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Sample records for phosphate acceptor site

  1. Photovoltaic activity of layered zirconium phosphates containing covalently grafted ruthenium tris(bipyridyl) and diquat phosphonates as electron donor/acceptor sites.

    PubMed

    Teruel, Laura; Alonso, Marina; Quintana, M Carmen; Salvador, Alvaro; Juanes, Olga; Rodriguez-Ubis, Juan Carlos; Brunet, Ernesto; García, Hermenegildo

    2009-04-28

    Two layered zirconium phosphates containing Ru(bpy)(3)(2+) mono- or diphosphonates and diquat, {Ru(bpy)(3)(2+)[]/ZrP/DQ(++)} and Ru(bpy)(3)(2+)[]/ZrP/DQ(++), covalently attached to the phosphate layers exhibit notable photovoltaic response (the maximum V(OC), J(SC), and FF were 0.093 V, 16.8 microA cm(-2) and 0.33, respectively). The photocurrent spectra indicate that the photovoltaic response is due predominantly to direct photoexcitation of gamma-ZrP host, Ru(bpy)(3)(2+) and diquat acting as hole and electron traps, respectively, for the charge separated state of the semiconductor.

  2. Engineered oligosaccharyltransferases with greatly relaxed acceptor site specificity

    PubMed Central

    Ollis, Anne A.; Zhang, Sheng; Fisher, Adam C.; DeLisa, Matthew P.

    2015-01-01

    The Campylobacter jejuni protein glycosylation locus (pgl) encodes machinery for asparagine-linked (N-linked) glycosylation and serves as the archetype for bacterial N-glycosylation. This machinery has been functionally transferred into Escherichia coli, thereby enabling convenient mechanistic dissection of the N-glycosylation process in this genetically tractable host. Here, we sought to identify sequence determinants in the oligosaccharyltransferase PglB that restrict its specificity to only those glycan acceptor sites containing a negatively charged residue at the −2 position relative to asparagine. This involved creation of a genetic assay named glycoSNAP (glycosylation of secreted N-linked acceptor proteins) that facilitates high-throughput screening of glycophenotypes in E. coli. Using this assay, we isolated several C. jejuni PglB variants that were capable of glycosylating an array of noncanonical acceptor sequences including one in a eukaryotic N-glycoprotein. Collectively, these results underscore the utility of glycoSNAP for shedding light on poorly understood aspects of N-glycosylation and for engineering designer N-glycosylation biocatalysts. PMID:25129029

  3. Relaxed acceptor site specificity of bacterial oligosaccharyltransferase in vivo.

    PubMed

    Schwarz, Flavio; Lizak, Christian; Fan, Yao-Yun; Fleurkens, Susanna; Kowarik, Michael; Aebi, Markus

    2011-01-01

    A number of proteobacteria carry the genetic information to perform N-linked glycosylation, but only the protein glycosylation (pgl) pathway of Campylobacter jejuni has been studied to date. Here, we report that the pgl gene cluster of Campylobacter lari encodes for a functional glycosylation machinery that can be reconstituted in Escherichia coli. We determined that the N-glycan produced in this system consisted of a linear hexasaccharide. We found that the oligosaccharyltransferase (OST) of C. lari conserved a predominant specificity for the primary sequence D/E-X(-1)-N-X(+1)-S/T (where X(-1) and X(+1) can be any amino acid but proline). At the same time, we observed that this enzyme exhibited a relaxed specificity toward the acceptor site and modified asparagine residues of a protein at sequences DANSG and NNNST. Moreover, C. lari pgl glycosylated a native E. coli protein. Bacterial N-glycosylation appears as a useful tool to establish a molecular description of how single-subunit OSTs perform selection of glycosyl acceptor sites.

  4. Identification of a High Affinity Nuclear Acceptor Site for Estrogen Receptor of Calf Uterus

    PubMed Central

    Puca, Giovanni Alfredo; Sica, Vincenzo; Nola, Ernesto

    1974-01-01

    By means of affinity chromatography, specific nuclear acceptor sites for estradiol receptors are identified in a fraction that can be solubilized from purified nuclei with 2 M NaCl. Interaction between these acceptor sites and crude or partially purified estradiol receptor shows a high association constant (over 109 M). Receptor-acceptor interaction is dependent on physiological concentrations of 17β-estradiol; it is disrupted by high ionic strength. The nuclear acceptor sites appear to be protein in nature and exist in 5- to 10-fold excess over the estrogen binding sites present in the cytosol. Single- or double-stranded DNA does not bind estrogen-receptor complexes. Acceptor sites appear to be associated with basic nuclear proteins as judged by hydroxyapatite chromatography. The nuclear acceptor sites probably represent less than 0.1% of the purified basic proteins from the nucleus. PMID:4362642

  5. Ligand-bound Structures and Site-directed Mutagenesis Identify the Acceptor and Secondary Binding Sites of Streptomyces coelicolor Maltosyltransferase GlgE.

    PubMed

    Syson, Karl; Stevenson, Clare E M; Miah, Farzana; Barclay, J Elaine; Tang, Minhong; Gorelik, Andrii; Rashid, Abdul M; Lawson, David M; Bornemann, Stephen

    2016-10-07

    GlgE is a maltosyltransferase involved in α-glucan biosynthesis in bacteria that has been genetically validated as a target for tuberculosis therapies. Crystals of the Mycobacterium tuberculosis enzyme diffract at low resolution so most structural studies have been with the very similar Streptomyces coelicolor GlgE isoform 1. Although the donor binding site for α-maltose 1-phosphate had been previously structurally defined, the acceptor site had not. Using mutagenesis, kinetics, and protein crystallography of the S. coelicolor enzyme, we have now identified the +1 to +6 subsites of the acceptor/product, which overlap with the known cyclodextrin binding site. The sugar residues in the acceptor subsites +1 to +5 are oriented such that they disfavor the binding of malto-oligosaccharides that bear branches at their 6-positions, consistent with the known acceptor chain specificity of GlgE. A secondary binding site remote from the catalytic center was identified that is distinct from one reported for the M. tuberculosis enzyme. This new site is capable of binding a branched α-glucan and is most likely involved in guiding acceptors toward the donor site because its disruption kinetically compromises the ability of GlgE to extend polymeric substrates. However, disruption of this site, which is conserved in the Streptomyces venezuelae GlgE enzyme, did not affect the growth of S. venezuelae or the structure of the polymeric product. The acceptor subsites +1 to +4 in the S. coelicolor enzyme are well conserved in the M. tuberculosis enzyme so their identification could help inform the design of inhibitors with therapeutic potential. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

  6. Ligand-bound Structures and Site-directed Mutagenesis Identify the Acceptor and Secondary Binding Sites of Streptomyces coelicolor Maltosyltransferase GlgE*

    PubMed Central

    Syson, Karl; Stevenson, Clare E. M.; Miah, Farzana; Barclay, J. Elaine; Tang, Minhong; Gorelik, Andrii; Rashid, Abdul M.; Lawson, David M.; Bornemann, Stephen

    2016-01-01

    GlgE is a maltosyltransferase involved in α-glucan biosynthesis in bacteria that has been genetically validated as a target for tuberculosis therapies. Crystals of the Mycobacterium tuberculosis enzyme diffract at low resolution so most structural studies have been with the very similar Streptomyces coelicolor GlgE isoform 1. Although the donor binding site for α-maltose 1-phosphate had been previously structurally defined, the acceptor site had not. Using mutagenesis, kinetics, and protein crystallography of the S. coelicolor enzyme, we have now identified the +1 to +6 subsites of the acceptor/product, which overlap with the known cyclodextrin binding site. The sugar residues in the acceptor subsites +1 to +5 are oriented such that they disfavor the binding of malto-oligosaccharides that bear branches at their 6-positions, consistent with the known acceptor chain specificity of GlgE. A secondary binding site remote from the catalytic center was identified that is distinct from one reported for the M. tuberculosis enzyme. This new site is capable of binding a branched α-glucan and is most likely involved in guiding acceptors toward the donor site because its disruption kinetically compromises the ability of GlgE to extend polymeric substrates. However, disruption of this site, which is conserved in the Streptomyces venezuelae GlgE enzyme, did not affect the growth of S. venezuelae or the structure of the polymeric product. The acceptor subsites +1 to +4 in the S. coelicolor enzyme are well conserved in the M. tuberculosis enzyme so their identification could help inform the design of inhibitors with therapeutic potential. PMID:27531751

  7. Characterization of Ruminococcus albus cellodextrin phosphorylase and identification of a key phenylalanine residue for acceptor specificity and affinity to the phosphate group.

    PubMed

    Sawano, Tatsuya; Saburi, Wataru; Hamura, Ken; Matsui, Hirokazu; Mori, Haruhide

    2013-09-01

    Ruminococcus albus has the ability to intracellularly degrade cello-oligosaccharides primarily via phosphorolysis. In this study, the enzymatic characteristics of R. albus cellodextrin phosphorylase (RaCDP), which is a member of glycoside hydrolase family 94, was investigated. RaCDP catalyzes the phosphorolysis of cellotriose through an ordered 'bi bi' mechanism in which cellotriose binds to RaCDP before inorganic phosphate, and then cellobiose and glucose 1-phosphate (Glc1P) are released in that order. Among the cello-oligosaccharides tested, RaCDP had the highest phosphorolytic and synthetic activities towards cellohexaose and cellopentaose, respectively. RaCDP successively transferred glucosyl residues from Glc1P to the growing cello-oligosaccharide chain, and insoluble cello-oligosaccharides comprising a mean of eight residues were produced. Sophorose, laminaribiose, β-1,4-xylobiose, β-1,4-mannobiose and cellobiitol served as acceptors for RaCDP. RaCDP had very low affinity for phosphate groups in both the phosphorolysis and synthesis directions. A sequence comparison revealed that RaCDP has Gln at position 646 where His is normally conserved in the phosphate binding sites of related enzymes. A Q646H mutant showed approximately twofold lower apparent K(m) values for inorganic phosphate and Glc1P than the wild-type. RaCDP has Phe at position 633 corresponding to Tyr and Val in the +1 subsites of cellobiose phosphorylase and N,N'-diacetylchitobiose phosphorylase, respectively. A F633Y mutant showed higher preference for cellobiose over β-1,4-mannobiose as an acceptor substrate in the synthetic reaction than the wild-type. Furthermore, the F633Y mutant showed 75- and 1100-fold lower apparent Km values for inorganic phosphate and Glc1P, respectively, in phosphorolysis and synthesis of cellotriose. © 2013 FEBS.

  8. Phosphate binding sites identification in protein structures

    PubMed Central

    Parca, Luca; Gherardini, Pier Federico; Helmer-Citterich, Manuela; Ausiello, Gabriele

    2011-01-01

    Nearly half of known protein structures interact with phosphate-containing ligands, such as nucleotides and other cofactors. Many methods have been developed for the identification of metal ions-binding sites and some for bigger ligands such as carbohydrates, but none is yet available for the prediction of phosphate-binding sites. Here we describe Pfinder, a method that predicts binding sites for phosphate groups, both in the form of ions or as parts of other non-peptide ligands, in proteins of known structure. Pfinder uses the Query3D local structural comparison algorithm to scan a protein structure for the presence of a number of structural motifs identified for their ability to bind the phosphate chemical group. Pfinder has been tested on a data set of 52 proteins for which both the apo and holo forms were available. We obtained at least one correct prediction in 63% of the holo structures and in 62% of the apo. The ability of Pfinder to recognize a phosphate-binding site in unbound protein structures makes it an ideal tool for functional annotation and for complementing docking and drug design methods. The Pfinder program is available at http://pdbfun.uniroma2.it/pfinder. PMID:20974634

  9. Evidence for specific DNA sequences in the nuclear acceptor sites of the avian oviduct progesterone receptor.

    PubMed Central

    Toyoda, H; Seelke, R W; Littlefield, B A; Spelsberg, T C

    1985-01-01

    Recent studies have shown that saturable high-capacity nuclear binding sites (termed acceptor sites) for the avian oviduct progesterone receptor can be reconstituted by rehybridizing a specific oviduct chromatin protein fraction (CP-3) to pure hen DNA to generate a reconstituted nucleoacidic protein (NAP). Only a limited number of acceptor sites can be generated on hen DNA even at high protein/DNA ratios. This suggests the existence of a limited number of specific sequences in the avian genome that can participate in the acceptor sites. The studies presented in this paper show a specificity as to the source of DNA that can generate acceptor sites using hen oviduct CP-3 protein. The acceptor protein binds to all DNAs but generates acceptor sites only on DNAs from certain animals. The acceptor sites for the progesterone receptor, generated with heterologous mammalian DNAs and the avian oviduct CP-3 fraction, show saturation not only in number of acceptor sites generated on the DNAs but also in progesterone receptor binding. Binding to these sites is also receptor dependent. Using oviduct receptors from particular physiological states of the birds wherein the receptors do not bind to nuclear sites in vivo, it was found that the cell-free binding to these heterologous complexes of hen CP-3 protein and DNA from another species, termed heterologous NAP, is similarly absent. Thus, the cell-free binding to the native oviduct NAP and the heterologous NAP markedly resembles the nuclear binding in vivo. Interestingly, synthetic DNAs rich in adenine and thymine, but not those rich in guanine and cytosine, are capable of generating acceptor sites. Species-specific DNA sequences, as well as specific chromatin proteins, therefore, appear to be involved in the nuclear acceptor sites for the avian oviduct progesterone receptor. The DNA sequences appear to be conserved throughout most of the vertebrates but not among nonvertebrates as are the steroid hormones and their receptors

  10. [Synthesis of 11-phenoxyundecyl phosphate and its use as an acceptor substrate in the reaction with UDP-GlcNAc : polyprenyl phosphate GlcNAc-phosphotransferase from Salmonella arizona O:59].

    PubMed

    Danilov, L L; Veselovskiĭ, V V; Balagurova, N M; Druzhinina, T N

    2009-01-01

    A new scheme of synthesis of 11-phenoxyundecyl phosphate from 11-bromoundecanoic acid was suggested for its ability to react as an acceptor of 2-acetamido-2-deoxy-alpha-D-glucopyranosyl phosphate in a reaction catalyzed by UDP-N-acetylglucosamine : polyprenyl phosphate N-acetylglucosamine phosphotransferase from Salmonella arizona O:59.

  11. Changes in phosphorylation of adenosine phosphate and redox state of nicotinamide-adenine dinucleotide (phosphate) in Geobacter sulfurreducens in response to electron acceptor and anode potential variation.

