fractions.  

PubMed

The interrogation of intact integral membrane proteins has long been a challenge for biological mass spectrometry. Here, we demonstrate the application of top down mass spectrometry to whole membrane proteins below 60 kDa with up to 8 transmembrane helices. Analysis of enriched mitochondrial membrane preparations from human cells yielded identification of 83 integral membrane proteins, along with 163 membrane-associated or soluble proteins, with a median q value of 3 × 10(-10). An analysis of matching fragment ions demonstrated that significantly more fragment ions were found within transmembrane domains than would be expected based upon the observed protein sequence. In total, 46 proteins from the complexes of oxidative phosphorylation were identified which exemplifies the increasing ability of top down proteomics to provide extensive coverage in a biological network. PMID:23305238

Catherman, Adam D; Li, Mingxi; Tran, John C; Durbin, Kenneth R; Compton, Philip D; Early, Bryan P; Thomas, Paul M; Kelleher, Neil L

2013-01-23

140

Membrane Reserves and Hypotonic Cell Swelling  

Microsoft Academic Search

To accommodate expanding volume (V) during hyposmotic swelling, animal cells change their shape and increase surface area\\u000a (SA) by drawing extra membrane from surface and intracellular reserves. The relative contributions of these processes, sources\\u000a and extent of membrane reserves are not well defined. In this study, the SA and V of single substrate-attached A549, 16HBE14o?, CHO and NIH 3T3 cells

Nicolas Groulx; Francis Boudreault; Sergei N. Orlov; Ryszard Grygorczyk

2006-01-01

141

Photothermal nanoblade for patterned cell membrane cutting.  

PubMed

We report a photothermal nanoblade that utilizes a metallic nanostructure to harvest short laser pulse energy and convert it into a highly localized and specifically shaped explosive vapor bubble. Rapid bubble expansion and collapse punctures a lightly-contacting cell membrane via high-speed fluidic flows and induced transient shear stress. The membrane cutting pattern is controlled by the metallic nanostructure configuration, laser pulse polarization, and energy. Highly controllable, sub-micron sized circular hole pairs to half moon-like, or cat-door shaped, membrane cuts were realized in glutaraldehyde treated HeLa cells. PMID:21164656

Wu, Ting-Hsiang; Teslaa, Tara; Teitell, Michael A; Chiou, Pei-Yu

2010-10-25

142

Photothermal nanoblade for patterned cell membrane cutting  

PubMed Central

We report a photothermal nanoblade that utilizes a metallic nanostructure to harvest short laser pulse energy and convert it into a highly localized and specifically shaped explosive vapor bubble. Rapid bubble expansion and collapse punctures a lightly-contacting cell membrane via high-speed fluidic flows and induced transient shear stress. The membrane cutting pattern is controlled by the metallic nanostructure configuration, laser pulse polarization, and energy. Highly controllable, sub-micron sized circular hole pairs to half moon-like, or cat-door shaped, membrane cuts were realized in glutaraldehyde treated HeLa cells.

Wu, Ting-Hsiang; Teslaa, Tara; Teitell, Michael A.; Chiou, Pei-Yu

2010-01-01

143

Durability of PEM Fuel Cell Membranes  

NASA Astrophysics Data System (ADS)

Durability is still a critical limiting factor for the commercialization of polymer electrolyte membrane (PEM) fuel cells, a leading energy conversion technology for powering future hydrogen fueled automobiles, backup power systems (e.g., for base transceiver station of cellular networks), portable electronic devices, etc. Ionic conducting polymer (ionomer) electrolyte membranes are the critical enabling materials for the PEM fuel cells. They are also widely used as the central functional elements in hydrogen generation (e.g., electrolyzers), membrane cell for chlor-alkali production, etc. A perfluorosulfonic acid (PFSA) polymer with the trade name Nafion® developed by DuPont™ is the most widely used PEM in chlor-alkali cells and PEM fuel cells. Similar PFSA membranes have been developed by Dow Chemical, Asahi Glass, and lately Solvay Solexis. Frequently, such membranes serve the dual function of reactant separation and selective ionic conduction between two otherwise separate compartments. For some applications, the compromise of the "separation" function via the degradation and mechanical failure of the electrolyte membrane can be the life-limiting factor; this is particularly the case for PEM in hydrogen/oxygen fuel cells.

Huang, Xinyu; Reifsnider, Ken

144

Lysophosphatidylcholine cell depolarization: increased membrane permeability for use in the determination of cell membrane potentials  

SciTech Connect

Current techniques for the determination of cellular membrane potentials based on the uptake of a radiolabeled lipophilic cation, (3H)triphenylmethylphosphonium, and the cyanine dye, DiOC5(3), were analyzed in terms of the proportions of these probes which are accumulated due to potential-dependent and potential-independent forces. Measurements were made of probe uptake in two model systems: rabbit type II pneumocytes and human promyelocytic HL60 cells. For both cell types, the membrane potential-independent component of triphenylmethylphosphonium uptake was found to be a function of several variables, including the length of exposure of the cells to the transport facilitator tetraphenylboron, the concentration of tetraphenylboron, and the integrity of the cell membrane. To accurately determine the magnitude of the potential-independent component of probe uptake by type II and HL60 cells, the cell-permeabilizing agent lysophosphatidylcholine was used. The ability of lysophosphatidylcholine to depolarize cell membranes and accurately predict membrane potential-independent accumulation was found to be equal to or superior to several other techniques commonly used to achieve membrane depolarization (e.g. gramicidin, valinomycin plus high external potassium). Lysophosphatidylcholine cell treatment was found to be a simple, rapid, and accurate technique to increase cell membrane permeability and allow equilibration of intra- and extracellular ions. The method is shown to be useful for determining membrane potential-independent accumulation of both radiolabeled and fluorescent probes of membrane potential.

Gallo, R.L.; Wersto, R.P.; Notter, R.H.; Finkelstein, J.N.

1984-12-01

145

MYADM regulates Rac1 targeting to ordered membranes required for cell spreading and migration  

PubMed Central

Membrane organization into condensed domains or rafts provides molecular platforms for selective recruitment of proteins. Cell migration is a general process that requires spatiotemporal targeting of Rac1 to membrane rafts. The protein machinery responsible for making rafts competent to recruit Rac1 remains elusive. Some members of the MAL family of proteins are involved in specialized processes dependent on this type of membrane. Because condensed membrane domains are a general feature of the plasma membrane of all mammalian cells, we hypothesized that MAL family members with ubiquitous expression and plasma membrane distribution could be involved in the organization of membranes for cell migration. We show that myeloid-associated differentiation marker (MYADM), a protein with unique features within the MAL family, colocalizes with Rac1 in membrane protrusions at the cell surface and distributes in condensed membranes. MYADM knockdown (KD) cells had altered membrane condensation and showed deficient incorporation of Rac1 to membrane raft fractions and, similar to Rac1 KD cells, exhibited reduced cell spreading and migration. Results of rescue-of-function experiments by expression of MYADM or active Rac1L61 in cells knocked down for Rac1 or MYADM, respectively, are consistent with the idea that MYADM and Rac1 act on parallel pathways that lead to similar functional outcomes.

Aranda, Juan F.; Reglero-Real, Natalia; Kremer, Leonor; Marcos-Ramiro, Beatriz; Ruiz-Saenz, Ana; Calvo, Maria; Enrich, Carlos; Correas, Isabel; Millan, Jaime; Alonso, Miguel A.

2011-01-01

146

Mechanical Properties of the Red Cell Membrane  

PubMed Central

The technique of Mitchison and Swann (1954) was modified for determining the resistance to deformation, or “stiffness,” of the red cell membrane and the pressure gradient across the cell wall. It requires a measure of the pressure needed to suck a portion of the cell into a micropipette. Stiffness of hypertonically crenated cells was less than that of biconcave discs or hypotonically swollen cells. Crenated cells showed zero pressure gradient and a stiffness, probably due to pure bending, equivalent to 0.007 ± 0.001 (SE) dynes/cm. Normal and swollen cells showed a pressure gradient of 2.3 ± 0.8 (SE) mm H2O and a stiffness, due to bending and tension in the membrane, equivalent to 0.019 ± 0.002 (SE) dynes/cm. No difference in stiffness was found between the rim and the biconcavity of the cell or between biconcave discs and hypotonically swollen cells. Micromanipulation showed that the membrane can withstand large bending strains but limited tangential strains (stretching). These results have significant implications in any theory explaining the cell shape. For example, the data give no indication that the physical properties of the membrane are different at the rim from those of the biconcavities, and the existence of a positive pressure in the normal cell is established. ImagesFigure 1Figure 8Figure 11Figure 12

Rand, R. P.; Burton, A. C.

1964-01-01

147

beta2-Adrenoceptor, Gs and adenylate cyclase coupling in purified detergent-resistant, low density membrane fractions.  

PubMed

Membrane rafts and caveolae are specialized microdomains of the cell membrane that form physical platforms for compartmentalization of signalling molecules. Here, we intended to gain insight into the consequences of caveolar localization in G protein-coupled receptor function. We analysed beta(2)-adrenoceptor signalling in purified CRLDF (caveolin-rich low density fractions) of beta(2)-adrenoceptor-overexpressing HEK-293 cells. beta(2)-adrenoceptor and Gs immunoreactivities and forskolin-stimulated adenylate cyclase activity were all detected in CRLDF obtained by the conventional raft purification method that uses Triton X-100 solubilization. However, Triton X-100 caused a complete loss of the functional coupling between beta(2)-adrenoceptor, Gs and adenylate cyclase. Therefore, we developed an optimized purification method based on n-octyl-beta-d-glucopyranoside solubilization, where the functional properties of beta(2)-adrenoceptor, Gs and adenylate cyclase were preserved in the CRLDF. Using this method, we showed that isoproterenol-stimulated adenylate cyclase activity was similar in CRLDF and bulk membrane preparations of HEK-293 cells that overexpress beta(2)-adrenoceptor or beta(2)-adrenoceptor-Gs fusion. Accordingly, treatment of cells with methyl-beta-cyclodextrin, a caveola-disrupting agent, did not affect beta(2)-adrenoceptor-induced cAMP response. Likewise, these responses were insensitive to caveolin 1 and 2 overexpression. On the other hand, methyl-beta-cyclodextrin treatment did decrease beta(2)-adrenoceptor-induced ERK phosphorylation. However, the latter effect of methyl-beta-cyclodextrin could be attributed to a non-specific effect rather than its ability to disrupt membrane microdomains. We showed that localization in the raft microdomains did not affect the signalling efficiency of beta(2)-adrenoceptor-Gs-adenylate cyclase pathway, and that methyl-beta-cyclodextrin may inhibit signalling by directly affecting the signalling system independently of its caveola-disrupting property. PMID:20045406

Oner, S Sadik; Kaya, Ali I; Onaran, H Ongun; Ozcan, Gülnihal; U?ur, Ozlem

2010-01-05

148

Vesicle trafficking and cell surface membrane patchiness.  

PubMed Central

Membrane proteins and lipids often appear to be distributed in patches on the cell surface. These patches are often assumed to be membrane domains, arising from specific molecular associations. However, a computer simulation (Gheber and Edidin, 1999) shows that membrane patchiness may result from a combination of vesicle trafficking and dynamic barriers to lateral mobility. The simulation predicts that the steady-state patches of proteins and lipids seen on the cell surface will decay if vesicle trafficking is inhibited. To test this prediction, we compared the apparent sizes and intensities of patches of class I HLA molecules, integral membrane proteins, before and after inhibiting endocytic vesicle traffic from the cell surface, either by incubation in hypertonic medium or by expression of a dominant-negative mutant dynamin. As predicted by the simulation, the apparent sizes of HLA patches increased, whereas their intensities decreased after endocytosis and vesicle trafficking were inhibited.

Tang, Q; Edidin, M

2001-01-01

149

On the Interactions of Lipids and Proteins in the Red Blood Cell Membrane*  

PubMed Central

The effects of temperature and of the action of a purified phospholipase C enzyme preparation on human red blood cell membranes has been investigated by chemical analyses, circular dichroism, and proton magnetic resonance measurements. The results indicate that a substantial fraction of the phospholipids and the proteins of the membranes can change structure independently of one another, suggesting a mosaic pattern for the organization of the lipids and proteins in membranes. Images

Glaser, Michael; Simpkins, Henry; Singer, S. J.; Sheetz, Michael; Chan, Sunney I.

1970-01-01

150

Membrane reserves and hypotonic cell swelling.  

PubMed

To accommodate expanding volume (V) during hyposmotic swelling, animal cells change their shape and increase surface area (SA) by drawing extra membrane from surface and intracellular reserves. The relative contributions of these processes, sources and extent of membrane reserves are not well defined. In this study, the SA and V of single substrate-attached A549, 16HBE14o(-), CHO and NIH 3T3 cells were evaluated by reconstructing cell three-dimensional topology based on conventional light microscopic images acquired simultaneously from two perpendicular directions. The size of SA reserves was determined by swelling cells in extreme 98% hypotonic (approximately 6 mOsm) solution until membrane rupture; all cell types examined demonstrated surprisingly large membrane reserves and could increase their SA 3.6 +/- 0.2-fold and V 10.7 +/- 1.5-fold. Blocking exocytosis (by N-ethylmaleimide or 10 degrees C) reduced SA and V increases of A549 cells to 1.7 +/- 0.3-fold and 4.4 +/- 0.9-fold, respectively. Interestingly, blocking exocytosis did not affect SA and V changes during moderate swelling in 50% hypotonicity. Thus, mammalian cells accommodate moderate (<2-fold) V increases mainly by shape changes and by drawing membrane from preexisting surface reserves, while significant endomembrane insertion is observed only during extreme swelling. Large membrane reserves may provide a simple mechanism to maintain membrane tension below the lytic level during various cellular processes or acute mechanical perturbations and may explain the difficulty in activating mechanogated channels in mammalian cells. PMID:17598067

Groulx, Nicolas; Boudreault, Francis; Orlov, Sergei N; Grygorczyk, Ryszard

2007-06-26

151

Characterization of fatty acids and proteins associated with the xanthophyll-enriched membrane fraction isolated from the thylakoid membranes of irradiance-stressed Dunaliella salina  

Microsoft Academic Search

It has been previously reported that a considerable amount of lutein and zeaxanthin could be fractionated, upon mild detergent\\u000a treatment, from the thylakoid membranes of irradiance-stressed unicellular green alga, Dunaliella salina, into a yellow pellet fraction. Such membrane pellet was found to be devoid of chlorophylls and any known proteins of photosynthesis\\u000a but rather contained a significant amount of unknown

Kittisak Yokthongwattana; Malinee Sriariyanun; Pallop Ekaratcharoenchai; Jisnuson Svasti

2010-01-01

152

Characterization and isolation of a rat liver plasma membrane NADH oxidase: Comparison to NADH oxidases from transformed cells  

Microsoft Academic Search

This work was to purify and characterize the hormone and growth factor-stimulated NADH oxidase from rat liver plasma membranes and compare it to the corresponding unregulated NADH oxidase of HeLa cell plasma membranes. Rat liver plasma membrane NADH oxidase activity was stimulated by GTP and the G protein mimicking peptide mastoparan. This activity was also stimulated by a protein fraction

James Byron Lawrence

1995-01-01

153

Stimulation of human B lymphocytes by Listeria cell wall fraction.  

PubMed Central

Cell wall fraction of Listeria monocytogenes (LCWF), a B cell mitogen for mouse spleen cells, is also mitogenic for human adult and cord peripheral blood lymphocytes. Purified B-cell suspensions responded to LCWF in vitro proliferation, to a similar extent as the unfractionated suspensions. Furthermore, LCWF-induced B cell differentiation into IgM-containing cells and their percentage correlated significantly with the extent of lymphocyte proliferation.

Ivanyi, L

1978-01-01

154

Preparation of cell membranes for high resolution imaging by AFM  

Microsoft Academic Search

Studies of cell membrane structure by atomic force microscopy (AFM) have been limited because of the softness of cell membranes. Here, we utilize a new technique of sample preparation to lay red blood cell membranes on the top of a mica surface to obtain high resolution images by in-situ AFM on both sides of cell membranes. Our results indicate that

Hongda Wang; Xian Hao; Yuping Shan; Junguang Jiang; Mingjun Cai; Xin Shang

2010-01-01

155

Etiolated cells of Chlamydomonas reinhardtii: choice material for characterization of mitochondrial membrane polypeptides.  

PubMed Central

We have investigated a light-conditional mutant of Chlamydomonas reinhardtii (J12) that is unable to synthesize chlorophyll in the dark with the aim of characterizing the mitochondrial membrane polypeptides of this alga. A crude membrane fraction derived from etiolated cells was analyzed by gel electrophoresis, immunoblot analysis, and pulse-labeling in the presence of specific protein synthesis inhibitors. This fraction contained both mitochondrial and etioplast membranes, and the latter contained appreciable amounts of subunits of the cytochrome b6f complex. The mitochondria-encoded subunit 1 of cytochrome-c oxidase called COX1 was identified, and its synthesis was detected in this membrane fraction. The redox-difference spectra of mitochondrial cytochromes were studied in whole cells and membrane fractions, in both respiratory-competent and -deficient strains. Mitochondrial membranes could be further purified after sucrose gradient centrifugation. The use of etiolated cells and their membrane extracts, in association with appropriate methodologies, opens ways to study the molecular genetics of mitochondria in C. reinhardtii and allows us to address the question of the cooperation established between the three genetic compartments of a plant cell. Images Fig. 1 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 8

Bennoun, P; Atteia, A; Pierre, Y; Delosme, M

1995-01-01

156

Distribution of Lipids in the Wall and Cytoplasmic Membrane Subfractions of the Cell Envelope of Escherichia coli  

PubMed Central

Cell wall and membrane subfractions of the cell envelope of Escherichia coli have been isolated by a procedure involving particle electrophoresis and sucrose gradient density centrifugation. The lipid content of each fraction has been investigated. The individual phospholipids of both fractions are quantitatively similar except that the proportion of lysophosphatidylethanolamine is greater in the wall than in the membrane. Fatty acid analysis of the phospholipids of each fraction revealed that the wall phospholipids contain a greater proportion of palmitic acid. Coenzyme Q is almost exclusively localized in the cell membrane.

White, David A.; Lennarz, W. J.; Schnaitman, Carl A.

1972-01-01

157

Fixed charge in the cell membrane  

PubMed Central

1. Focal electric field was generated by passing a current of 5 × 10-7 to 1 × 10-5 A from a micropipette into the culture medium. Movement of cells at a distance of 5-50 ? from the electrode tip was observed. In case of cells embedded in the culture only local deformation of the membrane was observed. 2. The cell species explored included neurones, glia, muscle fibres, connective cells, malignant cells and erythrocytes. All cells responded in a similar manner to the electric field, and the current required was in the same range. 3. Cells were attracted to a positive micropipette and repelled from a negative one: the only exception was observed in certain malignant cells which moved in the opposite direction. 4. Movement and membrane deformation could be obtained with electrodes filled with various concentrated and isotonic solutions. The composition of the culture medium also had no qualitative influence on these effects. 5. Metabolic poisons or rupture of the cell membrane had no effect on the movement. Isolated membrane fragments showed movement similar to that of intact cells. 6. The possibility of artifacts due to proximity of the focal electrode is considered. It is shown that electro-osmosis cannot account for the present observations. Some other artifacts are also excluded. 7. It is proposed that the most satisfactory way to account for the present observations is by a membrane carrying negative fixed charge of the order of 2·5 × 103 e.s.u./cm2. Some physiological consequences of presence of negative charge in the membrane are briefly discussed. ImagesFig. 1Fig. 2Fig. 3

Elul, R.

1967-01-01

158

Analysis of plasma membrane phosphoinositides from fusogenic carrot cells  

SciTech Connect

Phosphatidylinositol monophosphate (PIP) and phosphatidylinositol bisphosphate (PIP/sub 2/) were found to be associated with the plasma membrane-rich fractions isolated by aqueous polymer two-phase partitioning from fusogenic cells. They represented at least 5% and 0.7% of the total inositol-labeled lipids in the plasma membrane-rich fractions, respectively, and were present in a ratio of about 7:1 (PIP:PIP/sub 2/). In addition, two unidentified inositol-labeled compounds, which together were approximately 3% of the inositol-labeled lipids, were found predominantly in the plasma membrane-rich fractions and migrated between PIP/sub 2/ and PIP. The R/sub f/s of these compounds were approximately 0.31 and 0.34 in the solvent system CHCl/sub 3/:MeOH:15N NH/sub 4/OH:H/sub 2/O (90:90:7:22) using LK5 plates presoaked in 1% potassium oxalate. These compounds incorporated /sup 32/P/sub i/, (/sup 3/H)inositol and were hydrolyzed in mild base. These data suggested that they were glycero-phospholipids. Although the compounds did not comigrate with lysoPIP obtained from bovine brain (R/sub f/ approx. 0.35), when endogenous PIP was hydrolyzed to lysoPIP, the breakdown product migrated in the region of the unidentified inositol lipids.

Wheeler, J.J.; Boss, W.F.

1987-04-01

159

Continuous flow magnetic cell fractionation based on antigen expression level.  

PubMed

Cell separation is important in medical and biological research and plays an increasingly important role in clinical therapy and diagnostics, such as rare cancer cell detection in blood. The immunomagnetic labeling of cells with antibodies conjugated to magnetic nanospheres gives rise to a proportional relationship between the number of magnetic nanospheres attached to the cell and the cell surface marker number. This enables the potential fractionation of cell populations by magnetophoretic mobility (MM). We exploit this feature with our apparatus, the Dipole Magnet Flow Fractionator (DMFF), which consists of an isodynamic magnetic field, an orthogonally-oriented thin ribbon of cell suspension in continuous sheath flow, and ten outlet flows. From a sample containing a 1:1 mixture of immunomagnetically labeled (label+) and unlabeled (label-) cells, we achieved an increase in enrichment of the label+ cell fraction with increasing outlet numbers in the direction of the magnetic field gradient (up to 10-fold). The total recovery of the ten outlet fractions was 90.0+/-7.7%. The mean MM of label+ cells increased with increasing outlet number by up to a factor of 2.3. The postulated proportionality between the number of attached magnetic beads and the number of cell surface markers was validated by comparison of MM measured by cell tracking velocimetry (CTV) with cell florescence intensity measured by flow cytometry. PMID:16675023

Schneider, Thomas; Moore, Lee R; Jing, Ying; Haam, Seungjoo; Williams, P Stephen; Fleischman, Aaron J; Roy, Shuvo; Chalmers, Jeffrey J; Zborowski, Maciej

2006-03-29

160

Adenosinetriphosphatase Activity in the Cell Membranes of Kidney Tubule Cells  

Microsoft Academic Search

This cytochemical study demonstrates high levels of apparent ATPase ac- tivity in the infolded cell membranes of the proximal tubules (dog, rat, human, mouse, monkey, and opossum) and ascending loops of Henle (dog, rat, human and, to a variable degree, mouse). Electron microscopy has shown (see Rhodin (1)) that these membranes separate adjacent cells where they interlock with one another

HERMAN W. SPATER; ALEX B. NOVIKOFF; BERTHA MASEK

1958-01-01

161

Membrane-cell developments ease electrochemistry scaleup  

Microsoft Academic Search

This paper examines Steetley Engineering Limited's addition of a production-size cell to its dished electrode membrane line. The basic cell unit has a 1-m² electrode area, compared with the 0.25-m² pilot-plant size and 0.05-m² lab size the company began offering in 1983. An electro Prod cell for production applications was also introduced. Both cells are assembled in a manner similar

H. C. Short; R. Skole

1985-01-01

162

Fractionation of different PEGylated forms of a protein by chromatography using environment-responsive membranes.  

PubMed

PEGylation of therapeutic proteins can enhance their efficacy as biopharmaceuticals through increased stability and hydrophilicity, and decreased immunogenicity. A site-specific PEGylated protein (e.g. mono-PEGylated at N-terminus) is frequently desirable as a product. However, multiple-PEGylated forms are frequently produced as byproducts. In this paper we discuss the fractionation of the different PEGylated forms of a protein by hydrophobic interaction chromatography using a stack of hydrophilized PVDF membrane, which has been shown to be environment responsive, as stationary phase. With the model protein examined in this study (i.e. lysozyme), the apparent hydrophobicity in the presence of a lyotropic salt increased with the degree of PEGylation. Based on this, unmodified lysozyme and its mono-, di- and tri-PEGylated forms could each be resolved into separate chromatographic peaks. Such fractionation was not feasible using conventional hydrophobic interaction chromatography using a butyl column. The use of membrane chromatography also ensured that the fractionation was fast and hence suitable for analytical applications such as product purity determination and monitoring of the extent of PEGylation reactions. PMID:20638664

Yu, Deqiang; Shang, Xiaojiao; Ghosh, Raja

2010-06-26

163

Immunomodulating activities of Corynebacterium xerosis cell-wall fractions.  

PubMed

Corynebacterium xerosis cell-wall fractions were studied by electron microscopy and analysed for immunomodulating activity. Dramatic splenomegaly occurred following the injection of whole cells or a purified cell-wall fraction (PF), but not with a further purified peptidoglycan (PEP) fraction. Both PF and PEP acted as B-cell mitogens and had adjuvant capabilities comparable to commercial adjuvants. Only the PF fraction enhanced peritoneal natural killer cell (NK) activity, paralleling the splenomegaly response. When spleens from mice injected with PF or PEP were analysed for their abilities to respond to mitogens and for the presence of suppressor cells, reduced mitogenic responses occurred only in PF-injected mice during the peak of splenomegaly. Spleens from both PF- and PEP-injected mice contained suppressor cell activity which peaked 2 weeks post-injection. This activity was primarily directed at B-cell responses to lipopolysaccharide (LPS). C. xerosis cell-wall fractions thus offer great potential as a new immunomodulator. PMID:1406338

Paquet, A; Davis, T L; Gunter, E N; Barcellona, W J

1992-01-01

164

Basement Membranes: Cell Scaffoldings and Signaling Platforms  

PubMed Central

Basement membranes are widely distributed extracellular matrices that coat the basal aspect of epithelial and endothelial cells and surround muscle, fat, and Schwann cells. These extracellular matrices, first expressed in early embryogenesis, are self-assembled on competent cell surfaces through binding interactions among laminins, type IV collagens, nidogens, and proteoglycans. They form stabilizing extensions of the plasma membrane that provide cell adhesion and that act as solid-phase agonists. Basement membranes play a role in tissue and organ morphogenesis and help maintain function in the adult. Mutations adversely affecting expression of the different structural components are associated with developmental arrest at different stages as well as postnatal diseases of muscle, nerve, brain, eye, skin, vasculature, and kidney.

Yurchenco, Peter D.

2011-01-01

165

Field-flow fractionation of cells with chemiluminescence detection  

Microsoft Academic Search

Field-flow fractionation is a separation technique characterized by a retention mechanism which makes it suitable for sorting cells over a short analysis time, with low sample carry-over and preserving cell viability. Thanks to its high sensitivity, chemiluminescence detection is suitable for the quantification of just a few cells expressing chemiluminescence or bioluminescence. In this work, different formats for coupling gravitational

Dora Melucci; Barbara Roda; Andrea Zattoni; Sonia Casolari; Pierluigi Reschiglian; Aldo Roda

2004-01-01

166

Membranes in the plant cell  

Microsoft Academic Search

Summary 1.Existing evidence for the formation of morphological membranes at protoplasmic surfaces in the living plant protoplast is reviewed and judged inadequate.2.Cases from the literature and from the author's work are cited to show that micromanipulation may be employed in the investigation of this problem without perceptible disturbance of the normal condition of the protoplast.3.Investigation of plasmolyzed and unplasmolyzed protoplasts

Janet Q. Plowe

1931-01-01

167

Organization of the cell membrane in Euglena  

Microsoft Academic Search

Summary The cell membrane ofEuglena gracilis has been investigated with the freeze-fracture technique. When split, this membrane produces two fracture faces which are striking in their non-complementarity. The P fracture face is covered with a high density of 110 Å (average diameter) particles, while the E face is made up of a complex series of striations occurring at regular angles

K. R. Miller; Gayle J. Miller

1978-01-01

168

Polarized protein membrane for high cell seeding efficiency.  

PubMed

A new type of scaffold for tissue engineering was developed to give enhanced cell seeding in three dimensions. A gradient of either collagen or fibrin protein was prepared, supported by a knitted poly(ethylene terephtalate) PET fabric. The membranes were, after hydrolysis and acetic acid wash, submerged in a protein solution for adsorption followed by immersion into a gelling agent. The immediate contact between the protein solution held by the fabric and the gelling agent resulted in a dense, fibrous protein network with pore sizes around 0.5 microm at the surface, and larger pores of 10-50 microm size throughout the interior of the fabric as observed by scanning electron microscopy. By separating the fabric double layers holding this network, a gradient porosity membrane was produced. To evaluate the fractions of cells trapped in the matrix upon seeding, i.e. the seeding efficiency, 500 microl 3T3 fibroblasts cell suspension containing one million cells was seeded by filtering through the gradient protein membrane. For both the collagen and fibrin membranes, the seeding efficiency was approximately 93%, which was significantly higher than that of 28% from the corresponding PET fabric without protein immobilization. Attempt to seed cells from the dense side of the protein networks resulted in no cell penetration into the scaffold. Histology on subsequent culture of the cells in the scaffold demonstrated viability and proliferation in three dimensions throughout the scaffold. This new and simple way of producing scaffolds play an important role when the cells are precious or scarce and cell seeding in three dimensions is important. PMID:17443668

Atthoff, Björn; Aulin, Cecilia; Adelöw, Catharina; Hilborn, Jöns

2007-11-01

169

Cell membrane destabilizes progressively during repetitive mechanical rupture events  

Microsoft Academic Search

The postfusion oscillation cycle method of electrofused cells was applied to red blood cell membranes to induce repetitive membrane ruptures and test the mechanical membrane resistance against sequential events of membrane strain and rupture. After producing doublets from pairs of electrofused cells, they entered the oscillation cycle, providing a sequence of at least four consecutive colloidosmotic-driven rupture events. Different gradations

Martin Baumann

2002-01-01

170

Cell motility through plasma membrane blebbing  

PubMed Central

Plasma membrane blebs are dynamic cytoskeleton-regulated cell protrusions that have been implicated in apoptosis, cytokinesis, and cell movement. Influencing Rho–guanosine triphosphatase activities and subsequent actomyosin dynamics appears to constitute a core component for bleb formation. In this paper, we discuss recent evidence in support of a central role of nonapoptotic membrane blebbing for cell migration and cancer cell invasion as well as advances in our understanding of the underlying molecular mechanisms. Based on these studies, we propose that in a physiological context, bleb-associated cell motility reflects a cell's response to reduced substratum adhesion. The importance of blebbing as a functional protrusion is underscored by the existence of multiple molecular mechanisms that govern actin-mediated bleb retraction.

Fackler, Oliver T.; Grosse, Robert

2008-01-01

171

Structure and properties of cell membranes. Volume 3: Methodology and properties of membranes  

Microsoft Academic Search

This book covers the topics: Quantum chemical approach to study the mechanisms of proton translocation across membranes through protein molecules; monomolecular films as biomembrane models; planar lipid bilayers in relation to biomembranes; relation of liposomes to cell membranes; reconstitution of membrane transport systems; structure-function relationships in cell membranes as revealed by X-ray techniques; structure-function relationships in cell membranes as revealed

Benga

1985-01-01

172

Demonstration of a Sample Preparation Method for Biological Detection Based on a Novel Membrane Fractionation Technology.  

National Technical Information Service (NTIS)

L WI funding has been obtained to gather proof-of-concept data for passing DNA from lysed bacteria through a membrane and for concentrating DNA in the concentrator cell. AlburtyLab has data showing high efficiency ( approx. 99%) for passing Bovine serum a...

A. Page P. Murowchick

2008-01-01

173

Blend Concepts for Fuel Cell Membranes  

NASA Astrophysics Data System (ADS)

Differently cross-linked blend membranes were prepared from commercial arylene main-chain polymers from the classes of poly(ether-ketones) and poly(ethersulfones) modified with sulfonate groups, sulfinate cross-linking groups and basic N-groups. The following membrane types have been prepared: (a) van-der Waals/dipole-dipole blends by mixing a polysulfonate with unmodified PSU. This membrane type showed a heterogeneous morphology, leading to extreme swelling and even dissolution of the sulfonated component at elevated temperatures. (b) Hydrogen bridge blends by mixing a polysulfonate with a polyamide or polyetherimide. This membrane type showed a partially heterogeneous morphology, also leading to extreme swelling/dissolution of the sulfonated blend component at elevated temperatures. (c) Acid-base blends by mixing a polysulfonate with a polymeric N-base (self-developed/commercial). With this membrane type, we could reach a wide variability of properties by variation of different parameters. Membranes showing excellent stability and good fuel cell performance up to 100°C (PEFC) and 130°C (DMFC) were obtained. (d) Covalently cross-linked (blend) membranes by either mixing of a polysulfonate with a polysulfinate or by preparation of a polysulfinatesulfonate, followed by reaction of the sulfinate groups in solution with a dihalogeno compound under S-alkylation. Membranes were prepared that showed effective suppression of swelling without H+-conductivity loss. The membranes showed good PEFC (up to 100°C) and DMFC (up to 130°C) performance. (e) Covalent-ionically cross-linked blend membranes by mixing polysulfonates with polysulfinates and polybases or by mixing a polysulfonate with a polymer carrying both sulfinate and basic N-groups. The covalent-ionically cross-linked membranes were tested in DMFC up to 110°C and showed a good performance. (f) Differently cross-linked organic-inorganic blend composite membranes via different procedures. The best results were obtained with blend membranes having a layered zirconium phosphate “ZrP” phase: They were transparent, and showed good H+;-conductivity and stability. Application of one of these composite membranes to a PEFC yielded good performance up to T=115°C.