    PubMed

    Rose, Nicholas D; Regan, John M

    2015-12-01

    Geobacter sulfurreducens is one of the dominant bacterial species found in biofilms growing on anodes in bioelectrochemical systems. The intracellular concentrations of reduced and oxidized forms of nicotinamide-adenine dinucleotide (NADH and NAD(+), respectively) and nicotinamide-adenine dinucleotide phosphate (NADPH and NADP(+), respectively) as well as adenosine triphosphate (ATP), adenosine diphosphate (ADP), and adenosine monophosphate (AMP) were measured in G. sulfurreducens using fumarate, Fe(III)-citrate, or anodes poised at different potentials (110, 10, -90, and -190 mV (vs. SHE)) as the electron acceptor. The ratios of CNADH/CNAD+ (0.088±0.022) and CNADPH/CNADP+ (0.268±0.098) were similar under all anode potentials tested and with Fe(III)-citrate (reduced extracellularly). Both ratios significantly increased with fumarate as the electron acceptor (0.331±0.094 for NAD and 1.96±0.37 for NADP). The adenylate energy charge (the fraction of phosphorylation in intracellular adenosine phosphates) was maintained near 0.47 under almost all conditions. Anode-growing biofilms demonstrated a significantly higher molar ratio of ATP/ADP relative to suspended cultures grown on fumarate or Fe(III)-citrate. These results provide evidence that the cellular location of reduction and not the redox potential of the electron acceptor controls the intracellular redox potential in G. sulfurreducens and that biofilm growth alters adenylate phosphorylation.

  12. Modulation of acceptor specificity of Ruminococcus albus cellobiose phosphorylase through site-directed mutagenesis.

    PubMed

    Hamura, Ken; Saburi, Wataru; Matsui, Hirokazu; Mori, Haruhide

    2013-09-20

    Cellobiose phosphorylase (EC 2.4.1.20, CBP) catalyzes the reversible phosphorolysis of cellobiose to α-D-glucose 1-phosphate (Glc1P) and d-glucose. Cys485, Tyr648, and Glu653 of CBP from Ruminococcus albus, situated at the +1 subsite, were mutated to modulate acceptor specificity. C485A, Y648F, and Y648V were active enough for analysis. Their acceptor specificities were compared with the wild type based on the apparent kinetic parameters determined in the presence of 10 mM Glc1P. C485A showed higher preference for D-glucosamine than the wild type. Apparent kcat/Km values of Y648F for D-mannose and 2-deoxy-D-glucose were 8.2- and 4.0-fold higher than those of the wild type, respectively. Y648V had synthetic activity toward N-acetyl-D-glucosamine, while the other variants did not. The oligosaccharide production in the presence of the same concentrations of wild type and each mutant was compared. C485A produced 4-O-β-D-glucopyranosyl-D-glucosamine from 10 mM Glc1P and D-glucosamine at a rate similar to the wild type. Y648F and Y648V produced 4-O-β-D-glucopyranosyl-D-mannose and 4-O-β-D-glucopyranosyl-N-acetyl-D-glucosamine much more rapidly than the wild type when D-mannose and N-acetyl-D-glucosamine were used as acceptors, respectively. After a 4h reaction, the amounts of 4-O-β-D-glucopyranosyl-D-mannose and 4-O-β-D-glucopyranosyl-N-acetyl-D-glucosamine produced by Y648F and Y648V were 5.9- and 12-fold higher than the wild type, respectively. Copyright © 2013 Elsevier Ltd. All rights reserved.

  13. [Synthesis of 11-[(2-pyridyl)amino]- and 11-[(9-anthracenylcarbonyl)amino]undecyl phosphate and investigation of their acceptor properties in the enzymic reaction catalyzed by galactosylphosphotransferases from Salmonella].

    PubMed

    Danilov, L L; Balagurova, N M; Vinnikova, A N; Utkina, N S; Torgov, V I; Kalinchuk, N A; Druzhinina, T N; Veselovsky, V V

    2014-01-01

    11-[(2-Pyridyl)amino]undecyl phosphate and 11-[(9-anthracenylcarbonyl)amino]undecyl phosphate were chemically synthesized. The abiliy of these new fluorescent derivatives of undecyl phosphate to serve as acceptor substrate of galactosyl phosphate residue in the enzymic reaction catalyzed by galactosylphosphotransferase from Salmonella anatum or Salmonella newport membrane preparation was demonstrated.

  14. Positive cooperativity between acceptor and donor sites of the peptidoglycan glycosyltransferase.

    PubMed

    Bury, Daniel; Dahmane, Ismahene; Derouaux, Adeline; Dumbre, Shrinivas; Herdewijn, Piet; Matagne, André; Breukink, Eefjan; Mueller-Seitz, Erika; Petz, Michael; Terrak, Mohammed

    2015-01-15

    The glycosyltransferases of family 51 (GT51) catalyze the polymerization of lipid II to form linear glycan chains, which, after cross linking by the transpeptidases, form the net-like peptidoglycan macromolecule. The essential function of the GT makes it an attractive antimicrobial target; therefore a better understanding of its function and its mechanism of interaction with substrates could help in the design and the development of new antibiotics. In this work, we have used a surface plasmon resonance Biacore(®) biosensor, based on an amine derivative of moenomycin A immobilized on a sensor chip surface, to investigate the mechanism of binding of substrate analogous inhibitors to the GT. Addition of increasing concentrations of moenomycin A to the Staphylococcus aureus MtgA led to reduced binding of the protein to the sensor chip as expected. Remarkably, in the presence of low concentrations of the most active disaccharide inhibitors, binding of MtgA to immobilized moenomycin A was found to increase; in contrast competition with moenomycin A occurred only at high concentrations. This finding suggests that at low concentrations, the lipid II analogs bind to the acceptor site and induce a cooperative binding of moenomycin A to the donor site. Our results constitute the first indication of the existence of a positive cooperativity between the acceptor and the donor sites of peptidoglycan GTs. In addition, our study indicates that a modification of two residues (L119N and F120S) within the hydrophobic region of MtgA can yield monodisperse forms of the protein with apparently no change in its secondary structure content, but this is at the expense of the enzyme function.

  15. Beta zero thalassemia caused by a base substitution that creates an alternative splice acceptor site in an intron.

    PubMed Central

    Metherall, J E; Collins, F S; Pan, J; Weissman, S M; Forget, B G

    1986-01-01

    A thalassemic beta-globin gene cloned from a haplotype I chromosome contains a T to G transversion at position 116 of IVS1 which results in the generation of an abnormal alternative acceptor splice site. Transient expression studies revealed a 4-fold decrease in the amount of RNA produced with greater than 99% of it being abnormally spliced despite preservation of the normal acceptor splice site at position 130. These results suggest that the mutation at IVS1 position 116 results in beta zero thalassemia. A closely related mutation at position 110 of IVS1 also generates a novel acceptor site and results in a similar decrease in total mRNA produced, but approximately 20% of the mRNA produced is normally spliced and thus the phenotype is that of beta + thalassemia. These observations suggest that short range position effects may play a dramatic role in the choice of potential splice acceptor sites. We demonstrate the presence of abnormally spliced mRNA in reticulocytes of affected individuals and show the mutation at IVS1 position 116 segregating from the mutation at IVS1 position 110 in a three generation pedigree. The mutation results in the creation of a MaeI restriction site, as do a number of other thalassemic mutations, and we demonstrate some difficulties that may arise in the differential diagnosis of these mutations. Images Fig. 1. Fig. 2. Fig. 3. Fig. 4. PMID:3780671

  16. Selective elimination of a B cell subset having acceptor site(s) for T cell-replacing factor (TRF) with biotinylated antibody to the acceptor site(s) and avidin-ricin A-chain conjugate.

    PubMed

    Hashimoto, N; Takatsu, K; Masuho, Y; Kishida, K; Hara, T; Hamaoka, T

    1984-01-01

    A covalent conjugate of avidin with ricin subunit A-chain (avidin-RA) was prepared by using N-succinimidyl 3-(2-pyridyldithio)propionate as a coupling agent. Selective cytotoxic activity after the combined treatment of spleen cells with biotinylated antibody and avidin-RA was demonstrated by the fact that the responsiveness to LPS was selectively abrogated by pretreatment of the cells with biotinylated rabbit anti-mouse immunoglobulin (MIg) antibody, but not with biotinylated anti-Thy-1.2 antibody. Neither the biotinylated antibody alone nor avidin-RA alone was effective in decreasing the responses to mitogens. Moreover, a high anti-DNP PFC response elicited by DNP-KLH-primed BALB/c mouse spleen cells stimulated in vitro with DNP-KLH was mostly abrogated by the pretreatment of the cells with biotinylated anti-MIg antibody and avidin-RA. Again, neither the biotinylated antibody alone nor avidin-RA alone was effective in decreasing the anti-DNP PFC response. This cell-killing method with the use of biotinylated antibody and avidin-RA was applied and evaluated in experimental systems in which the helper action of T cells on B cells was mediated by T cell-replacing factor (TRF) or was performed by the direct interaction of T cells with B cells (cognate interaction). When DNP-KLH-primed splenic B cells, pretreated with biotinylated F(ab')2 fragment of DCF1 male anti-BALB/c-B IgG antibody against acceptor site(s) for TRF followed by treatment with avidin-RA, were stimulated with DNP-OVA in the presence of monoclonal TRF, the anti-DNP PFC response was significantly decreased, whereas the same treated B cells responded well to stimulation with DNP-PPD in the presence of Tbc-primed T cells (cognate interaction). These results indicate that B cells responsible for the cognate interaction and those having TRF acceptor site(s) belong to a distinct subpopulation of B cells, and that the cytocidal action of the noncovalent conjugate of the antibody and RA formed from the

  17. Nitrate as electron acceptor in in situ abandoned refinery site bioremediation

    SciTech Connect

    Battermann, G.; Meier-Loehr, M.

    1995-12-31

    The aquifer beneath an abandoned refinery site is highly polluted with benzene, toluene, ethylbenzene, and xylenes (BTEX). After removal of the free phase by hydraulic measures until 1986, the immobile residual concentration located 6 to 10 m beneath the surface is still present and causes hydrocarbon concentrations from 10 to 100 mg/L in the groundwater. Laboratory tests proved the biodegradability of the hydrocarbon compounds under denitrifying conditions. Based on the results of the pilot study, large-scale bioremediation covering an area of about 20 ha was initiated. About 500 m{sup 3}/h of groundwater were extracted, and 400 m{sup 3}/h were recharged. The large-scale plant has been operating since 1991. Nitrate as an electron acceptor has been used since 1992. About 300 metric tons (MT) of hydrocarbons have been removed to date. The area of groundwater pollution is diminished by a factor of about two. More than 60% of all groundwater observation wells are now free of dissolved hydrocarbons. In addition, the decrease of biological nitrate consumption gives evidence of advanced bioremediation of the soil.

  18. 76 FR 38389 - Caraleigh Phosphate and Fertlizer Works Superfund Site; Raleigh, Wake County, NC; Notice of...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-06-30

    ... response costs concerning the Caraleigh Phosphate and Fertilizer Works Superfund Site located in Raleigh...-0534 or Site name Caraleigh Phosphate and Fertilizer Works Superfund Site by one of the...

  19. 11-Phenoxyundecyl phosphate as a 2-acetamido-2-deoxy-α-d-glucopyranosyl phosphate acceptor in O-antigen repeating unit assembly of Salmonella arizonae O:59.

    PubMed

    Druzhinina, Tatyana N; Danilov, Leonid L; Torgov, Vladimir I; Utkina, Natalya S; Balagurova, Nadezhda M; Veselovsky, Vladimir V; Chizhov, Alexander O

    2010-12-10

    A synthesis of 11-phenoxyundecyl phosphate and its biochemical transformation (using GlcNAc-P transferase from Salmonella arizonae O:59 membranes catalysing transfer of GlcNc-phosphate from UDP-GlcNAc on lipid-phosphate) into P(1)-11-phenoxyundecyl, P(2)-2-acetamido-2-deoxy-α-D-glucopyranosyl diphosphate are described. Copyright © 2010 Elsevier Ltd. All rights reserved.

  20. Fluorescent mannosides serve as acceptor substrates for glycosyltransferase and sugar-1-phosphate transferase activities in Euglena gracilis membranes.

    PubMed

    Ivanova, Irina M; Nepogodiev, Sergey A; Saalbach, Gerhard; O'Neill, Ellis C; Urbaniak, Michael D; Ferguson, Michael A J; Gurcha, Sudagar S; Besra, Gurdyal S; Field, Robert A

    2017-01-13

    Synthetic hexynyl α-D-mannopyranoside and its α-1,6-linked disaccharide counterpart were fluorescently labelled through CuAAC click chemistry with 3-azido-7-hydroxycoumarin. The resulting triazolyl-coumarin adducts, which were amenable to analysis by TLC, HPLC and mass spectrometry, proved to be acceptor substrates for α-1,6-ManT activities in mycobacterial membranes, as well as α- and β-GalT activities in trypanosomal membranes, benchmarking the potential of the fluorescent acceptor approach against earlier radiochemical assays. Following on to explore the glycobiology of the benign protozoan alga Euglena gracilis, α-1,3- and α-1,2-ManT activities were detected in membrane preparations, along with GlcT, Glc-P-T and GlcNAc-P-T activities. These studies serve to demonstrate the potential of readily accessible fluorescent glycans as substrates for exploring carbohydrate active enzymes.

  1. Hexose phosphate binding sites of fructose-6-phosphate,2-kinase:fructose-2,6-bisphosphatase

    SciTech Connect

    Sakakibara, R.; Kitajima, S.; Hartman, F.C.; Uyeda, K.

    1984-11-25

    The hexose phosphate binding sites of a bifunctional enzyme, fructose-6-P,2-kinase:fructose-2,6-bisphosphatase were studied. N-Bromoacetylethanolamine phosphate is a competitive inhibitor with respect to fructose-6-P and a noncompetitive inhibitor with ATP (K/sub i/ = 0.8 mM). The reagent inactivates fructose-6-P,2-kinase but not fructose-2,6-bisphosphatase, and the inactivation is prevented by fructose-6-P. The inactivation reaction follows pseudo first-order kinetics to completion and with increasing concentrations of N-bromoacetylethanolamine phosphate a rate saturation effect is observed. The concentration of the reagent giving the half-maximum inactivation is 2.2 mM and the apparent first order rate constant is 0.0046 s/sup -1/. The enzyme alkylated by N-bromoacetylethanolamine-P has lost over 90% of the kinase activity, retains nearly full activity of fructose-2,6-bisphosphatase, and its inhibition by fructose-6-P is not altered. 3-Bromo-1,4-dihydroxy-2-butanone 1,4-bisphosphate is also a competitive inhibitor of fructose-6-P,2-kinase with respect to fructose-6-P in the forward reaction and fructose-2,6-P/sub 2/ in the reverse direction. This reagent inhibits 93% of fructose-6-P,2-kinase but activated fructose-2,6-bisphosphatase 3.7-fold. 3-Bromo-1,4-dihydroxy-2-butanone 1,4-bisphosphate alters the fructose-2,6-P/sub 2/ saturation kinetic curve from negative cooperativity to normal Michaelis-Menten kinetics with K/sub 0.5/ of 0.8 ..mu..M. The reagent, however, has no effect on the fructose-6-P inhibition of phosphatase. These results strongly suggest that hexose phosphate binding sites of fructose-6-P,2-kinase and fructose-2,6-bisphosphatase are distinct and located in different regions of this bifunctional enzyme. 19 references, 9 figures, 1 table.