Kerres, Jochen

174

The application of Dow Chemical's perfluorinated membranes in proton-exchange membrane fuel cells  

Microsoft Academic Search

Dow Chemical's research activities in fuel cells revolve around the development of perfluorosulfonic acid membranes useful as the proton transport medium and separator. Some of the performance characteristics which are typical for such membranes are outlined. The results of tests utilizing a new experimental membrane useful in proton-exchange membrane fuel cells are presented. The high voltage at low current densities

G. A. Eisman

1989-01-01

175

Analysis of the Oryza sativa plasma membrane proteome using combined protein and peptide fractionation approaches in conjunction with mass spectrometry.  

PubMed

To identify integral and peripheral plasma membrane (PM) proteins from Oryza sativa (rice), highly enriched PM fractions from rice suspension cultured cells were analyzed using two complementary approaches. The PM was enriched using aqueous two-phase partitioning and high pH carbonate washing to remove soluble, contaminating proteins and characterized using enzymatic and immunological analyses. Proteins from the carbonate-washed PM (WPM) were analyzed by either one-dimensional gel electrophoresis (1D-SDS-PAGE) followed by tryptic proteolysis or proteolysis followed by strong cation exchange liquid chromatography (LC) with subsequent analysis of the tryptic peptides by LC-MS/MS (termed Gel-LC-MS/MS and 2D-LC-MS/MS, respectively). Combining the results of these two approaches, 438 proteins were identified on the basis of two or more matching peptides, and a further 367 proteins were identified on the basis of single peptide matches after data analysis with two independent search algorithms. Of these 805 proteins, 350 were predicted to be PM or PM-associated proteins. Four hundred and twenty-five proteins (53%) were predicted to be integrally associated with a membrane, via either one or many (up to 16) transmembrane domains, a GPI-anchor, or membrane-spanning beta-barrels. Approximately 80% of the 805 identified proteins were assigned a predicted function, based on similarity to proteins of known function or the presence of functional domains. Proteins involved in PM-related activities such as signaling (21% of the 805 proteins), transporters and ATPases (14%), and cellular trafficking (8%), such as via vesicles involved in endo- and exocytosis, were identified. Proteins that are involved in cell wall biosynthesis were also identified (5%) and included three cellulose synthase (CESA) proteins, a cellulose synthase-like D (CSLD) protein, cellulases, and several callose synthases. Approximately 20% of the proteins identified in this study remained functionally unclassified despite being predicted to be membrane proteins. PMID:18260611

Natera, Siria H A; Ford, Kristina L; Cassin, Andrew M; Patterson, John H; Newbigin, Edward J; Bacic, Antony

2008-02-09

176

Glycosphingolipid Domains on Cell Plasma Membrane  

Microsoft Academic Search

In this study we analyzed by immunofluorescence, laser confocal microscopy, immunoelectron microscopy and label fracture technique the ganglioside distribution on the plasma membrane of several different cell types: human peripheral blood lymphocytes (PBL), Molt-4 lymphoid cells, and NIH 3T3 fibroblasts, which mainly express monosialoganglioside GM3, and murine NS20Y neuroblastoma cells, which have been shown to express a high amount of

Maurizio Sorice; Tina Garofalo; Roberta Misasi; Vincenza Dolo; Giuseppe Lucania; Tiziana Sansolini; Isabella Parolini; Massimo Sargiacomo; Maria Rosaria Torrisi; Antonio Pavan

1999-01-01

177

Hereditary spherocytosis, elliptocytosis, and other red cell membrane disorders.  

PubMed

Hereditary spherocytosis and elliptocytosis are the two most common inherited red cell membrane disorders resulting from mutations in genes encoding various red cell membrane and skeletal proteins. Red cell membrane, a composite structure composed of lipid bilayer linked to spectrin-based membrane skeleton is responsible for the unique features of flexibility and mechanical stability of the cell. Defects in various proteins involved in linking the lipid bilayer to membrane skeleton result in loss in membrane cohesion leading to surface area loss and hereditary spherocytosis while defects in proteins involved in lateral interactions of the spectrin-based skeleton lead to decreased mechanical stability, membrane fragmentation and hereditary elliptocytosis. The disease severity is primarily dependent on the extent of membrane surface area loss. Both these diseases can be readily diagnosed by various laboratory approaches that include red blood cell cytology, flow cytometry, ektacytometry, electrophoresis of the red cell membrane proteins, and mutational analysis of gene encoding red cell membrane proteins. PMID:23664421

Da Costa, Lydie; Galimand, Julie; Fenneteau, Odile; Mohandas, Narla

2013-05-09

178

Polyphosphoinositides are present in plasma membranes isolated from fusogenic carrot cells  

SciTech Connect

Fusogenic carrot cells grown in suspension culture were labeled 12 hours with myo-(2-/sup 3/H)inositol. Plasma membranes were isolated from the prelabeled fusogenic carrot cells by both aqueous polymer two-phase partitioning and Renografin density gradients. With both methods, the plasma membrane-enriched fractions, as identified by marker enzymes, were enriched in (/sup 3/H)inositol-labeled phosphatidylinositol monophosphate (PIP) and phosphatidylinositol bisphosphate (PIP/sub 2/). An additional (/sup 3/H)inositol-labeled lipid, lysophosphatidylinositol monophosphate, which migrated between PIP and PIP/sub 2/ on thin layer plates, was found primarily in the plasma membrane-rich fraction of the fusogenic cells. This was in contrast to lysophosphatidylinositol which is found primarily in the lower phase, microsomal/mitchrondrial-rich fraction.

Wheeler, J.J.; Boss, W.F.

1987-10-01

179

Studies of smectite membrane behavior Electrokinetic, osmotic, and isotopic fractionation processes at elevated pressures  

NASA Astrophysics Data System (ADS)

A 1.087 m NaCl brine was forced through a day membrane 0.32 cm thick at 294 ± 1°K. The clay membrane was made by compacting the 0.5 to 2.0 micron size fraction of Cheto montmorillonite from Chambers, Arizona. A confining pressure of 34.5 MPa (5000 psi) and a mean hydraulic pressure of 15.9 MPa (2300 psi) were chosen to simulate a depth of about 1.5 km (5000 ft) in sedimentary basins. Differential hydraulic pressure across the day was 13.8 MPa (2000 psi). This differential hydraulic pressure setting was disturbed for only brief intervals during the experimental run. Hydraulic flow rate, electrical conductance, electrical potential across the clay, electroosmotic flow rate, and the chemical composition of the brine were determined periodically until constancy of both effluent chemical composition and electrical potential across the clay was achieved. Then, osmotic flow rate and stable oxygen isotopic compositions of both input and effluent reservoirs were determined before the run was terminated. The experimental results conform to the predictions of nonequilibrium thermodynamics under these simulated subsurface conditions. The electroviscous effect caused a significant reduction in the hydraulic flow rate but did not disturb the linearity between the flow rate and differential hydraulic pressure. Osmotic and electroosmotic effects may be responsible for driving large amounts of cross-formatkmal subsurface fluid flow in nature. A measured 13 O fractionation of 0.25%. compares well with published field and laboratory data.

Demir, Ilham

1988-03-01

180

Membrane fluidity sensoring microbial fuel cell.  

PubMed

A study has been performed to examine the effect of temperature and ethanolic stresses on the coulombic efficiency of a microbial fuel cell. The conventional-type fuel cell containing Gram-negative bacteria, Proteus vulgaris, was investigated as a model system. From current output measurements, it was found that the coulombic yields were altered by environmental stresses such as temperature shock or ethanol treatment to the bacteria. While high-temperature or ethanolic shock led to a remarkable decrement in coulombic output, the low-temperature shock induced a slight increase in microbial fuel cell efficiency. These results indicate that the membrane fluidity is affected considerably by environmental stress, which in turn affects the electron transfer process through the bacterial cell membrane to and from the electrode. This interpretation was confirmed by the cyclic voltammetric study of a mediator on an electrode surface modified with the lipids extracted from the membrane of P. vulgaris under the given stress. Markedly different electrochemical behaviors were observed depending on the environmental stress. A reciprocal relationship between coulomb output and the ratio of saturation/unsaturation of fatty acids has been observed. This is the first report, to our knowledge, that the structural adaptation of membrane fatty acids in response to the environmental shock can regulate the coulombic efficiency of a microbial fuel cell. PMID:12699828

Choi, Youngjin; Jung, Eunkyoung; Kim, Sunghyun; Jung, Seunho

2003-04-01

181

[Effect of trehalose-loading on red blood cell membrane].  

PubMed

This study was purposed to evaluate the effect of trehalose-loading on physiological and biochemistry properties of red blood cell (RBC) membrane. The samples were divided into the control group (RBC without trehalose loading) and the test group (RBC with trehalose loading). Osmotic fragility reaction was used to determine the osmotic fragility change of loaded RBC membrane in NaCl solution of different osmotic concentration. Flow cytometry and deformeter were used to assay the integrality and deformability of the RBC, resectively. The results showed that the NaCl solution osmotic concentrations were 160 mOsm and 121.4 mOsm, respectively when the haemolysis rate was 50% of the control group and the test group. Flow cytometry data demonstrated that incubation of RBC in a hypertonic trehalose solution resulted in a fraction of cells with different complexity that attached to little Annexin V-FITC, and that it could be removed by washing and resuspending the RBC in an iso-osmotic (300 mOsm PBS) medium. The deformability of the loaded RBC descend, the statistical difference was significant between control and test groups (P < 0.01). It is concluded that the membrane physiological and biochemistry stability and membrane integrality of RBC in a hyper osmotic pressure can be retained after trehalose loading. PMID:23257456

Chen, Lin-Feng; Liu, Jing-Han; Zhuang, Yuan; Che, Ji; Wang, De-Qing; Li, Hui; Wang, Shan

2012-12-01

182

Model Assessment of Cell Membrane Breakdown in Clusters and Tissues Under High-Intensity Electric Pulsing  

Microsoft Academic Search

This paper presents a simulation study of cell membrane electroporation in clusters by high-intensity voltage pulses. The focus is on assessing effects associated with: 1) the variability in shape and randomness of the cells within clusters; 2) the density of clusters; 3) the effects in heterogeneous tissues; 4) the role of pulse width on fractional electroporation for given electrical characteristics;

Ravindra P. Joshi; Ashutosh Mishra; Karl H. Schoenbach

2008-01-01

183

PROCEED: A proteomic method for analysing plasma membrane proteins in living mammalian cells  

Microsoft Academic Search

Elucidating the profile of extracellular integral membrane proteins on live cells is vital for uncovering diagnostic disease biomarkers, therapeutic agents and drug receptor candidates. Exploring the realm of these proteins has proved to be an intricate task, mainly due to their hydrophobic nature and low abundance. Furthermore, the level of purity achieved by classical methods of purification and cell fractionation

Yaniv Bledi; Alex Inberg; Michal Linial

2003-01-01

184

Binding affinity of the methyl ester of AK-toxin I to membrane fractions from Japanese pear leaves.  

PubMed

The binding site of AK-toxin, a host-specific toxin against Japanese pear, was searched for in the membrane fractions of the pear leaves, using 3H-labeled AK-toxin I methyl ester. Binding activity, which was displaceable by the unlabeled ligand, was observed for microsomal fraction from a toxin-susceptible cultivar, Nijisseiki. However, the binding was also observed for those from toxin-resistant cultivars, Kosui and Hosui. Detection of the specific binding failed for the plasma membrane fraction which was prepared from microsomal fraction of the toxin-susceptible cultivar by aqueous two-phase separation, and the hitherto presumed model of the AK-toxin receptor in the plasma membrane could not be verified. PMID:11193431

Okada, M; Miyagawa, H; Nakagawa, Y; Ueno, T

2000-11-01

185

Membrane curvature and mechanisms of dynamic cell membrane remodelling  

Microsoft Academic Search

Membrane curvature is no longer seen as a passive consequence of cellular activity but an active means to create membrane domains and to organize centres for membrane trafficking. Curvature can be dynamically modulated by changes in lipid composition, the oligomerization of curvature scaffolding proteins and the reversible insertion of protein regions that act like wedges in membranes. There is an

Jennifer L. Gallop; Harvey T. McMahon

2005-01-01

186

Dynamic physical properties of dissociated tumor cells revealed by dielectrophoretic field-flow fractionation.  

PubMed

Metastatic disease results from the shedding of cancer cells from a solid primary tumor, their transport through the cardiovascular system as circulating tumor cells (CTCs) and their engraftment and growth at distant sites. Little is known about the properties and fate of tumor cells as they leave their growth site and travel as single cells. We applied analytical dielectrophoretic field-flow fractionation (dFFF) to study the membrane capacitance, density and hydrodynamic properties together with the size and morphology of cultured tumor cells after they were harvested and placed into single cell suspensions. After detachment, the tumor cells exhibited biophysical properties that changed with time through a process of cytoplasmic shedding whereby membrane and cytoplasm were lost. This process appeared to be distinct from the cell death mechanisms of apoptosis, anoikis and necrosis and it may explain why multiple phenotypes are seen among CTCs isolated from patients and among the tumor cells obtained from ascitic fluid of patients. The implications of dynamic biophysical properties and cytoplasmic loss for CTC migration into small blood vessels in the circulatory system, survival and gene expression are discussed. Because the total capacitance of tumor cells remained higher than blood cells even after they had shed cytoplasm, dFFF offers a compelling, antibody-independent technology for isolating viable CTCs from blood even when they are no larger than peripheral blood mononuclear cells. PMID:21691666

Shim, Sangjo; Gascoyne, Peter; Noshari, Jamileh; Hale, Katherine Stemke

2011-06-21

187

Functional imaging of microdomains in cell membranes  

Microsoft Academic Search

The presence of microdomains or rafts within cell membranes is a topic of intense study and debate. The role of these structures\\u000a in cell physiology, however, is also not yet fully understood with many outstanding problems. This problem is partly based\\u000a on the small size of raft structures that presents significant problems to their in vivo study, i.e., within live

James Duggan; Ghadir Jamal; Mark Tilley; Ben Davis; Graeme McKenzie; Kelly Vere; Michael G. Somekh; Paul O’Shea; Helen Harris

2008-01-01

188

Membrane-cell developments ease electrochemistry scaleup  

SciTech Connect

This paper examines Steetley Engineering Limited's addition of a production-size cell to its dished electrode membrane line. The basic cell unit has a 1-m/sup 2/ electrode area, compared with the 0.25-m/sup 2/ pilot-plant size and 0.05-m/sup 2/ lab size the company began offering in 1983. An electro Prod cell for production applications was also introduced. Both cells are assembled in a manner similar to a plate-and-frame filter press. An illustration is provided in the paper to clarify the assembly.

Short, H.C.; Skole, R.

1985-03-04

189

Transient translocation of hemidesmosomal bullous pemphigoid antigen 1 from cytosol to membrane fractions by 12- O-tetradecanoylphorbol-13-acetate treatment and Ca 2+-switch in a human carcinoma cell line  

Microsoft Academic Search

We previously showed that 12-O-tetradecanoylphorbol-13-acetate (TPA) and Ca2+-switch from low (0.07 mM) to normal (1.87 mM) concentration in culture medium, which were also linked to activation of protein kinase C (PKC), lead to phosphorylation of 180 kDa-bullous pemphigoid antigen (BPAG) 2, but not of 230 kDa-BPAG1, and possibly to its disassembly from hemidesmosomes in a human squamous cell carcinoma cell

Yuriko Matsuoka; Takahiro Yamada; Mariko Seishima; Yoshiaki Hirako; Katsushi Owaribe; Yasuo Kitajima

2001-01-01

190

Possible association of Neu2 with plasma membrane fraction from mouse thymus exhibited sialidase activity with fetuin at pH 7.0 but not at pH 4.5.  

PubMed

Compared to other organs, the mouse thymus exhibits a high level of sialidase activity in both the soluble and crude membrane fractions, as measured at neutral pH using 4MU-Neu5Ac as a substrate. The main purpose of the present study was to identify the sialidase with a high level of the activity at neutral pH in the crude membrane. Several parameters were analyzed using the soluble (S) fraction, N and D fractions that were obtained by NP-40 or DOC/NP-40 solubilization from the thymus crude membrane. The main sialidase activity in the N fraction exhibited almost the same pI as that of soluble Neu2 and 60% of the activity was removed from the membrane by three washes with 10?mM Tris-buffer, at pH 7.0. The N fraction preferentially hydrolyzed the sialic acid bond of glycoprotein and exhibited sialidase activity with fetuin at pH 7.0 but not at pH 4.5. The same activity was observed in a plasma membrane-rich fraction. To date, the removal of sialic acid from fetuin at pH 7.0 was reported only with soluble Neu2 and the membrane fraction from Neu2-transfected COS cells. We analyzed the gene that controls the sialidase activity in the crude membrane fraction at pH 7.0 using SMXA recombinant mice and found that compared with other three genes, Neu2 presented the best correlation with the activity level. We suggest that Neu2 is most likely responsible for the main activity in the N fraction, due to its association with the membrane by an unknown mechanism. PMID:23750721

Kijimoto-Ochiai, Shigeko; Doi, Naoko; Fujii, Miwako; Go, Shinji; Kabayama, Kazuya; Moriya, Setsuko; Miyagi, Taeko; Koda, Toshiaki

2013-08-01

191

The plasma membrane-enriched fraction proteome response during adaptation to hydrogen peroxide in Saccharomyces cerevisiae.  

PubMed

In Saccharomyces cerevisiae, adaptation to hydrogen peroxide (H?O?) decreases plasma membrane permeability to H?O?, changes its lipid composition and reorganizes ergosterol-rich microdomains by a still unknown mechanism. Here we show, by a quantitative analysis of the H?O?-induced adaptation effect on the S. cerevisiae plasma membrane-enriched fraction proteome, using two-dimensional gel electrophoresis, that 44 proteins are differentially expressed. Most of these proteins were regulated at a post-transcriptional level. Fourteen of these proteins contain redox-sensitive cysteine residues and nine proteins are associated with lipid and vesicle traffic. In particular, three proteins found in eisosomes and in the eisosome-associated membrane compartment occupied by Can1p were up-regulated (Pil1p, Rfs1p and Pst2p) during adaptation to H?O?. Survival studies after exposure to lethal H?O? doses using yeast strains bearing a gene deletion corresponding to proteins associated to lipid and vesicle traffic demonstrated for the first time that down-regulation of Kes1p, Vps4p and Ynl010wp and up-regulation of Atp1 and Atp2 increases resistance to H?O?. Moreover, for the pil1? strain, H?O? at low levels produces a hormetic effect by increasing proliferation. In conclusion, these data further confirms the plasma membrane as an active cellular site during adaptation to H?O? and shows that proteins involved in lipid and vesicle traffic are important mediators of H?O? adaptation. PMID:22712517

Pedroso, Nuno; Gomes-Alves, Patrícia; Marinho, H Susana; Brito, Verônica B; Boada, Cristina; Antunes, Fernando; Herrero, Enrique; Penque, Deborah; Cyrne, Luísa

2012-07-16

192

Sodium selectivity of Reissner's membrane epithelial cells  

PubMed Central

Background Sodium absorption by Reissner's membrane is thought to contribute to the homeostasis of the volume of cochlear endolymph. It was previously shown that the absorptive transepithelial current was blocked by amiloride and benzamil. The most commonly-observed target of these drugs is the epithelial sodium channel (ENaC), which is composed of the three subunits ?-,?- and ?-ENaC. However, other less-selective cation channels have also been observed to be sensitive to benzamil and amiloride. The aim of this study was to determine whether Reissner's membrane epithelial cells could support parasensory K+ absorption via amiloride- and benzamil-sensitive electrogenic pathways. Results We determined the molecular and functional expression of candidate cation channels with gene array (GEO GSE6196), RT-PCR, and whole-cell patch clamp. Transcript expression analysis of Reissner's membrane detected no amiloride-sensitive acid-sensing ion channels (ASIC1a, ASIC2a, ASIC2b) nor amiloride-sensitive cyclic-nucleotide gated channels (CNGA1, CNGA2, CNGA4, CNGB3). By contrast, ?-,?- and ?-ENaC were all previously reported as present in Reissner's membrane. The selectivity of the benzamil-sensitive cation currents was observed in whole-cell patch clamp recordings under Cl--free conditions where cations were the only permeant species. The currents were carried by Na+ but not K+, and the permeability of Li+ was greater than that of Na+ in Reissner's membrane. Complete replacement of bath Na+ with the inpermeable cation NMDG+ led to the same inward current as with benzamil in a Na+ bath. Conclusions These results are consistent with the amiloride/benzamil-sensitive absorptive flux of Reissner's membrane mediated by a highly Na+-selective channel that has several key characteristics in common with ???-ENaC. The amiloride-sensitive pathway therefore absorbs only Na+ in this epithelium and does not provide a parasensory K+ efflux route from scala media.

2011-01-01

193

Collective charge excitations along cell membranes  

NASA Astrophysics Data System (ADS)

A significant part of the thin layers of counter-ions adjacent to the exterior and interior surfaces of a cell membrane form quasi-two-dimensional (2D) layers of mobile charge. Collective charge density oscillations, known as plasmon modes, in these 2D charged systems of counter-ions are predicted in the present paper. This is based on a calculation of the self-consistent response of this system to a fast electric field fluctuation. The possibility that the membrane channels might be using these excitations to carry out fast communication is suggested and experiments are proposed to reveal the existence of such excitations.

Manousakis, E.

2005-07-01

194

Biogenesis of the red cell membrane and cytoskeletal proteins during erythropoiesis in vitro  

SciTech Connect

Purified erythroid progenitor cells (CFU-E) were used to study in vitro the production of the proteins present in the plasma membrane and the membrane skeleton. At different stages of erythropoiesis incorporation of ({sup 35}S)methionine was measured and membranes were isolated. Whereas incorporation in the total protein mass of the cells increased during erythropoiesis, the labeling of the membrane protein fraction decreased. The major erythrocyte membrane proteins were synthesized already in the CFU-E and continued to be made till the orthochromatic erythroblast stage. Band 3 protein, however, was made at a much lower rate. The incorporation in the late stages was only 5% of that in the CFU-E. The major changes in the protein composition of the membrane and its adherent skeleton occurred at the enucleation step.

Nijhof, W.; Wierenga, P.K. (State University of Groningen (Netherlands))

1988-08-01

195

An electrophoretic study of endogenous phosphorylation in vitro of the polypeptides of microsomal membrane fractions of mouse liver  

PubMed Central

1. The patterns of phosphopolypeptides produced by endogenous phosphorylation in vitro of rough- and smooth-membrane fractions of the microsomal fraction of mouse liver were studied by radioautographic analysis of sodium dodecyl sulphate/polyacrylamide-gel electrophoretograms. 2. A minimum of 17 polypeptides of both rough- and smooth-microsomal-membrane fractions were phosphorylated by using [?-32P]-ATP as the phosphate donor; only minor differences in phosphorylation pattern between the two membrane fractions were detected. 3. Phosphorylation in vitro by [?-32P]ATP was markedly stimulated by Mg2+, but not by cyclic AMP, cyclic GMP or Ca2+. The phosphorylation of certain polypeptides was preferentially stimulated by Mg2+. Addition of cyclic AMP resulted in a decrease in the amount of 32P detected in one polypeptide of mol.wt. approx. 56000, present in both the rough- and smooth-membrane fractions. 4. [?-32P]GTP was found to be a relatively poor donor of 32P as compared with [?-32P]ATP. However, incubation of rough- and smooth-membrane fractions with this compound resulted in the phosphorylation of one polypeptide of mol.wt. approx. 96000 that was scarcely or not at all phosphorylated by [?-32P]ATP. 5. Under the conditions of incubation used, appreciable incorporation of 32P from [?-32P]ATP occurred into products migrating at the front of the electrophoretograms; these products were identified as being principally comprised of 1-phosphatidylinositol 4-phosphate. Incorporation of 32P into this lipid was also markedly stimulated by Mg2+. 6. The overall results show that a considerable number of polypeptides of the rough- and smooth-microsomal-membrane fractions of mouse liver may be phosphorylated in vitro and indicate that the enzymes responsible are principally non-cyclic AMP-dependent protein kinases. ImagesFig. 1.Fig. 2.Fig. 3.Fig. 4.

Behar-Bannelier, Monique; Murray, Robert K.

1980-01-01

196

Comparative Membrane Extraction Methods for Identifying Membrane Proteome of SW900 Squamous Lung Cancer Cell Line  

Microsoft Academic Search

Although several methods for extracting and handling membrane proteins for proteomics experiments have been reported, the direct comparison of different methods has never been clarified for the identifying membrane proteome in lung cancer cell lines. This study was purposed to find a protocol suitable for membrane protein extraction and to identify the membrane proteome in lung cancer. Three detergent-based extraction

Suree Phutrakul; Shui-Tein Chen

197

Listeria cell wall fraction. Characterization of in vitro adjuvant activity.  

PubMed Central

We have previously described a crude cell wall fraction of Listeria monocytogenes (LCWF) which induces resistance to listeria infection in mice, is a murine B-cell mitogen and is an immunological adjuvant. Data reported here show that LCWF, which is effective over a wide dose range, exerts its adjuvant action on early events in the induction of an immune response. Moreover, LCWF stimulates nonadherent cells to respond to sheep red cells when adherent cells are severely depleted or absent, suggesting that LCWF can therefore act directly on lymphocytes present within the non-adherent population.

Schuffler, C; Campbell, P A

1976-01-01

198

Membrane protein expression: no cells required.  

PubMed

Structural and functional studies of membrane proteins have been severely hampered by difficulties in producing sufficient quantities of properly folded protein products. It is well established that cell-based expression of membrane proteins is generally problematic and frequently results in low yield, cell toxicity, protein aggregation and misfolding. Owing to its inherent open nature, cell-free protein expression has become a highly promising tool for the fast and efficient production of these difficult-to-express proteins. Here we review the most recent advances in this field, underscoring the potentials and weaknesses of the newly developed approaches and place specific emphasis on the use of nanolipoprotein particles (NLPs or nanodiscs). PMID:19616329

Katzen, Federico; Peterson, Todd C; Kudlicki, Wieslaw

2009-07-16

199

Membrane catalyst layer for fuel cells  

DOEpatents

A gas reaction fuel cell incorporates a thin catalyst layer between a solid polymer electrolyte (SPE) membrane and a porous electrode backing. The catalyst layer is preferably less than about 10 {mu}m in thickness with a carbon supported platinum catalyst loading less than about 0.35 mgPt/cm{sup 2}. The film is formed as an ink that is spread and cured on a film release blank. The cured film is then transferred to the SPE membrane and hot pressed into the surface to form a catalyst layer having a controlled thickness and catalyst distribution. The layer has adequate gas permeability so that cell performance is not affected and has a density and particle distribution effective to optimize proton access to the catalyst and electronic continuity for electron flow from the half-cell reaction occurring at the catalyst.

Wilson, M.S.

1991-02-19

200

Catalytic membranes for fuel cells  

DOEpatents

A fuel cell of the present invention comprises a cathode and an anode, one or both of the anode and the cathode including a catalyst comprising a bundle of longitudinally aligned graphitic carbon nanotubes including a catalytically active transition metal incorporated longitudinally and atomically distributed throughout the graphitic carbon walls of said nanotubes. The nanotubes also include nitrogen atoms and/or ions chemically bonded to the graphitic carbon and to the transition metal. Preferably, the transition metal comprises at least one metal selected from the group consisting of Fe, Co, Ni, Mn, and Cr.

Liu, Di-Jia (Naperville, IL); Yang, Junbing (Bolingbrook, IL); Wang, Xiaoping (Naperville, IL)

2011-04-19

201

Numerical study of a hybrid membrane cell with semi and fully permeable membrane sub-sections  

Microsoft Academic Search

Hybrid membrane cells with up to 128 sections, each one comprising a fully and a semi-permeable membrane sub-section and, the limit case of a cell with an infinite number of membrane sections were studied by numerical methods. These hybrid cells separate a feed stream into two parts: a solvent stream which crosses the semi-permeable membranes and a concentrate stream which

J. M. Miranda; J. B. L. M. Campos

2007-01-01

202

Noncontact microsurgery of living cell membrane using femtosecond laser pulses  

NASA Astrophysics Data System (ADS)

Near-infrared femtosecond laser pulses were applied to initiate reversible permeabilization of cell membrane and inject extrinsic substances into the target cells. Successful laser-based injection of a membrane impermeable dye, as well as plasmid DNA was demonstrated.

Ilina, I. V.; Ovchinnikov, A. V.; Sitnikov, D. S.; Chefonov, O. V.; Agranat, M. B.; Mikaelyan, A. S.

2013-06-01

203

Durability aspects of polymer electrolyte membrane fuel cells  

NASA Astrophysics Data System (ADS)

In order for the successful adoption of proton exchange membrane (PEM) fuel cell technology, it is imperative that durability is understood, quantified and improved. A number of mechanisms are known to contribute to PEMFC membrane electrode assembly (MEA) performance degradation. In this dissertation, we show, via experiments, some of the various processes that degrade the proton exchange membrane in a PEM fuel cell; and catalyst poisoning due to hydrogen sulfide (H2S) and siloxane. The effect of humidity on the chemical stability of two types of membranes, [i.e., perfluorosulfonic acid type (PFSA, NafionRTM 112) and biphenyl sulfone hydrocarbon type, (BPSH-35)] was studied by subjecting the MEAs to open-circuit voltage (OCV) decay and potential cycling tests at elevated temperatures and low inlet gas relative humidities. The BPSH-35 membranes showed poor chemical stability in ex situ Fenton tests compared to that of NafionRTM membranes. However, under fuel cell conditions, BPSH-35 MEAs outperformed NafionRTM 112 MEAs in both the OCV decay and potential cycling tests. For both membranes, (i) at a given temperature, membrane degradation was more pronounced at lower humidities and (ii) at a given relative humidity operation, increasing the cell temperature accelerated membrane degradation. Mechanical stability of these two types of membranes was also studied using relative humidity (RH) cycling. Hydrogen peroxide (H2O2) formation rates in a proton exchange membrane (PEM) fuel cell were estimated by studying the oxygen reduction reaction (ORR) on a rotating ring disc electrode (RRDE). Fuel cell conditions were replicated by depositing a film of Pt/Vulcan XC-72 catalyst onto the disk and by varying the temperature, dissolved O2 concentration and the acidity levels in HClO4. The HClO4 acidity was correlated to ionomer water activity and hence fuel cell humidity. H 2O2 formation rates showed a linear dependence on oxygen concentration and square dependence on water activity. The H2O 2 selectivity in ORR was independent of oxygen concentration but increased with decrease in water activity (i.e., decreased humidity). Presences of trace impurities (such as CO, H2S, NH3, etc.) in the fuel also affect PEMFC durability. Among these impurities, H 2S causes significantly higher performance loss and irreversible catalytic poisoning. A concise mechanism for the poisoning kinetics of H2S on composite solid polymer electrolyte Pt (SPE-Pt) electrode was validated experimentally by charge balances and theoretically by a model, which predicted the oxidation current as a function of the applied potential. H2S dissociatively adsorbed onto SPE-Pt electrode as linear and bridge bonded sulfur (S) species and, under favorable potentials, underwent electro-oxidation to sulfur and then to sulfur dioxide (SO2). Fraction of the adsorbed S species remained as 'hard-to-oxidize' adsorbents and caused irreversible loss of catalytic activity. Deactivation of bridge sites occurred first followed by the loss of linear sites. A method to estimate the catalytic sites irreversibly lost due to sulfur poisoning was developed.

Sethuraman, Vijay Anand

204

Investigation of Polyethylenimine/DNA Polyplex Transfection to Cultured Cells Using Radiolabeling and Subcellular Fractionation Methods.  

PubMed

Quantitative analysis of the intracellular trafficking of nonviral vectors provides critical information that can guide the rational design of improved cationic systems for gene delivery. Subcellular fractionation methods, combined with radiolabeling, produce quantitative measurements of the intracellular trafficking of nonviral vectors and the therapeutic payload. In this work, differential and density-gradient centrifugation techniques were used to determine the intracellular distribution of radiolabeled 25 kDa branched polyethylenimine (bPEI)/plasmid DNA complexes ("polyplexes") in HeLa cells over time. By differential centrifugation, [(14)C]bPEI was found mostly in the lighter fractions whereas [(3)H]DNA was found mostly in the heavier fractions. A majority of the intracellular polymer (?60%) and DNA (?90%) were found in the nuclear fraction. Polymer and DNA also differed in their distribution to heavier and denser organelles (lysosomes, mitochondria) in density-gradient centrifugation studies. An unexpected finding from this study was that between 18 and 50% of the DNA applied to the cells became cell-associated (either with the cell membrane and/or internalized), while only 1-6% of the polymer did so, resulting in an effective N/P ratio of less than 1. These results suggest that a significant amount of cationic polymer is dissociated from the DNA cargo early on in the transfection process. PMID:23406286

Shi, Julie; Chou, Brian; Choi, Jennifer L; Ta, Anh L; Pun, Suzie H

2013-03-05

205

Optical Measurement of Cell Membrane Tension  

NASA Astrophysics Data System (ADS)

Using a novel noncontact technique based on optical interferometry, we quantify the nanoscale thermal fluctuations of red blood cells (RBCs) and giant unilamellar vesicles (GUVs). The measurements reveal a nonvanishing tension coefficient for RBCs, which increases as cells transition from a discocytic shape to a spherical shape. The tension coefficient measured for GUVs is, however, a factor of 4 24 smaller. By contrast, the bending moduli for cells and vesicles have similar values. This is consistent with the cytoskeleton confinement model, in which the cytoskeleton inhibits membrane fluctuations [Gov et al., Phys. Rev. Lett. 90, 228101, (2003)PRLTAO0031-900710.1103/PhysRevLett.90.228101].

Popescu, Gabriel; Ikeda, Takahiro; Goda, Keisuke; Best-Popescu, Catherine A.; Laposata, Michael; Manley, Suliana; Dasari, Ramachandra R.; Badizadegan, Kamran; Feld, Michael S.