  2. Duchenne muscular dystrophy caused by a frame-shift mutation in the acceptor splice site of intron 26.

    PubMed

    Meregalli, Mirella; Maciotta, Simona; Angeloni, Valentina; Torrente, Yvan

    2016-08-11

    The dystrophin gene is the one of the largest described in human beings and mutations associated to this gene are responsible for Duchenne or Becker muscular dystrophies. Here we describe a nucleotide substitution in the acceptor splice site of intron 26 (c.3604-1G > C) carried by a 6-year-old boy who presented with a history of progressive proximal muscle weakness and elevated serum creatine kinase levels. RNA analysis showed that the first two nucleotides of the mutated intron 26 (AC) were not recognized by the splicing machinery and a new splicing site was created within exon 27, generating a premature stop codon and avoiding protein translation. The evaluation of the pathogenic effect of the mutation by mRNA analysis will be useful in the optics of an antisense oligonucleotides (AON)-based therapy.

  3. An investigation of hydrogen bonding between HCl and vinylacetylene: A molecule with two different π-acceptor sites

    NASA Astrophysics Data System (ADS)

    Kisiel, Z.; Fowler, P. W.; Legon, A. C.; Devanne, D.; Dixneuf, P.

    1990-11-01

    The ground state rotational spectrum of a hydrogen-bonded dimer formed by vinylacetylene and hydrogen chloride has been detected by the pulsed-nozzle, Fourier-transform microwave technique. Vinylacetylene has been chosen as a prototype acceptor molecule containing two different π-acceptor sites. Rotational constants A0, B0, C0, centrifugal distortion constants ΔJ, ΔJK, δJ, δK, and three components χaa, χbb-χcc, and χab of the Cl nuclear quadrupole coupling tensor have been determined for each of the three isotopomers CH2CHCCHṡṡṡ H35Cl, CH2CHCCHṡṡṡH37Cl, and CH2CHCCHṡṡṡD35Cl. These spectroscopic constants have been interpreted in terms of a dimer in which the HCl subunit forms a hydrogen bond to the C 3/4 C triple bond in a T-shape configuration, but is displaced from the center of the triple bond by d=0.04 Å towards the inner C atom, and makes an angle φ=34° with the vinylacetylene plane. The experimental angular geometry is in excellent agreement with that predicted by the Buckingham-Fowler electrostatic model which gives φ=27°.

  4. G to C transversion at a splice acceptor site causes exon skipping in the cystatin B gene.

    PubMed

    Bespalova, I N; Pranzatelli, M; Burmeister, M

    1997-09-01

    Several mutations have been described in the proteinase inhibitor cystatin B gene from individuals affected with progressive myoclonus epilepsy of the Unverricht-Lundborg type (EPM1). One of these mutations, a 1925G-->C transition at the 3'-splice acceptor site of the intron 1, was postulated to lead to inappropriate splicing of a primary transcript of the cystatin B gene in EPM1 patients. In an effort to understand the expression of the 1925G-->C mutation, the sequence of cystatin B mRNA transcripts from lymphoblastoid cell lines of heterozygous patients carrying the mutation were analyzed. RT-PCR of total mRNA showed two main products: the apparently normal transcript and an aberrant, 102 bp shorter transcript. Direct PCR sequencing showed that the aberrant transcript is a consequence of exon 2 skipping.

  5. Splicing in Caenorhabditis elegans does not require an AG at the 3' splice acceptor site.

    PubMed Central

    Aroian, R V; Levy, A D; Koga, M; Ohshima, Y; Kramer, J M; Sternberg, P W

    1993-01-01

    The dinucleotide AG, found at the 3' end of virtually all eukaryotic pre-mRNA introns, is thought to be essential for splicing. Reduction-of-function mutations in two Caenorhabditis elegans genes, the receptor tyrosine kinase gene let-23 and the collagen gene dpy-10, both alter the AG at the end of a short (ca. 50-nucleotide) intron to AA. The in vivo effects of these mutations were studied by sequencing polymerase chain reaction-amplified reverse-transcribed RNA isolated from the two mutants. As expected, we find transcripts that splice to a cryptic AG, skip an exon, and retain an unspliced intron. However, we also find significant levels of splicing at the mutated 3' splice site (AA) and at nearby non-AG dinucleotides. Our results indicate that for short C. elegans introns an AG is not required for splicing at either the correct 3' splice site or incorrect sites. Analysis of a splice site mutant involving a longer, 316-nucleotide C. elegans intron indicates that an AG is also not required there for splicing. We hypothesize that elements besides the invariant AG, e.g., an A-U-rich region, a UUUC motif, and/or a potential branch point sequence, are directing the selection of the 3' splice site and that in wild-type genes these elements cooperate so that proper splicing occurs. Images PMID:8417357

  6. Global transcriptional start site mapping in Geobacter sulfurreducens during growth with two different electron acceptors.

    PubMed

    González, Getzabeth; Labastida, Aurora; Jímenez-Jacinto, Verónica; Vega-Alvarado, Leticia; Olvera, Maricela; Morett, Enrique; Juárez, Katy

    2016-09-01

    Geobacter sulfurreducens is an anaerobic soil bacterium that is involved in biogeochemical cycles of elements such as Fe and Mn. Although significant progress has been made in the understanding of the electron transfer processes in G. sulfurreducens, little is known about the regulatory mechanisms involved in their control. To expand the study of gene regulation in G. sulfurreducens, we carried out a genome-wide identification of transcription start sites (TSS) by 5'RACE and by deep RNA sequencing of primary mRNAs in two growth conditions. TSSs were identified along G. sulfurreducens genome and over 50% of them were located in the upstream region of the associated gene, and in some cases we detected genes with more than one TSS. Our global mapping of TSSs contributes with valuable information, which is needed for the study of transcript structure and transcription regulation signals and can ultimately contribute to the understanding of transcription initiation phenomena in G. sulfurreducens.

  7. Profound biotinidase deficiency caused by a point mutation that creates a downstream cryptic 3' splice acceptor site within an exon of the human biotinidase gene.

    PubMed

    Pomponio, R J; Reynolds, T R; Mandel, H; Admoni, O; Melone, P D; Buck, G A; Wolf, B

    1997-05-01

    Biotinidase recycles the vitamin biotin from biocytin upon the degradation of the biotin-dependent carboxylases. We have identified a novel point mutation within the biotinidase gene that encodes the signal peptide in two unrelated individuals with profound biotinidase deficiency. Sequence analysis of genomic DNA from these individuals revealed a G to A transition (G100-->A) located 57 bases downstream of the authentic splice acceptor site in exon B. Although this mutation predicts a G34S substitution, it also generates a 3' splice acceptor site. Sequence of the PCR-amplified cDNA from the homozygous child revealed that all the product was shorter than that of normal individuals and was the result of aberrant splicing. The aberrantly spliced transcript lacked 57 bases, including a second in-frame ATG, that encode most of the putative signal peptide and results in an in-frame deletion of 19 amino acids. The mutation results in failure to secrete the aberrant protein into the blood. This is the first reported example in which a point mutation creates a cryptic 3' splice acceptor site motif that is used preferentially over the upstream authentic splice site. The preferential usage of the downstream splice site is not consistent with the 5'-3' scanning model, but is consistent with the exon definition model of RNA splicing.

  8. Characterization of an Additional Splice Acceptor Site Introduced into CYP4B1 in Hominoidae during Evolution.

    PubMed

    Schmidt, Eva M; Wiek, Constanze; Parkinson, Oliver T; Roellecke, Katharina; Freund, Marcel; Gombert, Michael; Lottmann, Nadine; Steward, Charles A; Kramm, Christof M; Yarov-Yarovoy, Vladimir; Rettie, Allan E; Hanenberg, Helmut

    2015-01-01

    CYP4B1 belongs to the cytochrome P450 family 4, one of the oldest P450 families whose members have been highly conserved throughout evolution. The CYP4 monooxygenases typically oxidize fatty acids to both inactive and active lipid mediators, although the endogenous ligand(s) is largely unknown. During evolution, at the transition of great apes to humanoids, the CYP4B1 protein acquired a serine instead of a proline at the canonical position 427 in the meander region. Although this alteration impairs P450 function related to the processing of naturally occurring lung toxins, a study in transgenic mice suggested that an additional serine insertion at position 207 in human CYP4B1 can rescue the enzyme stability and activity. Here, we report that the genomic insertion of a CAG triplet at the intron 5-exon 6 boundary in human CYP4B1 introduced an additional splice acceptor site in frame. During evolution, this change occurred presumably at the stage of Hominoidae and leads to two major isoforms of the CYP4B1 enzymes of humans and great apes, either with or without a serine 207 insertion (insSer207). We further demonstrated that the CYP4B1 enzyme with insSer207 is the dominant isoform (76%) in humans. Importantly, this amino acid insertion did not affect the 4-ipomeanol metabolizing activities or stabilities of the native rabbit or human CYP4B1 enzymes, when introduced as transgenes in human primary cells and cell lines. In our 3D modeling, this functional neutrality of insSer207 is compatible with its predicted location on the exterior surface of CYP4B1 in a flexible side chain. Therefore, the Ser207 insertion does not rescue the P450 functional activity of human CYP4B1 that has been lost during evolution.

  9. Analysis of the class I aldolase binding site architecture based on the crystal structure of 2-deoxyribose-5-phosphate aldolase at 0.99A resolution.

    PubMed

    Heine, Andreas; Luz, John G; Wong, Chi-Huey; Wilson, Ian A

    2004-10-29

    The crystal structure of the bacterial (Escherichia coli) class I 2-deoxyribose-5-phosphate aldolase (DERA) has been determined by Se-Met multiple anomalous dispersion (MAD) methods at 0.99A resolution. This structure represents the highest-resolution X-ray structure of an aldolase determined to date and enables a true atomic view of the enzyme. The crystal structure shows the ubiquitous TIM alpha/beta barrel fold. The enzyme contains two lysine residues in the active site. Lys167 forms the Schiff base intermediate, whereas Lys201, which is in close vicinity to the reactive lysine residue, is responsible for the perturbed pK(a) of Lys167 and, hence, also a key residue in the reaction mechanism. DERA is the only known aldolase that is able to use aldehydes as both aldol donor and acceptor molecules in the aldol reaction and is, therefore, of particular interest as a biocatalyst in synthetic organic chemistry. The uncomplexed DERA structure enables a detailed comparison with the substrate complexes and highlights a conformational change in the phosphate-binding site. Knowledge of the enzyme active-site environment has been the basis for exploration of catalysis of non-natural substrates and of mutagenesis of the phosphate-binding site to expand substrate specificity. Detailed comparison with other class I aldolase enzymes and DERA enzymes from different organisms reveals a similar geometric arrangement of key residues and implies a potential role for water as a general base in the catalytic mechanism.

  10. Biochemical identification of base and phosphate contacts between Fis and a high affinity DNA binding site

    PubMed Central

    Shao, Yongping; Feldman-Cohen, Leah S.; Osuna, Robert

    2008-01-01

    SUMMARY Fis is a nucleoid-associated protein in E. coli and other bacteria that stimulates certain site-specific DNA recombination events, alters DNA topology, and serves as a global gene regulator. DNA binding is central to the functions of Fis and involves a helix-turn-helix DNA binding motif located in the carboxy-terminal region. Specific DNA binding is observed at a number of sites exhibiting poorly related sequences. Such interactions require four critical base pairs positioned −7, −3, +3, and +7 nucleotides relative to the central nucleotide of a 15 bp core-binding site. To further understand how Fis interacts with DNA, we identified the positions of fourteen DNA phosphates (based on ethylation interference assays) that are required for Fis binding. These are the 5’ phosphates of the nucleotides at positions −8, −7, −6, +1, +2, +3, and +4 relative to the central nucleotide on both DNA strands. Another five phosphates located in the flanking regions from positions +10 through +14 can serve as additional contact sites. Using a combination of biochemical approaches and various mutant Fis proteins, we probed possible interactions between several key Fis residues and DNA bases or phosphates within a high-affinity binding site. We provide evidence in support of interactions between the R85 Fis residue and a highly conserved guanine at position −7, and between T87 and the critical base pairs at −3 and +3. In addition, we present evidence in support of interactions between N84 and the phosphate 5’ to the base at +4, between R89 and the −7 phosphate, between T87 and the +3 and +4 phosphates, and between K90 and the +3 phosphate. This work provides functional evidence for some of the most critical interactions between Fis and DNA required for a high binding affinity and demonstrates the large contribution made by numerous phosphates to the stability of the Fis-DNA complex. PMID:18514225

  11. Exposure of beta H-crystallin to hydroxyl radicals enhances the transglutaminase-susceptibility of its existing amine-donor and amine-acceptor sites.

    PubMed Central

    Groenen, P J; Seccia, M; Smulders, R H; Gravela, E; Cheeseman, K H; Bloemendal, H; de Jong, W W

    1993-01-01

    beta H-crystallin was exposed to radiolytically generated hydroxyl radicals at defined radical concentrations, and its capacity to act as an amine-acceptor substrate and as an amine-donor substrate for transglutaminase were investigated. [14C]Methylamine was used as a probe for labelling amine-acceptor sites; a novel biotinylated hexapeptide was used to label amine-donor sites. The results demonstrate that both primary amine incorporation and hexapeptide incorporation by transglutaminase are considerably increased after oxidative attack on the crystallin. The identity of the labelled subunits was established, and it is shown that, in both cases, this increased incorporation is not due to the production of new substrates, but that the existing incorporation sites become more susceptible. Moreover, using the newly developed probe, we could identify, for the first time, the major crystallin subunits active as amine-donor substrates (both before and after treatment) to be beta B1-, beta A3- and beta A4-crystallin. These data support the proposal that oxidative stress and transglutaminase activity may be jointly involved in the changes found in lens crystallins with age and in the development of cataract. Images Figure 1 Figure 2 Figure 3 PMID:7902086

  12. A novel pathogenic splice acceptor site germline mutation in intron 14 of the APC gene in a Chinese family with familial adenomatous polyposis

    PubMed Central

    Zhao, Guoru; Hu, Yuan; Liang, Shengran; Zhang, Xipeng

    2017-01-01

    Familial adenomatous polyposis (FAP) is an autosomal dominant precancerous condition, clinically characterized by the presence of multiple colorectal adenomas or polyps. Patients with FAP has a high risk of developing colorectal cancer (CRC) from these colorectal adenomatous polyps by the mean age of diagnosis at 40 years. Germline mutations of the APC gene cause familial adenomatous polyposis (FAP). Colectomy has recommended for the FAP patients with significant polyposis. Here, we present a clinical molecular study of a four generation Chinese family with FAP. Clinical diagnosis of FAP has been done according to the phenotype, family history and medical records. Patient's blood samples were collected and genomic DNA was extracted. In order to identify the pathogenic mutation underlying the disease phenotype targeted next-generation sequencing and confirmatory sanger sequencing has undertaken. Targeted next generation sequencing identified a novel heterozygous splice-acceptor site mutation [c.1744-1G>A] in intron 14 of APC gene, which is co-segregated with the FAP phenotypes in the proband and amongst all the affected family members. This mutation is not present in unaffected family members and in normal healthy controls of same ethnic origin. According to the LOVD database for Chinese colorectal cancer patients, in Chinese population, 60% of the previously reported APC gene mutations causes FAP, are missense mutations. This novel splice-acceptor site mutation causing FAP in this Chinese family expands the germline mutation spectrum of the APC gene in the Chinese population. PMID:28423518

  13. A novel pathogenic splice acceptor site germline mutation in intron 14 of the APC gene in a Chinese family with familial adenomatous polyposis.