2006-11-01

206

Studies of smectite membrane behavior: Electrokinetic, osmotic, and isotopic fractionation processes at elevated pressures  

SciTech Connect

A 1.087 m NaCl brine was forced through a clay membrane 0.32 cm thick at 294 {plus minus} 1{degree}K. The clay membrane was made by compacting the 0.5 to 2.0 micron size fraction of Cheto montmorillonite from Chambers, Arizona. A confining pressure of 34.5 MPa (5,000 psi) and a mean hydraulic pressure of 15.9 MPa (2,300 psi) were chosen to simulate a depth of about 1.5 km (5,000 ft) in sedimentary basins. Differential hydraulic pressure across the clay was 13.8 MPa (2,000 psi). This differential hydraulic pressure setting was disturbed for only brief intervals during the experimental run. Hydraulic flow rate, electrical conductance, electrical potential across the clay, electroosmotic flow rate, and the chemical composition of the brine were determined periodically until constancy of both effluent chemical composition and electrical potential across the clay was achieved. Then, osmotic flow rate and stable oxygen isotopic compositions of both input and effluent reservoirs were determined before the run was terminated. The experimental results conform to the predictions of nonequilibrium thermodynamics under these simulated subsurface conditions. The electroviscous effect caused a significant reduction in the hydraulic flow rate but did not disturb the linearity between the flow rate and differential hydraulic pressure. Osmotic and electroosmotic effects may be responsible for driving large amounts of cross-formational subsurface fluid flow in nature. A measured {sup 18}O fractionation of 0.25{per thousand} compares well with published field and laboratory data.

Demir, I. (Univ. of Illinois, Urbana (USA))

1988-03-01

207

Constrained diffusion or immobile fraction on cell surfaces: a new interpretation.  

PubMed Central

Protein lateral mobility in cell membranes is generally measured using fluorescence photobleaching recovery (FPR). Since the development of this technique, the data have been interpreted by assuming free Brownian diffusion of cell surface receptors in two dimensions, an interpretation that requires that a subset of the diffusing species remains immobile. The origin of this so-called immobile fraction remains a mystery. In FPR, the motions of thousands of particles are inherently averaged, inevitably masking the details of individual motions. Recently, tracking of individual cell surface receptors has identified several distinct types of motion (Gross and Webb, 1988; Ghosh and Webb, 1988, 1990, 1994; Kusumi et al. 1993; Qian et al. 1991; Slattery, 1995), thereby calling into question the classical interpretation of FPR data as free Brownian motion of a limited mobile fraction. We have measured the motion of fluorescently labeled immunoglobulin E complexed to high affinity receptors (Fc epsilon RI) on rat basophilic leukemia cells using both single particle tracking and FPR. As in previous studies, our tracking results show that individual receptors may diffuse freely, or may exhibit restricted, time-dependent (anomalous) diffusion. Accordingly, we have analyzed FPR data by a new model to take this varied motion into account, and we show that the immobile fraction may be due to particles moving with the anomalous subdiffusion associated with restricted lateral mobility. Anomalous subdiffusion denotes random molecular motion in which the mean square displacements grow as a power law in time with a fractional positive exponent less than one. These findings call for a new model of cell membrane structure.

Feder, T J; Brust-Mascher, I; Slattery, J P; Baird, B; Webb, W W

1996-01-01

208

Improved recovery and identification of membrane proteins from rat hepatic cells using a centrifugal proteomic reactor.  

PubMed

Despite their importance in many biological processes, membrane proteins are underrepresented in proteomic analysis because of their poor solubility (hydrophobicity) and often low abundance. We describe a novel approach for the identification of plasma membrane proteins and intracellular microsomal proteins that combines membrane fractionation, a centrifugal proteomic reactor for streamlined protein extraction, protein digestion and fractionation by centrifugation, and high performance liquid chromatography-electrospray ionization-tandem MS. The performance of this approach was illustrated for the study of the proteome of ER and Golgi microsomal membranes in rat hepatic cells. The centrifugal proteomic reactor identified 945 plasma membrane proteins and 955 microsomal membrane proteins, of which 63 and 47% were predicted as bona fide membrane proteins, respectively. Among these proteins, >800 proteins were undetectable by the conventional in-gel digestion approach. The majority of the membrane proteins only identified by the centrifugal proteomic reactor were proteins with ? 2 transmembrane segments or proteins with high molecular mass (e.g. >150 kDa) and hydrophobicity. The improved proteomic reactor allowed the detection of a group of endocytic and/or signaling receptor proteins on the plasma membrane, as well as apolipoproteins and glycerolipid synthesis enzymes that play a role in the assembly and secretion of apolipoprotein B100-containing very low density lipoproteins. Thus, the centrifugal proteomic reactor offers a new analytical tool for structure and function studies of membrane proteins involved in lipid and lipoprotein metabolism. PMID:21749988

Zhou, Hu; Wang, Fangjun; Wang, Yuwei; Ning, Zhibin; Hou, Weimin; Wright, Theodore G; Sundaram, Meenakshi; Zhong, Shumei; Yao, Zemin; Figeys, Daniel

2011-07-12

209

Proliferation of Schwann cells induced by axolemmal and myelin membranes  

SciTech Connect

Purified Schwann Cells were cultured from neonatal rat sciatic nerve using a modification of the method of Brockes. Schwann cells and contaminating fibroblasts were unambiguously identified using fluorescent antibodies of 2'3' cyclic nucleotide 3'-phosphodiesterase and the thy 1.1 antigen respectively. The Schwann cells were quiescent unless challenged with mitogens. They proliferated rapidly in response to the soluble mitogen, cholera toxin, or to membrane fractions from rat CNS or PNS, prepared by the method of DeVries. Mitogenic activity was present in both axolemmal and myelin enriched fractions and promoted a 10-15 fold increase in the rate of /sup 3/H-thymidine uptake. The axolemmal mitogen was sensitive to heat (80/sup 0/C for 10 minutes), trypsin digestion (0.05% x 30 mins) or to treatment with endoglycosidase D, suggesting that it could be a glycoprotein. Fifty percent of the axolemmal mitogenic activity was solubilized in 1% octyl-glucoside. The solubilized material, however, was very unstable and further purification was not possible. The myelin associated mitogenic activity was markedly different. It was resistant to freeze thaw cycles, trypsin digestion of endoglycosidase treatment and the activity was actually enhanced by heating at 100/sup 0/C for two hours. It is proposed that the axolemmal activity is responsible for Schwann cell proliferation during development and that the myelin associated activity promotes Schwann cell proliferation during Wallerian degeneration.

Dinneen, M..

1985-01-01

210

Proteomic Analysis of the Sarcosine-Insoluble Outer Membrane Fraction of Helicobacter pylori Strain 26695  

PubMed Central

Helicobacter pylori causes gastroduodenal disease, which is mediated in part by its outer membrane proteins (OMPs). To identify OMPs of H. pylori strain 26695, we performed a proteomic analysis. A sarcosine-insoluble outer membrane fraction was resolved by two-dimensional electrophoresis with immobilized pH gradient strips. Most of the protein spots, with molecular masses of 10 to 100 kDa, were visible on the gel in the alkaline pI regions (6.0 to 10.0). The proteome of the OMPs was analyzed by matrix-assisted laser desorption ionization-time-of-flight mass spectrometry. Of the 80 protein spots processed, 62 spots were identified; they represented 35 genes, including 16 kinds of OMP. Moreover, we identified 9 immunoreactive proteins by immunoblot analysis. This study contributes to the characterization of the H. pylori strain 26695 proteome and may help to further elucidate the biological function of H. pylori OMPs and the pathogenesis of H. pylori infection.

Baik, Seung-Chul; Kim, Kyung-Mi; Song, Su-Min; Kim, Do-Su; Jun, Jin-Su; Lee, Seung-Gyu; Song, Jae-Young; Park, Jeong-Uck; Kang, Hyung-Lyun; Lee, Woo-Kon; Cho, Myung-Je; Youn, Hee-Shang; Ko, Gyung-Hyuck; Rhee, Kwang-Ho

2004-01-01

211

Intrinsic segments of band 3 that are associated with anion transport across red blood cell membranes  

Microsoft Academic Search

Summary After treatment of red cell ghosts with chymotrypsin, the predominant intrinsic peptides remaining in the membrane fraction are 15,000 and 9,000 daltons mol wt. After partial extraction with Triton X-100, the residual membrane vesicles have almost no other stained peptides and such vesicles are reported to carry out anion transport activities sensitive to specific inhibitors. In vesicles derived from

M. Ramjeesingh; S. Grinstein; Aser Rothstein

1980-01-01

212

Detection of urease in the cell wall and membranes from leaf tissues of bromeliad species.  

PubMed

Urea is an important nitrogen source for some bromeliad species, and in nature it is derived from the excretion of amphibians, which visit or live inside the tank water. Its assimilation is dependent on the hydrolysis by urease (EC: 3.5.1.5), and although this enzyme has been extensively studied to date, little information is available about its cellular location. In higher plants, this enzyme is considered to be present in the cytoplasm. However, there is evidence that urease is secreted by the bromeliad Vriesea gigantea, implying that this enzyme is at least temporarily located in the plasmatic membrane and cell wall. In this article, urease activity was measured in different cell fractions using leaf tissues of two bromeliad species: the tank bromeliad V. gigantea and the terrestrial bromeliad Ananas comosus (L.) Merr. In both species, urease was present in the cell wall and membrane fractions, besides the cytoplasm. Moreover, a considerable difference was observed between the species: while V. gigantea had 40% of the urease activity detected in the membranes and cell wall fractions, less than 20% were found in the same fractions in A. comosus. The high proportion of urease found in cell wall and membranes in V. gigantea was also investigated by cytochemical detection and immunoreaction assay. Both approaches confirmed the enzymatic assay. We suggest this physiological characteristic allows tank bromeliads to survive in a nitrogen-limited environment, utilizing urea rapidly and efficiently and competing successfully for this nitrogen source against microorganisms that live in the tank water. PMID:19508368

Aguetoni Cambuí, Camila; Gaspar, Marília; Mercier, Helenice

2009-02-12

213

Fuel cell membranes and crossover prevention  

SciTech Connect

A membrane electrode assembly for use with a direct organic fuel cell containing a formic acid fuel includes a solid polymer electrolyte having first and second surfaces, an anode on the first surface and a cathode on the second surface and electrically linked to the anode. The solid polymer electrolyte has a thickness t:.gtoreq..times..times..times..times. ##EQU00001## where C.sub.f is the formic acid fuel concentration over the anode, D.sub.f is the effective diffusivity of the fuel in the solid polymer electrolyte, K.sub.f is the equilibrium constant for partition coefficient for the fuel into the solid polymer electrolyte membrane, I is Faraday's constant n.sub.f is the number of electrons released when 1 molecule of the fuel is oxidized, and j.sub.f.sup.c is an empirically determined crossover rate of fuel above which the fuel cell does not operate.

Masel, Richard I. (Champaign, IL); York, Cynthia A. (Newington, CT); Waszczuk, Piotr (White Bear Lake, MN); Wieckowski, Andrzej (Champaign, IL)

2009-08-04

214

Lipid A binding sites in membranes of macrophage tumor cells  

SciTech Connect

Lipopolysaccharide affects a variety of eukaryotic cells and mammalian organisms. These actions are involved in the pathogenesis of Gram-negative septicemia. Many of the actions of lipopolysaccharide are believed to be caused by its active moiety, lipid A. Our laboratory has previously identified a bioactive lipid A precursor, termed lipid IVA, which can be labeled with 32P of high specific activity and purified. In this work we have used the labeled probe, 4'-32P-lipid IVA, to develop a novel assay for the specific binding of lipid IVA to whole cells. We have also demonstrated its use in a ligand blotting assay of immobilized cellular proteins. Using the whole cell assay, we show that 4'-32P-lipid IVA specifically binds to RAW 264.7 macrophage-like cultured cells. The binding is saturable, is inhibited with excess unlabeled lipid IVA, and is proteinase K-sensitive. It displays cellular and pharmacological specificity. Using the ligand blotting assay, we show that several RAW 264.7 cell proteins can bind 4'-32P-lipid IVA. The two principal binding proteins have Mr values of 31 and 95 kDa, as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Fractionation studies indicate that the 31-kDa protein is enriched in the nuclear fraction and may be a histone, whereas the 95-kDa protein is enriched in the membrane fraction. The binding assays that we have developed should lead to a clearer understanding of lipid A/animal cell interactions.

Hampton, R.Y.; Golenbock, D.T.; Raetz, C.R.

1988-10-15

215

Molecular Basis of Red Cell Membrane Disorders  

Microsoft Academic Search

We will consider an array of genetic disorders of the red cell membrane. Some affect well-known genes. The mutations of most cases of hereditary spherocytosis (HS) are located in the following genes: ANK1, SPTB, SLC4A1, EPB42 and SPTA1, which encode ankyrin, spectrin ?-chain, the anion exchanger 1 (band 3), protein 4.2 and spectrin ?-chain, respectively. A dominant form of distal

Jean Delaunay

2002-01-01

216

Vaccination of feedlot cattle with extracts and membrane fractions from two Mycoplasma bovis isolates results in strong humoral immune responses but does not protect against an experimental challenge.  

PubMed

Mycoplasma bovis is one of the most significant contributors to the bovine respiratory syndrome (BRD) that causes major losses in feedlot and dairy farms. Current experimental vaccines against M. bovis are ineffective and in some cases seem to enhance disease. Experimental infection with M. bovis induces a predominantly Th2 response and high levels of IgG1, which is an inferior opsonin and hence lacks protective capacity. In an attempt to induce a balanced (Th1/Th2) immune response, we have used CpG ODN 2007 as an adjuvant in a trial involving vaccination of cattle with M. bovis total extracts and/or membrane fractions and subsequent intranasal inoculation with an infective dose of M. bovis prepared from two different clinical isolates. Significant IgG1 serum responses were observed against both, extracts and fractions while IgG2 responses were significant against the extracts only. Proliferation of peripheral blood mononuclear cells (PBMC) after incubation with M. bovis cells was only observed in post-challenge samples of cattle vaccinated with both extracts and fractions but not in samples of cattle immunized with the membrane fractions alone. All groups showed transient weight losses and increased temperatures however, there were no significant differences in clinical parameters and survival rates between the groups. PMID:23340004

Mulongo, Musa; Prysliak, Tracy; Perez-Casal, Jose

2013-01-20

217

Application of Dow Chemical's Perfluorinated Membranes in Proton-Exchange Membrane Fuel Cells. (Abstract Only).  

National Technical Information Service (NTIS)

Dow Chemical's research activities in fuel cell devices revolves around the development and subsequent investigation of the perfluorinated inomeric membrane separator useful in proton-exchange membrane systems. Work is currently focusing on studying the e...

G. A. Eisman

1989-01-01

218

Application of Dow Chemical's Perfluorinated Membranes in Proton-Exchange Membrane Fuel Cells.  

National Technical Information Service (NTIS)

Dow Chemical's research activities in fuel cells revolve around the development of perfluorosulfonic acid membranes useful as the proton transport medium and separator. Some of the performance characteristics which are typical for such membranes are outli...

G. A. Eisman

1989-01-01

219

Bioluminescence Assay for Detecting Cell Surface Membrane Protein Expression  

PubMed Central

Abstract We have developed a method to measure the amounts of cell surface-expressed membrane proteins with bioluminescence. Dinoflagellate luciferase was expressed on the surface of a mammalian cell as a chimeric fusion protein with a membrane protein of interest. Using a membrane-impermeable substrate to quantify the membrane-displayed luciferase, the expression of the membrane protein on the cell surface was determined. By inclusion of a quenching step for the luminescent activity of luciferase on the cell surface, we were able to monitor the membrane protein expression kinetics by measuring the luminescence recovery from the cell surface after quenching. The reported methods provide a convenient way to monitor the kinetics of expression and transport of membrane proteins to the cell surface. It is applicable to the high-throughput analysis of drugs or drug candidates concerning their effects on membrane protein expression.

Kato, Mieko; Chiba, Tomoki; Li, Min

2011-01-01

220

Membrane catalyst layer for fuel cells  

DOEpatents

A gas reaction fuel cell incorporates a thin catalyst layer between a solid polymer electrolyte (SPE) membrane and a porous electrode backing. The catalyst layer is preferably less than about 10 .mu.m in thickness with a carbon supported platinum catalyst loading less than about 0.35 mgPt/cm.sup.2. The film is formed as an ink that is spread and cured on a film release blank. The cured film is then transferred to the SPE membrane and hot pressed into the surface to form a catalyst layer having a controlled thickness and catalyst distribution. Alternatively, the catalyst layer is formed by applying a Na.sup.+ form of a perfluorosulfonate ionomer directly to the membrane, drying the film at a high temperature, and then converting the film back to the protonated form of the ionomer. The layer has adequate gas permeability so that cell performance is not affected and has a density and particle distribution effective to optimize proton access to the catalyst and electronic continuity for electron flow from the half-cell reaction occurring at the catalyst.

Wilson, Mahlon S. (Los Alamos, NM)

1993-01-01

221

Correlation of cell membrane dynamics and cell motility  

PubMed Central

Background Essential events of cell development and homeostasis are revealed by the associated changes of cell morphology and therefore have been widely used as a key indicator of physiological states and molecular pathways affecting various cellular functions via cytoskeleton. Cell motility is a complex phenomenon primarily driven by the actin network, which plays an important role in shaping the morphology of the cells. Most of the morphology based features are approximated from cell periphery but its dynamics have received none to scant attention. We aim to bridge the gap between membrane dynamics and cell states from the perspective of whole cell movement by identifying cell edge patterns and its correlation with cell dynamics. Results We present a systematic study to extract, classify, and compare cell dynamics in terms of cell motility and edge activity. Cell motility features extracted by fitting a persistent random walk were used to identify the initial set of cell subpopulations. We propose algorithms to extract edge features along the entire cell periphery such as protrusion and retraction velocity. These constitute a unique set of multivariate time-lapse edge features that are then used to profile subclasses of cell dynamics by unsupervised clustering. Conclusions By comparing membrane dynamic patterns exhibited by each subclass of cells, correlated trends of edge and cell movements were identified. Our findings are consistent with published literature and we also identified that motility patterns are influenced by edge features from initial time points compared to later sampling intervals.

2011-01-01

222

Heat-shock protein expression on the membrane of T cells undergoing apoptosis.  

PubMed Central

Heat-shock proteins (hsp) represent a highly conserved family of proteins, normally localized in the cytoplasm and nucleus, whose expression is induced in situations involving cell stress. This paper reports the unusual translocation of hsp to the cell membrane of T cells undergoing apoptosis. We observed that glucocorticosteroid-induced thymocyte death is associated to the surface expression of hsp 60 and hsp 70 in a discrete fraction of apoptotic cells. hsp surface expression is closely related to a thymic subset of immature CD3low/- T cells. The expression of surface hsp 60 appears early after treatment with dexamethasone (3 hr) whereas the membrane expression of hsp 70 follows different kinetics and peaks later. Morphological analysis of the hsp+ apoptotic cells suggest that this subset represents late-stage apoptotic cells at their minimal volume before fragmentation into apoptotic bodies. Membrane expression of hsp is also associated with apoptosis in peripheral blood mononuclear cells from AIDS patients cultured in vitro. Altogether, we show that a discrete fraction of cells undergoing apoptosis expresses membrane hsp 60 and hsp 70, supporting the hypothesis that apoptosis causes a radical alteration in the expression of cell surface molecules. Surface hsp expressed during apoptosis may constitute a novel immune-context able to generate packages of self- and exogenous antigens, originating from degradation of altered cells. Images Figure 1 Figure 3

Poccia, F; Piselli, P; Vendetti, S; Bach, S; Amendola, A; Placido, R; Colizzi, V

1996-01-01

223

Adenosinetriphosphatase Activity in the Cell Membranes of Kidney Tubule Cells  

PubMed Central

This cytochemical study demonstrates high levels of apparent ATPase activity in the infolded cell membranes of the proximal tubules (dog, rat, human, mouse, monkey, and opossum) and ascending loops of Henle (dog, rat, human and, to a variable degree, mouse). Electron microscopy has shown (see Rhodin (1)) that these membranes separate adjacent cells where they interlock with one another by multiple cytoplasmic lamellae containing oriented mitochondria. The significance of the high ATPase activity is considered in relation to possible movements of the membranes and to "active transport" believed to occur there. In the rat, enzyme activity in the proximal tubule membranes does not survive formol-calcium fixation, and it is therefore necessary to use unfixed sections for its demonstration. However, in edematous rats with experimental nephrosis (induced by the injection of aminonucleoside or with antikidney serum) marked ATPase activity is exhibited in these membranes even after formol-calcium fixation. When proximal tubule or Henle loop cells of the dog acquire an altered metabolism, as indicated by accumulated lipide spheres or by "droplets," the infolded ATPase-rich membranes are no longer demonstrable.

Spater, Herman W.; Novikoff, Alex B.; Masek, Bertha

1958-01-01

224

Fuel cell membrane hydration and fluid metering  

DOEpatents

A hydration system includes fuel cell fluid flow plate(s) and injection port(s). Each plate has flow channel(s) with respective inlet(s) for receiving respective portion(s) of a given stream of reactant fluid for a fuel cell. Each injection port injects a portion of liquid water directly into its respective flow channel in order to mix its respective portion of liquid water with the corresponding portion of the stream. This serves to hydrate at least corresponding part(s) of a given membrane of the corresponding fuel cell(s). The hydration system may be augmented by a metering system including flow regulator(s). Each flow regulator meters an injecting at inlet(s) of each plate of respective portions of liquid into respective portion(s) of a given stream of fluid by corresponding injection port(s).

Jones, Daniel O. (Glenville, NY); Walsh, Michael M. (Fairfield, CT)

1999-01-01

225

Cell membrane potentials induced during exposure to EMP fields  

Microsoft Academic Search

Internal current densities and electric fields induced in the human body during exposure to EMP fields are reviewed and used to predict resulting cell membrane potentials. Using several different approaches, membrane potentials of about 100 mV are predicted. These values are comparable to the static membrane potentials maintained by cells as a part of normal physiological function, but the EMP-induced

P. C. Gailey; C. E. Easterly

1994-01-01

226

The membrane proteome of the mouse lens fiber cell  

Microsoft Academic Search

Purpose: Fiber cells of the ocular lens are bounded by a highly specialized plasma membrane. Despite the pivotal role that membrane proteins play in the physiology and pathophysiology of the lens, our knowledge of the structure and composition of the fiber cell plasma membrane remains fragmentary. In the current study, we utilized mass spectrometry- based shotgun proteomics to provide a

Steven Bassnett; Phillip A. Wilmarth; Larry L. David

2009-01-01

227

Acetylcholine Receptor Organization in Membrane Domains in Muscle Cells  

PubMed Central

Nicotinic acetylcholine receptors (nAChR) in muscle fibers are densely packed in the postsynaptic region at the neuromuscular junction. Rapsyn plays a central role in directing and clustering nAChR during cellular differentiation and neuromuscular junction formation; however, it has not been demonstrated whether rapsyn is the only cause of receptor immobilization. Here, we used single-molecule tracking methods to investigate nAChR mobility in plasma membranes of myoblast cells during their differentiation to myotubes in the presence and absence of rapsyn. We found that in myoblasts the majority of nAChR were immobile and that ?20% of the receptors showed restricted diffusion in small domains of ?50 nm. In myoblasts devoid of rapsyn, the fraction of mobile nAChR was considerably increased, accompanied by a 3-fold decrease in the immobile population of nAChR with respect to rapsyn-expressing cells. Half of the mobile receptors were confined to domains of ?120 nm. Measurements performed in heterologously transfected HEK cells confirmed the direct immobilization of nAChR by rapsyn. However, irrespective of the presence of rapsyn, about one-third of nAChR were confined in 300-nm domains. Our results show (i) that rapsyn efficiently immobilizes nAChR independently of other postsynaptic scaffold components; (ii) nAChR is constrained in confined membrane domains independently of rapsyn; and (iii) in the presence of rapsyn, the size of these domains is strongly reduced.

Piguet, Joachim; Schreiter, Christoph; Segura, Jean-Manuel; Vogel, Horst; Hovius, Ruud

2011-01-01

228

Permeability of a Cell Membrane Junction  

PubMed Central

The ion permeability of the membrane junctions between Chironomus salivary gland cells is strongly depressed by treatments that are generally known to inhibit energy metabolism. These treatments include prolonged cooling at 6°–8°C, and exposure to dinitrophenol, cyanide, oligomycin, and N-ethylmaleimide. Intracellular injection of ATP appears to prevent depression of junctional permeability by dinitrophenol or to reverse it. Ouabain, azide, p-chloromercuriphenylsulfonic acid, reserpine, and acetazolamide fail to depress junctional permeability. Thus the ion permeability of the junctional membranes appears to depend on energy provided by oxidative phosphorylation. Possible energy-linked processes for maintaining junctional permeability are discussed, including processes involving transport of permeability-modifying species such as Ca++.

Politoff, A. L.; Socolar, S. J.; Loewenstein, W. R.

1969-01-01

229

Fractionation of the Hypericum perforatum L. extract: PMF, and PDT effects of the fractions against HL-60 leukemic cells  

NASA Astrophysics Data System (ADS)

In the last three years we have prepared and studied the polar methanolic extract PMF, of the herb Hypericum perforatum L, and studied as a new, alternative photosensitizing substance for PDT. Hypericum perforatum L., as well as PMF, contains a number of naphthodianthrone derivatives (hypericins), such as hypericin and pseudohypericin, as its main photosensitizing constituents. PMF has been tested as a PDT agent in vitro in bladder cancer cells, leukemia cells, and in vivo in rat tumor bearing urinary bladder. In order to evaluate the contribution of the hypericins in the overall PDT action, and prepare a better photosensitizing extract than PMF, we have separated the extract in four main fractions (1,2,3,4), and tested their PDT effects against the HL-60 leukemic cells. The concentration of hypericins in the extracts was found 0.08% for fraction 1, 0.09% for fraction 2, 0.8% for fraction 3, and 2,8% for fraction 4. The PDT activity observed among the fractions was proportional to their hypericins concentration, thus increasing in the order of increasing number: fraction 4 > fraction 3 > fraction 2 > fraction 1. Fraction 4 proved to be the most powerful fraction. However, despite its relatively high hypericins concentration (2.8%), compared with the total extract PMF (1.37%), fraction 4 proved to be less active in the cell line tested. This result indicates that there are other photosensitizing constituents within the PMF extract which contribute significantly in the overall PDT action, and therefore the extract should be used as it is for further PDT studies, without any further purification.

Tsontou, M.; Dimitriou, H.; Filippidis, G.; Tsimaris, I.; Kalmanti, M.; Skalkos, D.

2007-02-01

230

The effects of natural organic matter (NOM) fractions on fouling characteristics and flux recovery of ultrafiltration membranes  

Microsoft Academic Search

Natural organic matter (NOM) which is a complex mix of particulate and soluble materials in surface water has been identified and reported by previous studies as responsible for membrane fouling. However the component of NOM which primarily causes the fouling problem is still not well understood, especially relating to the specific fraction that is mainly responsible for flux decline. Therefore,

A. W. Zularisam; A. F. Ismail; M. R. Salim; Mimi Sakinah; H. Ozaki

2007-01-01

231

Fluorescence imaging of membrane dynamics in living cells  

NASA Astrophysics Data System (ADS)

Methods of wide-field fluorescence microscopy for measuring membrane dynamics of living cells are described, including spectral imaging as well as anisotropy imaging of the membrane marker 6-dodecanoyl-2-dimethylamino naphthalene (laurdan). Plasma membranes are selected by illumination with an evanescent electromagnetic field and distinguished from intracellular membranes assessed by whole-cell illumination. While fluorescence spectra of laurdan appeared red-shifted with decreasing membrane stiffness, fluorescence anisotropy and rotational correlation times were reduced with increasing membrane fluidity. Membrane stiffness was found to increase with decreasing temperature and increasing amounts of cholesterol and was always higher for the plasma membrane than for intracellular membranes. These effects may have some clinical relevance in the research of drug resistance or cell aging.

Weber, Petra; Wagner, Michael; Schneckenburger, Herbert

2010-07-01

232

The target cell plasma membrane is a critical interface for Salmonella cell entry effector-host interplay.  

PubMed

Salmonella species trigger host membrane ruffling to force their internalization into non-phagocytic intestinal epithelial cells. This requires bacterial effector protein delivery into the target cell via a type III secretion system. Six translocated effectors manipulate cellular actin dynamics, but how their direct and indirect activities are spatially and temporally co-ordinated to promote productive cytoskeletal rearrangements remains essentially unexplored. To gain further insight into this process, we applied mechanical cell fractionation and immunofluorescence microscopy to systematically investigate the subcellular localization of epitope-tagged effectors in transiently transfected and Salmonella-infected cultured cells. Although five effectors contain no apparent membrane-targeting domains, all six localized exclusively in the target cell plasma membrane fraction and correspondingly were visualized at the cell periphery, from where they induced distinct effects on the actin cytoskeleton. Unexpectedly, no translocated effector pool was detectable in the cell cytosol. Using parallel in vitro assays, we demonstrate that the prenylated cellular GTPase Cdc42 is necessary and sufficient for membrane association of the Salmonella GTP exchange factor and GTPase-activating protein mimics SopE and SptP, which have no intrinsic lipid affinity. The data show that the host plasma membrane is a critical interface for effector-target interaction, and establish versatile systems to further dissect effector interplay. PMID:15522075

Cain, Robert J; Hayward, Richard D; Koronakis, Vassilis

2004-11-01

233

Identification of effluent organic matter fractions responsible for low-pressure membrane fouling.  

PubMed

Anion exchange resin (AER), powder activated carbon (PAC) adsorption and ozonation treatments were applied on biologically treated wastewater effluent with the objective to modify the effluent organic matter (EfOM) matrix. Both AER and PAC led to significant total organic carbon (TOC) removal, while the TOC remained nearly constant after ozonation. Liquid Chromatography-Organic Carbon Detection (LC-OCD) analysis showed that the AER treatment preferentially removed high and intermediate molecular weight (MW) humic-like structures while PAC removed low MW compounds. Only a small reduction of the high MW colloids (i.e. biopolymers) was observed for AER and PAC treatments. Ozonation induced a large reduction of the biopolymers and an important increase of the low MW humic substances (i.e. building blocks). Single-cycle microfiltration (MF) and ultrafiltration (UF) tests were conducted using commercially available hollow fibres at a constant flux. After reconcentration to their original organic carbon content, the EfOM matrix modified by AER and PAC treatments exhibited higher UF membrane fouling compared to untreated effluent; result that correlated with the higher concentration of biopolymers. On the contrary, ozonation which induced a significant degradation of the biopolymers led to a minor flux reduction for both UF and MF filtration tests. Based on a single filtration, results indicate that biopolymers play a major role in low pressure membrane fouling and that intermediate and low MW compounds have minor impact. Thus, this approach has shown to be a valid methodology to identify the foulant fractions of EfOM. PMID:22884373

Filloux, Emmanuelle; Gallard, Hervé; Croue, Jean-Philippe

2012-07-31

234

Inhibition of Adenosine Triphosphatase Activity of the Plasma Membrane Fraction of Oat Roots by Diethylstilbestrol 1  

PubMed Central

Diethylstibestrol (DES) inhibited noncompetitively the ATPase in the plasma membrane fraction from Avena sativa L. cv. Goodfield roots when assayed in the presence of MgSO4 or MgSO4 plus KCl. In the presence of MgSO4, 7.1×10?5 molar DES inhibited the enzyme 50%; whereas in the presence of MgSO4 and KCl, 1.3×10?4 molar DES was required for the same inhibition. Dixon plots indicated that in the presence of MgSO4, one molecule of DES bound to one molecule of ATPase; however, in the presence of MgSO4 and KCl, two or more molecules bound to one ATPase molecule. These results suggested that KCl causes a conformational change in the enzyme which exposes additional binding sites for DES, but that these sites are not as inhibitory as the first binding site. In addition to KCl, other factors also affected the DES inhibition of the ATPase. Plasma membrane vesicles warmed to 38 C were inhibited more than vesicles kept on ice prior to assay. DES inhibited the Triton X-100-treated ATPase less than the ATPase which was not detergent-treated. Finally, studies with DES analogs showed that the hydroxyl groups of DES were essential for inhibition and that steric configurations of the molecule were important. DES inhibition of the ATPase suggests that DES inhibits K+ absorption in oat roots by inhibiting the ATPase. Inhibition of K+ absorption was greater than inhibition of the ATPase, and thus DES may also inhibit other aspects of metabolism that are involved with ion absorption.

Balke, Nelson E.; Hodges, Thomas K.

1979-01-01

235

Combination of FASP and StageTip-based fractionation allows in-depth analysis of the hippocampal membrane proteome.  

PubMed

Membrane proteomics is challenging because the desirable strong detergents are incompatible with downstream analysis. Recently, we demonstrated efficient removal of SDS by the filter aided sample preparation method (FASP). Here we combine FASP with our previously described small-scale membrane enrichment protocol. Analysis of a single mouse hippocampus enables identification of more than 1000 membrane proteins in a single LC-MS/MS run without protein or peptide prefractionation. To extend proteome coverage, we developed a simple anion exchange fractionation method in a StageTip format. When separating peptides into six fractions, a duplicate analysis resulted in identification of 4206 proteins of which 64% were membrane proteins. This data set covers 83% of glutamate and GABA receptor subunits identified in hippocampus in the Allen Brain Atlas and adds further isoforms. The combined method provides a streamlined protocol for rapid and sensitive membrane proteome mapping. We also provide a generic protocol for combining FASP with StageTip-based ion exchange fractionation, which is generally applicable to proteome analysis. PMID:19848406

Wi?niewski, Jacek R; Zougman, Alexandre; Mann, Matthias

2009-12-01

236

Effect of Hydroperoxides on Red Blood Cell Membrane Mechanical Properties  

Microsoft Academic Search

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

2011-01-01

237

Durable, Low-Cost, Improved Fuel Cell Membranes.  

National Technical Information Service (NTIS)

The development of low cost, durable membranes and membranes electrode assemblies (MEAs) that operate under reduced relative humidity (RH) conditions remain a critical challenge for the successful introduction of fuel cells into mass markets. It was the g...

C. Roger D. Mountz T. Zhang W. He

2011-01-01

238

Preparation of cell membranes for high resolution imaging by AFM.  

PubMed

Studies of cell membrane structure by atomic force microscopy (AFM) have been limited because of the softness of cell membranes. Here, we utilize a new technique of sample preparation to lay red blood cell membranes on the top of a mica surface to obtain high resolution images by in-situ AFM on both sides of cell membranes. Our results indicate that the location of oligosaccharides and proteins in red blood cell membranes might be different from the current membrane model. The inner membrane leaflet is covered by dense proteins with fewer free lipids than expected. In contrast, the outer membrane leaflet is quite smooth; oligosaccharides and peptides supposed to protrude out of the outer membrane leaflet surface might be actually hidden in the middle of hydrophilic lipid heads; transmembrane proteins might form domains in the membranes revealed by PNGase F and trypsin digestion. Our result could be significant to interpret some functions about red blood cell membranes and guide to heal the blood diseases related to cell membranes. PMID:20097008

Wang, Hongda; Hao, Xian; Shan, Yuping; Jiang, Junguang; Cai, Mingjun; Shang, Xin

2010-01-04

239

Distribution of Intact and Core Membrane Lipids of Archaeal Glycerol Dialkyl Glycerol Tetraethers among Size-Fractionated Particulate Organic Matter in Hood Canal, Puget Sound  

PubMed Central

There is great interest in the membrane lipids of archaea (glycerol dialkyl glycerol tetraethers [GDGTs]) as tracers of archaeal biomass because of their utility as paleoproxies and because of the biogeochemical importance of archaea. While core GDGTs (formed by hydrolysis of polar head groups of intact GDGTs after cell death) are appropriate for paleostudies, they have also been used to trace archaeal populations. Also, despite the small size (0.2 by 0.7 ?m) of cultivated marine archaea, 0.7-?m glass-fiber filters (GFFs) are typically used to collect GDGTs from natural waters. We quantified both core and intact GDGTs in free-living (0.2- to 0.7-?m), suspended (0.7- to 60-?m), and aggregate (>60-?m) particle size fractions in Puget Sound (Washington State). On average, the free-living fraction contained 36% of total GDGTs, 90% of which were intact. The intermediate-size fraction contained 62% of GDGTs, and 29% of these were intact. The aggregate fraction contained 2% of the total GDGT pool, and 29% of these were intact. Our results demonstrate that intact GDGTs are largely in the free-living fraction. Because only intact GDGTs are present in living cells, protocols that target this size fraction and analyze the intact GDGT pool are necessary to track living populations in marine waters. Core GDGT enrichment in larger-size fractions indicates that archaeal biomass may quickly become attached or entrained in particles once the archaea are dead or dying. While the concentrations of the two pools were generally not correlated, the similar sizes of the core and intact GDGT pools suggest that core GDGTs are removed from the water column on timescales similar to those of cell replication, on timescales of days to weeks.

Huguet, Carme; Truxal, Laura T.

2012-01-01

240

Quantitation of virus-induced (mlr) and normal (thy.1.2) Cell surface antigens in isolated plasma membranes and the extracellular ascites fluid of mouse leukemia cells  

Microsoft Academic Search

SUMMARY Plasma membranes were isolated by two methods from mouse leukemia cells containing mammary tumor virus-induced (MLr) and normal (Thy.l.2) antigens on their surfaces. A number of chemical components, enzymic activities, and the antigenic contents were determined in subcellular fractions and found to be specifically concen- trated in the plasma membrane fractions. The major part of the cellular MLr, in

W. J. Van Blitterswijk; P. Emmelot; J. Hilgers; D. Kamlag; C. A. Feltkamp

1975-01-01

241

The plasma membrane lipid composition affects fusion between cells and model membranes  

Microsoft Academic Search

Investigations were carried out on the effect of plasma membrane lipid modifications on the fusogenic capacity of control and ras-transformed fibroblasts. The plasma membrane lipid composition was modified by treatment of cells with exogenous phospholipases C and D, sphingomyelinase and cyclodextrin. The used enzymes hydrolyzed definite membrane lipids thus inducing specific modifications of the lipid composition while cyclodextrin treatment reduced

Roumen Pankov; Tania Markovska; Peter Antonov; Lidia Ivanova; Albena Momchilova

2006-01-01

242

?-D-glucan-hydrolase activities in pure cell-wall-enriched fractions from Valerianella olitoria cells  

Microsoft Academic Search

An effective method for the preparation of purified cell walls from mesophyll cells of Valerianella olitoria has been developed. Cells were isolated by a mechanical procedure only and crude cell walls were prepared from cell homogenates. Crude wall suspensions were fractionated in a discontinuous sucrose gradient and the wall fragments recovered were examined by scanning electron microscopy. An evaluation of

Y. Lienart; F. Barnoud

1985-01-01

243

Cell Separation by Dielectrophoretic Field-flow-fractionation  

PubMed Central

Dielectrophoretic field-flow-fractionation (DEP-FFF) was applied to several clinically relevant cell separation problems, including the purging of human breast cancer cells from normal T-lymphocytes and from CD34+ hematopoietic stem cells, the separation of the major leukocyte subpopulations, and the enrichment of leukocytes from blood. Cell separations were achieved in a thin chamber equipped with a microfabricated, interdigitated electrode array on its bottom wall that was energized with AC electric signals. Cells were levitated by the balance between DEP and sedimentation forces to different equilibrium heights and were transported at differing velocities and thereby separated when a velocity profile was established in the chamber. This bulk-separation technique adds cell intrinsic dielectric properties to the catalog of physical characteristics that can be applied to cell discrimination. The separation process and performance can be controlled through electronic means. Cell labeling is unnecessary, and separated cells may be cultured and further analyzed. It can be scaled up for routine laboratory cell separation or implemented on a miniaturized scale.

Wang, Xiao-Bo; Yang, Jun; Huang, Ying; Vykoukal, Jody; Becker, Frederick F.; Gascoyne, Peter R. C.

2009-01-01

244

Cell separation by dielectrophoretic field-flow-fractionation.  

PubMed

Dielectrophoretic field-flow-fractionation (DEP-FFF) was applied to several clinically relevant cell separation problems, including the purging of human breast cancer cells from normal T-lymphocytes and from CD34+ hematopoietic stem cells, the separation of the major leukocyte subpopulations, and the enrichment of leukocytes from blood. Cell separations were achieved in a thin chamber equipped with a microfabricated, interdigitated electrode array on its bottom wall that was energized with AC electric signals. Cells were levitated by the balance between DEP and sedimentation forces to different equilibrium heights and were transported at differing velocities and thereby separated when a velocity profile was established in the chamber. This bulk-separation technique adds cell intrinsic dielectric properties to the catalog of physical characteristics that can be applied to cell discrimination. The separation process and performance can be controlled through electronic means. Cell labeling is unnecessary, and separated cells may be cultured and further analyzed. It can be scaled up for routine laboratory cell separation or implemented on a miniaturized scale. PMID:10701270

Wang, X B; Yang, J; Huang, Y; Vykoukal, J; Becker, F F; Gascoyne, P R

2000-02-15

245

Fractional derivatives embody essential features of cell rheological behavior.  

PubMed

Mechanical moduli of cultured airway smooth muscle cells (Fabry, B., et al. Phys. Rev. Lett. 87:148102, 2001) reveal that the frequency dependence of cell rheological behavior conforms to a weak power-law relationship over a wide range of frequency (10(-2)-10(3) Hz). Such a behavior cannot be accounted for by standard viscoelastic models characterized by a discrete number of time constants that have been commonly used in previous studies of cell viscoelasticity. Fractional calculus, by contrast, provides a natural framework for describing weak power-law relationships and requires no assumptions about the type of material, the time constant distribution or the time/frequency interval in which rheological observations are made. In this study, we developed a rheological model of the cell using methods of fractional calculus. We used a least-squares technique to fit the model to data previously obtained from measurements on airway smooth muscle cells. The fit provided an excellent correspondence to the data, and the estimated values of model parameters were physically plausible. The model leads to a novel and unexpected empirical link between dynamic viscoelastic behavior of the cytoskeleton and the static contractile stress that it bears. PMID:12797619

Djordjevi?, Vladan D; Jari?, Jovo; Fabry, Ben; Fredberg, Jeffrey J; Stamenovi?, Dimitrije

2003-06-01

246

Plasma membrane microdomains from hybrid aspen cells are involved in cell wall polysaccharide biosynthesis.  

PubMed

Detergent-resistant plasma membrane microdomains [DRMs (detergent-resistant membranes)] were isolated recently from several plant species. As for animal cells, a large range of cellular functions, such as signal transduction, endocytosis and protein trafficking, have been attributed to plant lipid rafts and DRMs. The data available are essentially based on proteomics and more approaches need to be undertaken to elucidate the precise function of individual populations of DRMs in plants. We report here the first isolation of DRMs from purified plasma membranes of a tree species, the hybrid aspen Populus tremula x tremuloides, and their biochemical characterization. Plasma membranes were solubilized with Triton X-100 and the resulting DRMs were isolated by flotation in sucrose density gradients. The DRMs were enriched in sterols, sphingolipids and glycosylphosphatidylinositol-anchored proteins and thus exhibited similar properties to DRMs from other species. However, they contained key carbohydrate synthases involved in cell wall polysaccharide biosynthesis, namely callose [(1-->3)-beta-D-glucan] and cellulose synthases. The association of these enzymes with DRMs was demonstrated using specific glucan synthase assays and antibodies, as well as biochemical and chemical approaches for the characterization of the polysaccharides synthesized in vitro by the isolated DRMs. More than 70% of the total glucan synthase activities present in the original plasma membranes was associated with the DRM fraction. In addition to shedding light on the lipid environment of callose and cellulose synthases, our results demonstrate the involvement of DRMs in the biosynthesis of important cell wall polysaccharides. This novel concept suggests a function of plant membrane microdomains in cell growth and morphogenesis. PMID:19216717

Bessueille, Laurence; Sindt, Nicolas; Guichardant, Michel; Djerbi, Soraya; Teeri, Tuula T; Bulone, Vincent

2009-04-28

247

Membrane Purification Cell for Aluminum Recycling  

SciTech Connect

Recycling mixed aluminum scrap usually requires adding primary aluminum to the scrap stream as a diluent to reduce the concentration of non-aluminum constituents used in aluminum alloys. Since primary aluminum production requires approximately 10 times more energy than melting scrap, the bulk of the energy and carbon dioxide emissions for recycling are associated with using primary aluminum as a diluent. Eliminating the need for using primary aluminum as a diluent would dramatically reduce energy requirements, decrease carbon dioxide emissions, and increase scrap utilization in recycling. Electrorefining can be used to extract pure aluminum from mixed scrap. Some example applications include producing primary grade aluminum from specific scrap streams such as consumer packaging and mixed alloy saw chips, and recycling multi-alloy products such as brazing sheet. Electrorefining can also be used to extract valuable alloying elements such as Li from Al-Li mixed scrap. This project was aimed at developing an electrorefining process for purifying aluminum to reduce energy consumption and emissions by 75% compared to conventional technology. An electrolytic molten aluminum purification process, utilizing a horizontal membrane cell anode, was designed, constructed, operated and validated. The electrorefining technology could also be used to produce ultra-high purity aluminum for advanced materials applications. The technical objectives for this project were to: - Validate the membrane cell concept with a lab-scale electrorefining cell; - Determine if previously identified voltage increase issue for chloride electrolytes holds for a fluoride-based electrolyte system; - Assess the probability that voltage change issues can be solved; and - Conduct a market and economic analysis to assess commercial feasibility. The process was tested using three different binary alloy compositions (Al-2.0 wt.% Cu, Al-4.7 wt.% Si, Al-0.6 wt.% Fe) and a brazing sheet scrap composition (Al-2.8 wt.% Si-0.7 wt.% Fe-0.8 wt.% Mn),. Purification factors (defined as the initial impurity concentration divided by the final impurity concentration) of greater than 20 were achieved for silicon, iron, copper, and manganese. Cell performance was measured using its current and voltage characteristics and composition analysis of the anode, cathode, and electrolytes. The various cells were autopsied as part of the study. Three electrolyte systems tested were: LiCl-10 wt. % AlCl3, LiCl-10 wt. % AlCl3-5 wt.% AlF3 and LiF-10 wt.% AlF3. An extended four-day run with the LiCl-10 wt.% AlCl3-5 wt.% AlF3 electrolyte system was stable for the entire duration of the experiment, running at energy requirements about one third of the Hoopes and the conventional Hall-Heroult process. Three different anode membranes were investigated with respect to their purification performance and survivability: a woven graphite cloth with 0.05 cm nominal thickness & > 90 % porosity, a drilled rigid membrane with nominal porosity of 33%, and another drilled rigid graphite membrane with increased thickness. The latter rigid drilled graphite was selected as the most promising membrane design. The economic viability of the membrane cell to purify scrap is sensitive to primary & scrap aluminum prices, and the cost of electricity. In particular, it is sensitive to the differential between scrap and primary aluminum price which is highly variable and dependent on the scrap source. In order to be economically viable, any scrap post-processing technology in the U.S. market must have a total operating cost well below the scrap price differential of $0.20-$0.40 per lb to the London Metal Exchange (LME), a margin of 65%-85% of the LME price. The cost to operate the membrane cell is estimated to be < $0.24/lb of purified aluminum. The energy cost is estimated to be $0.05/lb of purified aluminum with the remaining costs being repair and maintenance, electrolyte, labor, taxes and depreciation. The bench-scale work on membrane purification cell process has demonstrated technological advantages and subs

David DeYoung; James Wiswall; Cong Wang

2011-11-29

248

Membrane thickness is an important variable in membrane scaffolds: Influence of chitosan membrane structure on the behavior of cells  

PubMed Central

Cell and tissue responses to polymeric materials are orchestrated in part by the conformations of adsorbed plasma proteins. Thus, the chemical properties of a polymer membrane that govern protein adsorption behaviour can play an important role in determining the biological properties of tissue engineered scaffolds derived from that polymer. In this study, we explored the role of membrane thickness as a factor influencing cell adhesion and proliferation on chitosan membranes with and without covalently-attached glycosaminoglycans. Rat mesenchymal stem cells cultured on chitosan membranes of various thicknesses demonstrated significantly improved cell adhesion, spreading and proliferation as membrane thickness was increased. Hepatocytes displayed increased spreading on the substrate with increasing membrane thickness similar to MSCs. Increased thickness reduced the overall crystallinity of the membrane, and the data indicate that the improved cellular responses were likely due to enhanced adsorption of serum vitronectin, presumably due to reduced membrane crystallinity. These results demonstrate that membrane thickness is an important design variable that can be manipulated in chitosan-based scaffolds to achieve enhanced cell spreading, proliferation and function.

Uygun, Basak E.; Bou-Akl, Therese; Albanna, Mohammad

2009-01-01

249

Ca 2+-dependent membrane bound protein fraction from rabbit gastric mucosa contains a protein whose histidyl residue is phosphorylated 1 This research was supported in part by a grant from the University of Tsukuba Special Research Project on Metabolism. 1  

Microsoft Academic Search

We found an autophosphorylated protein with a molecular weight of 40 kDa (p40) in the crude annexin fraction of rabbit gastric mucosa, i.e., the materials released by EGTA from the membrane fraction obtained in the presence of Ca2+. This protein was enriched in chief cells in the gastric glands, and also found in the heart and the liver by Western

Tetsuro Urushidani; Taku Nagao

1997-01-01

250

Cell membrane structure of human giant-celled glioblastoma  

Microsoft Academic Search

A giant-cell glioblastoma was examined by electron microscopy and by the freeze-fracture technique. The cell membranes bordering the extensive extracellular space often showed complicated undulations and peripheral vacuoles as well as occasional microvilli or filopodia. The undulations were mainly composed of plasmalemmal vesicles as well as of large (400–800 nm in diameter) and small (30–50 nm in diameter) localized protrusions

Eiichi Tani; Masaru Nakano; Tetsuya Itagaki; Toyokazu Fukumori

1978-01-01

251

Modeling of a polymer electrolyte membrane fuel cell cathode  

NASA Astrophysics Data System (ADS)

Two models have been presented in this dissertation for an air cathode of a polymer electrolyte membrane fuel cell: a steady state impedance model and a steady state polarization model. Two impedance loops have been predicted on an air cathode by our steady state impedance model at a high steady state current density. The high frequency impedance loop is associated with the effective charge transfer resistance and double layer charging, and the low frequency impedance loop is associated with gas phase transport limitations. They are in agreement with the predictions by a similar impedance model in the literature. Several problems in the latter model have been addressed in our impedance model. By using the steady state polarization model presented in this dissertation, five parameters for an air cathode (the volume fraction of gas pores in the gas diffusion layer, the volume fraction of gas pores in the catalyst layer, the exchange current density for the O2 reduction reaction, the effective ionic conductivity in the catalyst layer, and the ratio of the effective diffusion coefficient of dissolved O2 in a spherical agglomerate particle to the square of the particle radius) have been determined by least square fitting of polarization curves of an air cathode. A decoupling method for calculating the model equations and the sensitivity equations has first been proposed to optimize the numerical efficiency in the estimation of parameters. The polarization curves of an air cathode have been obtained by correcting the experimental polarization curves of an air/H2 polymer electrolyte membrane fuel cell for the voltage drop across the membrane. The validity of the correction method for the voltage drop across the membrane has been justified. A more robust correction method has also been presented. The possible influence on the parameter estimation accuracy of the assumption that a H 2 anode was always at its equilibrium in our experiments has been discussed. The parameter estimates obtained in this dissertation indicate that ionic conduction in the catalyst layer and the gas phase transport in the gas diffusion layer are two processes influencing the polarization performance of an air cathode significantly. The goodness of our steady state polarization model has been demonstrated by comparing our model to a polarization model in the literature. An equation used in our polarization model to describe the O 2 reaction current density in the catalyst layer, which is capable of predicting a change of Tafel slope, has been noticed to be superior to a simple Tafel equation used in the literature.

Guo, Qingzhi

252

The influence of saponins on cell membrane cholesterol.  

PubMed

We studied the influence of structurally different saponins on the cholesterol content of cellular membranes. Therefore a cell culture model using ECV-304 urinary bladder carcinoma cells was developed. To measure the cholesterol content we used radiolabeled (3)H-cholesterol which is chemically and physiologically identical to natural cholesterol. The cells were pre-incubated with (3)H-cholesterol and after a medium change, they were treated with saponins to assess a saponin-induced cholesterol liberation from the cell membrane. In another experiment the cells were pre-incubated with saponins and after a medium change, they were treated with (3)H-cholesterol to assess a saponin-induced inhibition of cholesterol uptake into the cell membrane. Furthermore, the membrane toxicity of all applied saponins was analyzed using extracellular LDH quantification and the general cytotoxicity was analyzed using a colorimetric MTT-assay and DNA quantification. Our results revealed a correlation between membrane toxicity and general cytotoxicity. We also compared the results from the experiments on the saponin-induced cholesterol liberation as well as the saponin-induced inhibition of cholesterol uptake with the membrane toxicity. A significant reduction in the cell membrane cholesterol content was noted for those saponins who showed membrane toxicity (IC50 <60?M). These potent membrane toxic saponins either liberated (3)H-cholesterol from intact cell membranes or blocked the integration of supplemented (3)H-cholesterol into the cell membrane. Saponins with little influence on the cell membrane (IC50 >100?M) insignificantly altered the cell membrane cholesterol content. The results suggested that the general cytotoxicity of saponins is mainly dependent on their membrane toxicity and that the membrane toxicity might be caused by the loss of cholesterol from the cell membrane. We also analyzed the influence of a significantly membrane toxic saponin on the cholesterol content of intracellular membranes such as those of endosomes and lysosomes. In these experiments ECV-304 cells were either incubated with (3)H-cholesterol or with (3)H-cholesterol and 5?M saponin. After isolation of the endosomes/lysosomes their (3)H-cholesterol content was measured. A significant influence of the saponins on the cholesterol content of endosomal/lysosomal membranes was not detected. PMID:24084294

Böttger, Stefan; Melzig, Matthias F

2013-09-14

253

Kinetics and mechanism of cell membrane electrofusion.  

PubMed Central

A new quantitative approach to study cell membrane electrofusion has been developed. Erythrocyte ghosts were brought into close contact using dielectrophoresis and then treated with one square or even exponentially decaying fusogenic pulse. Individual fusion events were followed by lateral diffusion of the fluorescent lipid analogue 1,1'-dihexadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Dil) from originally labeled to unlabeled adjacent ghosts. It was found that ghost fusion can be described as a first-order rate process with corresponding rate constants; a true fusion rate constant, k(f), for the square waveform pulse and an effective fusion rate constant, k(ef), for the exponential pulse. Compared with the fusion yield, the fusion rate constants are more fundamental characteristics of the fusion process and have implications for its mechanisms. Values of k(f) for rabbit and human erythrocyte ghosts were obtained at different electric field strength and temperatures. Arrhenius k(f) plots revealed that the activation energy of ghost electrofusion is in the range of 6-10 kT. Measurements were also made with the rabbit erythrocyte ghosts exposed to 42 degrees C for 10 min (to disrupt the spectrin network) or 0.1-1.0 mM uranyl acetate (to stabilize the bilayer lipid matrix of membranes). A correlation between the dependence of the fusion and previously published pore-formation rate constants for all experimental conditions suggests that the cell membrane electrofusion process involve pores formed during reversible electrical breakdown. A statistical analysis of fusion products (a) further supports the idea that electrofusion is a stochastic process and (b) shows that the probability of ghost electrofusion is independent of the presence of Dil as a label as well as the number of fused ghosts.

Abidor, I G; Sowers, A E

1992-01-01

254

Exocytosis and Endocytosis in Neuroendocrine Cells: Inseparable Membranes!  

PubMed Central

Although much has been learned concerning the mechanisms of secretory vesicle formation and fusion at donor and acceptor membrane compartments, relatively little attention has been paid toward understanding how cells maintain a homeostatic membrane balance through vesicular trafficking. In neurons and neuroendocrine cells, release of neurotransmitters, neuropeptides, and hormones occurs through calcium-regulated exocytosis at the plasma membrane. To allow recycling of secretory vesicle components and to preserve organelles integrity, cells must initiate and regulate compensatory membrane uptake. This review relates the fate of secretory granule membranes after full fusion exocytosis in neuroendocrine cells. In particular, we focus on the potential role of lipids in preserving and sorting secretory granule membranes after exocytosis and we discuss the potential mechanisms of membrane retrieval.

Houy, Sebastien; Croise, Pauline; Gubar, Olga; Chasserot-Golaz, Sylvette; Tryoen-Toth, Petra; Bailly, Yannick; Ory, Stephane; Bader, Marie-France; Gasman, Stephane

2013-01-01

255

Formation of p -coumaric acid and o -coumaric acid from l-phenylalanine by microsomal membrane fractions from potato: Evidence of membrane-bound enzyme complexes  

Microsoft Academic Search

The enzymes described here are the membrane-bound l-phenylalanine ammonia-lyase and cinnamate hydroxylase. Microsomes prepared from tubers of Solanum tuberosum L. are capable of converting l-phenylalanine into both o- and p-coumaric acid. Three microsomal fractions obtained by density gradient centrifugation were characterized by their equilibrium densities. Within various subfractions we found different patterns of distribution of the two enzymes, probably because

Ursula Czichi; Helmut Kindl

1975-01-01

256

Nano thermo-hydrodynamics method for investigating cell membrane fluidity  

Microsoft Academic Search

As a barrier to compartmentalize cells, membranes form the interface between a cell and its surroundings. The essential function\\u000a of a membrane is to maintain a relatively stable environment in the cell, exchange substances selectively and transfer energy\\u000a and information continually from the outside. It is intriguing that above the phase transition temperature, the membrane lipid\\u000a molecule will have three

Yang Yang; Jing Liu

2008-01-01

257

Apparatus for exposing cell membranes to rapid temperature transients  

Microsoft Academic Search

We seek to determine whether cell membranes contain sensors that trigger a downstream response to temperature excursions. To do this, we have developed a novel apparatus for exposing a cell membrane to an extremely rapid temperature excursion in the nanosecond range. Cells are plated on a gold surface that is back-heated by a pulsed laser and cooled by conduction of

B. Steel; M. M. Bilek; C. G. dos Remedios; D. R. McKenzie

2004-01-01

258

Integrated system of fuel cell for polymer electrolyte membrane  

Microsoft Academic Search

The polymer electrolyte membrane fuel cell (PEMFC) is an ionic conducting electrolyte polymer membrane. The factors which influence the performance of PEMFC include relative humidity, reaction temperature, gas inlet temperature, gas inlet pressure, and hydrogen and air flow rate. The safety control methodology strongly depends on the fuel cell operation voltage and current. In order to run the fuel cell

Jenn-Kun Kuo; Yuan-Yao Hsu; Shiuh Ming Chang

2011-01-01

259

Fractionation of Tetrahymena ciliary membranes with triton X-114 and the identification of a ciliary membrane ATPase  

PubMed Central

Cilia were isolated from Tetrahymena thermophila, extracted with Triton X-114, and the detergent-soluble membrane + matrix proteins separated into Triton X-114 aqueous and detergent phases. The aqueous phase polypeptides include a high molecular mass polypeptide previously identified as a membrane dynein, detergent-soluble alpha and beta tubulins, and numerous polypeptides distinct from those found in axonemes. Integral membrane proteins partition into the detergent phase and include two major polypeptides of 58 and 50 kD, a 49-kD polypeptide, and 5 polypeptides in relatively minor amounts. The major detergent phase polypeptides are PAS-positive and are phosphorylated in vivo. A membrane-associated ATPase, distinct from the dynein-like protein, partitions into the Triton X-114 detergent phase and contains nearly 20% of the total ciliary ATPase activity. The ATPase requires Mg++ or Ca++ and is not inhibited by ouabain or vanadate. This procedure provides a gentle and rapid technique to separate integral membrane proteins from those that may be peripherally associated with the matrix or membrane.

1988-01-01

260

Enhancement of natural killer cell activity by Nocardia opaca fractions.  

PubMed

Three molecules derived from Nocardia opaca bacteria, NDCM, NWSMP, and PG, have been shown to express immunomodulating properties. The present study was aimed at assessing the effects of these derivatives on natural killer (NK) activity. Two experimental protocols were adopted, consisting of incubating whole or Percoll fractionated NK cells in vitro with those substances, and the other in which the derivatives were administered in vivo to mice and the activity assessed later. Incubation of spleen cells in vitro with NWSMP or its precursor NDCM promoted NK activity. This effect could be observed after only 2 h of incubation and continued until day 2. Percoll fractions 1-3, which contain most of the NK activity, were enhanced to a similar extent. Band 4, which is usually devoid of such activity, remained unresponsive even after contact with the N. opaca derivatives. PG was practically ineffective upon all the subsets. The results of experiments in vivo correlated with those obtained in vitro in that NWSMP and NDCM, but not PG, promoted NK activity. Bands 1-3 were similarly enhanced, the effect was observed after short treatment times, and could be partially cancelled by the concomitant administration of anti-interferon antibodies (anti-IFN Ab). All these findings suggest that the promoting effects of N. opaca derivatives are mediated through alpha/beta IFN. In contrast to the results observed on spleen NK cells, NK cells from the peritoneum displayed susceptibility mainly to PG, and much less to NWSMP or NDCM. The administration of PG to mice in vivo had a particularly marked promoting effect upon the cytotoxic activity of peritoneal cells. One logical explanation for the difference observed between PG and NWSMP or NDCM may be related to the specific IFN inducing properties of these compounds as well as to the different responsiveness of the NK cells present in the spleen and peritoneal cavity. PMID:2466328

Barot-Ciorbaru, R; Linna, T J; Patel, M R; Altman, J; Carnaud, C

1989-02-01

261

How to measure slow diffusion in yeast cell membranes  

NASA Astrophysics Data System (ADS)

Here we present two complementary methods for accurate diffusion measurements in yeast cell membranes. Fluorescence spreading after photobleaching analyzes the blurring of an initially sharp border between bleached and unbleached parts of the membrane. Two-focus scanning fluorescence correlation spectroscopy requires only a low concentration of labeled fluorophores and allows for very long measurement times due to correction for instabilities necessary to probe the slow diffusion in yeast plasma membranes. We apply these techniques to study the dynamics of different transmembrane proteins in the plasma membrane of the yeast Saccharomyces cerevisiae. The differences in the diffusion coefficients support the idea of co-existing membrane microdomains in the yeast plasma membrane.

Ries, Jonas; Klose, Christian; Walch-Solimena, Christiane; Schwille, Petra

2008-05-01

262

Membrane dynamics of the water transport protein aquaporin-1 in intact human red cells.  

PubMed Central

Aquaporin-1 (AQP1) is the prototype integral membrane protein water channel. Although the three-dimensional structure and water transport function of the molecule have been described, the physical interactions between AQP1 and other membrane components have not been characterized. Using fluorescein isothiocyanate-anti-Co3 (FITC-anti-Co3), a reagent specific for an extracellular epitope on AQP1, the fluorescence photobleaching recovery (FPR) and fluorescence imaged microdeformation (FIMD) techniques were performed on intact human red cells. By FPR, the fractional mobility of fluorescently labeled AQP1 (F-alphaAQP1) in the undeformed red cell membrane is 66 +/- 10% and the average lateral diffusion coefficient is (3.1 +/- 0.5) x 10(-11) cm2/s. F-alphaAQP1 fractional mobility is not significantly affected by antibody-induced immobilization of the major integral proteins band 3 or glycophorin A, indicating that AQP1 does not exist as a complex with these proteins. FIMD uses pipette aspiration of individual red cells to create a constant but reversible skeletal density gradient. F-alphaAQP1 distribution, like that of lipid-anchored proteins, is not at equilibrium after microdeformation. Over time, approximately 50% of the aspirated F-alphaAQP1 molecules migrate toward the membrane portion that had been maximally dilated, the aspirated cap. Based on the kinetics of migration, the F-alphaAQP1 lateral diffusion coefficient in the membrane projection is estimated to be 6 x 10(-10) cm2/s. These results suggest that AQP1 lateral mobility is regulated in the unperturbed membrane by passive steric hindrance imposed by the spectrin-based membrane skeleton and/or by skeleton-linked membrane components, and that release of these constraints by dilatation of the skeleton allows AQP1 to diffuse much more rapidly in the plane of the membrane.

Cho, M R; Knowles, D W; Smith, B L; Moulds, J J; Agre, P; Mohandas, N; Golan, D E

1999-01-01

263

The plasma membrane lipid composition affects fusion between cells and model membranes.  

PubMed

Investigations were carried out on the effect of plasma membrane lipid modifications on the fusogenic capacity of control and ras-transformed fibroblasts. The plasma membrane lipid composition was modified by treatment of cells with exogenous phospholipases C and D, sphingomyelinase and cyclodextrin. The used enzymes hydrolyzed definite membrane lipids thus inducing specific modifications of the lipid composition while cyclodextrin treatment reduced significantly the level of cholesterol. The cells with modified membranes were used for assessment of their fusogenic capacity with model membranes with a constant lipid composition. Treatment with phospholipases C and D stimulated the fusogenic potential of both cell lines whereas the specific reduction of either sphingomyelin or cholesterol induced the opposite effect. The results showed that all modifications of the plasma membrane lipid composition affected the fusogenic capacity irrespective of the initial differences in the membrane lipid composition of the two cell lines. These results support the notion that the lipid composition plays a significant role in the processes of membrane-membrane fusion. This role could be either direct or through modulation of the activity of specific proteins which regulate membrane fusion. PMID:17098217

Pankov, Roumen; Markovska, Tania; Antonov, Peter; Ivanova, Lidia; Momchilova, Albena

2006-11-13

264

Preparation of basal cell membranes for scanning probe microscopy.  

PubMed

Scanning probe microscopy has the potential for investigating membranes in a physiological environment. We prepared with a lysis-squirting protocol basal cell membranes, that are suitable for scanning probe microscopy. Investigations using atomic force microscopy under liquid revealed cellular filaments which correlated perfectly with fluorescently stained actin filaments. Globular structures with a diameter as little as 10 nm could be resolved by stripping cytoplasmic components from the membranes. Therefore, cytoplasmic sides of supported basal cell membranes prove useful to gain high resolution with scanning probe microscopy in studies of plasma membrane associated structures and processes under buffer solution. PMID:9781674

Ziegler, U; Vinckier, A; Kernen, P; Zeisel, D; Biber, J; Semenza, G; Murer, H; Groscurth, P

1998-10-01

265

Membrane fouling in microfiltration used for cell harvesting  

NASA Astrophysics Data System (ADS)

In the present study the membrane fouling in microfiltration used for cell harvesting in a deadend system has been investigated. Experimental results were analysed in terms of existing membrane filtration models and membrane resistances. The cake filtration model (CFM) and standard blocking model (SBM) have been considered in this study. Various membrane resistances were determined at different processing time, feed concentration and stirring speed. Resistances to permeation in this system include filter medium, pore blocking, adsorption, cake layer and concentration polarization.