    PubMed

    Wang, Dan; Liang, Shengyun; Zhang, Zhao; Zhao, Guoru; Hu, Yuan; Liang, Shengran; Zhang, Xipeng; Banerjee, Santasree

    2017-03-28

    Familial adenomatous polyposis (FAP) is an autosomal dominant precancerous condition, clinically characterized by the presence of multiple colorectal adenomas or polyps. Patients with FAP has a high risk of developing colorectal cancer (CRC) from these colorectal adenomatous polyps by the mean age of diagnosis at 40 years. Germline mutations of the APC gene cause familial adenomatous polyposis (FAP). Colectomy has recommended for the FAP patients with significant polyposis. Here, we present a clinical molecular study of a four generation Chinese family with FAP. Clinical diagnosis of FAP has been done according to the phenotype, family history and medical records. Patient's blood samples were collected and genomic DNA was extracted. In order to identify the pathogenic mutation underlying the disease phenotype targeted next-generation sequencing and confirmatory sanger sequencing has undertaken. Targeted next generation sequencing identified a novel heterozygous splice-acceptor site mutation [c.1744-1G>A] in intron 14 of APC gene, which is co-segregated with the FAP phenotypes in the proband and amongst all the affected family members. This mutation is not present in unaffected family members and in normal healthy controls of same ethnic origin. According to the LOVD database for Chinese colorectal cancer patients, in Chinese population, 60% of the previously reported APC gene mutations causes FAP, are missense mutations. This novel splice-acceptor site mutation causing FAP in this Chinese family expands the germline mutation spectrum of the APC gene in the Chinese population.

  14. Analysis of the Plastidic phosphate translocator Gene Family in Arabidopsis and Identification of New phosphate translocator-Homologous Transporters, Classified by Their Putative Substrate-Binding Site1

    PubMed Central

    Knappe, Silke; Flügge, Ulf-Ingo; Fischer, Karsten

    2003-01-01

    Analysis of the Arabidopsis genome revealed the complete set of plastidic phosphate translocator (pPT) genes. The Arabidopsis genome contains 16 pPT genes: single copies of genes coding for the triose phosphate/phosphate translocator and the xylulose phosphate/phosphate translocator, and two genes coding for each the phosphoenolpyruvate/phosphate translocator and the glucose-6-phosphate/phosphate translocator. A relatively high number of truncated phosphoenolpyruvate/phosphate translocator genes (six) and glucose-6-phosphate/phosphate translocator genes (four) could be detected with almost conserved intron/exon structures as compared with the functional genes. In addition, a variety of PT-homologous (PTh) genes could be identified in Arabidopsis and other organisms. They all belong to the drug/metabolite transporter superfamily showing significant similarities to nucleotide sugar transporters (NSTs). The pPT, PTh, and NST proteins all possess six to eight transmembrane helices. According to the analysis of conserved motifs in these proteins, the PTh proteins can be divided into (a) the lysine (Lys)/arginine group comprising only non-plant proteins, (b) the Lys-valine/alanine/glycine group of Arabidopsis proteins, (c) the Lys/asparagine group of Arabidopsis proteins, and (d) the Lys/threonine group of plant and non-plant proteins. None of these proteins have been characterized so far. The analysis of the putative substrate-binding sites of the pPT, PTh, and NST proteins led to the suggestion that all these proteins share common substrate-binding sites on either side of the membrane each of which contain a conserved Lys residue. PMID:12644669

  15. [Synthesis and acceptor properties of 11-[(9'-anthracenyl)methoxy]undecyl phosphate and P1-{11-[(9'-anthracenyl)methoxy]undecyl}-P2-(alpha-D-galactopyranosyl) diphosphate in the enzymic reactions catalyzed by galactosylphosphotransferase and mannosyltransferase from Salmonella newport].

    PubMed

    Vinnikova, A N; Utkina, N S; Danilov, L L; Torgov, V I; Druzhinina, T N; Veselovskiĭ, V V

    2013-01-01

    Fluorescent 11-[(9'-anthracenyl)methoxy]undecyl phosphate and P1-{11-[(9'-anthracenyl)methoxy]undecyl}-P2-(alpha-D-galactopyranosyl) diphosphate were chemically synthesized for the first time. The ability of the first compound to serve as substrate-acceptor ofgalactosyl phosphate residue and the second compound of mannosyl residue in enzymic reactions catalyzed by galactosylphosphotransferase and mannosyltransferase from Salmonella newport membrane preparation was demonstrated.

  16. Investigating the hydrogen-bond acceptor site of the nicotinic pharmacophore model: a computational and experimental study using epibatidine-related molecular probes

    NASA Astrophysics Data System (ADS)

    Dallanoce, Clelia; Grazioso, Giovanni; Pomè, Diego Yuri; Sciaccaluga, Miriam; Matera, Carlo; Gotti, Cecilia; Fucile, Sergio; De Amici, Marco

    2013-11-01

    The binding mode of nicotinic agonists has been thoroughly investigated in the last decades. It is now accepted that the charged amino group is bound by a cation-π interaction to a conserved tryptophan residue, and that the aromatic moiety is projected into a hydrophobic pocket deeply located inside the binding cleft. A hydrogen bond donor/acceptor, maybe a water molecule solvating this receptor subsite, contributes to further stabilize the nicotinic ligands. The position of this water molecule has been established by several X-ray structures of the acetylcholine-binding protein. In this study, we computationally analyzed the role of this water molecule as a putative hydrogen bond donor/acceptor moiety in the agonist binding site of the three most relevant heteromeric (α4β2, α3β4) and homomeric (α7) neuronal nicotinic acetylcholine receptor (nAChR) subtypes. Our theoretical investigation made use of epibatidine 1 and deschloroepibatidine 2 as molecular probes, and was then extended to their analogues 3 and 4, which were subsequently synthesized and tested at the three target receptor subtypes. Although the pharmacological data for the new ligands 3 and 4 indicated a reduction of the affinity at the studied nAChRs with respect to reference agonists, a variation of the selectivity profile was clearly evidenced.

  17. Activating the phosphate nucleophile at the catalytic site of purine nucleoside phosphorylase: a vibrational spectroscopic study.

    PubMed

    Deng, Hua; Lewandowicz, Andrzej; Schramm, Vern L; Callender, Robert

    2004-08-11

    Difference Raman and FTIR studies complemented by vibrational analysis based on ab initio calculations show that the dianionic phosphate in the PNP.ImmH.PO4 complex is forced into a unique bonding arrangement in which one of the PO bonds is greatly polarized by enzyme active site interactions, such that it resembles a PO bond that is about one-quarter of the way toward forming a bridging P-O-C single P-O bond.

  18. Purification to homogeneity and partial amino acid sequence of a fragment which includes the methyl acceptor site of the human DNA repair protein for O6-methylguanine.

    PubMed

    Major, G N; Gardner, E J; Carne, A F; Lawley, P D

    1990-03-25

    DNA repair by O6-methylguanine-DNA methyltransferase (O6-MT) is accomplished by removal by the enzyme of the methyl group from premutagenic O6-methylguanine-DNA, thereby restoring native guanine in DNA. The methyl group is transferred to an acceptor site cysteine thiol group in the enzyme, which causes the irreversible inactivation of O6-MT. We detected a variety of different forms of the methylated, inactivated enzyme in crude extracts of human spleen of molecular weights higher and lower than the usually observed 21-24kDa for the human O6-MT. Several apparent fragments of the methylated form of the protein were purified to homogeneity following reaction of partially-purified extract enzyme with O6-[3H-CH3]methylguanine-DNA substrate. One of these fragments yielded amino acid sequence information spanning fifteen residues, which was identified as probably belonging to human methyltransferase by virtue of both its significant sequence homology to three procaryote forms of O6-MT encoded by the ada, ogt (both from E. coli) and dat (B. subtilis) genes, and sequence position of the radiolabelled methyl group which matched the position of the conserved procaryote methyl acceptor site cysteine residue. Statistical prediction of secondary structure indicated good homologies between the human fragment and corresponding regions of the constitutive form of O6-MT in procaryotes (ogt and dat gene products), but not with the inducible ada protein, indicating the possibility that we had obtained partial amino acid sequence for a non-inducible form of the human enzyme. The identity of the fragment sequence as belonging to human methyltransferase was more recently confirmed by comparison with cDNA-derived amino acid sequence from the cloned human O6-MT gene from HeLa cells (1). The two sequences compared well, with only three out of fifteen amino acids being different (and two of them by only one nucleotide in each codon).

  19. Recombinant hnRNP protein A1 and its N-terminal domain show preferential affinity for oligodeoxynucleotides homologous to intron/exon acceptor sites.

    PubMed Central

    Buvoli, M; Cobianchi, F; Biamonti, G; Riva, S

    1990-01-01

    The reported binding preference of human hnRNP protein A1 for the 3'-splice site of some introns (Swanson and Dreyfuss (1988) EMBO J. 7, 3519-3529; Mayrand and Pederson (1990) Nucleic Acids Res. 18, 3307-3318) was tested by assaying in vitro the binding of purified recombinant A1 protein (expressed in bacteria) to synthetic oligodeoxynucleotides (21-mers) of suitable sequence. In such a minimal system we find preferential binding of protein A1 to oligodeoxynucleotide sequences corresponding to the 3'-splice site of IVS1 of human beta-globin pre-mRNA and of IVS1 of Adenovirus type 2 major late transcript. Mutation studies demonstrate that the binding specificity is dependent on the known critical domains of this intron region, the AG splice site dinucleotide and polypyrimidine tract, and resides entirely in the short oligonucleotide sequence. Moreover specific binding does not require the presence of other hnRNP proteins or of snRNP particles. Studies with a truncated recombinant protein demonstrated that the minimal protein sequence determinants for A1 recognition of 3'-splice acceptor site reside entirely in the N-terminal 195 aa of the unmodified protein. Images PMID:2251120

  20. Donor assists acceptor binding and catalysis of human α1,6-fucosyltransferase.

    PubMed

    Kötzler, Miriam P; Blank, Simon; Bantleon, Frank I; Wienke, Martin; Spillner, Edzard; Meyer, Bernd

    2013-08-16

    α1,6-Core-fucosyltransferase (FUT8) is a vital enzyme in mammalian physiological and pathophysiological processes such as tumorigenesis and progress of, among others, non-small cell lung cancer and colon carcinoma. It was also shown that therapeutic antibodies have a dramatically higher efficacy if the α1,6-fucosyl residue is absent. However, specific and potent inhibitors for FUT8 and related enzymes are lacking. Hence, it is crucial to elucidate the structural basis of acceptor binding and the catalytic mechanism. We present here the first structural model of FUT8 in complex with its acceptor and donor molecules. An unusually large acceptor, i.e., a hexasaccharide from the core of N-glycans, is required as minimal structure. Acceptor substrate binding of FUT8 is being dissected experimentally by STD NMR and SPR and theoretically by molecular dynamics simulations. The acceptor binding site forms an unusually large and shallow binding site. Binding of the acceptor to the enzyme is much faster and stronger if the donor is present. This is due to strong hydrogen bonding between O6 of the proximal N-acetylglucosamine and an oxygen atom of the β-phosphate of GDP-fucose. Therefore, we propose an ordered Bi Bi mechanism for FUT8 where the donor molecule binds first. No specific amino acid is present that could act as base during catalysis. Our results indicate a donor-assisted mechanism, where an oxygen of the β-phosphate deprotonates the acceptor. Knowledge of the mechanism of FUT8 is now being used for rational design of targeted inhibitors to address metastasis and prognosis of carcinomas.

  1. Water-quality and hydrogeologic data for three phosphate industry waste-disposal sites in central Florida, 1979-80

    USGS Publications Warehouse

    Miller, Ronald L.; Sutcliffe, Horace

    1982-01-01

    This report is a complilation of geologic, hydrologic, and water-quality data and information on test holes collected in the vicinity of gypsum stack complexes at two phosphate chemical plants and one phosphatic clayey waste disposal pond at a phosphate mine and beneficiation plant in central Florida. The data were collected from September 1979 to October 1980 at thee AMAX Phosphate, Inc., chemical plant, Piney Point; the USS AgriChemicals chemical plant, Bartow; and the International Minerals and Chemical Corporation Clear Springs mine, Bartow. Approximmmtely 5,400 field and laboratory water-quality determinations on water samples were collected from about 78 test holes and 31 surface-water, rainfall, and other sampling sites at phosphate industry beneficiation and chemical plant waste-disposal operations. Maps show locations of sampling sites. (USGS)

  2. Effects of three phosphate industrial sites on ground-water quality in central Florida, 1979 to 1980

    USGS Publications Warehouse

    Miller, R.L.; Sutcliffe, Horace

    1984-01-01

    Geologic, hydrologic, and water quality data and information on test holes collected in the vicinity of gypsum stack complexes at two phosphate chemical plants and one phosphatic clayey waste disposal pond at a phosphate mine and beneficiation plant in central Florida are presented. The data were collected from September 1979 to October 1980 at the AMAX Phosphate, Inc. chemical plant, Piney Point; the USS Agri-Chemicals chemical plant, Bartow; and the International Minerals and Chemical Corporation Clear Springs mine, Bartow. Approximately 5,400 field and laboratory water quality determinations on water samples collected from about 100 test holes and 28 surface-water , 5 rainfall, and other sampling sites at phosphate industry beneficiation and chemical plant waste disposal operations are tabulated. Maps are included to show sampling sites. (USGS)

  3. Structural basis for phosphatidylinositol-phosphate biosynthesis

    NASA Astrophysics Data System (ADS)

    Clarke, Oliver B.; Tomasek, David; Jorge, Carla D.; Dufrisne, Meagan Belcher; Kim, Minah; Banerjee, Surajit; Rajashankar, Kanagalaghatta R.; Shapiro, Lawrence; Hendrickson, Wayne A.; Santos, Helena; Mancia, Filippo

    2015-10-01

    Phosphatidylinositol is critical for intracellular signalling and anchoring of carbohydrates and proteins to outer cellular membranes. The defining step in phosphatidylinositol biosynthesis is catalysed by CDP-alcohol phosphotransferases, transmembrane enzymes that use CDP-diacylglycerol as donor substrate for this reaction, and either inositol in eukaryotes or inositol phosphate in prokaryotes as the acceptor alcohol. Here we report the structures of a related enzyme, the phosphatidylinositol-phosphate synthase from Renibacterium salmoninarum, with and without bound CDP-diacylglycerol to 3.6 and 2.5 Å resolution, respectively. These structures reveal the location of the acceptor site, and the molecular determinants of substrate specificity and catalysis. Functional characterization of the 40%-identical ortholog from Mycobacterium tuberculosis, a potential target for the development of novel anti-tuberculosis drugs, supports the proposed mechanism of substrate binding and catalysis. This work therefore provides a structural and functional framework to understand the mechanism of phosphatidylinositol-phosphate biosynthesis.