Kaghazchi, Tahereh; Zokaee, Farzin; Zare, Abbas

2001-03-01

266

Silver--zinc electric storage cells. [semipermeable membrane as separator  

Microsoft Academic Search

A rechargeable silver--zinc electric storage cell is described which comprises a casing enclosing a silver electrode and a zinc electrode, a separator comprising an imperforate semi-permeable membrane disposed between the electrodes, and an electrolyte. The membrane is sealed to the casing so that the only ion path between the electrodes is through the membrane. The imperforate semi-permeable membrane comprises a

H. T. Mote; L. Hajdu; B. Ronay

1974-01-01

267

Microspectrofluorometry and polarization microscopy of membrane dynamics in living cells  

NASA Astrophysics Data System (ADS)

Membrane dynamics of human glioblastoma cells were investigated using the intercalating fluorescence marker 6-dodecanoyl-2-dimethylamino naphthalene (laurdan). In particular its generalized polarization (GP), which describes a spectral shift depending on the phase of membrane lipids, was used as a measure of membrane stiffness, whereas its fluorescence lifetime ? and its rotational diffusion time tr were used to characterize membrane fluidity. Upon excitation with linearly polarized pulsed laser light the parallel and perpendicular components of fluorescence from the sample were measured simultaneously using an imaging device with polarization sensitivity. So far, membrane dynamics depended on temperature and cell age as well as the on intracellular amount of cholesterol. In addition, the plasma membrane (assessed by illumination with an evanescent electromagnetic wave) appeared to be stiffer than intracellular membranes (assessed by epiillumination of the cells).

Wagner, Michael; Weber, Petra; Schneckenburger, Herbert

2006-05-01

268

Isolation and Characterization of Low Density Detergent-Insoluble Membrane (LD-DIM) Fraction from Sea Urchin Sperm  

Microsoft Academic Search

The low density detergent-insoluble membrane (LD-DIM) fraction was obtained by a sucrose-density gradient centrifugation from sperm of three sea urchin species, Hemicentrotus pulcherrimus, Strongylocentrotus purpuratus, and Anthocidaris crassispina. These LD-DIM preparations were characterized by enriched glycosphingolipids (GSL) including gangliosides and sulfatide (SLF), having more than 50% of the total amount of GSL present in these sperm. Interestingly, a minor component

Kaoru Ohta; Chihiro Sato; Tsukasa Matsuda; Masaru Toriyama; William J. Lennarz; Ken Kitajima

1999-01-01

269

Effect of NaCl on lipid content of plasma membranes isolated from roots and cell suspension cultures of the dicot halophyte Kosteletzkya virginica (L.) Presl  

Microsoft Academic Search

Lipid concent was examined in plasma membrane fractions isolated by discontinuous sucrose density-gradient centrifugation from both salinized and unsalinized roots and cell suspension cultures of Kosteletzkva virginica (L.) Presl., seashore mallow, a halophytic dicot. The distribution of marker enzymes along the gradient indicated that plasma membranes of roots and cell cultures accumulated primarily at the 34%\\/45% interface. Total sterol and

K. C. Blits; J. L. Gallagher

1990-01-01

270

Fluorescence and polarization imaging of membrane dynamics in living cells  

NASA Astrophysics Data System (ADS)

Methods of wide field fluorescence microscopy for measuring membrane dynamics in living cells are described. These methods are based on laser pulse excitation of the membrane marker 6-dodecanoyl-2-dimethylamino naphthalene (laurdan) whose emission spectra, fluorescence decay kinetics and anisotropies are sensitive to membrane stiffness and fluidity. Plasma membranes are selected by illumination with an evanescent electromagnetic field and distinguished from intracellular membranes assessed by whole cell illumination. While fluorescence spectra of laurdan appeared red-shifted with decreasing membrane stiffness, fluorescence anisotropy and rotational relaxation times were reduced with increasing membrane fluidity. Membrane stiffness was found to increase with decreasing temperature and increasing amounts of cholesterol. In addition, membrane stiffness of the plasma membrane was always higher than that of intracellular membranes. These effects may have some influence on pathogenesis of certain diseases, uptake of pharmaceutical agents or cell aging. Present experiments are limited to fluorescence microscopy with total internal reflection (TIR) or epi-illumination, but corresponding methods can also be used for screening of larger cell collectives, e.g. in microtiter plates.

Wagner, M.; Weber, P.; Bruns, T.; Strauss, W. S. L.; Schneckenburger, H.

2009-02-01

271

Exo70 generates membrane curvature for morphogenesis and cell migration.  

PubMed

Dynamic shape changes of the plasma membrane are fundamental to many processes, ranging from morphogenesis and cell migration to phagocytosis and viral propagation. Here, we demonstrate that Exo70, a component of the exocyst complex, induces tubular membrane invaginations toward the lumen of synthetic vesicles in vitro and generates protrusions on the surface of cells. Biochemical analyses using Exo70 mutants and independent molecular dynamics simulations based on Exo70 structure demonstrate that Exo70 generates negative membrane curvature through an oligomerization-based mechanism. In cells, the membrane-deformation function of Exo70 is required for protrusion formation and directional cell migration. Exo70 thus represents a membrane-bending protein that may couple actin dynamics and plasma membrane remodeling for morphogenesis. PMID:23948253

Zhao, Yuting; Liu, Jianglan; Yang, Changsong; Capraro, Benjamin R; Baumgart, Tobias; Bradley, Ryan P; Ramakrishnan, N; Xu, Xiaowei; Radhakrishnan, Ravi; Svitkina, Tatyana; Guo, Wei

2013-08-12

272

Process Engineering and Economic Evaluations of Diaphragm and Membrane Chlorine Cell Technologies. Final Report.  

National Technical Information Service (NTIS)

The chlor-alkali manufacturing technologies of (1), diaphragm cells (2), current technology membrane cells (3), catalytic cathode membrane cells (4), oxygen-cathode membrane cells and to a lesser extent several other related emerging processes are studied...

1980-01-01

273

Allogeneic Stimulation of Cytotoxic T Cells by Supported Planar Membranes  

NASA Astrophysics Data System (ADS)

Phospholipid vesicles containing the transmembrane protein H-2Kk spontaneously fuse to form planar membranes when incubated on treated glass surfaces. Pattern photobleaching of fluorescent lipid probes indicates that these planar membranes are continuous and that the lipids are as mobile as they are in conventional fluid bilayers or monolayers. H-2Kk molecules in these planar membranes are immobile. These membranes stimulate cytotoxic T lymphocytes when cultured with immune spleen cells. The response to H-2Kk in planar membranes is greatly enhanced by the addition of supernatant from concanavalin A-stimulated spleen cells, indicating that relatively little antigen processing or presentation by accessory cells occurs. Cytotoxic T cells induced by purified alloantigen are found to be as susceptible to antibody blockade as are effectors from conventional mixed lymphocyte culture, where the antibody is directed against a T-cell surface antigen reputed to strengthen target cell adhesion through an interaction independent of major histocompatibility antigens.

Brian, Adrienne A.; McConnell, Harden M.

1984-10-01

274

The isolation and characterization of right-side-out plasma membrane vesicles from barley aleurone cells.  

PubMed

Examination of organelle- and membrane-specific processes such as signal transduction necessitates the use of plasma membrane vesicles with cytoplasmic side-in orientation. We are interested in the structural identity and subcellular localization of in vivo [32P]phosphoric acid ([32Pi])-labeled phosphoinositides, including the recently discovered phosphatidyl-scyllo-inositol, for signal transduction studies. In the first part of this investigation, plasma membrane vesicles from barley aleurone cells were isolated employing the aqueous polymer (Dextran and polyethylene glycol) two-phase partition method. The membrane vesicles that partitioned into the upper and lower phases of the aqueous polymer two-phase system were characterized and the purity of the vesicles ascertained by assaying for two marker enzymes, K+-stimulated, Mg2+-dependent adenosine triphosphatase (EC 3.6.1.3, ATPase), localized in the plasma membranes, and cytochrome c oxidase, localized in the mitochondria. Inhibitors for ATPases such as azide, molybdate, and vanadate were used to distinguish between plasma membrane-associated and intracellular membrane-associated ATPases. These inhibitor studies suggest that the plasma membrane preparation contained about 7% of intracellular membrane vesicles and the intracellular membrane fraction contained about 6% of plasma membrane vesicles. Orientation of the plasma membrane vesicles was ascertained by measuring the latent ATPase activity. These latency studies suggest that about 95% of the plasma membrane vesicles were of cytoplasmic side-in orientation. In the second part of this investigation, intracellular distribution and in vivo [32Pi] labeling of phosphoinositides in the plasma membranes and intracellular membranes were investigated. Preferential accumulation of [32Pi]-labeled phosphatidyl-myo-inositol monophosphate (myo-PIP) and phosphatidyl-myo-inositol bisphosphate (myo-PIP2) was observed in the plasma membrane. However, scyllo-phosphatidylinositol (scyllo-PI) was detected in both the plasma membrane and the intracellular membranes. The cellular concentration of myo-phosphoinositides was determined, and, after 24 h of labeling with [32Pi], the ratio of radiolabel in myo-PI, PIP, and PIP2 paralleled the relative concentrations in aleurone cells. PMID:10188600

Robbins, K M; Bhuvarahamurthy, N; Pliska-Matyshak, G; Murthy, P P

1999-01-01

275

Preparation of a human lung purified plasma membrane fraction: Confirmation by enzyme markers, electron microscopy, and histamine H 1 receptor binding  

Microsoft Academic Search

Summary A simple and rapid method of isolating plasma membranes from human peripheral lung tissue is described. The method involves homogenization of tissue in 0.25m sucrose-buffered medium followed by differential and sucrose density gradient centrifugation. Enzymatic and morphological characterization of the plasma membrane fraction revealed minimal contamination by nonplasma membrane fragments. The isolated plasma membranes showed an 18-fold purification of

Thomas B. Casale; Marc Friedman; Nereida Parada; Julie Plekes; Michael Kaliner

1984-01-01

276

Sedimentation field flow fractionation purification of immature neural cells from a human tumor neuroblastoma cell line.  

PubMed

The use of stem cells for therapeutic applications is now an important objective for the future. Stem cell preparation is difficult and time-consuming depending on the origin of cells. Sedimentation field flow fractionation (SdFFF) is an effective tool for cell separation, respecting integrity and viability. We used the human neuroblastic SH-SY5Y clone of the SK-N-SH cell line as a source of immature neural cells. Our results demonstrated that by using SdFFF cell sorter under strictly defined conditions, and immunological cell characterization, we are now able to provide, in less than 15 min, a sterile, viable, usable and purified immature neural cell fraction without inducting cell differentiation. PMID:12798175

Lautrette, C; Cardot, P J P; Vermot-Desroches, C; Wijdenes, J; Jauberteau, M O; Battu, S

2003-07-01

277

Molecular Forces Governing Non-Electrolyte Permeation through Cell Membranes  

Microsoft Academic Search

The relations between the chemical structure of non-electrolytes and their ability to permeate cell membranes are analysed at the level of molecular forces, using the measurements of reflexion coefficients in gall-bladder epithelial cells tabulated in the preceding paper. Stronger solute: water forces and weaker solute: membrane forces are associated with lower permeating power. The portions of the membrane controlling non-electrolyte

Jared M. Diamond; Ernest M. Wright

1969-01-01

278

Organic-Inorganic Membranes for Fuel Cell Application  

NASA Astrophysics Data System (ADS)

Organic-inorganic membranes are worldwide under investigation with the purpose of achieving reduced methanol crossover for direct methanol fuel cell (DMFC) and increasing the proton conductivity at temperatures higher than 100°C in hydrogen fuel cells. The advantages and disadvantages of these membranes are discussed here with membrane examples containing aerosol, layered silicates, and modified silica as passive fillers as well as zirconium phosphate and heteropolyacids as conductive fillers.

Nunes, Suzana Pereira

279

An ESR study of pathologic red blood cell membranes (RBCM).  

PubMed

A comparative study of red blood cell membranes from normal subjects and beta-thalassemia and sickle cell anemia patients was performed by spin labeling at the lipidic and protein phase. The results show that the quantity of bound spin label is the same for sickle, thalassemic, and normal membranes. The data from 5-doxyl stearic acid suggest an increase in fluidity for the thalassemic membrane. PMID:2175007

Perussi, J R; Costa, F F; Baffa, O; Zago, M A; Tinto, M H; Tabak, M

1990-10-01

280

Surface functionalization of gold nanoparticles with red blood cell membranes.  

PubMed

Gold nanoparticles are enclosed in cellular membranes derived from natural red blood cells (RBCs) by a top-down approach. The gold nanoparticles exhibit a complete membrane surface layer and biological characteristics of the source cells. The combination of inorganic gold nanoparticles with biological membranes is a compelling way to develop biomimetic gold nanostructures for future applications, such as those requiring evasion of the immune system. PMID:23712782

Gao, Weiwei; Hu, Che-Ming J; Fang, Ronnie H; Luk, Brian T; Su, Jing; Zhang, Liangfang

2013-05-27

281

Cardiotoxicity of Kenyan green mamba (Dendroaspis angusticeps) venom and its fractionated components in primary cultures of rat myocardial cells.  

PubMed

The cardiotoxic actions of Kenyan green mamba (Dendroaspis angusticeps) venom have been investigated using primary myocardial cell cultures isolated from neonatal rat hearts. The cardiotoxic actions of the whole venom and its fractionated components were evaluated on the basis of leakage of lactate dehydrogenase (LDH), changes in morphology, cell membrane lysis, decreases in viability and inhibition of spontaneous beating activity. The whole venom caused time- and concentration-dependent arrest of myocardial contraction, leakage of LDH, extensive disruption of cell monolayer, and decreases in viability. The venom was separated into 6 (DaI to DaVI) fractions by gel permeation chromatography on Sephadex G-50. Spontaneous beating activity was abolished by DaI to DaVI at high concentrations, while at lower doses they induced progressive depression of beating frequency after a 3-h treatment period. DaI to DaIV caused significant leakage of LDH, morphological damage, and decreases in viability after a 6-h incubation period. The most cardiotoxic fraction (DaIV), which also contains about 54% of the total protein of the whole venom, was fractionated into 18 polypeptides (Da1 to Da18) by ion exchange chromatography on Bio-Rex 70. On the basis of their ability to abolish myocardial contractility, release LDH, alter cellular structure, lyse cell membranes and reduce viability, the 18 fractions have been divided into 4 arbitrary subgroups of cytotoxins: cardiotoxins, Da1 to Da3; cardiotoxin-like polypeptides, Da4 to Da12, Da14; less active membrane lytic polypeptides, Da13, Da15 to Da17; and membrane lytic polypeptide, Da18. Marked synergistic cell membrane lysis occurred in myocardial cell cultures treated simultaneously with 2 cardiotoxin-like polypeptides, Da7 and Da11. It is suggested that the additive and synergistic cardiotoxic effects of high molecular weight cytotoxic proteins (DaI to DaIII), very low molecular weight cholinomimetic substances (DaV to DaVI) and the 4 subgroups of cardiotoxins may directly contribute to the pronounced cardiovascular problems observed in victims of green mamba bites. PMID:3188032

Mbugua, P M; Welder, A A; Acosta, D

1988-11-14

282

Effect of EMP fields on cell membrane potentials  

SciTech Connect

A simple model is presented for cell membrane potentials induced during exposure to electromagnetic pulse (EMP). Using calculated values of internal electric field strength induced during EMP exposure, the model predicts that cell membrane potentials of about 100 mV may be induced for time frames on the order of 10 ns. Possible biological effects of these potentials including electroporation area discussed.

Gailey, P.C.; Easterly, C.E.

1993-06-01

283

Patterns of Nonelectrolyte Permeability in Human Red Blood Cell Membrane  

Microsoft Academic Search

The permeability of human red cell membrane to 90 different molecules has been measured. These solutes cover a wide spectrum of non- electrolytes with varying chemical structure, chain length, lipid solubility, chemical reactive group, ability to form hydrogen bonds, and other properties. In general, the present study suggests that the permeability of red cell membrane to a large solute is

P. Naccache; R. I. SHA' AFI

1973-01-01

284

Cell membrane receptors for cardiac glycosides in the heart  

Microsoft Academic Search

Summary Cell membranes contain special binding proteins for hormones and drugs. These binding sites (“receptors”) located on the outside surface are linked to or are part of an enzyme facing the inner side of the membrane and are transducing and probably amplifying the information carried by the pharmacological agent to the cell.

E. Erdmann

1977-01-01

285

Cell evolution and the problem of membrane topology  

Microsoft Academic Search

Cells somehow evolved from primordial chemistry and their emergence depended on the co-evolution of the cytoplasm, a genetic system and the cell membrane. It is widely believed that the cytoplasm evolved inside a primordial lipid vesicle, but here I argue that the earliest cytoplasm could have co-evolved to high complexity outside a vesicle on the membrane surface. An invagination of

Gareth Griffiths

2007-01-01

286

THE ENZYMATIC IODINATION OF THE RED CELL MEMBRANE  

Microsoft Academic Search

An enzymatic iodination procedure utilizing lactoperoxidase (LPO), radioactive iodide, and hydrogen peroxide generated by a glucose oxidase-glucose system has been described and utilized for a study of the red cell membrane . 97 % of the incorporated isotope is in the erythrocyte ghost and 3 % is associated with hemoglobin . No significant labeling of the red cell membrane occurs

ANN L. HUBBARD; ZANVIL A. COHN

1972-01-01

287

Effect of EMP fields on cell membrane potentials  

Microsoft Academic Search

A simple model is presented for cell membrane potentials induced during exposure to elecrromagnetic Duke EMPL Usinp calculated values of intemal electric field strength induced durinn EMP mosure. the model medias that cell membrane potentials of about 100 mV may be induced for rime frames on the order of 10 ns. Possible bioloaical effects of these Dotentiah includinn electrouoration are

Paul C. Gailey; Clay E. Easterly

1993-01-01

288

Mathematical modeling of proton exchange membrane fuel cells  

Microsoft Academic Search

A one-dimensional non-isothermal model of a proton exchange membrane (PEM) fuel cell has been developed to investigate the effect of various design and operating conditions on the cell performance, thermal response and water management, and to understand the underlying mechanism. The model includes variable membrane hydration, ternary gas mixtures for both reactant streams, phase change of water in the electrodes

Andrew Rowe; Xianguo Li

2001-01-01

289

Membrane electrode assemblies for unitised regenerative polymer electrolyte fuel cells  

Microsoft Academic Search

Membrane electrode assemblies for regenerative polymer electrolyte fuel cells were made by hot pressing and sputtering. The different MEAs are examined in fuel cell and water electrolysis mode at different pressure and temperature conditions. Polarisation curves and ac impedance spectra are used to investigate the influence of the changes in coating technique. The hydrogen gas permeation through the membrane is

U. Wittstadt; E. Wagner; T. Jungmann

2005-01-01

290

Chloride conductance of the Amphiuma red cell membrane  

Microsoft Academic Search

Summary Like most other red cells, the giant erythrocytes ofAmphiuma means possess a system for rapid exchange of chloride across the membrane. Also, there are indications that the net transport of chloride in these cells is slow. The size ofAmphiuma erythrocytes allows direct measurements of membrane potential with microelectrodes. The present work exploits the possibility that such measurements can be

U. V. Lassen; L. Pape; B. Vestergaard-Bogind

1978-01-01

291

The functional activity of cell membranes in multiple sclerosis  

Microsoft Academic Search

The approach of the present study was determined by the marked interest in recent years in the problems of the pathogenesis of a number of diseases from the perspectives of the pathological chemistry of cell membranes. Studies devoted to the investigation of the structure and function of cell membranes in progressive muscular dystrophies [2, 15], disturbances in cerebral circulation [8,

P. V. Predtechenskaya; A. P. Ierusalimskii

1993-01-01

292

Size-fractionation and characterization of refuse landfill leachate by sequential filtration using membranes with varied porosity.  

PubMed

Fresh leachate and effluents samples were collected from the holding tank, anaerobic, anoxic, and aerobic lagoons at Shanghai Laogang Refuse Landfill, the largest landfill in China with a placement scale of 9000 t refuse per day. To characterize the difference in leachate along the treatment processes, especially the information about size distribution of colloids in those leachate, the organic matters were size-fractioned into suspended particles (SP, >1.2 microm), coarse colloids (CC, 1.2-0.45 microm), fine colloids (FC, 0.45 microm to 1 kDa MW, 1 Da=1/16 O atomic mass unit), and dissolved organic matters (DM, <1 kDa MW) using micro-filtration and ultra-filtration membranes in order. The parameters, such as COD (chemical oxygen demand), TOC (total organic carbon), TS (total solid), pH, TP (total phosphate), TN (total nitrogen), FS (fixed solid), NH4+, IC (inorganic carbon), TC (total carbon), color, turbidity and conductivity in the filtrates resulting from sequential filtration of leachate, were then determined, and quantitative relationships between these parameters and the membrane molecular sizes used were established. Typically, the total removal of COD, NH4+, conductivity and P were found to be 75%, 75%, 42% and 85%, respectively, after the biological treatment processes used at Laogang Refuse Landfill. Dissolved fractions were predominant in fresh leachate and in effluents from treatment processes in terms of TOC with a content of over 47%. The molecular weight (MW) percentage distribution in leachate varied as the leachate was treated in the biological treatment stages. The percentages of TOC of fine colloid fractions increased from 6% to 38% while those of dissolved fractions decreased from 78% to 47%. TN in leachate also predominated in the dissolved fraction, occupying over 58%, while those TP in leachate were combined with the SS and CC fractions. The ratios of ortho-phosphate/TP and NH4+/TN in leachate and effluents were over 50% and 80%, respectively. PMID:17296264

Ziyang, Lou; Youcai, Zhao

2007-01-13

293

Novel Unitized Regenerative Proton Exchange Membrane Fuel Cell.  

National Technical Information Service (NTIS)

A difficulty encountered in designing a unitized regenerative proton exchange membrane (PEM) fuel cell lies in the incompatibility of electrode structures and electrocatalyst materials optimized for either of the two functions (fuel cell or electrolyzer) ...

O. J. Murphy A. J. Cisar A. Gonzalez-martin C. E. Salinas S. F. Simpson

1995-01-01

294

Band 3 and glycophorin are progressively aggregated in density-fractionated sickle and normal red blood cells. Evidence from rotational and lateral mobility studies.  

PubMed Central

Band 3 aggregation in the plane of the red blood cell (RBC) membrane is postulated to be important in the pathophysiology of hemolysis of dense sickle and normal RBCs. We used the fluorescence photobleaching recovery and polarized fluorescence depletion techniques to measure the lateral and rotational mobility of band 3, glycophorins, and phospholipid analogues in membranes of density-separated intact RBCs from seven patients with sickle cell disease and eight normal controls. The fractions of laterally mobile band 3 and glycophorin decreased progressively as sickle RBC density increased. Normal RBCs also showed a progressive decrease in band 3 fractional mobility with increasing buoyant density. Rapidly rotating, slowly rotating, and rotationally immobile forms of band 3 were observed in both sickle and normal RBC membranes. The fraction of rapidly rotating band 3 progressively decreased and the fraction of rotationally immobile band 3 progressively increased with increasing sickle RBC density. Changes in the fraction of rotationally immobile band 3 were not reversible upon hypotonic swelling of dense sickle RBCs, and normal RBCs osmotically shrunken in sucrose buffers failed to manifest band 3 immobilization at median cell hemoglobin concentration values characteristic of dense sickle RBCs. We conclude that dense sickle and normal RBCs acquire irreversible membrane abnormalities that cause transmembrane protein immobilization and band 3 aggregation. Band 3 aggregates could serve as cell surface sites of autologous antibody binding and thereby lead to removal of dense sickle and normal (senescent) RBCs from the circulation.

Corbett, J D; Golan, D E

1993-01-01

295

Obtención de una fracción crotálida con actividad hemoaglutinante y evaluación in vivo e in vitro del probable daño a tejidos Purification of a hemagglutinant fraction from crotalid venom: in vitro and in vivo evaluation of cell damage  

Microsoft Academic Search

Some crotalid venoms have a hemagglutinant fraction with affinity to cell receptors. This can be used as an antiviral agent that blocks adsorption of the virus in the cell membrane. One of these fractions was isolated and its innocuity compared to the effect of complete venoms. A. piscivorus, A. contortix and C. scutulatus venoms were tested, with the first exhibiting

Arcelia Alvarado Islas; Octavio de Paz Villafána; Yolanda León Campos; Álvaro Aguilar Setién

296

Cell membrane thermal gradients induced by electromagnetic fields  

NASA Astrophysics Data System (ADS)

While electromagnetic fields induce structural changes in cell membranes, particularly electroporation, much remains to be understood about membrane level temperature gradients. For instance, microwaves induce cell membrane temperature gradients (?T) and bioeffects with little bulk temperature change. Recent calculations suggest that nanosecond pulsed electric fields (nsPEFs) may also induce such gradients that may additionally impact the electroporation threshold. Here, we analytically and numerically calculate the induced ?T as a function of pulse duration and pulse repetition rate. We relate ?T to the thermally induced cell membrane electric field (Em) by assuming the membrane behaves as a thermoelectric such that Em ~ ?T. Focusing initially on applying nsPEFs to a uniform membrane, we show that reducing pulse duration and increasing pulse repetition rate (or using higher frequency for alternating current (AC) fields) maximizes the magnitude and duration of ?T and, concomitantly, Em. The maximum ?T initially occurs at the interface between the cell membrane and extracellular fluid before becoming uniform across the membrane, potentially enabling initial molecular penetration and subsequent transport across the membrane. These results, which are equally applicable to AC fields, motivate further studies to elucidate thermoelectric behavior in a model membrane system and the coupling of the Em induced by ?T with that created directly by the applied field.

Garner, Allen L.; Deminsky, Maxim; Bogdan Neculaes, V.; Chashihin, V.; Knizhnik, Andrey; Potapkin, Boris

2013-06-01

297

Analysis for nonextractable (bound) residues of pentachlorophenol in plant cells using a cell wall fractionation procedure  

SciTech Connect

When plant cell cultures or aseptically grown wheat plants were treated with (/sup 14/C)-pentachlorophenol (PCP) a major part of the label was found in a nonextractable or bound residue fraction. Soluble polar conjugates participated in the formation of these residues which were mainly located in the plant cell walls. By a sequential fractionation procedure using enzymatic and chemical methods, 90 to 95% of the bound radioactivity could be attributed to individual cell wall components. The /sup 14/C label from PCP was found mainly in hemicellulose, lignin, and protein fractions. Associations of hemicellulose with PCP derivatives with molecular weights up to 500,000 were purified to constant specific radioactivity. Hydrolysis of this fraction released 32% PCP and other unidentified products.

Langebartels, C.; Harms, H.

1985-10-01

298

The Role of Cell Membranes in the Regulation of Lignification in Pine Cells.  

National Technical Information Service (NTIS)

The identity of pine cell membranes bearing PAL enzyme activity, the isolation of a plasma membrane preparation from pine cells for testing as a regulatory barrier in lignification, and the measurement of the geopotential effect in pine stems are presente...

D. L. Hendrix

1978-01-01

299

Molecular basis of red cell membrane disorders.  

PubMed

We will consider an array of genetic disorders of the red cell membrane. Some affect well-known genes. The mutations of most cases of hereditary spherocytosis (HS) are located in the following genes: ANK1, SPTB, SLC4A1, EPB42 and SPTA1, which encode ankyrin, spectrin beta-chain, the anion exchanger 1 (band 3), protein 4.2 and spectrin alpha-chain, respectively. A dominant form of distal renal tubular acidosis also stems from distinct mutations in the SLC4A1 gene. The mutations responsible for hereditary elliptocytosis (HE) and its aggravated form, poikilocytosis (HP), lie in the SPTA1 and SPTB gene, already mentioned, and in the EPB41 gene encoding protein 4.1. Whereas in HS, the SPTA1 and SPTB gene mutations tend to abolish the synthesis of the corresponding chains, in HE/HP, they hinder spectrin tetramerization. Allele alpha(LELY) is a common polymorphic allele which plays the role of an aggravating factor when it occurs in trans of an elliptocytogenic allele of the SPTA1 gene. Southeast Asian ovalocytosis results from a 27- nucleotide deletion in the SLC4A1 gene. Besides these conditions in which the mutations were reached from known alterations in the proteins, other conditions required a positional cloning approach. Such are the genetic disorders of membrane permeability to monovalent cations. Knowledge is the most advanced as regards dehydrated hereditary stomatocytois (DHS). DHS was shown to belong to a pleiotropic syndrome: DHS + fetal edema + pseudohyperkalemia, which maps to 16q23-24. Concerning DHS and another disease of the same class, overhydrated hereditary stomatocytosis, splenectomy almost certainly appears to elicit thromboembolic accidents. PMID:12432217

Delaunay, Jean

2002-01-01

300

Lactobacillus casei combats acid stress by maintaining cell membrane functionality.  

PubMed

Lactobacillus casei strains have traditionally been recognized as probiotics and frequently used as adjunct culture in fermented dairy products where lactic acid stress is a frequently encountered environmental condition. We have investigated the effect of lactic acid stress on the cell membrane of L. casei Zhang [wild type (WT)] and its acid-resistant mutant Lbz-2. Both strains were grown under glucose-limiting conditions in chemostats; following challenge by low pH, the cell membrane stress responses were investigated. In response to acid stress, cell membrane fluidity decreased and its fatty acid composition changed to reduce the damage caused by lactic acid. Compared with the WT, the acid-resistant mutant exhibited numerous survival advantages, such as higher membrane fluidity, higher proportions of unsaturated fatty acids, and higher mean chain length. In addition, cell integrity analysis showed that the mutant maintained a more intact cellular structure and lower membrane permeability after environmental acidification. These results indicate that alteration in membrane fluidity, fatty acid distribution, and cell integrity are common mechanisms utilized by L. casei to withstand severe acidification and to reduce the deleterious effect of lactic acid on the cell membrane. This detailed comparison of cell membrane responses between the WT and mutant add to our knowledge of the acid stress adaptation and thus enable new strategies to be developed aimed at improving the industrial performance of this species under acid stress. PMID:22366811

Wu, Chongde; Zhang, Juan; Wang, Miao; Du, Guocheng; Chen, Jian

2012-02-26

301

Microfabricated electroporation chip for single cell membrane permeabilization  

Microsoft Academic Search

Silicon microfabrication technology was used to develop a chip that can incorporate a live biological cell in its electrical circuit and thereby induce controlled electroporation in the cell. Electroporation employs electrical pulses applied across a cell for cell membrane permeabilization. Commonly used in biotechnology for genetic engineering of cells in a batch, this chip is the first microfabricated device in

Yong Huang; Boris Rubinsky

2001-01-01

302

Axially resolved polarisation microscopy of membrane dynamics in living cells  

NASA Astrophysics Data System (ADS)

Membrane dynamics has a large impact on cellular uptake and release of various metabolites or pharmaceutical agents. For a deeper understanding of the cellular processes involved, we used U373-MG human glioblastoma cells as a model system. As conventional microscopy does not permit to investigate individual layers in living cells, we used structured illumination techniques and total internal reflection fluorescence microscopy (TIRFM) to analyse the plasma membrane and intracellular membranes of living cells selectively. Optical image sections provide a high resolution and the possibility of 3D reconstruction. Membranes of living cells were characterized by the membrane marker 6-dodecanoyl-2-dimethylamino naphthalene (laurdan). Due to its spectral and kinetic properties this fluorescence marker appears appropriate for measuring membrane stiffness and fluidity. After excitation with linearly polarized laser pulses, membrane fluidity of human glioblastoma cells was determined by measurements of steady-state and time-resolved fluorescence anisotropy r(t), since with increasing viscosity of the environment, the rotation of an excited molecule is impeded. The corresponding time constant ?r of molecular relaxation decreased with temperature and increased with the amount of cholesterol. In addition, fluorescence anisotropy r(t) values of the plasma membrane were larger than the values of intracellular membranes for all temperatures in the range of 16°C<=T<=41°C.

Wagner, Michael; Weber, Petra; Schneckenburger, Herbert

2007-06-01

303

Purification and characterization of thiol-reagent-sensitive glycerol-3-phosphate acyltransferase from the membrane fraction of an oleaginous fungus.  

PubMed Central

Glycerol-3-phosphate acyltransferase (GPAT), responsible for the first committed, rate-limiting, step of glycerolipid synthesis, was purified to homogeneity from the membrane fraction of an oleaginous fungus, Mortierella ramanniana var. angulispora. The enzyme was solubilized from the membrane fraction by pretreatment with 0.05% Triton X-100 and treatment of the resulting pellet with 0.3% Triton X-100. The enzyme was subsequently purified by column chromatography on heparin-Sepharose, Yellow 86 agarose, a second heparin-Sepharose column, Superdex-200 and hydroxylapatite Bio-Gel. Enzyme activity was finally enriched 1308-fold over that of the starting membrane fraction. SDS/PAGE of the purified fraction revealed a single band with a molecular mass of 45 kDa. Native PAGE showed a major band that corresponded to GPAT activity. Enzyme activity was inhibited by thiol reagents, suggesting that it originated from microsomes rather than mitochondria. Purified GPAT depended on exogenous oleoyl-CoA and sn-glycerol-3-phosphate, with the highest activity at approx. 50 and 250 microM, respectively, and preferred oleoyl-CoA 5.4-fold over palmitoyl-CoA as an acyl donor. Anionic phospholipids, such as phosphatidic acid and phosphatidylserine, were absolutely required for activity of the purified enzyme, and their ability to activate GPAT was influenced by the purity of the GPAT preparation. Bivalent cations, such as Mg(2+) and Ca(2+), inhibited purified GPAT activity, whereas 5 mM Mn(2+) elevated activity approx. 2-fold. These results provide new insights into the molecular characterization of microsomal GPAT, which has not been well characterized compared with mitochondrial and plastidic GPAT.