  4. Structural basis for phosphatidylinositol-phosphate biosynthesis

    PubMed Central

    Clarke, Oliver B.; Tomasek, David; Jorge, Carla D.; Dufrisne, Meagan Belcher; Kim, Minah; Banerjee, Surajit; Rajashankar, Kanagalaghatta R.; Shapiro, Lawrence; Hendrickson, Wayne A.; Santos, Helena; Mancia, Filippo

    2015-01-01

    Phosphatidylinositol is critical for intracellular signalling and anchoring of carbohydrates and proteins to outer cellular membranes. The defining step in phosphatidylinositol biosynthesis is catalysed by CDP-alcohol phosphotransferases, transmembrane enzymes that use CDP-diacylglycerol as donor substrate for this reaction, and either inositol in eukaryotes or inositol phosphate in prokaryotes as the acceptor alcohol. Here we report the structures of a related enzyme, the phosphatidylinositol-phosphate synthase from Renibacterium salmoninarum, with and without bound CDP-diacylglycerol to 3.6 and 2.5 Å resolution, respectively. These structures reveal the location of the acceptor site, and the molecular determinants of substrate specificity and catalysis. Functional characterization of the 40%-identical ortholog from Mycobacterium tuberculosis, a potential target for the development of novel anti-tuberculosis drugs, supports the proposed mechanism of substrate binding and catalysis. This work therefore provides a structural and functional framework to understand the mechanism of phosphatidylinositol-phosphate biosynthesis. PMID:26510127

  5. A G-to-T transversion at the splice acceptor site of dystrophin exon 14 shows multiple splicing outcomes that are not exemplified by transition mutations.

    PubMed

    Ota, Mitsunori; Takeshima, Yasuhiro; Nishida, Atsushi; Awano, Hiroyuki; Lee, Tomoko; Yagi, Mariko; Matsuo, Masafumi

    2012-01-01

    Mutations at splicing consensus sequences have been shown to induce splicing errors such as exon skipping or cryptic splice site activation. Here, we identified eight splicing products caused by a G-to-T transversion mutation at the splice acceptor site of exon 14 of the dystrophin gene (c.1603-1G>T). Unexpectedly, the most abundant product showed skipping of the two consecutive exons 14 and 15, and exon 14 skipping was observed as the second most abundant product. To examine the cause of this splicing multiplicity, minigenes containing dystrophin exons 14 and 15 with their flanking introns were constructed and subjected to in vitro splicing. Minigenes with the wild-type sequence or a G>A transition at position c.1603-1 produced only the mature mRNA. On the other hand, the minigenes with a G>T or G>C transversion mutation produced multiple splicing products. A time-course analysis of the in vitro splicing revealed that splicing of the middle intron, intron 14, was the first step in transcript maturation for all four minigene constructs. The identity of the mutant nucleotide, but not its position, is a factor leading to multiple splicing outcomes. Our results suggest that exon skipping therapy for Duchenne's muscular dystrophy should be carefully monitored for their splicing outcomes.

  6. Combining Higher-Energy Collision Dissociation and Electron-Transfer/Higher-Energy Collision Dissociation Fragmentation in a Product-Dependent Manner Confidently Assigns Proteomewide ADP-Ribose Acceptor Sites.

    PubMed

    Bilan, Vera; Leutert, Mario; Nanni, Paolo; Panse, Christian; Hottiger, Michael O

    2017-02-07

    Protein adenosine diphosphate (ADP)-ribosylation is a physiologically and pathologically important post-translational modification. Recent technological advances have improved analysis of this complex modification and have led to the discovery of hundreds of ADP-ribosylated proteins in both cultured cells and mouse tissues. Nevertheless, accurate assignment of the ADP-ribose acceptor site(s) within the modified proteins identified has remained a challenging task. This is mainly due to poor fragmentation of modified peptides. Here, using an Orbitrap Fusion Tribrid mass spectrometer, we present an optimized methodology that not only drastically improves the overall localization scores for ADP-ribosylation acceptor sites but also boosts ADP-ribosylated peptide identifications. First, we systematically compared the efficacy of higher-energy collision dissociation (HCD), electron-transfer dissociation with supplemental collisional activation (ETcaD), and electron-transfer/higher-energy collision dissociation (EThcD) fragmentation methods when determining ADP-ribose acceptor sites within complex cellular samples. We then tested the combination of HCD and EThcD fragmentation, which were employed in a product-dependent manner, and the unique fragmentation properties of the ADP-ribose moiety were used to trigger targeted fragmentation of only the modified peptides. The best results were obtained with a workflow that included initial fast, high-energy HCD (Orbitrap, FT) scans, which produced intense ADP-ribose fragmentation ions. These potentially ADP-ribosylated precursors were then selected and analyzed via subsequent high-resolution HCD and EThcD fragmentation. Using these resulting high-quality spectra, we identified a xxxxxxKSxxxxx modification motif where lysine can serve as an ADP-ribose acceptor site. Due to the appearance of serine within this motif and its close presence to the lysine, further analysis revealed that serine serves as a new ADP-ribose acceptor site

  7. Evidence for a reactive cysteine at the nucleotide binding site of spinach ribulose-5-phosphate kinase

    SciTech Connect

    Omnaas, J.; Porter, M.A.; Hartman, F.C.

    1985-02-01

    Ribulose-5-phosphate kinase from spinach was rapidly inactivated by N-bromoacetylethanolamine phosphate in a bimolecular fashion with a k2 of 2.0 m s at 2C and pH 8.0. Ribulose 5-phosphate had little effect on the rate of inactivation, whereas complete protection was afforded by ADP or ATP. The extent of incorporation as determined with UC-labeled reagent was about 1 molar equivalent per subunit in the presence of ATP with full retention of enzymatic activity, and about 2 molar equivalents per subunit in the completely inactivated enzyme. Amino acid analyses of enzyme derivatized with UC-labeled reagent reveal that all of the covalently incorporated reagent was associated with cysteinyl residues. Hence, two sulfhydryls are reactive, but the inactivation correlates with alkylation of one cysteinyl residue at or near the enzyme's nucleotide binding site. The kinase was also extremely sensitive to the sulfhydryl reagents 5,5'-dithiobis(2-nitrobenzoic acid) and N-ethylmaleimide. The reactive sulfhydryl groups are likely to be those generated by reduction of a disulfide during activation. 20 references, 3 figures, 2 tables.

  8. An acceptor-substrate binding site determining glycosyl transfer emerges from mutant analysis of a plant vacuolar invertase and a fructosyltransferase.

    PubMed

    Altenbach, Denise; Rudiño-Pinera, Enrique; Olvera, Clarita; Boller, Thomas; Wiemken, Andres; Ritsema, Tita

    2009-01-01

    Glycoside hydrolase family 32 (GH32) harbors hydrolyzing and transglycosylating enzymes that are highly homologous in their primary structure. Eight amino acids dispersed along the sequence correlated with either hydrolase or glycosyltransferase activity. These were mutated in onion vacuolar invertase (acINV) according to the residue in festuca sucrose:sucrose 1-fructosyltransferase (saSST) and vice versa. acINV(W440Y) doubles transferase capacity. Reciprocally, saSST(C223N) and saSST(F362Y) double hydrolysis. SaSST(N425S) shows a hydrolyzing activity three to four times its transferase activity. Interestingly, modeling acINV and saSST according to the 3D structure of crystallized GH32 enzymes indicates that mutations saSST(N425S), acINV(W440Y), and the previously reported acINV(W161Y) reside very close together at the surface in the entrance of the active-site pocket. Residues in- and outside the sucrose-binding box determine hydrolase and transferase capabilities of GH32 enzymes. Modeling suggests that residues dispersed along the sequence identify a location for acceptor-substrate binding in the 3D structure of fructosyltransferases.

  9. A new VCAN/versican splice acceptor site mutation in a French Wagner family associated with vascular and inflammatory ocular features

    PubMed Central

    Brézin, Antoine P.; Nedelec, Brigitte; Barjol, Amandine; Rothschild, Pierre-Raphael; Delpech, Marc

    2011-01-01

    Purpose To detail the highly variable ocular phenotypes of a French family affected with an autosomal dominantly inherited vitreoretinopathy and to identify the disease gene. Methods Sixteen family members with ten affected individuals underwent detailed ophthalmic evaluation. Genetic linkage analysis and gene screening were undertaken for genes known to be involved in degenerative and exudative vitreoretinopathies. Qualitative reverse transcriptase-PCR analysis of the versiscan (VCAN) transcripts was performed after mutation detection in the VCAN gene. Results The first index patient of this French family was referred to us because of a chronic uveitis since infancy; this uveitis was associated with exudative retinal detachment in the context of a severe uncharacterized familial vitreoretinopathy. Genetic linkage was obtained to the VCAN locus, and we further identified a new pathogenic mutation at the highly conserved splice acceptor site in intron 7 of the VCAN gene (c.4004–2A>T), which produced aberrantly spliced VCAN transcripts. Conclusions Extensive molecular investigation allowed us to classify this familial vitreoretinopathy as Wagner syndrome. This study illustrates the need to confirm clinical diagnosis by molecular genetic testing and adds new ocular phenotypes to the Wagner syndrome, such as vascular and inflammatory features. PMID:21738396

  10. The conservation of phosphate-binding residues among PHT1 transporters suggests that distinct transport affinities are unlikely to result from differences in the phosphate-binding site.

    PubMed

    Ceasar, S Antony; Baker, Alison; Muench, Stephen P; Ignacimuthu, S; Baldwin, Stephen A

    2016-10-15

    The plant PHosphate Transporter 1 (PHT1) family of membrane proteins belongs to the major facilitator super family and plays a major role in the acquisition of inorganic phosphate (Pi) from the soil and its transport within the plant. These transporters have been well characterized for expression patterns, localization, and in some cases affinity. Furthermore, the crystal structure of a high-affinity eukaryotic phosphate transporter from the fungus Piriformospora indica (PiPT) has revealed important information on the residues involved in Pi transport. Using multiple-sequence alignments and homology modelling, the phosphate-binding site residues were shown to be well conserved between all the plant PHT1 proteins, Saccharomyces cerevisiae PHO84 and PiPT. For example, Asp 324 in PiPT is conserved in the equivalent position in all plant PHT1 and yeast transporters analyzed, and this residue in ScPHO84 was shown by mutagenesis to be important for both the binding and transport of Pi. Moreover, Asp 45 and Asp 149, which are predicted to be involved in proton import, and Lys 459, which is putatively involved in Pi-binding, are all fully conserved in PHT1 and ScPHO84 transporters. The conserved nature of the residues that play a key role in Pi-binding and transport across the PHT1 family suggests that the differing Pi affinities of these transporters do not reside in differences in the Pi-binding site. Recent studies suggest that phosphate transporters could possess dual affinity and that post-translational modifications may be important in regulating affinity for phosphate. © 2016 The Author(s); published by Portland Press Limited on behalf of the Biochemical Society.

  11. Depupylase Dop Requires Inorganic Phosphate in the Active Site for Catalysis.

    PubMed

    Bolten, Marcel; Vahlensieck, Christian; Lipp, Colette; Leibundgut, Marc; Ban, Nenad; Weber-Ban, Eilika

    2017-03-10

    Analogous to eukaryotic ubiquitination, proteins in actinobacteria can be post-translationally modified in a process referred to as pupylation, the covalent attachment of prokaryotic ubiquitin-like protein Pup to lysine side chains of the target protein via an isopeptide bond. As in eukaryotes, an opposing activity counteracts the modification by specific cleavage of the isopeptide bond formed with Pup. However, the enzymes involved in pupylation and depupylation have evolved independently of ubiquitination and are related to the family of ATP-binding and hydrolyzing carboxylate-amine ligases of the glutamine synthetase type. Furthermore, the Pup ligase PafA and the depupylase Dop share close structural and sequence homology and have a common evolutionary history despite catalyzing opposing reactions. Here, we investigate the role played by the nucleotide in the active site of the depupylase Dop using a combination of biochemical experiments and X-ray crystallographic studies. We show that, although Dop does not turn over ATP stoichiometrically with substrate, the active site nucleotide species in Dop is ADP and inorganic phosphate rather than ATP, and that non-hydrolyzable analogs of ATP cannot support the enzymatic reaction. This finding suggests that the catalytic mechanism is more similar to the mechanism of the ligase PafA than previously thought and likely involves the transient formation of a phosphorylated Pup-intermediate. Evidence is presented for a mechanism where the inorganic phosphate acts as the nucleophilic species in amide bond cleavage and implications for Dop function are discussed.

  12. Differential Site-Based Expression of Pentose Phosphate Pathway-Related Proteins among Breast Cancer Metastases

    PubMed Central

    Cha, Yoon Jin; Jung, Woo Hee

    2017-01-01

    Purpose. We aimed to investigate the expression of pentose phosphate pathway- (PPP-) related proteins in metastatic breast cancer and its relationship with clinicopathologic factors. Methods. Tissue samples from 126 metastatic breast cancers were included in a tissue microarray. Expression of PPP-related proteins [glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconolactonase (6PGL), 6-phosphogluconate dehydrogenase (6PGDH), and nuclear factor erythroid 2-related factor (NRF2)] was determined by immunohistochemistry. Results. G6PDH (p = 0.011) and cytoplasmic NRF2 (p = 0.001) showed the highest expression in brain metastases. Human epidermal growth factor receptor (HER-2) positivity was associated with G6PDH (p < 0.001) and cytoplasmic NRF2 (p = 0.015) positivity. A high Ki-67 labeling index (LI) was correlated with nuclear NRF2 positivity (p = 0.037), and HER-2-positive luminal B type was associated with G6PDH positivity (p = 0.001). On multivariate Cox analysis, independent risk factors of short overall survival were 6PGL positivity in bone metastasis (HR 4.180, 95% CI 1.160–15.06, p = 0.029) and low Ki-67 LI in lung metastasis (HR 11.853, 95% CI 1.841–76.30, p = 0.009). Conclusion. Differential expression of PPP-related proteins correlated with different prognoses and metastatic sites, with the highest expression in brain metastases, and could be a potential therapeutic target. PMID:28260828

  13. Inhibitory effect of pyridoxal 5'-phosphate on the DNA binding site of ATP-dependent deoxyribonuclease from Bacillus laterosporus.

    PubMed

    Fujiyoshi, T; Nakayama, J; Anai, M

    1981-04-01

    Bacillus laterosporus ATP-dependent deoxyribonuclease has been found to be inhibited by pyridoxal 5'-phosphate. The inhibition is specific for pyridoxal 5'-phosphate and pyridoxal which are required in relatively high concentrations. Pyridoxamine 5'-phosphate, pyridoxamine, and pyridoxine are ineffective. The inhibition is reversed by dilution or dialysis but can be changed to an irreversible inactivation by reduction of the enzyme . pyridoxal 5'-phosphate complex with sodium borohydride. The compound is a competitive inhibitor with respect to DNA but not ATP. Moreover, the presence of DNA substrate protects the enzyme against this inactivation but the presence of ATP shows no effect. The reduced enzyme . pyridoxal 5'-phosphate complex displays a new absorption maximum at 325 nm and a fluorescence emission at 390-400 nm when excited at 325 nm which are characteristic for epsilon-N-(phosphopyridoxyl)lysine. Thus, B. laterosporus DNase appears to have an essential lysine residue at the DNA binding site of the enzyme, and the enzyme possess two different active sites, a DNA binding site and an ATP binding site.

  14. ABCC4 functional SNP in the 3' splice acceptor site of exon 8 (G912T) is associated with unfavorable clinical outcome in children with acute lymphoblastic leukemia.

    PubMed

    Mesrian Tanha, Hamzeh; Rahgozar, Soheila; Mojtabavi Naeini, Marjan

    2017-07-01

    ATP-binding cassette subfamily C member 4 (ABCC4) encoding MRP4 protein is involved in pediatric acute lymphoblastic leukemia (ALL) drug resistance. The nonsynonymous single nucleotide polymorphism (SNP) rs2274407 (G912T; K304N) is located in the 3' splice acceptor site of exon 8 of ABCC4 pre-mRNA. The aim of this study was to investigate the prognostic value of rs2274407 in childhood ALL and its possible functional effect on MRP4. ABCC4 G912T SNP was genotyped in 145 Iranian Philadelphia-negative (Ph(-)) children with ALL using modified tetra-primer ARMS PCR and evaluated for possible association with 3-year disease-free survival (3DFS). In addition, functional impact of rs2274407 on the MRP4 activity and possible post-transcriptional modifications were bioinformatically and experimentally studied. ABCC4 912T allele carriers (G/T and T/T genotypes) are associated with worse 3DFS in Pre-B cell ALL [P = 0.00019, OR (95% CI) = 13.17 (2.55-68.11)]. In addition, computational studies showed that K304N alteration has no impact on the MRP4 activity. However, it may disrupt the normal splicing process of ABCC4 pre-mRNA. To date, this is the first study that shows the potential functional impact of rs2274407 SNP on the aberrant splicing of ABCC4 mRNA. We also demonstrated a robust association between G912T and pediatric ALL negative outcome, which may be explained by the novel computational studies performed in this study.

  15. Identification of beta1C-2, a novel variant of the integrin beta1 subunit generated by utilization of an alternative splice acceptor site in exon C.

    PubMed Central

    Svineng, G; Fässler, R; Johansson, S

    1998-01-01

    A new splice variant of the human integrin subunit beta1 has been identified and designated beta1C-2. It differs from the previously reported beta1C (in this report designated beta1C-1) by 18 nucleotides, and is generated by splicing from exon 6 to an alternative splice acceptor site within exon C, causing an in-frame deletion of six amino acids of the cytoplasmic region of beta1C-1. The beta1C-2 mRNA is present in several human cell lines and tissues at low levels, similarly to beta1C-1. In peripheral T-lymphocytes, beta1C-2 is the selectively expressed isoform. Neither beta1C-1 nor beta1C-2 mRNA could be detected in mouse tissues, and Southern hybridization of a mouse genomic beta1 clone with a human exon-C-specific probe failed to identify a corresponding mouse exon. The antisense orientation of exon C is highly homologous to an Alu element. Since Alu elements are restricted to primates, the beta1C-1 and beta1C-2 variants of the integrin subunit beta1 are specific for these species. The protein coded for by the beta1C-2 cDNA can be expressed and localized to the surface of beta1 deficient mouse cells. However, while stable transformed clones expressing high levels of the beta1A were commonly found, the beta1C-1 and beta1C-2 expressing clones expressed barely detectable amounts of the beta1 protein. Hence, high levels of beta1C-2 may be incompatible with cell proliferation, as previously suggested for beta1C-1. PMID:9494094

  16. Overview of Phosphate-Based Remediation Technologies At The Hanford Site, Richland Washington

    NASA Astrophysics Data System (ADS)

    Thompson, K. M.; Fruchter, J. S.

    2009-12-01

    Phosphate-based technologies have been tested to sequester strontium-90 and uranium at the Hanford Site, part of the U.S. Department of Energy's (DOE)nuclear weapons complex that encompasses approximately 586 square miles in southeast Washington State. The Columbia River flows through the site (Hanford Reach) where localized groundwater plumes upwell into the river. Efforts to reduce the flux of Sr-90 to the Columbia River from Hanford Site 100-N Area past practice liquid waste disposal sites have been underway since the early 1990s. Termination of all liquid discharges to the ground in 1993 was a major step toward meeting this goal. However, Sr 90 adsorbed onto sediment beneath liquid waste disposal sites, and onto sediment that extends beneath the near-shore riverbed, remains a continuing contaminant source for impacting groundwater and the Columbia River. Initial remediation efforts using a pump-and treat system proved to be ineffective as a long-term solution because of the geochemical characteristics of Sr-90. Following an evaluation of potential Sr-90 treatment technologies and their applicability under 100-N Area hydrogeologic conditions, the U.S. Department of Energy and the Washington State Department of Ecology agreed to evaluate apatite sequestration as the primary remedial technology, combined with a secondary polishing step utilizing phytoextraction if necessary. DOE is also evaluating the efficacy of using polyphosphate to reduce uranium concentrations in the groundwater with the goal of meeting drinking water standards (30 μg/L). This technology works by forming phosphate minerals (autunite and apatite) in the aquifer that directly sequester the existing aqueous uranium in autunite minerals and precipitates apatite minerals for sorption and long-term treatment of uranium migrating into the treatment zone, thus reducing current and future aqueous uranium concentrations. These remedial technologies are being developed by Pacific Northwest National

  17. Identification of phosphorylation sites for adenosine 3',5'-cyclic phosphate dependent protein kinase on the voltage-sensitive sodium channel from Electrophorus electricus.

    PubMed

    Emerick, M C; Agnew, W S

    1989-10-17

    The voltage-sensitive sodium channel from the electroplax of Electrophorus electricus is selectively phosphorylated by the catalytic subunit of cyclic-AMP-dependent protein kinase (protein kinase A) but not by protein kinase C. Under identical limiting conditions, the protein was phosphorylated 20% as rapidly as the synthetic model substrate kemptamide. A maximum of 1.7 +/- 0.6 equiv of phosphate is incorporated per mole. Phosphoamino acid analysis revealed labeled phosphoserine and phosphothreonine at a constant ratio of 3.3:1. Seven distinct phosphopeptides were identified among tryptic fragments prepared from radiolabeled, affinity-purified protein and resolved by HPLC. The three most rapidly labeled fragments were further purified and sequenced. Four phosphorylated amino acids were identified deriving from three consensus phosphorylation sites. These were serine 6, serine 7, and threonine 17 from the amino terminus and a residue within 47 amino acids of the carboxyl terminus, apparently serine 1776. The alpha-subunits of brain sodium channels, like the electroplax protein, are readily phosphorylated by protein kinase A. However, these are also phosphorylated by protein kinase C and exhibit a markedly different pattern of incorporation. Each of three brain alpha-subunits displays an approximately 200 amino acid segment between homologous repeat domains I and II, which is missing from the electroplax and skeletal muscle proteins [Noda et al. (1986) Nature (London) 320, 188; Kayano et al. (1988) FEBS Lett. 228, 1878; Trimmer et al. (1989) Neuron 3, 33]. Most of the phosphorylation of the brain proteins occurs on a cluster of consensus phosphorylation sites located in this segment. This contrasts with the pattern of highly active sites on the amino and carboxyl termini of the electroplax protein. The detection of seven labeled tryptic phosphopeptides compared to the maximal labeling stoichiometry of approximately 2 suggests that many of the acceptor sites on the

  18. Influence of poultry carcass skin sample site on the effectiveness of trisodium phosphate against Listeria monocytogenes.

    PubMed

    Capita, Rosa; Alonso-Calleja, Carlos; Rodríguez-Pérez, Roberto; Moreno, Benito; García-Fernández, María del Camino

    2002-05-01

    The aim of this study was to determine the influence of skin sample site on the efficacy of trisodium phosphate (TSP) solutions in reducing Listeria monocytogenes populations on chicken carcasses during refrigerated storage. Chicken skin samples from the legs, the breasts, and the dorsal area inoculated with L. monocytogenes (10(8) CFU/ml) were dipped for 15 min in sterile tap water (control) or in 8, 10, or 12% TSP. L. monocytogenes counts and surface pH values were determined after 0, 1, 3, and 5 days of storage at 2 degrees C. For all sampling times and TSP concentrations, the reductions in L. monocytogenes numbers in breast skin were significantly larger (P < 0.05) than those in leg skin or dorsal skin. No significant differences were found in pH values as an effect of skin site. Our results suggest that skin sampling site is an important factor that needs to be considered when decontamination protocols are developed for poultry carcasses with the TSP treatment.

  19. T-->A transversion 11 bp from a splice acceptor site in the human gene for steroidogenic acute regulatory protein causes congenital lipoid adrenal hyperplasia.

    PubMed

    Tee, M K; Lin, D; Sugawara, T; Holt, J A; Guiguen, Y; Buckingham, B; Strauss, J F; Miller, W L

    1995-12-01

    Congenial lipoid adrenal hyperplasia (lipoid CAH) is the most severe form of CAH. Affected individuals can make no adrenal or gonadal steroids. All affected individuals are phenotypic females irrespective of gonadal sex, and frequently die in infancy if mineralocorticoid and glucocorticoid replacements are not instituted. Recent data implicate the steroidogenic acute regulatory (StAR) protein in this disorder. We now describe a 46,XY patient of Vietnamese ancestry with lipoid CAH who had a somewhat milder form of the disease. Diagnosis was at 10 weeks of age, and low levels of plasma progesterone, corticosterone, 180H-corticosterone and androstenedione were detectable. Testicular RNA for StAR was reverse transcribed, amplified, cloned and sequenced, revealing a 185 bp deletion corresponding to all of exon 5. The corresponding mRNA did not encode active protein in transfected cells. Cloned genomic DNA from the patient revealed only a T-->A transversion in intron 4,11 bp from the splice acceptor site of exon 5. This transversion destroys an NcoI site; digestion of PCR-amplified genomic DNA from the patient and both parents confirmed that the patient was homozygous and the parents were heterozygous. Expression vectors for StAR minigenes were constructed containing all StAR exons plus introns 4, 5 and 6 either with or without the T-->A mutation in intron 4. RNase protection assays showed that expression of the vector with normal intron 4 yielded correctly spliced StAR mRNA in transfected COS-1 cells, while most, but not all StAR mRNA from the vector with the T-->A transversion in intron 4 was abnormally spliced. RNase protection of the patient's testicular RNA confirmed that most, but not all StAR mRNA was similarly spliced abnormally. Splicing errors appear to be a rare cause of genetic diseases, but subtle intronic mutations may be missed when genomic DNA is the only material available for study. The low level of normal StAR mRNA produced may account for the later

  20. A splice acceptor site mutation in TaGW2-A1 increases thousand grain weight in tetraploid and hexaploid wheat through wider and longer grains.

    PubMed

    Simmonds, James; Scott, Peter; Brinton, Jemima; Mestre, Teresa C; Bush, Max; Del Blanco, Alicia; Dubcovsky, Jorge; Uauy, Cristobal

    2016-06-01

    Across 13 experiments the gw2 - A1 mutant allele shifts grain size distribution consistently across all grains significantly increasing grain weight (6.6 %), width (2.8 %) and length (2.1 %) in tetraploid and hexaploid wheat. There is an urgent need to identify, understand and incorporate alleles that benefit yield in polyploid wheat. The rice OsGW2 gene functions as a negative regulator of grain weight and width and is homologous to the wheat TaGW2 gene. Previously it was shown that transcript levels of the A-genome homoeologue, TaGW2-A1, are negatively associated with grain width in hexaploid wheat. In this study we screened the tetraploid Kronos TILLING population to identify mutants in TaGW2-A1. We identified a G to A transition in the splice acceptor site of exon 5 which leads to mis-splicing in TaGW2-A1. We backcrossed the mutant allele into tetraploid and hexaploid wheat and generated a series of backcross derived isogenic lines which were evaluated in glasshouse and field conditions. Across 13 experiments the GW2-A1 mutant allele significantly increased thousand grain weight (6.6 %), grain width (2.8 %) and grain length (2.1 %) in tetraploid and hexaploid wheat compared to the wild type allele. In hexaploid wheat, this led to an increase in spike yield since no differences were detected for spikelet or grain number between isogenic lines. The increase in grain width and length was consistent across grains of different sizes, suggesting that the effect of the mutation is stable across the ear and within spikelets. Differences in carpel size and weight between alleles were identified as early as 5 days before anthesis, suggesting that TaGW2-A1 acts on maternal tissue before anthesis to restrict seed size. A single nucleotide polymorphism marker was developed to aid the deployment of the mutant allele into breeding programmes.