Mishra, S; Kamisaka, Y

2001-01-01

304

Ca binding to the human red cell membrane: Characterization of membrane preparations and binding sites  

Microsoft Academic Search

Summary Inside out and right side out vesicles were used to study the sidedness of Ca binding to the human red cell membrane. It was shown that these vesicles exhibited only a limited permeability to Ca, enabling the independent characterization of Ca binding to the extracellular and cytoplasmic membrane surfaces. Ca binding was studied in 10 mM Tris HCl at

Carl M. Cohen; A. K. Solomon

1976-01-01

305

Inorganic–Polymer Composite Membranes for Proton Exchange Membrane Fuel Cells  

Microsoft Academic Search

Composite membranes consisting primarily of a polymer and an inorganic proton conducting particle or a proton conducting polymer containing inorganic particles for use as proton exchange membranes in low and intermediate temperature fuel cells are reviewed. The chemistry of major inorganic additives that have been used is described in terms of their structure and intrinsic ability to conduct protons. Composites

Andrew M. Herring

2006-01-01

306

Evaluating the interfacial reaction kinetics of the bipolar membrane interface in the bipolar membrane fuel cell.  

PubMed

A reaction kinetic model of the bipolar membrane interface in the bipolar membrane fuel cell (BPMFC) was proposed based on the p-n junction theory and chemical reaction kinetics. It verified the self-humidification feasibility of the BPMFC successfully. PMID:23744271

Peng, Sikan; Lu, Shanfu; Zhang, Jin; Sui, Pang-Chieh; Xiang, Yan

2013-06-06

307

Novel Fusogenic Liposomes for Fluorescent Cell Labeling and Membrane Modification.  

PubMed

Efficient delivery of biomolecules into membranes of living cells as well as cell surface modifications are major biotechnological challenges. Here, novel liposome systems based on neutral and cationic lipids in combination with lipids modified by aromatic groups are introduced for such applications. The fusion efficiency of these liposome systems was tested on single cells in culture like HEK293, myofibroblasts, cortical neurons, human macrophages, smooth muscle cells, and even on tissue. Fusogenic liposomes enabled highly efficient incorporation of molecules into mammalian cell membranes within 1 to 30 min at fully unchanged cell growth conditions and did not affect cell behavior. We hypothesize that membrane fusions were induced in all cases by the interaction of the positively charged lipids and the delocalized electron system of the aromatic group generating local dipoles and membrane instabilities. Selected applications ranging from basic research to biotechnology are envisaged here. PMID:20184308

Csisza?r, Agnes; Hersch, Nils; Dieluweit, Sabine; Biehl, Ralf; Merkel, Rudolf; Hoffmann, Bernd

2010-02-25

308

Rapid and efficient purification of plasma membrane from cultured cells: characterization of epidermal growth factor binding  

SciTech Connect

The authors have devised a rapid and simple protocol for the purification of the plasma membrane from several lines of transformed cultured cells. A431 or KB plasmalemma was purified in 90 min with a two-step centrifugation cycle after selectively inducing microsomal aggregation by the addition of calcium to homogenized cells. Relative specific activity analysis using membrane marker enzymes on the various fractions indicated that the isolated plasmalemma was purified 8-12-fold over the starting homogenate and contained a high density of epidermal growth factor (EGF) receptors. Transmission electron microscopy showed the final membrane suspension consisted of unilamellar vesicles with an average diameter of approximately 100 A. The purified membrane vesicles avidly bound to /sup 125/I-EGF and reached equilibrium within 30 min. Microfiltration assays indicated more than 90% of the total binding can be displaced by excess unlabeled ligand. Equilibrium binding analysis showed a single class of high-affinity /sup 125/I-EGF binding site. Gel electrophoresis of /sup 125/I-EGF cross-linked to membrane EGF receptors showed a distinct autoradiographic band at 170 kilodaltons, which could be displaced with excessive amounts of unlabeled EGF. Finally, EGF-dependent autophosphorylation of the EGF receptor was clearly demonstrated with the purified membrane preparation. Membrane vesicles purified in this manner can be stored in liquid nitrogen for several months without losing their biological activity.

Lin, P.H.; Selinfreund, R.; Wakshull, E.; Wharton, W.

1987-02-10

309

Cell membrane potentials induced during exposure to EMP fields  

SciTech Connect

Internal current densities and electric fields induced in the human body during exposure to EMP fields are reviewed and used to predict resulting cell membrane potentials. Using several different approaches, membrane potentials of about 100 mV are predicted. These values are comparable to the static membrane potentials maintained by cells as a part of normal physiological function, but the EMP-induced potentials persist for only about 10 ns. Possible biological implications of EMP-induced membrane potentials including conformational changes and electroporation are discussed.

Gailey, P.C.; Easterly, C.E.

1994-09-01

310

Coherence properties of red blood cell membrane motions  

NASA Astrophysics Data System (ADS)

We use a highly sensitive, noncontact, optical interferometric technique to quantify the red blood cell membrane fluctuations at the nanometer and millisecond scales. The results reveal significant properties of both temporal and spatial coherence associated with the membrane dynamics. We show that these correlations can be accounted for by the viscoelastic properties of the cell membrane. From this measurement, we extract the loss and storage moduli associated with the membrane and find a crossover frequency at which the buffer viscosity seems to become dominant.

Popescu, Gabriel; Park, Yongkeun; Dasari, Ramachandra R.; Badizadegan, Kamran; Feld, Michael S.

2007-09-01

311

Optimization of polyelectrolyte-based membrane-electrode assemblies for fuel cells  

NASA Astrophysics Data System (ADS)

Dependence of the specific power of a hydrogen fuel cell (FC) on various factors involved in the fabrication of membrane-electrode assemblies (MEAs) based on polyelectrolyte membranes has been studied. The MEA technology has been optimized with respect to the following parameters determining the FC structure and characteristics: weight fractions of the Pt/C catalyst powder and carbon nanotubes (CNTs), content of polymer solution, and polymer type (Nafion 212, MF4-SK). MEAs with specific powers above 210 mW/cm2 are obtained for air-hydrogen FCs operating at room temperature and nearly atmospheric hydrogen pressure.

Gurevich, S. A.; Gorokhov, M. V.; Zelenina, N. K.; Kozhevin, V. M.; Terukova, E. E.; Tomasov, A. A.

2009-10-01

312

Immunomodulation by bacterial fractions.  

PubMed

The cells of Nocardia opaca are a source of potent immunostimulating substances, differing in solubility and in the presence or absence of peptidoglycan. Three classes of N. opaca fractions have been investigated: (1) NDCM (Nocardia delipidated cell mitogen), the starting fraction; (2) PG (peptidoglycan)-containing fractions: CW (cell walls), PG, and fractions containing soluble PG derivatives such as NWSM (Nocardia water soluble mitogen) and NSPD (Nocardia soluble peptidoglycan derivative); and (3) soluble fractions devoid of PG, such as NWSMP (NWSP-pellet) and CyI (cytoplasmic membrane). This report summarizes our results on the relationship between the structure of N. opaca fractions and their stimulatory activities on mouse, rabbit, germ-free piglet and human lymphocytes and monocytes/macrophages. The studies of biological properties of these compounds are the result of an extensive collaborative effort of several teams. PMID:7927995

Barot-Ciorbaru, R

313

Cell Membranes Under Hydrostatic Pressure Subjected to Micro-Injection  

NASA Astrophysics Data System (ADS)

The work is concerned with the determination of the mechanical behaviour of cell membranes under uniform hydrostatic pressure subject to micro-injections. For that purpose, assuming that the shape of the deformed cell membrane is axisymmetric a variational statement of the problem is developed on the ground of the so-called spontaneous curvature model. In this setting, the cell membrane is regarded as an axisymmetric surface in the three-dimensional Euclidean space providing a stationary value of the shape energy functional under the constraint of fixed total area and fixed enclosed volume. The corresponding Euler-Lagrange equations and natural boundary conditions are derived, analyzed and used to express the forces and moments in the membrane. Several examples of such surfaces representing possible shapes of cell membranes under pressure subjected to micro injection are determined numerically.

Vassilev, Vassil M.; Kostadinov, Kostadin G.; Mladenov, Ivaïlo M.; Shulev, Assen A.; Stoilov, Georgi I.; Djondjorov, Peter A.

2011-04-01

314

Red cell membrane lipid peroxidation and hemolysis secondary to phototherapy.  

PubMed

The exposure of red cells to phototherapy light in the presence of a sensitizer (bilirubin) resulted in oxidative injury to the red cell membrane as manifested by a significant increase in the concentration of the products of lipid peroxidation (TBA reactants and diene conjugation) in the membrane and hemolysis. To induce a photo-oxidized membrane injury, the sensitizer (bilirubin) has to be membrane bound. Thus, by altering the availability of free bilirubin in the red cell suspension through changes in the molar concentration ratio of bilirubin to albumin, one is able to regulate the occurrence and extent of the oxidative red cell membrane injury. The clinical implications of these findings are discussed. PMID:4003061

Ostrea, E M; Cepeda, E E; Fleury, C A; Balun, J E

1985-05-01

315

Membrane trafficking in guard cells during stomatal movement  

PubMed Central

Pairs of guard cells form small pores called stoma in the epidermis, and the reversible swelling and shrinking of these guard cells regulate the stomatal apertures. The well-documented changes in guard cell volume have been associated with their vacuolar structures. To investigate the contribution of the guard cell vacuoles to stomatal movement, the dynamics of these vacuolar structures were recently monitored during stomatal movement in vacuolar-membrane visualized Arabidopsis plants. Calculation of the vacuolar volume and surface area after reconstruction of three-dimensional images revealed a decrease in the vacuolar volume but an increase in the vacuolar surface area upon stomatal closure. These results implied the possible acceleration of membrane trafficking to the vacuole upon stomatal closure and membrane recycling from the vacuole to the plasma membrane upon stomatal opening. To clarify and quantify membrane trafficking during stomatal movement, we describe in this addendum our development of an improved image processing system.

Kutsuna, Natsumaro; Hasezawa, Seiichiro; Tanaka, Yoko

2008-01-01

316

Fractionation of whey protein hydrolysates using charged UF\\/NF membranes  

Microsoft Academic Search

The possibility to separate peptides from a tryptic hydrolysates of whey proteins with charged UF\\/NF membranes has been investigated. A total hydrolysate (TH) was prepared by tryptic hydrolysis of a commercial whey protein isolate followed by UF-treatment using a 10kDa MWCO in order to remove the enzyme and non-hydrolyzed material from the reaction mixture. Firstly, five different membrane materials were

Y. Pouliot; M. C. Wijers; S. F. Gauthier; L. Nadeau

1999-01-01

317

Isolation, Solubilization, Fractionation by Electrofocusing, and Immobilization of Skim Milk Membranes1  

Microsoft Academic Search

A 300-nm pore diameter glycerol- propyl-glass matrix was used for chro- matographic purification of vesicles of skim milk membrane. Electrofocusing of these membrane proteins solubilized in 1% polyoxyethylene-9-1auryl ether per- mitted resolution of activities of 7- glutamyltransferase, alkaline phosphatase, sulfhydryl oxidase, and xanthine oxidase. This resolution of activities indicates that these are separate and distinct enzymes, a conclusion that is

Violeta G. Janolino; Harold E. Swaisgood

1984-01-01

318

Membrane transport of anandamide through resealed human red blood cell membranes.  

PubMed

The use of resealed red blood cell membranes (ghosts) allows the study of the transport of a compound in a nonmetabolizing system with a biological membrane. Transmembrane movements of anandamide (N-arachidonoylethanolamine, arachidonoylethanolamide) have been studied by exchange efflux experiments at 0 degrees C and pH 7.3 with albumin-free and albumin-filled human red blood cell ghosts. The efflux kinetics is biexponential and is analyzed in terms of compartment models. The distribution of anandamide on the membrane inner to outer leaflet pools is determined to be 0.275 +/- 0.023, and the rate constant of unidirectional flux from inside to outside is 0.361 +/- 0.023 s(-1). The rate constant of unidirectional flux from the membrane to BSA in the medium ([BSA]o) increases with the square root of [BSA]o in accordance with the theory of an unstirred layer around ghosts. Anandamide passed through the red blood cell membrane very rapidly, within seconds. At a molar ratio of anandamide to BSA of <1, membrane binding of anandamide increases with increasing temperatures between 0 degrees C and 37 degrees C, and the equilibrium dissociation constants are in the nanomolar range. The nature of membrane binding and the mechanism of membrane translocation are discussed. PMID:15930521

Bojesen, Inge N; Hansen, Harald S

2005-06-01

319

Models of dynamic extraction of lipid tethers from cell membranes.  

PubMed

When a ligand that is bound to an integral membrane receptor is pulled, the membrane and the underlying cytoskeleton can deform before either the membrane delaminates from the cytoskeleton or the ligand detaches from the receptor. If the membrane delaminates from the cytoskeleton, it may be further extruded and form a membrane tether. We develop a phenomenological model for this process by assuming that deformations obey Hooke's law up to a critical force at which the cell membrane locally detaches from the cytoskeleton and a membrane tether forms. We compute the probability of tether formation and show that tethers can be extruded only within an intermediate range of force loading rates and pulling velocities. The mean tether length that arises at the moment of ligand detachment is computed as are the force loading rates and pulling velocities that yield the longest tethers. PMID:20453295

Nowak, Sarah A; Chou, Tom

2010-05-07

320

Megakaryocyte cell sorting from diosgenin-differentiated human erythroleukemia cells by sedimentation field-flow fractionation.  

PubMed

Anticancer differentiation therapy could be one strategy to stop cancer cell proliferation. Human erythroleukemia (HEL) cell line, incubated with 10 microM diosgenin, underwent megakaryocytic differentiation. Thus, the association diosgenin/HEL could be used as a model of chemically induced cellular differentiation and anticancer treatment. The goal of this work was to determine the capacity of sedimentation field-flow fractionation (SdFFF) to sort megakaryocytic differentiated cells. SdFFF cell sorting was associated with cellular characterization methods to calibrate specific elution profiles. As demonstrated by cell size measurement methods, cellular morphology, ploidy, and phenotype, we obtained an enriched, sterile, viable, and functional fraction of megakaryocytic cells. Thus, SdFFF is proposed as a routine method to prepare differentiated cells that will be further used to better understand the megakaryocytic differentiation process. PMID:16806034

Léger, D Y; Battu, S; Liagre, B; Beneytout, J L; Cardot, P J P

2006-06-12

321

Time-resolved molecular transport across living cell membranes.  

PubMed

It is shown that the nonlinear optical phenomenon known as second-harmonic generation can be used for label-free, time-resolved study of the transport of molecules through living cell membranes. The adsorption and transport of a 300-Da molecular-mass hydrophobic ion at the Escherichia coli membrane is observed. Remarkably, at low ion concentrations, the second-harmonic generation technique clearly exposes a multistep molecular transport process: Transport of the molecular ion across the outer and cytoplasmic membranes of the Gram-negative bacteria is recorded, in sequence, in time. Fitting of the data to a multiprocess kinematic model reveals that the transport of this hydrophobic ion through the outer membrane is much faster than through the cytoplasmic membrane, likely reflecting the effectiveness of ion transport porins. The observations illustrate an experimental means for studying the interactions of small molecules with cell membranes. PMID:23332066

Zeng, Jia; Eckenrode, Heather M; Dounce, Susan M; Dai, Hai-Lung

2013-01-08

322

Measurement of the nonlinear elasticity of red blood cell membranes  

NASA Astrophysics Data System (ADS)

The membranes of human red blood cells (RBCs) are a composite of a fluid lipid bilayer and a triangular network of semiflexible filaments (spectrin). We perform cellular microrheology using the dynamic membrane fluctuations of the RBCs to extract the elastic moduli of this composite membrane. By applying known osmotic stresses, we measure the changes in the elastic constants under imposed strain and thereby determine the nonlinear elastic properties of the membrane. We find that the elastic nonlinearities of the shear modulus in tensed RBC membranes can be well understood in terms of a simple wormlike chain model. Our results show that the elasticity of the spectrin network can mostly account for the area compression modulus at physiological osmolality, suggesting that the lipid bilayer has significant excess area. As the cell swells, the elastic contribution from the now tensed lipid membrane becomes dominant.

Park, Yongkeun; Best, Catherine A.; Kuriabova, Tatiana; Henle, Mark L.; Feld, Michael S.; Levine, Alex J.; Popescu, Gabriel

2011-05-01

323

Measurement of the nonlinear elasticity of red blood cell membranes.  

PubMed

The membranes of human red blood cells (RBCs) are a composite of a fluid lipid bilayer and a triangular network of semiflexible filaments (spectrin). We perform cellular microrheology using the dynamic membrane fluctuations of the RBCs to extract the elastic moduli of this composite membrane. By applying known osmotic stresses, we measure the changes in the elastic constants under imposed strain and thereby determine the nonlinear elastic properties of the membrane. We find that the elastic nonlinearities of the shear modulus in tensed RBC membranes can be well understood in terms of a simple wormlike chain model. Our results show that the elasticity of the spectrin network can mostly account for the area compression modulus at physiological osmolality, suggesting that the lipid bilayer has significant excess area. As the cell swells, the elastic contribution from the now tensed lipid membrane becomes dominant. PMID:21728589

Park, YongKeun; Best, Catherine A; Kuriabova, Tatiana; Henle, Mark L; Feld, Michael S; Levine, Alex J; Popescu, Gabriel

2011-05-27

324

Characterization of Lens Fiber Cell Triton Insoluble Fraction Reveals ERM (Ezrin, Radixin, Moesin) proteins as Major Cytoskeletal-associated Proteins  

PubMed Central

To understand lens fiber cell elongation- and differentiation-associated cytoskekeletal remodeling, here we identified and characterized the major protein components of lens fiber cell triton X-100 insoluble fraction by mass spectrometry and immunoblot analysis. This analysis identified spectrin, filensin, vimentin, tubulin, phakinin and ?-actin as major cytoskeletal proteins in the lens fibers. Importantly, ezrin, radixin and moesin (ERM), heat-shock cognate protein 70, and ?/?-crystallins were identified as major cytoskeletal-associated proteins. ERM proteins were confirmed to exist as active phosphorylated forms that exhibited intense distribution in the organelle free-zone fibers. Furthermore, ERM protein phosphorylation was found to be dramatically reduced in Rho GTPase-targeted transgenic mouse lenses. These data identify the ERM proteins, which crosslink the plasma membrane and actin, as major and stable cytoskeletal-associated proteins in lens fibers, and indicate a potential role(s) for the ERMs in fiber cell actin cytoskeletal and membrane organization.

Vasantha Rao, P.; Ho, Tammy; Skiba, Nikolai P.; Maddala, Rupalatha

2008-01-01

325

Systems analysis of endothelial cell plasma membrane proteome of rat lung microvasculature  

PubMed Central

Background Endothelial cells line all blood vessels to form the blood-tissue interface which is critical for maintaining organ homeostasis and facilitates molecular exchange. We recently used tissue subcellular fractionation combined with several multi-dimensional mass spectrometry-based techniques to enhance identification of lipid-embedded proteins for large-scale proteomic mapping of luminal endothelial cell plasma membranes isolated directly from rat lungs in vivo. The biological processes and functions of the proteins expressed at this important blood-tissue interface remain unexplored at a large scale. Results We performed an unbiased systems analysis of the endothelial cell surface proteome containing over 1800 proteins to unravel the major functions and pathways apparent at this interface. As expected, many key functions of plasma membranes in general (i.e., cell surface signaling pathways, cytoskeletal organization, adhesion, membrane trafficking, metabolism, mechanotransduction, membrane fusion, and vesicle-mediated transport) and endothelial cells in particular (i.e., blood vessel development and maturation, angiogenesis, regulation of endothelial cell proliferation, protease activity, and endocytosis) were significantly overrepresented in this proteome. We found that endothelial cells express multiple proteins that mediate processes previously reported to be restricted to neuronal cells, such as neuronal survival and plasticity, axon growth and regeneration, synaptic vesicle trafficking and neurotransmitter metabolic process. Surprisingly, molecular machinery for protein synthesis was also detected as overrepresented, suggesting that endothelial cells, like neurons, can synthesize proteins locally at the cell surface. Conclusion Our unbiased systems analysis has led to the potential discovery of unexpected functions in normal endothelium. The discovery of the existence of protein synthesis at the plasma membrane in endothelial cells provides new insight into the blood-tissue interface and endothelial cell surface biology.

2011-01-01

326

Alternative Sources of Adult Stem Cells: Human Amniotic Membrane  

Microsoft Academic Search

\\u000a Human amniotic membrane is a highly promising cell source for tissue engineering. The cells thereof, human amniotic epithelial\\u000a cells (hAEC) and human amniotic mesenchymal stromal cells (hAMSC), may be immunoprivileged, they represent an early developmental\\u000a status, and their application is ethically uncontroversial. Cell banking strategies may use freshly isolated cells or involve\\u000a in vitro expansion to increase cell numbers. Therefore,

Susanne Wolbank; Martijn van Griensven; Regina Grillari-Voglauer; Anja Peterbauer-Scherb

2010-01-01

327

Human hepatocytes and endothelial cells in organotypic membrane systems.  

PubMed

The realization of organotypic liver model that exhibits stable phenotype is a major challenge in the field of liver tissue engineering. In this study we developed liver organotypic co-culture systems by using synthetic and biodegradable membranes with primary human hepatocytes and human umbilical vein endothelial cells (HUVEC). Synthetic membranes prepared by a polymeric blend constituted of modified polyetheretherketone (PEEK-WC) and polyurethane (PU) and biodegradable chitosan membranes were developed by phase inversion technique and used in homotypic and organotypic culture systems. The morphological and functional characteristics of cells in the organotypic co-culture membrane systems were evaluated in comparison with homotypic cultures and traditional systems. Hepatocytes in the organotypic co-culture systems exhibit compact polyhedral cells with round nuclei and well demarcated cell-cell borders like in vivo, as a result of heterotypic interaction with HUVECs. In addition HUVECs formed tube-like structures directly through the interactions with the membranes and hepatocytes and indirectly through the secretion of ECM proteins which secretion improved in the organotypic co-culture membrane systems. The heterotypic cell-cell contacts have beneficial effect on the hepatocyte albumin production, urea synthesis and drug biotransformation. The developed organotypic co-culture membrane systems elicit liver specific functions in vitro and could be applied for the realization of engineered liver tissues to be used in tissue engineering, drug metabolism studies and bioartificial liver devices. PMID:21871658

Salerno, Simona; Campana, Carla; Morelli, Sabrina; Drioli, Enrico; De Bartolo, Loredana

2011-08-25

328

Improved Membrane Materials for PEM Fuel Cell Application  

SciTech Connect

The overall goal of this project is to collect and integrate critical structure/property information in order to develop methods that lead to significant improvements in the durability and performance of polymer electrolyte membrane fuel cell (PEMFC) materials. This project is focused on the fundamental improvement of PEMFC membrane materials with respect to chemical, mechanical and morphological durability as well as the development of new inorganically-modified membranes.

Kenneth A. Mauritz; Robert B. Moore

2008-06-30

329

Affinity of PIP-aquaporins to sterol-enriched domains in plasma membrane of the cells of etiolated pea seedlings  

Microsoft Academic Search

The hypothesis that sterol-enriched domains represent sites of preferred localization of PIP-aquaporins was tested in experiments\\u000a on plasma membranes isolated from cells of etiolated pea (Pisum sativum L.) seedlings. Plasma membranes were isolated from microsomes by the partition in the aqueous two-phase polymer system and\\u000a separated into vesicle fractions of different buoyant density by flotation in discontinuous OptiPrep gradient. Two

B. V. Belugin; I. M. Zhestkova; M. S. Trofimova

2011-01-01

330

Vaccination against Marek's disease: Immunizing effect of purified turkey herpes virus and cellular membranes from infected cells  

Microsoft Academic Search

One-day-old chickens susceptible to Marek's disease were vaccinated with experimental vaccines prepared from purified turkey herpes virus (HVT), inactivated HVT preparations or a membrane fraction isolated from HTV-infected chicken embryo fibroblasts, respectively. Purified HVT was found to be as effective in immunization against Marek's disease as cell-associated virus. The specific mortality of chickens twice vaccinated with cellular membranes from HVT-infected

O.-R. Kaaden; B. Dietzschold; S. UeberschÄr

1974-01-01

331

Effect of Hydroperoxides on Red Blood Cell Membrane Mechanical Properties  

PubMed Central

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.

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

2011-01-01

332

Effect of hydroperoxides on red blood cell membrane mechanical properties.  

PubMed

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

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

2011-10-19

333

Layer-by-layer cell membrane assembly.  

PubMed

Eukaryotic subcellular membrane systems, such as the nuclear envelope or endoplasmic reticulum, present a rich array of architecturally and compositionally complex supramolecular targets that are as yet inaccessible. Here we describe layer-by-layer phospholipid membrane assembly on microfluidic droplets, a route to structures with defined compositional asymmetry and lamellarity. Starting with phospholipid-stabilized water-in-oil droplets trapped in a static droplet array, lipid monolayer deposition proceeds as oil/water-phase boundaries pass over the droplets. Unilamellar vesicles assembled layer-by-layer support functional insertion both of purified and of in situ expressed membrane proteins. Synthesis and chemical probing of asymmetric unilamellar and double-bilayer vesicles demonstrate the programmability of both membrane lamellarity and lipid-leaflet composition during assembly. The immobilized vesicle arrays are a pragmatic experimental platform for biophysical studies of membranes and their associated proteins, particularly complexes that assemble and function in multilamellar contexts in vivo. PMID:24153375

Matosevic, Sandro; Paegel, Brian M

2013-09-29

334

Cytoskeletal control of the red-blood cell membrane  

NASA Astrophysics Data System (ADS)

We have shown (Physical Review Letters, 90, 228101 (2003)) that the thermal fluctuations of red blood cells can be accounted for by a model of a nearly-free, but confined bilayer membrane with a finite tension; both the confinement and tension arise from the coupling of the membrane with the cytoskeleton. Recently, we have shown that these relatively gentle effects of the cytoskeleton-membrane couplings on the membrane fluctuations are due to the dilute nature of the coupling molecules. To quantify this, we predict the fluctuation amplitude for a microscopic model of the inhomogeneous coupling of a fluid membrane and a fixed cytoskeleton. The coupling is modeled as periodic and harmonic, and we consider the linear response of the membrane. We find that there is indeed, an effective surface tension and confinement of such a membrane, in accord with our phenomenological model, and relate these quantities to the strength and periodicity of the microscopic coupling. We also find, surprisingly, that the membrane can develop a spontaneous breaking of the cytoskeleton symmetry, at low confinements. Finally we address the role of ATP activity on the cytoskeleton-driven fluctuations and the equilibrium shape of the cell. We examine in detail the role of spectrin disconnections as the main ATP-activated network defects on the global cell shape and membrane fluctuations.

Gov, Nir; Safran, Sam

2004-03-01

335

Direct measurements of membrane potential and membrane resistance of human red cells  

PubMed Central

1. In order to evaluate the membrane potentials calculated from the distribution of chloride ions in human red cells and plasma, it is desirable to have a direct measurement of the transmembrane potential of these cells. 2. A method has been devised for introducing a capillary micro-electrode into human red cells. The method allows simultaneous measurements of potential and membrane resistance with only one micro-electrode located in the cell. 3. Upon impalement of single cells in plasma, a scatter of membrane potentials and of resistance values was obtained. The potential drop never exceeded -14 mV and the maximum resistances were about 7 ?. cm2. Positive potentials were obtained on impalement of red cell aggregates. 4. Arguments are given to support the view that it is in these cells which suffer least damage from the impalement that maximum values of membrane potentials and resistances are observed. The errors caused by the change in the liquid junction during the impalement have been estimated. 5. As judged from this study, it seems permissible under normal conditions to calculate the membrane potential of the red cell from the chloride concentrations in plasma and in intracellular water.

Lassen, U. V.; Sten-Knudsen, O.

1968-01-01

336

Membrane ultrastructure preservation and membrane potentials after isolation of rabbit retinal glial (Müller) cells by papain.  

PubMed

Enzymatically isolated retinal glial (Müller) cells have been the subject of many electrophysiological studies. Local high membrane conductivities for potassium ions have been speculated to correspond with local occurrence of orthogonal arrays of intramembranous particles (OAP) observed in freeze-fracture replicas of retinal Müller cells in situ. We studied whether such OAP are preserved after enzymatic digestion of the retinal tissue which is necessary for isolation of living cells for electrophysiology. We found that strong papain digestion leads not only to disturbances in the cell's ultrastructure as seen in ultrathin sections but evokes both a redistribution of intramembranous particles and a disappearance of OAP as seen in the freeze-fracture replica. Furthermore, such isolated cells have low membrane potentials and lose their topographical specialization in K+ conductance. If, however, the retinae were exposed to papain as short as possible to get just some isolated cells, their cytoplasmic and membranous ultrastructure was preserved very well, and high resting membrane potentials were recorded in cells with marked regional specialization of membrane conductivity. Our results show that indeed sites of high K+ conductance may correspond with the occurrence of OAP, even in isolated cells. PMID:2385140

Reichenbach, A; Wolburg, H; Richter, W; Eberhardt, W

1990-06-01

337

Radiation Interaction with Therapeutic Drugs and Cell Membranes  

SciTech Connect

This transient permeabilized state of the cell membrane, named the 'cell electroporation' (CE) can be used to increase cells uptake of drugs that do not readily pass cell membrane, thus enabling their cytotoxicity. The anticancer drugs, such as bleomycin (BL) and cisplatin, are the most candidates for the combined use with ionizing and non-ionizing radiation fields. The methods and installations for the cell electroporation by electron beam (EB) and microwave (MW) irradiation are presented. The viability tests of the human leukocytes under EB and MW exposure with/without the BL in the cell cultures are discussed.

Martin, Diana I.; Manaila, Elena N.; Matei, Constantin I.; Iacob, Nicusor I.; Ighigeanu, Daniel I.; Craciun, Gabriela D. [Accelerators Laboratory, National Institute for Lasers, Plasma and Radiation Physics, 409, Atomistilor St., 077125 Magurele (Romania); Moisescu, Mihaela I.; Savopol, Tudor D.; Kovacs, Eugenia A. [Carol Davila University of Medicine and Pharmacy, 8, Eroii Sanitari St., 050474 Bucharest (Romania); Cinca, Sabin A. [Oncology Institute Prof. A. Trestioreanu, 252, Fundeni St., 022328 Bucharest (Romania); Margaritescu, Irina D. [Military Clinical Hospital, 88, Mircea Vulcanescu St., 010825 Bucharest (Romania)

2007-04-23

338

Radiation Interaction with Therapeutic Drugs and Cell Membranes  

NASA Astrophysics Data System (ADS)

This transient permeabilized state of the cell membrane, named the ``cell electroporation'' (CE) can be used to increase cells uptake of drugs that do not readily pass cell membrane, thus enabling their cytotoxicity. The anticancer drugs, such as bleomycin (BL) and cisplatin, are the most candidates for the combined use with ionizing and non-ionizing radiation fields. The methods and installations for the cell electroporation by electron beam (EB) and microwave (MW) irradiation are presented. The viability tests of the human leukocytes under EB and MW exposure with/without the BL in the cell cultures are discussed.

Martin, Diana I.; Manaila, Elena N.; Moisescu, Mihaela I.; Savopol, Tudor D.; Kovacs, Eugenia A.; Cinca, Sabin A.; Matei, Constantin I.; Margaritescu, Irina D.; Iacob, Nicusor I.; Ighigeanu, Daniel I.; Craciun, Gabriela D.

2007-04-01

339

Automated membrane test cell apparatus and method for so using  

SciTech Connect

An automated electrolytic membrane test cell apparatus adaptable for the purpose of accurately measuring cationic transport and water transport numbers for membranes used in chlor-alkali cells under operating conditions similar to those used in such cells is disclosed. The apparatus comprises a test cell, said test cell being adapted to hold a permselective membrane sealingly supported therein so as to create separate anode and cathode compartments, each of said compartments having a suitable electrode, and heating electrolyte inlet and outlet means attached thereto. The apparatus further comprises means to select one of a plurality of anolyte and catholyte test solutions and control means adapted to control the electrolysis, circulation and heating of said solutions and the generation of all test samples needed to perform the measurements necessary to calculate said transport numbers. When used in conjunction with radioactive tracer techniques, considerably improvements are possible in the accuracy and ease with which transport phenomena in said membrane can be studied.

Yeager, H.L.; Malinsky, J.D.

1984-11-20

340

Several membrane polypeptides of the live vaccine strain Francisella tularensis LVS stimulate T cells from naturally infected individuals.  

PubMed Central

The currently used live vaccine strain Francisella tularensis LVS was derived several decades ago from a wild strain of the species. In the present report, several membrane polypeptides of LVS are shown to be recognized by T cells from individuals immunized by natural infection with F. tularensis. Bacterial membranes of a capsule-deficient mutant of LVS were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Thereafter, gels were divided into seven fractions, each fraction containing a different number of peptide bands. From other gels, four bands were excised, each containing one major polypeptide. Eluates of each fraction and of each polypeptide band induced a proliferative response and an interleukin-2 response in lymphocytes from most of the individuals. When the lymphocytes were separated after induction, most of the proliferative response was found to occur in CD4+ T cells. Lymphocytes from nonimmune individuals responded poorly to all membrane polypeptides. To study the possible heterogeneity of antigen determinants among the polypeptides, T-cell clones were raised towards F. tularensis and tested for proliferative response to the four major membrane polypeptides. Five clones, all CD4+ CD8-, responded to one or more of the polypeptides, each clone with a unique pattern of response. In conclusion, F. tularensis possesses a high number of T-cell-reactive membrane polypeptides. There seems to be a heterogeneity of T-cell determinants among these polypeptides. Determinants involved in immunization by natural infection are well conserved in LVS. Images

Sjostedt, A; Sandstrom, G; Tarnvik, A

1990-01-01

341

T cell antigen recognition at the cell membrane  

PubMed Central

T cell antigen receptors (TCR) on the surface of T cells bind specifically to particular peptide bound major histocompatibility complexes (pMHC) presented on the surface of antigen presenting cells (APC). This interaction is a key event in T cell antigen recognition and activation. Most studies have used surface plasmon resonance (SPR) to measure the in vitro binding kinetics of TCR-pMHC interactions in solution using purified proteins. However, these measurements are not physiologically precise, as both TCRs and pMHCs are membrane-associated molecules which are regulated by their cellular environments. Recently, single-molecule förster resonance energy transfer (FRET) and single-molecule mechanical assays were used to measure the in situ binding kinetics of TCR-pMHC interactions on the surface of live T cells. These studies have provided exciting insights into the biochemical basis of T cell antigen recognition and suggest that TCRs serially engage with a small number of antigens with very fast kinetics in order to maximize TCR signaling and sensitivity.

Huang, Jun; Meyer, Christina; Zhu, Cheng

2012-01-01

342

Atrazine and PCB 153 and their effects on the proteome of subcellular fractions of human MCF-7 cells.  

PubMed

Several man-made organic pollutants including polychlorinated biphenyls (PCBs) and several pesticides may exhibit endocrine disrupting (ED) properties. These ED molecules can be comparatively persistent in the environment, and have shown to perturb hormonal activity and several physiological functions. The objective of this investigation was to study the impact of PCB 153 and atrazine on human MCF-7 cells, and to search for marker proteins of their exposure. Cells were exposed to environmentally high but relevant concentrations of atrazine (200ppb), PCB 153 (500ppb), 17-? estradiol (positive control, 10nM) and DMSO (0.1%, negative control) for t=36h (n=3 replicates/exposure group). Proteins from cell membrane and cytosol were isolated, and studied by 2D-DiGE. Differentially regulated proteins were trypsin-digested and identified by MALDI-ToF-ToF and NCBInr database. A total of 36 differentially regulated proteins (>|1.5| fold change, P<0.05) were identified in the membrane fraction and 22 in the cytosol, and were mainly involved in cell structure and in stress response, but also in xenobiotic metabolism. 67% (membrane) and 50% (cytosol) of differentially regulated proteins were more abundant following atrazine exposure whereas nearly 100% (membrane) and 45% (cytosol) were less abundant following PCB 153 exposure. Western blots of selected proteins (HSBP1, FKBP4, STMN1) confirmed 2D-DiGE results. This study emphasizes the numerous potential effects that ED compounds could have on exposed humans. PMID:22516319

Lasserre, Jean-Paul; Fack, Fred; Serchi, Tommaso; Revets, Dominique; Planchon, Sébastien; Renaut, Jenny; Hoffmann, Lucien; Gutleb, Arno C; Muller, Claude P; Bohn, Torsten

2012-04-16

343

Computer Simulations of Protein Diffusion in Compartmentalized Cell Membranes  

Microsoft Academic Search

The diffusion of proteins in the cell membrane is investigated using computer simulations of a two-dimensional model. The membrane is assumed to be divided into compartments, with adjacent compartments separated by a barrier of stationary obstacles. Each compartment contains traps represented by stationary attractive disks. Depending on their size, these traps are intended to model either smaller compartments or binding

Bong June Sung; Arun Yethiraj

2009-01-01

344

Alkaline fuel cell membranes from xylylene block ionenes  

Microsoft Academic Search

A new class of anion-exchange membranes, based on xylylene ionene segmented block copolymers, has been fabricated and characterized for possible use in alkaline fuel cells. The ionene materials were composed of non-polar blocks which, in principle, conferred mechanical strength and water swelling control to the membrane, and polar blocks with quaternary dibenzyl dimethyl ammonium groups located on the polymer backbone

Kyung Min Lee; Ryszard Wycisk; Morton Litt; Peter N. Pintauro

2011-01-01

345

Cytoskeletal control of the red-blood cell membrane  

Microsoft Academic Search

We have shown (Physical Review Letters, 90, 228101 (2003)) that the thermal fluctuations of red blood cells can be accounted for by a model of a nearly-free, but confined bilayer membrane with a finite tension; both the confinement and tension arise from the coupling of the membrane with the cytoskeleton. Recently, we have shown that these relatively gentle effects of

Nir Gov; Sam Safran

2004-01-01

346

Molecular Engine for Transporting Drugs Across Cell Membranes  

Microsoft Academic Search

A molecular engine has been developed from first principles to transport drugs from endosomes to the cytosol of cells. The engine is powered by the pH differential across the endosomal membrane, does not disrupt the endosomal membrane, and is disassembled into innocuous components after carrying out its transport function.

James Summerton; Dwight Weller

1997-01-01

347

Aquaporins: water channel proteins of the cell membrane  

Microsoft Academic Search

Aquaporins (AQP) are integral membrane proteins that serve as channels in the transfer of water, and in some cases, small solutes across the membrane. They are conserved in bacteria, plants, and animals. Structural analyses of the molecules have revealed the presence of a pore in the center of each aquaporin molecule. In mammalian cells, more than 10 isoforms (AQP0–AQP10) have

Kuniaki Takata; Toshiyuki Matsuzaki; Yuki Tajika

2004-01-01

348

Membrane associated proteoglycans in rat testicular peritubular cells  

Microsoft Academic Search

Confluent testicular peritubular cells derived from immature rats were used to study membrane associated proteoglycans (PG) Peripheral material (heparin releasable), membrane and intracellular material (Triton X-100 releasable) were collected, purified by anion exchange chromatography then characterized by gel filtration and by hydrophobic interaction chromatography, followed by enzymatic digestion and chemical treatment. The peripheral material was constituted of two populations of

Lahcen Bichoualne; Bénédicte Thiébot; Monique Langris; Pierre Barbey; Hamid Oulhaj; Jean Bocquet

1994-01-01

349

Membrane-electrode assemblies for electrochemical cells  

DOEpatents

A combination, unitary, membrane and electrode assembly with a solid polymer electrolyte membrane, and first and second electrodes at least partially embedded in opposed surfaces of the membrane. The electrodes each comprise a respective group of finely divided carbon particles, very finely divided catalytic particles supported on internal and external surfaces of the carbon particles and a proton conductive material intermingled with the catalytic and carbon particles. A first group of finely divided carbon particles forming the first electrode has greater water attraction and retention properties, and is more hydrophilic than a second group of carbon particles forming the second electrode. In a preferred method, the membrane electrode assembly of the invention is prepared by forming a slurry of proton conductive material and at least one group of the carbon and catalyst particles. The slurry is applied to the opposed surfaces of the membrane and heated while being pressed to the membrane for a time and at a temperature and compressive load sufficient to embed at least a portion of the particles into the membrane.

Swathirajan, Sundararajan (Troy, MI); Mikhail, Youssef M. (Sterling Heights, MI)

1993-01-01

350

Blend Concepts for Fuel Cell Membranes  

Microsoft Academic Search

\\u000a Differently cross-linked blend membranes were prepared from commercial arylene main-chain polymers from the classes of poly(ether-ketones)\\u000a and poly(ethersulfones) modified with sulfonate groups, sulfinate cross-linking groups and basic N-groups. The following membrane\\u000a types have been prepared: (a) van-der Waals\\/dipole-dipole blends by mixing a polysulfonate with unmodified PSU. This membrane\\u000a type showed a heterogeneous morphology, leading to extreme swelling and even dissolution

Jochen Kerres

2009-01-01

351

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

NASA Astrophysics Data System (ADS)

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 temperature, is less temperature-dependent in hydrated membranes than dry membranes and is slightly higher in the composite membranes. Stress-relaxation also follows two distinct behaviors depending on its temperature, humidity and degree of strain. The water sorption and desorption dynamics are not controlled by diffusion rates but by interfacial mass transport resistance and, during sorption, by the kinetics of swelling and stress-relaxation. Pressure exerted by a swelling membrane scales with membrane thickness, is slightly higher for the composite membranes and is relevant to fuel cell design.

Satterfield, May Barclay

352

Concomitant Alterations of Sodium Flux and Membrane Phospholipid Metabolism in Red Blood Cells: Studies in Hereditary Spherocytosis*  

PubMed Central

The role of membrane phosphatides in transport processes has been investigated in red cells from splenectomized patients with hereditary spherocytosis (HS). Incorporation of inorganic 32phosphate into the membrane phosphatides of HS red cells was approximately twice normal, coinciding with the nearly twofold increment in flux of sodium ions in the cells. A consistent, inordinate increase in specific activity of a chromatographic fraction containing phosphatidylserine provided the bulk of the over-all increase in labeling of HS red cell phosphatides. The specific activity of phosphatidic acid was increased but not consistently. Radioactivity of the “acidic phosphatides” (phosphatidylserine and phosphatidic acid fractions) decreased, in general, when the sodium flux was low, i.e., when the cells were suspended in media of low sodium content. When the cation flux was elevated (hypotonic media), there was a marked (ca. 35%) increase in the labeling of phosphatidylserine fractions. Normal red cells whose permeability to cations was increased by exposure to 0.5 N butanol also exhibited increased labeling of acidic phosphatides. Considerations of the stoichiometry of cation transport and phosphatide labeling make it unlikely that phospholipids act directly as carrier molecules for cations in red cell membranes. On the other hand, the involvement of these lipid substances in cation movements is substantiated by correlating several different states of sodium flux with the labeling of the phosphatidic acid and phosphatidylserine fractions. Images

Jacob, Harry S.; Karnovsky, Manfred L.

1967-01-01

353

The anti-angiogenic peptide anginex disrupts the cell membrane.  

PubMed

Anginex is a synthetic beta-sheet peptide with anti-angiogenic and anti-tumor activity. When added to cultured endothelial cells at concentrations ranging from 2.5 microM to 25 microM, anginex induced cell death, which was reflected by a strong increase of subdiploid cells and fragments, loss of cellular ATP, and LDH release. Cytotoxicity remained the same whether cells were treated with anginex at 4 degrees C or at 37 degrees C. At low temperatures, fluorescein-conjugated anginex accumulated on the endothelial surface, but did not reach into the cytoplasm, indicating that the cell membrane is the primary target for the peptide. Within minutes of treatment, anginex caused endothelial cells to take up propidium iodide and undergo depolarization, both parameters characteristic for permeabilization of the cell membrane. This process was amplified when cells were activated with hydrogen peroxide. Red blood cell membranes were essentially unaffected by anginex. Anginex bound lipid bilayers with high affinity and with a clear preference for anionic over zwitterionic phospholipids. Structural studies by circular dichroism and solid-state nuclear magnetic resonance showed that anginex forms a beta-sheet and adopts a unique and highly ordered conformation upon binding to lipid membranes. This is consistent with lipid micellization or the formation of pore-forming beta-barrels. The data suggest that the cytotoxicity of anginex stems from its ability to target and disrupt the endothelial cell membrane, providing a possible explanation for the angiostatic activity of the peptide. PMID:16403516

Pilch, Jan; Franzin, Carla M; Knowles, Lynn M; Ferrer, Fernando J; Marassi, Francesca M; Ruoslahti, Erkki

2005-12-20

354

Bi(o)communications among peripheral blood fractions: a focus on NK and NKT cell biology in rheumatoid arthritis.  

PubMed

Rheumatoid Arthritis (RA) is an autoimmune disease with unknown pathophysiology involving many interwoven signalling cascades. ROS, NK and NKT cells might be crucial in the disease severity of RA of which the role of NK and NKT cells are controversial in literature. However, the role of oxidative stress, its impact on NK and NKT cell immunobiology and disease activity (DAS28) is largely unknown. Therefore, we studied the role of oxidative stress and NK cell subsets in the pathogenesis of RA. The state of oxidative stress in various peripheral blood fractions, percentage NK and NKT cell expression, their altered apoptotic signaling pathways involving mitochondrial membrane potential, FAS associated death domain (FADD) mediated pathways and DNA damage were analyzed. Results indicated a state of profound oxidative stress in the peripheral blood of RA patients where percentage of NK and NKT cell subsets diminished while ROS levels increased. The depolarized mitochondrial membrane potential, FAS, FASL and active caspase-3 positive NK and NKT cell subsets were considerably elevated in patients. The DNA damage, assessed as percentage of DNA in comet tail, was significantly elevated. Findings of the present work indicate increased apoptosis of peripheral NK and NKT cells in the diseased condition. PBMC and RBC are the major sites of enhanced oxidative stress. The state of oxidative stress and altered immunobiology of NK and NKT cells strongly correlated with Disease activity score. The present study strongly supports the protective role of NK cell subsets in the pathogenesis of RA. PMID:23215763

Aggarwal, Ashish; Sharma, Aman; Bhatnagar, Archana

2013-06-01

355

Speciation in metal contaminated soils as revealed by an ion exchange resin membrane fractionation procedure  

Microsoft Academic Search

Ion exchangers have proven to be a useful tool in the study of metal speciation in aquatic environments, but have seen little application in the study of metal behavior in soil environments. The labile metal species in polluted soils were evaluated by equilibrating soil suspensions with ion exchange resin membranes of different types at pH values ranging from 3 to

J. Liang; J. J. Schoenau

1996-01-01

356

Membrane proteins implicated in long-chain fatty acid uptake by mammalian cells: CD36, FATP and FABPm  

Microsoft Academic Search

Long-chain fatty acids can transfer passively across mammalian cell membranes. However, under physiological conditions of low fatty acid to albumin ratios in the circulation, the major fraction of uptake appears to be mediated by a saturable, protein-facilitated component. A simple diffusion process becomes significant at high molar ratios of fatty acid to albumin as the concentration of free fatty acid

Nada Abumrad; Chris Coburn; Azeddine Ibrahimi

1999-01-01

357

Dynamics of cell membrane permeability changes at supraphysiological temperatures.  

PubMed Central

A quantitative fluorescent microscopy system was developed to characterize, in real time, the effects of supraphysiological temperatures between 37 degrees and 70 degrees C on the plasma membrane of mouse 3T3 fibroblasts and isolated rat skeletal muscle cells. Membrane permeability was assessed by monitoring the leakage as a function of time of the fluorescent membrane integrity probe calcein. The kinetics of dye leakage increased with increasing temperature in both the 3T3 fibroblasts and the skeletal muscle cells. Analytical solutions derived from a two-compartment transport model showed that, for both cell types, a time-dependent permeability assumption provided a statistically better fit of the model predictions to the data than a constant permeability assumption. This finding suggests that the plasma membrane integrity is continuously being compromised while cells are subjected to supraphysiological temperatures. Images FIGURE 1 FIGURE 2 FIGURE 3

Bischof, J C; Padanilam, J; Holmes, W H; Ezzell, R M; Lee, R C; Tompkins, R G; Yarmush, M L; Toner, M

1995-01-01

358

[Membrane contacts of endoplasmic reticulum with plasmalemma in plant cells].  

PubMed

Close contacts of endoplasmatic reticulum membrane with plasmalemma have been shown in common wheat root cells by means of electron microscopy. Qualitative analogy of these contacts with high-permeable intercellular contacts in animals has been preliminary established. PMID:20352693

Velikanov, G A; Ponomareva, A A; Belova, L P; Levanov, V Iu

2010-01-01

359

Subnanosecond electric pulses cause membrane permeabilization and cell death.  

PubMed

Subnanosecond electric pulses (200 ps) at electric field intensities on the order of 20 kV/cm cause the death of B16.F10 murine melanoma cells when applied for minutes with a pulse repetition rate of 10 kHz. The lethal effect of the ultrashort pulses is found to be caused by a combination of thermal effects and electrical effects. Studies on the cellular level show increased transport across the membrane at much lower exposure times or number of pulses. Exposed to 2000 pulses, NG108 cells exhibit an increase in membrane conductance, but only allow transmembrane currents to flow, if the medium is positively biased with respect to the cell interior. This means that the cell membrane behaves like a rectifying diode. This increase in membrane conductance is a nonthermal process, since the temperature rise due to the pulsing is negligible. PMID:21303739

Xiao, Shu; Guo, Siqi; Nesin, Vasyl; Heller, Richard; Schoenbach, Karl H

2011-02-07

360

Perceptual Grouping of Membrane Signals in Cell-based Assays  

SciTech Connect

Membrane proteins organize themselves in a linear fashion where adjacent cells are attached together along the basal-lateral region. Their intensity distributions are often heterogeneous and may lack specificity. Grouping of these linear structures can aid in segmentation and quantitative representation of protein localization. However, quantitative analysis of these signals is often hindered by noise, variation in scale, and perceptual features. This paper introduces an iterative voting method for inferring the membrane signal as it relates to continuity. A unique aspect of this technique is in the topography of the voting kernel, which is refined and reoriented iteratively. The technique can cluster and group membrane signals along the tangential direction. It has an excellent noise immunity and is tolerant to perturbations in scale. Application of this technique to quantitative analysis of cell-cell adhesion mediated by integral cell membrane proteins is demonstrated.

Chang, Hang; Andarawewa, Punya Kumari; Han, Ju; Barcellos-Hoff,Mary Helen; Parvin, Bahram

2007-02-02

361

PVDF/PVIm polymer blend films for fuel cell membranes  

NASA Astrophysics Data System (ADS)

We report the preparation and characterization of binary blend films of poly(vinylidene fluoride) (PVDF) and poly(1-ethyl-3-vinylimidazolium trifluoromethylsulfonimide) (PVIm+TFSI-). The potential utility of such materials in proton exchange membrane fuel cells is of particular interest. Thin PVDF/ PVIm+TFSI- films were fabricated from solutions of dimethly formamide by doctor blading. The nature of the PVDF crystalline polymorph and degree of crystallinity was evaluated as a function of the volume fraction of imidazolium polymer and thermal treatment. The morphology, thermal and mechanical characteristics of the blend films was studied by wide angle X-ray diffraction, thermogravimetry, calorimetry, and Fourier transform infrared spectroscopy. In these materials, conditions such as choice of solvent, drying conditions, and thermal treatment affect the crystal phase, crystallite size, and degree of crystallinity of PVDF as well as the distribution of PVIm+TFSI-. The beta phase of PVDF crystals dominates in as-cast films, while the alpha phase is observed after cooling from the melt. PVDF imparts mechanical strength and chemical stability to the composite films, and because of its high crystal melting point (Tm > 160 C), serves to improve the high temperature stability of resulting films.

Huang, Wenwen; Zhao, Meng; Yang, Fan; Farovitch, Lorne; Haghighi, Parisa; Macisco, Leonard; Swob, Tyler; Smith, Thomas; Cebe, Peggy

2012-02-01

362

Membrane Composition Tunes the Outer Hair Cell Motor  

NASA Astrophysics Data System (ADS)

Cholesterol and docosahexaenoic acid (DHA), an ?-3 fatty acid, affect membrane mechanical properties in different ways and modulate the function of membrane proteins. We have probed the functional consequence of altering cholesterol and DHA levels in the membranes of OHCs and prestin expressing HEK cells. Large, dynamic and reversible changes in prestin-associated charge movement and OHC motor activity result from altering the concentration of membrane cholesterol. Increasing membrane cholesterol shifts the q/V function ~ 50 mV in the hyperpolarizing direction, possibly a response related to increases in membrane stiffness. The voltage shift is linearly related to total membrane cholesterol. Increasing cholesterol also decreases the total charge moved in a linear fashion. Decreasing membrane cholesterol shifts the q/V function ~ 50 mV in the depolarizing direction with little or no effect on the amount of charge moved. In vivo increases in membrane cholesterol transiently increase but ultimately lead to decreases in DPOAE. Docosahexaenoic acid shifts the q/V function in the hyperpolarizing direction < 15 mV and increases total charge moved. Tuning of cochlear function by membrane cholesterol contributes to the exquisite temporal and frequency processing of mammalian hearing by optimizing the cochlear amplifier.

Rajagopalan, L.; Sfondouris, J.; Oghalai, J. S.; Pereira, F. A.; Brownell, W. E.

2009-02-01

363

Modeling of interactions between nanoparticles and cell membranes  

NASA Astrophysics Data System (ADS)

Rapid development of nanotechnology and ability to manufacture materials and devices with nanometer feature size leads to exciting innovations in many areas including the medical and electronic fields. However, the possible health and environmental impacts of manufactured nanomaterials are not fully known. Recent experimental reports suggest that some of the manufactured nanomaterials, such as fullerenes and carbon nanotubes, are highly toxic even in small concentrations. The goal of the current work is to understand the mechanisms responsible for the toxicity of nanomaterials. In the current study coarse-grained molecular dynamics simulations are employed to investigate the interactions between NPs and cellular membranes at a molecular level. One of the possible toxicity mechanisms of the nanomaterials is membrane disruption. Possibility of membrane disruption exposed to the manufactured nanomaterials are examined by considering chemical reactions and non-reactive physical interactions as chemical as well as physical mechanisms. Mechanisms of transport of carbon-based nanoparticles (fullerene and its derivative) across a phospholipid bilayer are investigated. The free energy profile is obtained using constrained simulations. It is shown that the considered nanoparticles are hydrophobic and therefore they tend to reside in the interior of the lipid bilayer. In addition, the dynamics of the membrane fluctuations is significantly affected by the nanoparticles at the bilayer-water interface. The hydrophobic interaction between the particles and membrane core induces the strong coupling between the nanoparticle motion and membrane deformation. It is observed that the considered nanoparticles affect several physical properties of the membrane. The nanoparticles embedded into the membrane interior lead to the membrane softening, which becomes more significant with increase in CNT length and concentration. The lateral pressure profile and membrane energy in the membrane containing the nanoparticles exhibit localized perturbation around the nanoparticle. The nanoparticles are not likely to affect membrane protein function by the weak perturbation of the internal stress in the membrane. Due to the short-ranged interactions between the nanoparticles, the nanoparticles would not form aggregates inside membranes. The effect of lipid peroxidation on cell membrane deformation is assessed. The peroxidized lipids introduce a perturbation to the internal structure of the membrane leading to higher amplitude of the membrane fluctuations. Higher concentration of the peroxidized lipids induces more significant perturbation. Cumulative effects of lipid peroxidation caused by nanoparticles are examined for the first time. The considered amphiphilic particle appears to reduce the perturbation of the membrane structure at its equilibrium position inside the peroxidized membrane. This suggests a possibility of antioxidant effect of the nanoparticle.

Ban, Young-Min

364

Cancer stem cell sorting from colorectal cancer cell lines by sedimentation field flow fractionation.  

PubMed

Recently, cancer stem cells (CSCs) have been identified in many types of cancers, such as colorectal cancer (CRC). CSCs seem to be involved in initiation, growth, and tumor metastasis, as well as in radio- and chemotherapy failures. CSCs appears as new biological targets for cancer therapy, requiring the development of noninvasive cell sorting methods. In this study, we used sedimentation field flow fractionation (SdFFF) to prepare enriched populations of CSCs from eight cell lines corresponding to different CRC grades. On the basis of phenotypic and functional characterizations, "hyperlayer" elution resulted in a fraction overexpressing CSC markers (CD44, CD166, EpCAM) for all cell lines. CSCs were eluted in the last fraction for seven out of eight cell lines, but in the first for HCT116. These results suggest, according to the literature, that two different pools of CSCs exist, quiescent and activated, which can both be sorted by SdFFF. Moreover, according to CSC properties, enriched fractions are able to form colonies. PMID:22236375

Mélin, Carole; Perraud, Aurélie; Akil, Hussein; Jauberteau, Marie-Odile; Cardot, Philippe; Mathonnet, Muriel; Battu, Serge

2012-01-09

365

Cell-free transfer of sterols by plant fractions  

SciTech Connect

Microsomes from etiolated hypocotyls of soybean or leaves of light-grown spinach radiolabeled in vivo with ({sup 3}H)acetate or in vitro with ({sup 3}H)squalene or ({sup 3}H)cholesterol as donor transferred radioactivity to unlabeled acceptor membranes immobilized on nitrocellulose. Most efficient transfer was with plasma membrane or tonoplast as the acceptor. The latter were highly purified by aqueous two-phase partition (plasma membrane) and preparative free-flow electrophoresis (tonoplast and plasma membrane). Plasma membrane- and tonoplast-free microsomes and purified mitochondria were less efficient acceptors. Sterol transfer was verified by thin-layer chromatography of extracted lipids. Transfer was time- and temperature-dependent, required ATP but was not promoted by cytosol. The nature of the donor (endoplasmic reticulum, Golgi apparatus or both) and of the transfer mechanism is under investigation.

Morre, D.J.; Wilkinson, F.E.; Morre, D.M. (Purdue Univ., West Lafayette, IN (USA)); Moreau, P. (CNRS, Boreaux (France)); Sandelius, A.S. (Univ. of Goteborg (Sweden)); Penel, C.; Greppin, H. (Univ. of Geneva (Switzerland))

1990-05-01

366

Cytotopographical specialization of enzymatically isolated rabbit retinal Müller (glial) cells: K+ conductivity of the cell membrane.  

PubMed

Müller (radial glial) cells were isolated from rabbit retinae by means of papaine and mechanical dissociation. Regional membrane properties of these cells were studied by intracellular microelectrode recordings of potential responses to local application of high K+ solutions. When different parts of the cell membrane were exposed to high K+, the amplitude of the depolarizing responses varied greatly, indicating a strong regional specialization of the membrane properties. Using morphometrical data of isolated rabbit Müller cells, and a simple circuit model, we calculated the endfoot membrane to constitute more than 80% of the total K+ conductance of the cell; the specific resistivity of the endfoot membrane was about 400 omega cm2, i.e., more than 40 times less than that of the membrane of the vitread process, which is immediately adjacent. This kind of regional membrane specialization seems to be optimized in respect to the Müller cells' ability to carry spatial buffering K+ currents. PMID:2976038

Reichenbach, A; Eberhardt, W

1988-01-01

367

Electron Spin Resonance Studies of Spin-Labeled Mammalian Cells by Detection of Surface-Membrane Signals  

Microsoft Academic Search

Lipid-soluble spin labels were incorporated into human lymphocytes and mouse L-cells and the resulting electron spin resonance spectra were compared with spectra obtained from similarly labeled human erythrocytes. Spin labels were found in all subcellular fractions of the nucleated cells that contained membranes. Spin-labeled cells remained viable and capable of replicating in vitro. Electron spin resonance signals from spin-labeled nucleated

Joseph Kaplan; Peter G. Canonico; William J. Caspary

1973-01-01

368

Amniotic membrane transplantation for partial limbal stem cell deficiency  

Microsoft Academic Search

AIMTo examine the efficacy, safety, and long term outcomes of amniotic membrane transplantation for corneal surface reconstruction in cases of partial limbal stem cell deficiency.METHODS17 eyes of 15 patients with partial limbal stem cell deficiency underwent superficial keratectomy of the conjunctivalised corneal surface followed by amniotic membrane transplantation. Cases were followed up for at least a year.RESULTSAll eyes exhibited a

David F Anderson; Pierre Ellies; Renato T F Pires; Scheffer C G Tseng

2001-01-01

369

Selective and Asymmetric Molecular Transport Across Electroporated Cell Membranes  

Microsoft Academic Search

Transport of a divalent cation (Ca2+) and three DNA indicators [ethidium bromide (EB), propidium iodide (PI), and ethidium homodimer (EthD-1)] across electroporated membranes of several mammalian cell lines was found to be selective and asymmetrical. In low salt medium, Ca2+ and EB were preferentially transported across the anode-facing cell membrane while PI and EthD-1 predominately entered at the site facing

Ephrem Tekle; R. Dean Astumian; P. Boon Chock

1994-01-01

370

Fibronectin coating of oxygenator membranes enhances endothelial cell attachment  

PubMed Central

Background Extracorporeal membrane oxygenation (ECMO) can replace the lungs’ gas exchange capacity in refractory lung failure. However, its limited hemocompatibility, the activation of the coagulation and complement system as well as plasma leakage and protein deposition hamper mid- to long-term use and have constrained the development of an implantable lung assist device. In a tissue engineering approach, lining the blood contact surfaces of the ECMO device with endothelial cells might overcome these limitations. As a first step towards this aim, we hypothesized that coating the oxygenator’s gas exchange membrane with proteins might positively influence the attachment and proliferation of arterial endothelial cells. Methods Sheets of polypropylene (PP), polyoxymethylpentene (TPX) and polydimethylsiloxane (PDMS), typical material used for oxygenator gas exchange membranes, were coated with collagen, fibrinogen, gelatin or fibronectin. Tissue culture treated well plates served as controls. Endothelial cell attachment and proliferation were analyzed for a period of 4 days by microscopic examination and computer assisted cell counting. Results Endothelial cell seeding efficiency is within range of tissue culture treated controls for fibronectin treated surfaces only. Uncoated membranes as well as all other coatings lead to lower cell attachment. A confluent endothelial cell layer develops on fibronectin coated PDMS and the control surface only. Conclusions Fibronectin increases endothelial cells’ seeding efficiency on different oxygenator membrane material. PDMS coated with fibronectin shows sustained cell attachment for a period of four days in static culture conditions.

2013-01-01

371

Importance of the Sampled Milk Fraction for the Prediction of Total Quarter Somatic Cell Count  

Microsoft Academic Search

This study investigated the changes in somatic cell counts (SCC) in different fractions of milk, with special emphasis on the foremilk and cisternal milk fractions. Therefore, in Experiment 1, quarter milk samples were defined as strict foremilk (F), cisternal milk (C), first 400 g of alveolar milk (A1), and the remaining alveolar milk (A2). Experiment 2 included 6 foremilk fractions

H. Sarikaya; R. M. Bruckmaier

2006-01-01

372

Materials issues in polymer electrolyte membrane fuel cells  

Microsoft Academic Search

Fuel cells have the potential to reduce the nation's energy use through increased energy conversion efficiency and dependence on imported petroleum by the use of hydrogen from renewable resources. The US DOE Fuel Cell subprogram emphasizes polymer electrolyte membrane (PEM) fuel cells as replacements for internal combustion engines in light-duty vehicles to support the goal of reducing oil use in

N. L. Garland; T. G. Benjamin; J. P. Kopasz

2008-01-01

373

Cell membranes: The electromagnetic environment and cancer promotion  

Microsoft Academic Search

Use of weak electromagnetic fields to study the sequence and energetics of events that couple humoral stimuli from surface receptor sites to the cell interior has identified cell membranes as a primary site of interaction, with these low frequency fields. Field modulation of cell surface chemical events indicates a major amplification of initial weak triggers associated with binding of hormones,

W. R. Adey

1988-01-01

374

A novel unitized regenerative proton exchange membrane fuel cell  

Microsoft Academic Search

A difficulty encountered in designing a unitized regenerative proton exchange membrane (PEM) fuel cell lies in the incompatibility of electrode structures and electrocatalyst materials optimized for either of the two functions (fuel cell or electrolyzer) with the needs of the other function. This difficulty is compounded in previous regenerative fuel cell designs by the fact that water, which is needed

O. J. Murphy; A. J. Cisar; A. Gonzalez-Martin; C. E. Salinas; S. F. Simpson

1995-01-01

375

Computational modeling and optimization of proton exchange membrane fuel cells  

Microsoft Academic Search

Improvements in performance, reliability and durability as well as reductions in production costs, remain critical prerequisites for the commercialization of proton exchange membrane fuel cells. In this thesis, a computational framework for fuel cell analysis and optimization is presented as an innovative alternative to the time consuming trial-and-error process currently used for fuel cell design. The framework is based on

Marc Secanell Gallart

2007-01-01

376

Controlled permeation of cell membrane by single bubble acoustic cavitation  

PubMed Central

Sonoporation is the membrane disruption generated by ultrasound and has been exploited as a non-viral strategy for drug and gene delivery. Acoustic cavitation of microbubbles has been recognized to play an important role in sonoporation. However, due to the lack of adequate techniques for precise control of cavitation activities and real-time assessment of the resulting sub-micron process of sonoporation, limited knowledge has been available regarding the detail processes and correlation of cavitation with membrane disruption at the single cell level. In the current study, we developed a combined approach including optical, acoustic, and electrophysiological techniques to enable synchronized manipulation, imaging, and measurement of cavitation of single bubbles and the resulting cell membrane disruption in real-time. Using a self-focused femtosecond laser and high frequency (7.44 MHz) pulses, a single microbubble was generated and positioned at a desired distance from the membrane of a Xenopus oocyte. Cavitation of the bubble was achieved by applying a low frequency (1.5 MHz) ultrasound pulse (duration 13.3 or 40 µs) to induce bubble collapse. Disruption of the cell membrane was assessed by the increase in the transmembrane current (TMC) of the cell under voltage clamp. Simultaneous high-speed bright field imaging of cavitation and measurements of the TMC were obtained to correlate the ultrasound-generated bubble activities with the cell membrane poration. The change in membrane permeability was directly associated with the formation of a sub-micrometer pore from a local membrane rupture generated by bubble collapse or bubble compression depending on ultrasound amplitude and duration. The impact of the bubble collapse on membrane permeation decreased rapidly with increasing distance (D) between the bubble (diameter d) and the cell membrane. The effective range of cavitation impact on membrane poration was determined to be D/d = 0.75. The maximum mean radius of the pores was estimated from the measured TMC to be 0.106 ± 0.032 µm (n = 70) for acoustic pressure of 1.5 MPa (duration 13.3 µs), and increased to 0.171 ± 0.030 µm (n = 125) for acoustic pressure of 1.7 MPa and to 0.182 ± 0.052 µm (n=112) for a pulse duration of 40 µs (1.5 MPa). These results from controlled cell membrane permeation by cavitation of single bubbles revealed insights and key factors affecting sonoporation at the single cell level.

Zhou, Y.; Yang, K.; Cui, J.; Ye, J. Y.; Deng, C. X.

2011-01-01

377

Dynamic continuity of cytoplasmic and membrane compartments between plant cells  

PubMed Central

Fluorescence photobleaching was employed to examine the intercellular movement of fluorescein and carboxyfluorescein between contiguous soybean root cells (SB-1 cell line) growing in tissue culture. Results of these experiments demonstrated movement of these fluorescent probes between cytoplasmic (symplastic) compartments. This symplastic transport was inhibited with Ca2+ in the presence of ionophore A23187, and also with the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA). Both of these agents have previously been demonstrated to inhibit gap junction-mediated cell-cell communication in animal cells. In a companion experiment, a fluorescent phospholipid analogue, N-4- nitrobenzo-2-oxa-1,3-diazole phosphatidylcholine (NBD-PC), was incorporated into soybean cell membranes to examine whether dynamic membrane continuity existed between contacting cells, a transport route not existing between animal cells. Photobleaching single soybean cells growing in a filamentous strand demonstrated that phospholipid did exchange between contiguous cells.