  1. Structural definition of the active site and catalytic mechanism of 3,4-dihydroxy-2-butanone-4-phosphate synthase.

    PubMed

    Liao, Der-Ing; Zheng, Ya-Jun; Viitanen, Paul V; Jordan, Douglas B

    2002-02-12

    X-ray crystal structures of L-3,4-dihydroxy-2-butanone-4-phosphate synthase from Magnaporthe grisea are reported for the E-SO(4)(2-), E-SO(4)(2-)-Mg(2+), E-SO(4)(2)(-)-Mn(2+), E-SO(4)(2)(-)-Mn(2+)-glycerol, and E-SO(4)(2)(-)-Zn(2+) complexes with resolutions that extend to 1.55, 0.98, 1.60, 1.16, and 1.00 A, respectively. Active-site residues of the homodimer are fully defined. The structures were used to model the substrate ribulose 5-phosphate in the active site with the phosphate group anchored at the sulfate site and the placement of the ribulose group guided by the glycerol site. The model includes two Mg(2+) cations that bind to the oxygen substituents of the C2, C3, C4, and phosphate groups of the substrate, the side chains of Glu37 and His153, and water molecules. The position of the metal cofactors and the substrate's phosphate group are further stabilized by an extensive hydrogen-bond and salt-bridge network. On the basis of their proximity to the substrate's reaction participants, the imidazole of an Asp99-His136 dyad from one subunit, the side chains of the Asp41, Cys66, and Glu174 residues from the other subunit, and Mg(2+)-activated water molecules are proposed to serve specific roles in the catalytic cycle as general acid-base functionalities. The model suggests that during the 1,2-shift step of the reaction, the substrate's C3 and C4 hydroxyl groups are cis to each other. A cis transition state is calculated to have an activation barrier that is 2 kcal/mol greater than that of the trans transition state in the absence of the enzyme.

  2. Structural definition of the active site and catalytic mechanism of 3,4-dihydroxy-2-butanone 4-phosphate synthase

    SciTech Connect

    Liao, D.-I.; Zheng, Y.-J.; Viitanen, P.V.; Jordan, D.B.

    2010-03-08

    X-ray crystal structures of L-3,4-dihydroxy-2-butanone-4-phosphate synthase from Magnaporthe grisea are reported for the E-SO{sub 4}{sup 2-}, E-{sub 4}{sup 2-}-Mg{sup 2+}, E-SO{sub 4}{sup 2-}-Mn{sup 2+}, E-SO{sub 4}{sup 2-}-Mn{sup 2+}-glycerol, and E-SO{sub 4}{sup 2-}-Zn{sup 2+} complexes with resolutions that extend to 1.55, 0.98, 1.60, 1.16, and 1.00 {angstrom}, respectively. Active-site residues of the homodimer are fully defined. The structures were used to model the substrate ribulose 5-phosphate in the active site with the phosphate group anchored at the sulfate site and the placement of the ribulose group guided by the glycerol site. The model includes two Mg{sup 2+} cations that bind to the oxygen substituents of the C2, C3, C4, and phosphate groups of the substrate, the side chains of Glu37 and His153, and water molecules. The position of the metal cofactors and the substrate's phosphate group are further stabilized by an extensive hydrogen-bond and salt-bridge network. On the basis of their proximity to the substrate's reaction participants, the imidazole of an Asp99-His136 dyad from one subunit, the side chains of the Asp41, Cys66, and Glu174 residues from the other subunit, and Mg{sup 2+}-activated water molecules are proposed to serve specific roles in the catalytic cycle as general acid-base functionalities. The model suggests that during the 1,2-shift step of the reaction, the substrate's C3 and C4 hydroxyl groups are cis to each other. A cis transition state is calculated to have an activation barrier that is 2 kcal/mol greater than that of the trans transition state in the absence of the enzyme.

  3. Inositol phosphate pathway controls transcription of telomeric expression sites in trypanosomes.

    PubMed

    Cestari, Igor; Stuart, Ken

    2015-05-26

    African trypanosomes evade clearance by host antibodies by periodically changing their variant surface glycoprotein (VSG) coat. They transcribe only one VSG gene at a time from 1 of about 20 telomeric expression sites (ESs). They undergo antigenic variation by switching transcription between telomeric ESs or by recombination of the VSG gene expressed. We show that the inositol phosphate (IP) pathway controls transcription of telomeric ESs and VSG antigenic switching in Trypanosoma brucei. Conditional knockdown of phosphatidylinositol 5-kinase (TbPIP5K) or phosphatidylinositol 5-phosphatase (TbPIP5Pase) or overexpression of phospholipase C (TbPLC) derepresses numerous silent ESs in T. brucei bloodstream forms. The derepression is specific to telomeric ESs, and it coincides with an increase in the number of colocalizing telomeric and RNA polymerase I foci in the nucleus. Monoallelic VSG transcription resumes after reexpression of TbPIP5K; however, most of the resultant cells switched the VSG gene expressed. TbPIP5K, TbPLC, their substrates, and products localize to the plasma membrane, whereas TbPIP5Pase localizes to the nucleus proximal to telomeres. TbPIP5Pase associates with repressor/activator protein 1 (TbRAP1), and their telomeric silencing function is altered by TbPIP5K knockdown. These results show that specific steps in the IP pathway control ES transcription and antigenic switching in T. brucei by epigenetic regulation of telomere silencing.

  4. Comparison of Saccharomyces cerevisiae F-BAR Domain Structures Reveals a Conserved Inositol Phosphate Binding Site

    DOE PAGES

    Moravcevic, Katarina; Alvarado, Diego; Schmitz, Karl R.; ...

    2015-01-22

    F-BAR domains control membrane interactions in endocytosis, cytokinesis, and cell signaling. Although they are generally thought to bind curved membranes containing negatively charged phospholipids, numerous functional studies argue that differences in lipid-binding selectivities of F-BAR domains are functionally important. Here in this paper, we compare membrane-binding properties of the Saccharomyces cerevisiae F-BAR domains in vitro and in vivo. Whereas some F-BAR domains (such as Bzz1p and Hof1p F-BARs) bind equally well to all phospholipids, the F-BAR domain from the RhoGAP Rgd1p preferentially binds phosphoinositides. We determined X-ray crystal structures of F-BAR domains from Hof1p and Rgd1p, the latter bound tomore » an inositol phosphate. The structures explain phospholipid-binding selectivity differences and reveal an F-BAR phosphoinositide binding site that is fully conserved in a mammalian RhoGAP called Gmip and is partly retained in certain other F-BAR domains. In conclusion, our findings reveal previously unappreciated determinants of F-BAR domain lipid-binding specificity and provide a basis for its prediction from sequence.« less

  5. Inositol phosphate pathway controls transcription of telomeric expression sites in trypanosomes

    PubMed Central

    Cestari, Igor; Stuart, Ken

    2015-01-01

    African trypanosomes evade clearance by host antibodies by periodically changing their variant surface glycoprotein (VSG) coat. They transcribe only one VSG gene at a time from 1 of about 20 telomeric expression sites (ESs). They undergo antigenic variation by switching transcription between telomeric ESs or by recombination of the VSG gene expressed. We show that the inositol phosphate (IP) pathway controls transcription of telomeric ESs and VSG antigenic switching in Trypanosoma brucei. Conditional knockdown of phosphatidylinositol 5-kinase (TbPIP5K) or phosphatidylinositol 5-phosphatase (TbPIP5Pase) or overexpression of phospholipase C (TbPLC) derepresses numerous silent ESs in T. brucei bloodstream forms. The derepression is specific to telomeric ESs, and it coincides with an increase in the number of colocalizing telomeric and RNA polymerase I foci in the nucleus. Monoallelic VSG transcription resumes after reexpression of TbPIP5K; however, most of the resultant cells switched the VSG gene expressed. TbPIP5K, TbPLC, their substrates, and products localize to the plasma membrane, whereas TbPIP5Pase localizes to the nucleus proximal to telomeres. TbPIP5Pase associates with repressor/activator protein 1 (TbRAP1), and their telomeric silencing function is altered by TbPIP5K knockdown. These results show that specific steps in the IP pathway control ES transcription and antigenic switching in T. brucei by epigenetic regulation of telomere silencing. PMID:25964327

  6. Identification of critical amino acid residues of Saccharomyces cerevisiae carbamoyl-phosphate synthetase: definition of the ATP site involved in carboxy-phosphate formation.

    PubMed

    Zheng, W; Lim, A L; Powers-Lee, S G

    1997-08-15

    Carbamoyl-phosphate synthetases (CPSases) utilize two molecules of ATP at two homologous domains, B and C, with ATP(B) used to form the enzyme-bound intermediate carboxy-phosphate and ATP(C) used to phosphorylate the carbamate intermediate. To further define the role of one CPSase peptide suggested by affinity labeling studies to be near the ATP(B) site, we have carried out site-directed mutagenic analysis of peptide 234-242 of the Saccharomyces cerevisiae arginine-specific CPSase. Mutants E234A, E234D, E236A, E236D and E238A were unable to complement the CPSase-deficient yeast strain LPL26 whereas mutants Y237A, E238D, R241K, R241E and R241P supported LPL26 growth as well as wild-type CPSase. Kinetic analysis of E234A and Y237A indicated impaired utilization of ATP(B) but not of ATP(C). D242A, a temperature-sensitive mutant, retained no detectable activity when assayed in vitro. These findings, together with the affinity labeling data and primary sequence analysis, strongly suggest that the yeast CPSase peptide 234-242 is located at the ATP(B) site and that some of its residues are important for functioning of the enzyme. D242 appears to occupy a critical structural position and E234, E236 and E238 appear to be critical for function, with the spatial arrangement of the carboxyl side chain also critical for E234 and E236.

  7. Cysteine-S-conjugate beta-lyase activity and pyridoxal phosphate binding site of onion alliin lyase.

    PubMed

    Kitamura, N; Shimomura, N; Iseki, J; Honma, M; Chiba, S; Tahara, S; Mizutani, J

    1997-08-01

    Purification of onion alliin lyase gave two fractions by cation exchange chromatography. Both fractions showed the comparable high catalytic activity of cysteine-S-conjugate beta-lyase with that of alliin lyase using S-(2-chloro-6-nitrophenyl)-L-cysteine and alliin, S-allyl-L-cysteine sulfoxide as substrates. All the active substrates tested with onion alliin lyase were also active to the cysteine-S-conjugate beta-lyase of Mucor javanicus, but the catalytic activity of the Mucor enzyme was lower for all the substrates. The pyridoxal phosphate binding site of the onion alliin lyase was identified as Lys 285 in the amino acid sequence deduced from cDNA which has been reported. This lysine was conserved in all the sequences from the alliin lyase cDNAs, while similarity was not found between the sequences around pyridoxal phosphate binding sites of both the onion alliin lyase and the Mucor cysteine-S-conjugate beta-lyase.

  8. Substitutions at the cofactor phosphate-binding site of a clostridial alcohol dehydrogenase lead to unexpected changes in substrate specificity.

    PubMed

    Maddock, Danielle J; Patrick, Wayne M; Gerth, Monica L

    2015-08-01

    Changing the cofactor specificity of an enzyme from nicotinamide adenine dinucleotide 2'-phosphate (NADPH) to the more abundant NADH is a common strategy for increasing overall enzyme efficiency in microbial metabolic engineering. The aim of this study was to switch the cofactor specificity of the primary-secondary alcohol dehydrogenase from Clostridium autoethanogenum, a bacterium with considerable promise for the bio-manufacturing of fuels and other petrochemicals, from strictly NADPH-dependent to NADH-dependent. We used insights from a homology model to build a site-saturation library focussed on residue S199, the position deemed most likely to disrupt binding of the 2'-phosphate of NADPH. Although the CaADH(S199X) library did not yield any NADH-dependent enzymes, it did reveal that substitutions at the cofactor phosphate-binding site can cause unanticipated changes in the substrate specificity of the enzyme. Using consensus-guided site-directed mutagenesis, we were able to create an enzyme that was stringently NADH-dependent, albeit with a concomitant reduction in activity. This study highlights the role that distal residues play in substrate specificity and the complexity of enzyme-cofactor interactions.

  9. Site-specific adsorption of 1,3-dinitrobenzene to bacterial surfaces: a mechanism of n-pi electron-donor-acceptor interactions.

    PubMed

    Qu, Xiaolei; Xiao, Lin; Zhu, Dongqiang

    2008-01-01

    Surface and subsurface contamination with nitroaromatic compounds (NACs) has drawn considerable attention, and biosorption may play an important role in the fate and transport of these compounds in the environment. We studied the sorption of polar 1,3-dinitrobenzene (DNB) as a representative NAC and 2,6-dichlorobenzonitrile and nonpolar phenanthrene and 1,2,4,5-tetrachlorobenzene from the aqueous phase to two common bacteria, gram-negative Escherichia coli and gram-positive Bacillus subtilis. Sorption of DNB is highly nonlinear and is well described by the Langmuir model and shows the highest capacity among all tested solutes (up to 2.4% of E. coli biomass and 7.6% of B. subtilis biomass by weight) despite the lowest solute hydrophobicity. These results indicate that strong specific sorptive interactions exist between DNB and bacterial surfaces. We propose a mechanism of n-pi electron-donor-acceptor interactions between the oxygen electron pairs of deprotonated carboxyl groups (electron donors) of bacterial surfaces and DNB (electron acceptor). Biosorption of DNB increases with deprotonation of functional groups as pH increases, which rules out hydrophobic effects and H-bonding as major sorption driving forces because they are both favored by protonation of functional groups as pH decreases.

  10. Alteration of the Donor/Acceptor Spectrum of the (S)-Amine Transaminase from Vibrio fluvialis.

    PubMed

    Genz, Maika; Vickers, Clare; van den Bergh, Tom; Joosten, Henk-Jan; Dörr, Mark; Höhne, Matthias; Bornscheuer, Uwe T

    2015-11-11

    To alter the amine donor/acceptor spectrum of an (S)-selective amine transaminase (ATA), a library based on the Vibrio fluvialis ATA targeting four residues close to the active site (L56, W57, R415 and L417) was created. A 3DM-derived alignment comprising fold class I pyridoxal-5'-phosphate (PLP)-dependent enzymes allowed identification of positions, which were assumed to determine substrate specificity. These positions were targeted for mutagenesis with a focused alphabet of hydrophobic amino acids to convert an amine:α-keto acid transferase into an amine:aldehyde transferase. Screening of 1200 variants revealed three hits, which showed a shifted amine donor/acceptor spectrum towards aliphatic aldehydes (mainly pentanal), as well as an altered pH profile. Interestingly, all three hits, although found independently, contained the same mutation R415L and additional W57F and L417V substitutions.

  11. Alteration of the Donor/Acceptor Spectrum of the (S)-Amine Transaminase from Vibrio fluvialis

    PubMed Central

    Genz, Maika; Vickers, Clare; van den Bergh, Tom; Joosten, Henk-Jan; Dörr, Mark; Höhne, Matthias; Bornscheuer, Uwe T.