1988-01-01

378

Redistribution of membrane proteins in isolated mouse intestinal epithelial cells  

PubMed Central

Single mouse intestinal epithelial cells (IEC) may be isolated by the use of a combination of methods used for the isolation of IEC from other species. Isolated cells remain viable for several hours. The membrane integral enzymes alkaline phosphatase and leucine aminopeptidase of isolated IEC are localized to the brush borders of IEC in tissue and in most newly isolated IEC. With time, both enzymes are found distributed over the entire cell surface. Redistribution appears to occur by diffusion in the plane of the membrane. It is slowed, but not blocked, if cells are maintained at 0 degrees C instead of at 37 degrees C, and it is not blocked by fixation in 0.5-3% paraformaldehyde. Drugs that alter cell membrane potential or that affect cell levels of ATP enhance the rate of redistribution of the enzymes.

1980-01-01

379

Transepithelial transport of a viral membrane glycoprotein implanted into the apical plasma membrane of Madin-Darby canine kidney cells. II. Immunological quantitation  

PubMed Central

The envelope of vesicular stomatitis virus was fused with the apical plasma membrane of Madin-Darby canine kidney cells by low pH treatment. The fate of the implanted G protein was then followed using a protein A- binding assay, which was designed to quantitate the amount of G protein in the apical and the basolateral membranes. The implanted G protein was rapidly internalized at 31 degrees C, whereas at 10 degrees C no uptake was observed. Already after 15 min at 31 degrees C, a fraction of the G protein could be detected at the basolateral membrane. After 60 min 25-48% of the G protein was basolateral as measured by the protein A-binding assay. At the same time, 25-33% of the implanted G protein was detected at the apical membrane. Internalization of G protein was not affected by 20 mM ammonium chloride or by 10 microM monensin. However, the endocytosed G protein accumulated in intracellular vacuoles and redistribution back to the plasma membrane was inhibited. We conclude that the implanted G protein was rapidly internalized from the apical surface of Madin-Darby canine kidney cells and a major fraction was routed to the basolateral domain.

1983-01-01

380

Identification of laminin binding proteins in cell membranes of a human colon adenocarcinoma cell line  

Microsoft Academic Search

The invasion of malignant cells through the basement membrane is a critical step in local infiltration and metastasis. Adhesion and invasion of malignant cells may be modulated by their receptor mediated binding to the basement membrane glycoprotein laminin. We studied the specific adhesion of human colon adenocarcinoma derived HT 29 cells to laminin and its proteolytic fragments. The major cell

A Stallmach; D Schuppan; J Dax; C Hanski; E O Riecken

1990-01-01

381

Toward mechanical manipulations of cell membranes and membrane proteins using an atomic force microscope  

Microsoft Academic Search

Recent advances in the use of the atomic force microscope (AFM) for manipulating cell membranes and membrane proteins are\\u000a reviewed. Early pioneering work on measurements of the magnitude of the force required to create indentations with defined\\u000a depth on their surfaces and to separate interacting pairs of avidin-biotin, antigen-antibody, and complementary DNA pairs\\u000a formed the basis of this field. The

Atsushi Ikai; Rehana Afrin

2003-01-01

382

Cryopreservation of fractionated, highly motile human spermatozoa: effect on membrane phosphatidylserine externalization and lipid peroxidation  

Microsoft Academic Search

INTRODUCTION: This study investigated lipid peroxidation (LPO) and membrane integrity following cryopreserv- ation-thawing. METHODS: Infertile men (study group) and donors (control group) were examined. Purified populations of highly motile spermatozoa were cryopreserved using TEST-yolk buffer and glycerol (TYB-G) followed by quick thaw. LPO was measured by a spectrophotometric assay, with and without a ferrous ion promoter. Annexin V binding was

Alessandro Schuffner; Mahmood Morshedi; Sergio Oehninger

383

Controlled electroporation of the plasma membrane in microfluidic devices for single cell analysis  

PubMed Central

Chemical cytometry on a single cell level is of interest to various biological fields ranging from cancer to stem cell research. The impact chemical cytometry can exert in these fields depends on the dimensionality of the retrievable analytes content. To this point, the number of different analytes identifiable and additionally their subcellular localization is of interest. To address this, we present an electroporation based approach for selective lysis of only the plasma membrane, which permits analysis of the dissolved cytoplasm, while reducing contributions from the nucleus and membrane bound fractions of the cell analytes. The use of 100 ?s long pulse and a well defined DC electric field gradient of ?4.5 kV·cm?1 generated by 3D electrodes initiates release of a cytoplasm marker in ?1 s, while retaining nuclear fluorescence markers.

Shah, Duoaud; Steffen, Milan; Lilge, Lothar

2012-01-01

384

Anaerobic digestion of the organic fraction of municipal solid waste in a two-stage membrane process.  

PubMed

A batch of the Organic Fraction of Municipal Solid Waste (OFMSW) was treated in a two-step process with effluent recirculation comprising a novel hydrolytic reactor (HR) followed by a Submerged Anaerobic Membrane Bioreactor (SAMBR) operating at a stable permeate flux of 5.6 L/m(2) hr (LMH). A soluble COD removal higher than 95% was obtained from the SAMBR. The soluble COD as well as the Total Suspended Solids (TSS) did not build up due to efficient hydrolysis inside the SAMBR, and no VFA accumulation occurred due to the complete retention of methanogens by the membrane as well as the formation of syntrophic associations. Because of the microfiltration membrane in the second reactor a stabilized leachate was obtained from the very first days of the treatment and the highly stable process enabled shorter treatment periods compared to traditional leach bed processes. This experiment showed that the recycle of the stabilised leachate does not lead to a build up of SCOD. Size exclusion chromatography analysis confirmed that high molecular weight compounds were completely degraded and did not appear in the SAMBR permeate, and that low molecular weight fulvic-like and medium MW material were present in the permeate of the SAMBR but their concentration remained stable with time. PMID:19844043

Trzcinski, A P; Stuckey, D C

2009-01-01

385

Elastic Membrane Heterogeneity of Living Cells Revealed by Stiff Nanoscale Membrane Domains  

PubMed Central

Many approaches have been developed to characterize the heterogeneity of membranes in living cells. In this study, the elastic properties of specific membrane domains in living cells are characterized by atomic force microscopy. Our data reveal the existence of heterogeneous nanometric scale domains with specific biophysical properties. We focused on glycosylphosphatidylinositol (GPI)-anchored proteins, which play an important role in membrane trafficking and cell signaling under both physiological and pathological conditions and which are known to partition preferentially into cholesterol-rich microdomains. We demonstrate that these GPI-anchored proteins reside within domains that are stiffer than the surrounding membrane. In contrast, membrane domains containing the transferrin receptor, which does not associate with cholesterol-rich regions, manifest no such feature. The heightened stiffness of GPI domains is consistent with existing data relating to the specific condensation of lipids and the slow diffusion rates of lipids and proteins therein. Our quantitative data may forge the way to unveiling the links that exist between membrane stiffness, molecular diffusion, and signaling activation.

Roduit, Charles; van der Goot, F. Gisou; De Los Rios, Paolo; Yersin, Alexandre; Steiner, Pascal; Dietler, Giovanni; Catsicas, Stefan; Lafont, Frank; Kasas, Sandor

2008-01-01

386

Elastic membrane heterogeneity of living cells revealed by stiff nanoscale membrane domains.  

PubMed

Many approaches have been developed to characterize the heterogeneity of membranes in living cells. In this study, the elastic properties of specific membrane domains in living cells are characterized by atomic force microscopy. Our data reveal the existence of heterogeneous nanometric scale domains with specific biophysical properties. We focused on glycosylphosphatidylinositol (GPI)-anchored proteins, which play an important role in membrane trafficking and cell signaling under both physiological and pathological conditions and which are known to partition preferentially into cholesterol-rich microdomains. We demonstrate that these GPI-anchored proteins reside within domains that are stiffer than the surrounding membrane. In contrast, membrane domains containing the transferrin receptor, which does not associate with cholesterol-rich regions, manifest no such feature. The heightened stiffness of GPI domains is consistent with existing data relating to the specific condensation of lipids and the slow diffusion rates of lipids and proteins therein. Our quantitative data may forge the way to unveiling the links that exist between membrane stiffness, molecular diffusion, and signaling activation. PMID:17981897

Roduit, Charles; van der Goot, F Gisou; De Los Rios, Paolo; Yersin, Alexandre; Steiner, Pascal; Dietler, Giovanni; Catsicas, Stefan; Lafont, Frank; Kasas, Sandor

2007-11-02

387

Fractionation of different PEGylated forms of a protein by chromatography using environment-responsive membranes  

Microsoft Academic Search

PEGylation of therapeutic proteins can enhance their efficacy as biopharmaceuticals through increased stability and hydrophilicity, and decreased immunogenicity. A site-specific PEGylated protein (e.g. mono-PEGylated at N-terminus) is frequently desirable as a product. However, multiple-PEGylated forms are frequently produced as byproducts. In this paper we discuss the fractionation of the different PEGylated forms of a protein by hydrophobic interaction chromatography using

Deqiang Yu; Xiaojiao Shang; Raja Ghosh

2010-01-01

388

Simultaneous manipulation and detection of living cell membrane dynamics  

NASA Astrophysics Data System (ADS)

We report a novel optical-tweezers-based method to study the membrane motion at the leading edge of biological cells with nanometer spatial and microsecond temporal resolution. A diffraction-limited laser spot was positioned at the leading edge of a cell, and the forward scattered light was imaged on a quadrant photodiode that served as a position sensitive device. The universality of this technique is demonstrated with different cell types. We investigated the membrane motion at the leading edge of red blood cells in detail and showed that this technique can achieve simultaneous manipulation and detection of cellular edge dynamics with unprecedented precision.

Gögler, Michael; Betz, Timo; Alfons Käs, Josef

2007-07-01

389

Gaseous oxide toxicity evaluated with cell monolayers on collagen-coated, gas-permeable teflon membranes  

SciTech Connect

A system was developed to evaluate the cytotoxic potential of gaseous oxides in vitro. Target cells were MRC-5 human lung fibroblasts cultivated as monolayers on gas-permeable, FEP-Teflon membranes. Membranes were secured in Chamber/Dishes with a 25 mm diameter well. To promote attachment of fibroblasts to the membranes, the latter were incubated in collagen (Vitrogen) solutions for 10 min prior to plating the cells. The collagen pretreatment was significantly more effective than poly-L-lysine, fetal calf serum, polybrene and bovine serum albumin. Several types (mouse and calf) of acid-soluble and alcohol-soluble collagen fractions were evaluated, and all of them promoted cell attachment with equivalent efficiency. Cells on membranes were exposed to gases in a Plexiglass chamber with a gas flow of 2L/min. Sulfur dioxide caused a marked loss in cell viability (as indicated by ATP content of the monolayer) after 30 min exposure to 0.01% and 0.005%. A level of 0.001% did not affect viability, and none of the levels tested caused a sloughing of the monolayer after 90 min. Nitrogen dioxide induced a more modest drop in cell viability after 30 min exposure to 0.1%, while 0.005% and 0.05% were nontoxic. No cell sloughing occurred with NO/sub 2/ exposures, and exposures to CO/sub 2/ at levels of 20% for 90 min were nontoxic. This system, with cell culture monolayers on gas-permeable Teflon membranes, is simple and convenient. As such, it has potential application to cytotoxicity evaluations with numerous gases. 18 references, 6 figures, 1 table.

Gabridge, M.G.; Gladd, M.F.

1984-03-01

390

Recent developments in proton exchange membranes for fuel cells  

SciTech Connect

Proton exchange membranes (PEMs) that operate at temperatures above 120 °C are needed to avoid catalyst poisoning, speed up electrochemical reactions, simplify the design and reduce the cost of fuel cells. This review summarizes developments in PEMs over the last five years. In order to design new membranes for elevated temperature operation, one must understand the chemistry, morphology and dynamics of protons and small molecules in existing membranes. The integration of experiments with modeling and simulation can shed light on the hierarchical structure of the membrane and dynamical processes associated with molecular transport. Based on such a fundamental understanding, membranes can be modified by controlling the polymer chemistry and architecture or adding inorganic fillers that can retain water under low relative humidity conditions. In addition, the development of anhydrous membranes based on phosphoric acid doped polymers, ionic liquid-infused polymer gels and solid acids can enable fuel cell operation above 150 °C. Considerable work remains to be done to identify proton transport mechanisms in novel membranes and evaluate membrane durability under real world operating conditions.

Devanathan, Ramaswami

2008-07-23

391

Membrane Targeting of P-type ATPases in Plant Cells  

SciTech Connect

How membrane proteins are targeted to specific subcellular locations is a very complex and poorly understood area of research. Our long-term goal is to use P-type ATPases (ion pumps), in a model plant system Arabidopsis, as a paradigm to understand how members of a family of closely related membrane proteins can be targeted to different subcellular locations. The research is divided into two specific aims. The first aim is focused on determining the targeting destination of all 10 ACA-type calcium pumps (Arabidopsis Calcium ATPase) in Arabidopsis. ACAs represent a plant specific-subfamily of plasma membrane-type calcium pumps. In contrast to animals, the plant homologs have been found in multiple membrane systems, including the ER (ACA2), tonoplast (ACA4) and plasma membrane (ACA8). Their high degree of similarity provides a unique opportunity to use a comparative approach to delineate the membrane specific targeting information for each pump. One hypothesis to be tested is that an endomembrane located ACA can be re-directed to the plasma membrane by including targeting information from a plasma membrane isoform, ACA8. Our approach is to engineer domain swaps between pumps and monitor the targeting of chimeric proteins in plant cells using a Green Fluorescence Protein (GFP) as a tag. The second aim is to test the hypothesis that heterologous transporters can be engineered into plants and targeted to the plasma membrane by fusing them to a plasma membrane proton pump. As a test case we are evaluating the targeting properties of fusions made between a yeast sodium/proton exchanger (Sod2) and a proton pump (AHA2). This fusion may potentially lead to a new strategy for engineering salt resistant plants. Together these aims are designed to provide fundamental insights into the biogenesis and function of plant cell membrane systems.

Jeffrey F. Harper, Ph.D.

2004-06-30

392

Cdc42 localization and cell polarity depend on membrane traffic  

PubMed Central

Cell polarity is essential for cell division, cell differentiation, and most differentiated cell functions including cell migration. The small G protein Cdc42 controls cell polarity in a wide variety of cellular contexts. Although restricted localization of active Cdc42 seems to be important for its distinct functions, mechanisms responsible for the concentration of active Cdc42 at precise cortical sites are not fully understood. In this study, we show that during directed cell migration, Cdc42 accumulation at the cell leading edge relies on membrane traffic. Cdc42 and its exchange factor ?PIX localize to intracytosplasmic vesicles. Inhibition of Arf6-dependent membrane trafficking alters the dynamics of Cdc42-positive vesicles and abolishes the polarized recruitment of Cdc42 and ?PIX to the leading edge. Furthermore, we show that Arf6-dependent membrane dynamics is also required for polarized recruitment of Rac and the Par6–aPKC polarity complex and for cell polarization. Our results demonstrate influence of membrane dynamics on the localization and activation of Cdc42 and consequently on directed cell migration.

Osmani, Nael; Peglion, Florent; Chavrier, Philippe

2010-01-01

393

Sequential CD34 cell fractionation by magnetophoresis in a magnetic dipole flow sorter  

PubMed Central

Cell separation and fractionation based on fluorescent and magnetic labeling procedures are common tools in contemporary research. These techniques rely on binding of fluorophores or magnetic particles conjugated to antibodies to target cells. Cell surface marker expression levels within cell populations vary with progression through the cell cycle. In an earlier work we showed the reproducible magnetic fractionation (single pass) of the Jurkat cell line based on the population distribution of CD45 surface marker expression. Here we present a study on magnetic fractionation of a stem and progenitor cell (SPC) population using the established acute myelogenous leukemia cell line KG-1a as a cell model. The cells express a CD34 cell surface marker associated with the hematopoietic progenitor cell activity and the progenitor cell lineage commitment (related to the CD34 marker expression level). The CD34 expression level is approximately an order of magnitude lower than that of the CD45 marker, which required further improvements of the magnetic fractionation apparatus. The cells were immuno-magnetically labeled using a sandwich of anti CD34 antibody-phycoerythrin (PE) conjugate and anti PE magnetic nanobead and fractionated into eight components using a continuous flow dipole magnetophoresis apparatus. The CD34 marker expression distribution between sorted fractions was measured by quantitative PE flow cytometry (using QuantiBRITE™ PE calibration beads), and it was shown to be correlated with the cell magnetophoretic mobility distribution. A flow outlet addressing scheme based on the concept of the transport lamina thickness was used to control cell distribution between the eight outlet ports. The fractional cell distributions showed good agreement with numerical simulations of the fractionation based on the cell magnetophoretic mobility distribution in the unsorted sample.

Schneider, Thomas; Karl, Stephan; Moore, Lee R.; Chalmers, Jeffrey J.; Williams, P. Stephen; Zborowski, Maciej

2010-01-01

394

Cytotoxic effects of Kingella kingae outer membrane vesicles on human cells.  

PubMed

Kingella kingae is an emerging pathogen causing osteoarticular infections in pediatric patients. Electron microscopy of K. kingae clinical isolates revealed the heterogeneously-sized membranous structures blebbing from the outer membrane that were classified as outer membrane vesicles (OMVs). OMVs purified from the secreted fraction of a septic arthritis K. kingae isolate were characterized. Among several major proteins, K. kingae OMVs contained virulence factors RtxA toxin and PilC2 pilus adhesin. RtxA was also found secreted as a soluble protein in the extracellular environment indicating that the bacterium may utilize different mechanisms for the toxin delivery. OMVs were shown to be hemolytic and possess some leukotoxic activity while high leukotoxicity was detected in the non-hemolytic OMV-free component of the secreted fraction. OMVs were internalized by human osteoblasts and synovial cells. Upon interaction with OMVs, the cells produced increased levels of human granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 6 (IL-6) suggesting that these cytokines might be involved in the signaling response of infected joint and bone tissues during natural K. kingae infection. This study is the first report of OMV production by K. kingae and demonstrates that OMVs are a complex virulence factor of the organism causing cytolytic and inflammatory effects on host cells. PMID:21443941

Maldonado, R; Wei, R; Kachlany, S C; Kazi, M; Balashova, N V

2011-04-02

395

Cytotoxic effects of Kingella kingae outer membrane vesicles on human cells  

PubMed Central

Kingella kingae is an emerging pathogen causing osteoarticular infections in pediatric patients. Electron microscopy of K. kingae clinical isolates revealed the heterogeneously-sized membranous structures blebbing from the outer membrane that were classified as outer membrane vesicles (OMVs). OMVs purified from the secreted fraction of a septic arthritis K. kingae isolate were characterized. Among several major proteins, K. kingae OMVs contained virulence factors RtxA toxin and PilC2 pilus adhesin. RtxA was also found secreted as a soluble protein in the extracellular environment indicating that the bacterium may utilize different mechanisms for the toxin delivery. OMVs were shown to be hemolytic and possess some leukotoxic activity while high leukotoxicity was detected in the non-hemolytic OMV-free component of the secreted fraction. OMVs were internalized by human osteoblasts and synovial cells. Upon interaction with OMVs, the cells produced increased levels of human granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleuskin 6 (IL-6) suggesting that these cytokines might be involved in the signaling response of infected joint and bone tissues during natural K. kingae infection. This study is the first report of OMV production by K. kingae and demonstrates that OMVs are a complex virulence factor of the organism causing cytolytic and inflammatory effects on host cells.

Maldonado, R; Wei, R; Kachlany, SC; Kazi, M; Balashova, NV

2011-01-01

396

Fuel cell electrolyte membrane with basic polymer  

SciTech Connect

The present invention is an electrolyte membrane comprising an acid and a basic polymer, where the acid is a low-volatile acid that is fluorinated and is either oligomeric or non-polymeric, and where the basic polymer is protonated by the acid and is stable to hydrolysis.

Larson, James M. (Saint Paul, MN); Pham, Phat T. (Little Canada, MN); Frey, Matthew H. (Cottage Grove, MN); Hamrock, Steven J. (Stillwater, MN); Haugen, Gregory M. (Edina, MN); Lamanna, William M. (Stillwater, MN)

2010-11-23

397

Fuel cell electrolyte membrane with basic polymer  

SciTech Connect

The present invention is an electrolyte membrane comprising an acid and a basic polymer, where the acid is a low-volatile acid that is fluorinated and is either oligomeric or non-polymeric, and where the basic polymer is protonated by the acid and is stable to hydrolysis.

Larson, James M.; Pham, Phat T.; Frey, Matthew H.; Hamrock, Steven J.; Haugen, Gregory M.; Lamanna, William M.

2012-12-04

398

Contrasting molecular dynamics in red and purple membrane fractions of the Halobacterium halobium  

SciTech Connect

/sup 2/H-nuclear magnetic resonance (NMR) has been used to study the dynamics of amino acid residues in bacteriorhodopsin with results that depend on the method of sample preparation. We show here that in (/sup 2/H)-leucine-labeled samples the intensity of the isotropic signal varies according to the degree of residual contamination of the sample with red membrane. We conclude that few of the surface leucine residues of bacteriorhodopsin are moving isotropically on the /sup 2/H-NMR time scale.

Herzfeld, J.; Mulliken, C.M.; Siminovitch, D.J.; Griffin, R.G.

1987-11-01

399

Incorporation of Photosynthetic Reaction Centers in the Membrane of Human Cells: Toward a New Tool for Optical Control of Cell Activity  

SciTech Connect

The Photosystem I (PSI) reaction center is a photosynthetic membrane complex in which light-induced charge separation is accompanied by the generation of an electric potential. It has been recently proposed as a means to confer light sensitivity to cells possessing voltage-activated ion channels, but the feasibility of heterologous incorporation has not been demonstrated. In this work, methods of delivery and detection of PSI in the membrane of human cells are presented. Purified fractions of PSI were reconstituted in proteoliposomes that were used as vehicles for the membrane incorporation. A fluorescent impermeable dye was entrapped in the vesicles to qualitatively analyze the nature of the vesicle cell interaction. After incorporation, the localization and orientation of the complexes in the membrane was studied using immuno-fluorescence microscopy. The results showed complexes oriented as in native membranes, which were randomly distributed in clusters over the entire surface of the cell. Additionally, analysis of cell viability showed that the incorporation process does not damage the cell membrane. Taken together, the results of this work suggest that the mammalian cellular membrane is a reasonable environment for the incorporation of PSI complexes, which opens the possibility of using these molecular photovoltaic structures for optical control of cell activity.

Pennisi, Cristian P. [Aalborg University, Aalborg, Denmark; Jensen, Poul Erik [VKR Research Center, University of Copenhagen, Denmark; Zachar, Vladimir [Laboratory for Stem Cell Research, Aalborg University, Aalborg, Denmark; Greenbaum, Elias [ORNL; Yoshida, Ken [Aalborg University, Aalborg, Denmark

2009-01-01

400

Nitrogen Isotope Fractionation Increases with the Cell-Specific Dissimilatory Nitrate Reduction Rate  

NASA Astrophysics Data System (ADS)

The use of the nitrogen (N) isotopes to estimate the impacts and rates of different N transformations depends on knowledge of their extent of isotope fractionation under environmentally relevant physico-chemical conditions. Though the extent of N isotope fractionation during denitrification by pure cultures of bacteria has been determined in the past, relatively large variation in the isotope effect during apparently replicate experiments has been perplexing and the values that should be most relevant for environmental applications have not been clear. We measured the extent of N and O isotope fractionation during nitrate reduction by two bacterial denitrifiers, Pseudomonas chlororaphis ATCC 43928 and Paracoccus denitrificans ATCC 19367 that were grown in 1L batch reactors in the presence of differing carbon sources that included complex organic (e.g, bactopeptone and casein) or defined (e.g., glucose and acetate) carbon compounds and varying concentrations of dissolved oxygen (0 - 4 mM) and nitrate (25 - 800 mM) in the assay medium. For P. denitrificans and P. Chlororaphis , the total range of the N isotope effect (15?) varied from 22.3 to 9.3 ‰ and 34.3 to 15.6 ‰, respectively. Despite this large variation, the O-to-N isotope effect ratio centered around 1, consistent with our previous work. A systematic pattern that has emerged from these studies is that the N and O isotope effect during denitrification increases with increasing cell specific nitrate reduction (CSNR) rate. This sense of variation runs counter to expectations from studies of carbon and sulfur isotope effects during methanogenesis and sulfate reduction, respectively, in which higher substrate consumption rates are associated with lower isotope effects. As with many multi-step microbial processes, variability in the dissimilatory nitrate reduction isotope effect may arise from variation in the “relative” rate and reversibility of (1) nitrate uptake into the denitrifying cell, and/or (2) nitrate binding by dissimilatory nitrate reductase. As an example of a plausible explanation for the isotope effect/CSNR rate relationship that involves cellular uptake, an increase in the CSNR rate may be matched by an even greater increase in nitrate uptake across the cell membrane, leading to more nitrate efflux from the cell and thus more complete expression of the nitrate reductase isotope effect in the media. In addition to discussing such mechanistic possibilities and their physiological implications, we will consider the significance of our findings for the interpretation of oceanic nitrate isotope data.

Kritee, K.; Sigman, D. M.; Granger, J.

2009-12-01

401

Fractional proliferation: a method to deconvolve cell population dynamics from single-cell data.  

PubMed

We present an integrated method that uses extended time-lapse automated imaging to quantify the dynamics of cell proliferation. Cell counts are fit with a quiescence-growth model that estimates rates of cell division, entry into quiescence and death. The model is constrained with rates extracted experimentally from the behavior of tracked single cells over time. We visualize the output of the analysis in fractional proliferation graphs, which deconvolve dynamic proliferative responses to perturbations into the relative contributions of dividing, quiescent (nondividing) and dead cells. The method reveals that the response of 'oncogene-addicted' human cancer cells to tyrosine kinase inhibitors is a composite of altered rates of division, death and entry into quiescence, a finding that challenges the notion that such cells simply die in response to oncogene-targeted therapy. PMID:22886092

Tyson, Darren R; Garbett, Shawn P; Frick, Peter L; Quaranta, Vito

2012-08-12

402

Fractional Proliferation: A method to deconvolve cell population dynamics from single-cell data  

PubMed Central

We present an integrated method that exploits extended time-lapse automated imaging to quantify dynamics of cell proliferation. Cell counts are fit with a Quiescence-Growth model that estimates rates of cell division, entry into quiescence and death. The model is constrained with rates extracted experimentally from the behavior of tracked single cells over time. We visualize the output of the analysis in Fractional Proliferation graphs, which deconvolve dynamic proliferative responses to perturbations into the relative contributions of dividing, quiescent (non-dividing) and dead cells. The method reveals that the response of “oncogene-addicted” human cancer cells to tyrosine kinase inhibitors is a composite of altered rates of division, death and entry into quiescence, challenging the notion that such cells simply ‘die’ in response to oncogene-targeted therapy.

Tyson, Darren R.; Garbett, Shawn P.; Frick, Peter L.; Quaranta, Vito

2012-01-01

403

Role of Rab GTPases in Membrane Traffic and Cell Physiology  

PubMed Central

Intracellular membrane traffic defines a complex network of pathways that connects many of the membrane-bound organelles of eukaryotic cells. Although each pathway is governed by its own set of factors, they all contain Rab GTPases that serve as master regulators. In this review, we discuss how Rabs can regulate virtually all steps of membrane traffic from the formation of the transport vesicle at the donor membrane to its fusion at the target membrane. Some of the many regulatory functions performed by Rabs include interacting with diverse effector proteins that select cargo, promoting vesicle movement, and verifying the correct site of fusion. We describe cascade mechanisms that may define directionality in traffic and ensure that different Rabs do not overlap in the pathways that they regulate. Throughout this review we highlight how Rab dysfunction leads to a variety of disease states ranging from infectious diseases to cancer.

HUTAGALUNG, ALEX H.; NOVICK, PETER J.

2013-01-01

404

Accumulation of an Antidepressant in Vesiculogenic Membranes of Yeast Cells Triggers Autophagy  

PubMed Central

Many antidepressants are cationic amphipaths, which spontaneously accumulate in natural or reconstituted membranes in the absence of their specific protein targets. However, the clinical relevance of cellular membrane accumulation by antidepressants in the human brain is unknown and hotly debated. Here we take a novel, evolutionarily informed approach to studying the effects of the selective-serotonin reuptake inhibitor sertraline/Zoloft® on cell physiology in the model eukaryote Saccharomyces cerevisiae (budding yeast), which lacks a serotonin transporter entirely. We biochemically and pharmacologically characterized cellular uptake and subcellular distribution of radiolabeled sertraline, and in parallel performed a quantitative ultrastructural analysis of organellar membrane homeostasis in untreated vs. sertraline-treated cells. These experiments have revealed that sertraline enters yeast cells and then reshapes vesiculogenic membranes by a complex process. Internalization of the neutral species proceeds by simple diffusion, is accelerated by proton motive forces generated by the vacuolar H+-ATPase, but is counteracted by energy-dependent xenobiotic efflux pumps. At equilibrium, a small fraction (10–15%) of reprotonated sertraline is soluble while the bulk (90–85%) partitions into organellar membranes by adsorption to interfacial anionic sites or by intercalation into the hydrophobic phase of the bilayer. Asymmetric accumulation of sertraline in vesiculogenic membranes leads to local membrane curvature stresses that trigger an adaptive autophagic response. In mutants with altered clathrin function, this adaptive response is associated with increased lipid droplet formation. Our data not only support the notion of a serotonin transporter-independent component of antidepressant function, but also enable a conceptual framework for characterizing the physiological states associated with chronic but not acute antidepressant administration in a model eukaryote.

Lee, Sean; Perlstein, Ethan O.

2012-01-01

405

Accumulation of an antidepressant in vesiculogenic membranes of yeast cells triggers autophagy.  

PubMed

Many antidepressants are cationic amphipaths, which spontaneously accumulate in natural or reconstituted membranes in the absence of their specific protein targets. However, the clinical relevance of cellular membrane accumulation by antidepressants in the human brain is unknown and hotly debated. Here we take a novel, evolutionarily informed approach to studying the effects of the selective-serotonin reuptake inhibitor sertraline/Zoloft® on cell physiology in the model eukaryote Saccharomyces cerevisiae (budding yeast), which lacks a serotonin transporter entirely. We biochemically and pharmacologically characterized cellular uptake and subcellular distribution of radiolabeled sertraline, and in parallel performed a quantitative ultrastructural analysis of organellar membrane homeostasis in untreated vs. sertraline-treated cells. These experiments have revealed that sertraline enters yeast cells and then reshapes vesiculogenic membranes by a complex process. Internalization of the neutral species proceeds by simple diffusion, is accelerated by proton motive forces generated by the vacuolar H(+)-ATPase, but is counteracted by energy-dependent xenobiotic efflux pumps. At equilibrium, a small fraction (10-15%) of reprotonated sertraline is soluble while the bulk (90-85%) partitions into organellar membranes by adsorption to interfacial anionic sites or by intercalation into the hydrophobic phase of the bilayer. Asymmetric accumulation of sertraline in vesiculogenic membranes leads to local membrane curvature stresses that trigger an adaptive autophagic response. In mutants with altered clathrin function, this adaptive response is associated with increased lipid droplet formation. Our data not only support the notion of a serotonin transporter-independent component of antidepressant function, but also enable a conceptual framework for characterizing the physiological states associated with chronic but not acute antidepressant administration in a model eukaryote. PMID:22529904

Chen, Jingqiu; Korostyshevsky, Daniel; Lee, Sean; Perlstein, Ethan O

2012-04-18

406

Electrical Resistance of Cell Membranes of Avena coleoptiles.  

PubMed

The cell membrane resistance to direct current was measured in single cells for the first time in a higher plant tissue, oat coleoptiles (Avena sativa). On the assumption that the current density over the cell surface was uniform, a mean value of about 1300 ohm-cm(2) was found for cells in an external nutrient medium containing 1 mmole each of K(+), Na(+), and Ca(++) per liter. As expected, either decreasing K(+) concentration or increasing Ca(++) concentration increased the resistance. PMID:17807848

Higinbotham, N; Hope, A B; Findlay, G P

1964-03-27

407

Rapid purification of human ductal cells from human pancreatic fractions with surface antibody CA19-9.  

PubMed

Generating human insulin-secreting cells for cell therapy of diabetes represents a highly competitive world challenge. Human ductal cells can give rise to islets in vivo and in vitro. The goal of this study was to devise a rapid sorting method to highly purify human ductal cells from pancreatic tissue using a pan-ductal membrane antibody carbohydrate antigen 19-9 (CA19-9). Human pancreatic sections confirmed antibody specificity. The human exocrine fraction (30% ductal cells) was sorted with magnetic bead technology or by FACS. Immunocytochemistry post-sorting determined ductal cell content. The manual magnetic bead technique resulted in 74%+/-2 (n = 4) CA19 positive cells. Whereas the automated AutoMACS technique (n = 5) yielded 92.6%+/-0.5 CA19-9 positive cells with only a minor beta cell contamination (0.2%+/-0.03); cell yield post-sorting was 12.9%+/-2.5 (1.69+/-0.41 x 10(6) cells) with 51.7%+6.5 (n = 5) viability post-sorting. The FACS (n = 6) resulted in 97.1%+/-0.82 CA19-9 positive cells, a cell yield of 25.5%+/-5.6 (5.03+/-1.0 x 10(6)), with 72.1%+/-6.1 viability post-sorting. PMID:15207697

Gmyr, Valéry; Belaich, Sandrine; Muharram, Ghaffar; Lukowiak, Bruno; Vandewalle, Brigitte; Pattou, François; Kerr-Conte, Julie

2004-07-16