    2015-01-01

    To alter the amine donor/acceptor spectrum of an (S)-selective amine transaminase (ATA), a library based on the Vibrio fluvialis ATA targeting four residues close to the active site (L56, W57, R415 and L417) was created. A 3DM-derived alignment comprising fold class I pyridoxal-5′-phosphate (PLP)-dependent enzymes allowed identification of positions, which were assumed to determine substrate specificity. These positions were targeted for mutagenesis with a focused alphabet of hydrophobic amino acids to convert an amine:α-keto acid transferase into an amine:aldehyde transferase. Screening of 1200 variants revealed three hits, which showed a shifted amine donor/acceptor spectrum towards aliphatic aldehydes (mainly pentanal), as well as an altered pH profile. Interestingly, all three hits, although found independently, contained the same mutation R415L and additional W57F and L417V substitutions. PMID:26569229

  12. Atomic basis of the exquisite specificity of phosphate and sulfate transport receptors.

    PubMed

    Quiocho, F A

    1996-04-01

    We have determined, by the method of x-ray crystallography, the 1.7 A resolution three-dimensional structures of the ligand-bound form of the phosphate receptor as well as the sulfate receptor. These protein structures provide an unprecedented atomic-level understanding of the mechanism governing the exquisite specificity of each receptor. Although they lack amino acid sequence homology, both receptors have very similar three-dimensional structure. The structure consists of two globular domains separated by a deep cleft which contains the ligand-binding site. The bound phosphate and sulfate are totally devoid of water of hydration. The bound phosphate is tightly held in place by 12 hydrogen bonds, 11 with donor and 1 with acceptor groups. The acceptor group (an Asp carboxylate side chain) plays three key roles. It confers specificity by directly recognizing one proton of either the monobasic or dibasic phosphate. It also assists in the recognition of another proton of the monobasic phosphate. Finally, because of charge repulsion, it disallows binding of fully ionized sulfate. The sulfate bound to the sulfate receptor makes seven hydrogen bonds with uncharged polar groups exclusively. The absence of an acceptor group in the binding site of the sulfate receptor is not conducive to phosphate binding.

  13. Electrochemical synthesis and characterisation of alternating tripyridyl-dipyrrole molecular strands with multiple nitrogen-based donor-acceptor binding sites.

    PubMed

    Tabatchnik-Rebillon, Alexandra; Aubé, Christophe; Bakkali, Hicham; Delaunay, Thierry; Manh, Gabriel Thia; Blot, Virginie; Thobie-Gautier, Christine; Renault, Eric; Soulard, Marine; Planchat, Aurélien; Le Questel, Jean-Yves; Le Guével, Rémy; Guguen-Guillouzo, Christiane; Kauffmann, Brice; Ferrand, Yann; Huc, Ivan; Urgin, Karène; Condon, Sylvie; Léonel, Eric; Evain, Michel; Lebreton, Jacques; Jacquemin, Denis; Pipelier, Muriel; Dubreuil, Didier

    2010-10-18

    Synthesis of alternating pyridine-pyrrole molecular strands composed of two electron-rich pyrrole units (donors) sandwiched between three pyridinic cores (acceptors) is described. The envisioned strategy was a smooth electrosynthesis process involving ring contraction of corresponding tripyridyl-dipyridazine precursors. 2,6-Bis[6-(pyridazin-3-yl)]pyridine ligands 2a-c bearing pyridine residues at the terminal positions were prepared in suitable quantities by a Negishi metal cross-coupling procedure. The yields of heterocyclic coupling between 2-pyridyl zinc bromide reagents 12a-c and 2,6-bis(6-trifluoromethanesulfonylpyridazin-3-yl)pyridine increased from 68 to 95% following introduction of electron-donating methyl groups on the metallated halogenopyridine units. Favorable conditions for preparative electrochemical reduction of tripyridyl-dipyridazines 2b,c were established in THF/acetate buffer (pH 4.6)/acetonitrile to give the targeted 2,6-bis[5-(pyridin-2-yl)pyrrol-2-yl]pyridines 1b and 1c in good yields. The absorption behavior of the donor-acceptor tripyridyl-dipyrrole ligands was evaluated and compared to theoretical calculations. Highly fluorescent properties of these chromophores were found (ν(em)≈2 × 10(4) cm(-1) in MeOH and CH(2)Cl(2)), and both pyrrolic ligands exhibit a remarkable quantum yield in CH(2)Cl(2) (φ(f)=0.10). Structural studies in the solid state established the preferred cis conformation of the dipyrrolic ligands, which adopting a planar arrangement with an embedded molecule of water having a complexation energy exceeding 10 kcal mol(-1). The ability of the tripyridyl-dipyrrole to complex two copper(II) ions in a pentacoordinate square was investigated.

  14. The Ala95-to-Gly substitution in Aerococcus viridans l-lactate oxidase revisited - structural consequences at the catalytic site and effect on reactivity with O2 and other electron acceptors.

    PubMed

    Stoisser, Thomas; Rainer, Daniela; Leitgeb, Stefan; Wilson, David K; Nidetzky, Bernd

    2015-02-01

    Aerococcus viridansl-lactate oxidase (avLOX) is a biotechnologically important flavoenzyme that catalyzes the conversion of L-lactate and O₂ into pyruvate and H₂O₂. The enzymatic reaction underlies different biosensor applications of avLOX for blood L-lactate determination. The ability of avLOX to replace O₂ with other electron acceptors such as 2,6-dichlorophenol-indophenol (DCIP) allows the possiblity of analytical and practical applications. The A95G variant of avLOX was previously shown to exhibit lowered reactivity with O₂ compared to wild-type enzyme and therefore was employed in a detailed investigation with respect to the specificity for different electron acceptor substrates. From stopped-flow experiments performed at 20 °C (pH 6.5), we determined that the A95G variant (fully reduced by L-lactate) was approximately three-fold more reactive towards DCIP (1.0 ± 0.1 × 10(6) M(-1) ·s(-1) ) than O₂, whereas avLOX wild-type under the same conditions was 14-fold more reactive towards O₂(1.8 ± 0.1 × 10(6) m(-1) ·s(-1)) than DCIP. Substituted 1,4-benzoquinones were up to five-fold better electron acceptors for reaction with L-lactate-reduced A95G variant than wild-type. A 1.65-Å crystal structure of oxidized A95G variant bound with pyruvate was determined and revealed that the steric volume created by removal of the methyl side chain of Ala95 and a slight additional shift in the main chain at position Gly95 together enable the accomodation of a new active-site water molecule within hydrogen-bond distance to the N5 of the FMN cofactor. The increased steric volume available in the active site allows the A95G variant to exhibit a similar trend with the related glycolate oxidase in electron acceptor substrate specificities, despite the latter containing an alanine at the analogous position.

  15. Alternansucrase acceptor products

    USDA-ARS?s Scientific Manuscript database

    The regioselectivity of alternansucrase (EC 2.4.1.140) differs from dextransucrase (EC 2.4.1.5) in ways that can be useful for the synthesis of novel oligosaccharide structures. For example, it has been recently shown that the major oligosaccharides produced when maltose is the acceptor include one...

  16. On the effect of nuclear bridge modes on donor-acceptor electronic coupling in donor-bridge-acceptor molecules

    NASA Astrophysics Data System (ADS)

    Davis, Daly; Toroker, Maytal Caspary; Speiser, Shammai; Peskin, Uri

    2009-03-01

    We report a theoretical study of intra-molecular electronic coupling in a symmetric DBA (donor-bridge-acceptor) complex, in which a donor electronic site is coupled to an acceptor site by way of intervening orbitals of a molecular bridge unit. In the off-resonant (deep tunneling) regime of electronic transport, the lowest unoccupied molecular orbitals (MO's) of the DBA system are split into distinguishable donor/acceptor and bridge orbitals. The effect of geometrical changes at the bridge on the donor/acceptor electronic energy manifold is studied for local stretching and bending modes. It is demonstrated that the energy splitting in the manifold of donor/acceptor unoccupied MOs changes in response to such changes, as assumed in simple McConnell-type models. Limitations of the simple models are revealed where the electronic charging of the bridge orbitals correlates with increasing donor/acceptor orbital energy splitting only for stretching but not for bending bridge modes.

  17. Analogues of the Nicotinic Acid Adenine Dinucleotide Phosphate (NAADP) Antagonist Ned-19 Indicate Two Binding Sites on the NAADP Receptor*

    PubMed Central

    Rosen, Daniel; Lewis, Alexander M.; Mizote, Akiko; Thomas, Justyn M.; Aley, Parvinder K.; Vasudevan, Sridhar R.; Parkesh, Raman; Galione, Antony; Izumi, Minoru; Ganesan, A.; Churchill, Grant C.

    2009-01-01

    Nicotinic acid adenine dinucleotide phosphate (NAADP) is a Ca2+-releasing messenger. Biological data suggest that its receptor has two binding sites: one high-affinity locking site and one low-affinity opening site. To directly address the presence and function of these putative binding sites, we synthesized and tested analogues of the NAADP antagonist Ned-19. Ned-19 itself inhibits both NAADP-mediated Ca2+ release and NAADP binding. A fluorometry bioassay was used to assess NAADP-mediated Ca2+ release, whereas a radioreceptor assay was used to assess binding to the NAADP receptor (only at the high-affinity site). In Ned-20, the fluorine is para rather than ortho as in Ned-19. Ned-20 does not inhibit NAADP-mediated Ca2+ release but inhibits NAADP binding. Conversely, Ned-19.4 (a methyl ester of Ned-19) inhibits NAADP-mediated Ca2+ release but cannot inhibit NAADP binding. Furthermore, Ned-20 prevents the self-desensitization response characteristic of NAADP in sea urchin eggs, confirming that this response is mediated by a high-affinity allosteric site to which NAADP binds in the radioreceptor assay. Collectively, these data provide the first direct evidence for two binding sites (one high- and one low-affinity) on the NAADP receptor. PMID:19826006

  18. Probing the Acceptor Active Site Organization of the Human Recombinant β1,4-Galactosyltransferase 7 and Design of Xyloside-based Inhibitors*

    PubMed Central

    Saliba, Mineem; Ramalanjaona, Nick; Gulberti, Sandrine; Bertin-Jung, Isabelle; Thomas, Aline; Dahbi, Samir; Lopin-Bon, Chrystel; Jacquinet, Jean-Claude; Breton, Christelle; Ouzzine, Mohamed; Fournel-Gigleux, Sylvie

    2015-01-01

    Among glycosaminoglycan (GAG) biosynthetic enzymes, the human β1,4-galactosyltransferase 7 (hβ4GalT7) is characterized by its unique capacity to take over xyloside derivatives linked to a hydrophobic aglycone as substrates and/or inhibitors. This glycosyltransferase is thus a prime target for the development of regulators of GAG synthesis in therapeutics. Here, we report the structure-guided design of hβ4GalT7 inhibitors. By combining molecular modeling, in vitro mutagenesis, and kinetic measurements, and in cellulo analysis of GAG anabolism and decorin glycosylation, we mapped the organization of the acceptor binding pocket, in complex with 4-methylumbelliferone-xylopyranoside as prototype substrate. We show that its organization is governed, on one side, by three tyrosine residues, Tyr194, Tyr196, and Tyr199, which create a hydrophobic environment and provide stacking interactions with both xylopyranoside and aglycone rings. On the opposite side, a hydrogen-bond network is established between the charged amino acids Asp228, Asp229, and Arg226, and the hydroxyl groups of xylose. We identified two key structural features, i.e. the strategic position of Tyr194 forming stacking interactions with the aglycone, and the hydrogen bond between the His195 nitrogen backbone and the carbonyl group of the coumarinyl molecule to develop a tight binder of hβ4GalT7. This led to the synthesis of 4-deoxy-4-fluoroxylose linked to 4-methylumbelliferone that inhibited hβ4GalT7 activity in vitro with a Ki 10 times lower than the Km value and efficiently impaired GAG synthesis in a cell assay. This study provides a valuable probe for the investigation of GAG biology and opens avenues toward the development of bioactive compounds to correct GAG synthesis disorders implicated in different types of malignancies. PMID:25568325

  19. Candidatus Accumulibacter phosphatis clades enriched under cyclic anaerobic and microaerobic conditions simultaneously use different electron acceptors

    EPA Science Inventory

    Lab- and pilot-scale simultaneous nitrification, denitrification and phosphorus removal-sequencing batch reactors were operated under cyclic anaerobic and micro-aerobic conditions. The use of oxygen, nitrite, and nitrate as electron acceptors by Candidatus Accumulibacter phosphat...

  20. Candidatus Accumulibacter phosphatis clades enriched under cyclic anaerobic and microaerobic conditions simultaneously use different electron acceptors

    EPA Science Inventory

    Lab- and pilot-scale simultaneous nitrification, denitrification and phosphorus removal-sequencing batch reactors were operated under cyclic anaerobic and micro-aerobic conditions. The use of oxygen, nitrite, and nitrate as electron acceptors by Candidatus Accumulibacter phosphat...

  1. Structural and functional analysis of the two haemoglobins of the antarctic seabird Catharacta maccormicki characterization of an additional phosphate binding site by molecular modelling.

    PubMed

    Tamburrini, M; Riccio, A; Romano, M; Giardina, B; di Prisco, G

    2000-10-01

    The amino-acid sequence and the oxygen-binding properties of the two haemoglobins of the Antarctic seabird south polar skua have been investigated. The two haemoglobins showed peculiar functional features, which were probably acquired to meet special needs in relation to the extreme environmental conditions. Both haemoglobins showed a weak alkaline Bohr effect which, during prolonged flight, may protect against sudden and uncontrolled stripping of oxygen in response to acidosis. We suggest that a weak Bohr effect in birds may reflect adaptation to extreme life conditions. The values of heat of oxygenation suggest different functional roles of the two haemoglobins. The experimental evidence suggests that both haemoglobins may bind phosphate at two distinct binding sites. In fact, analysis of the molecular models revealed that an additional phosphate binding site, formed by residues NA1alpha, G6alpha and HC3alpha, is located between the two alpha chains. This additional site may act as an entry/leaving site, thus increasing the probability of capturing phosphate and transferring it to the main binding site located between the two beta chains by means of a site-site migratory mechanism, thereby favouring the release of oxygen. It is suggested that most haemoglobins possess an additional phosphate binding site, having such a role in oxygen transport.

  2. The homing of bone marrow MSCs to non-osseous sites for ectopic bone formation induced by osteoinductive calcium phosphate

    PubMed Central

    Song, Guodong; Habibovic, Pamela; Bao, Chongyun; Hu, Jing; van Blitterswijk, Clemens A.; Yuan, Huipin; Chen, Wenchuan; Xu, Hockin H.K.

    2013-01-01

    Osteoinductive biomaterials are promising for bone repair. There is no direct proof that bone marrow mesenchymal stem cells (BMSCs) home to non-osseous sites and participate in ectopic bone formation induced by osteoinductive bioceramics. The objective of this study was to use a sex-mismatched beagle dog model to investigate BMSC homing via blood circulation to participate in ectopic bone formation via osteoinductive biomaterial. BMSCs of male dogs were injected into female femoral marrow cavity. The survival and stable chimerism of donor BMSCs in recipients were confirmed with polymerase chain reaction (PCR) and fluorescence in situ hybridization (FISH). Biphasic calcium phosphate (BCP) granules were implanted in dorsal muscles of female dogs. Y chromosomes were detected in samples harvested from female dogs which had received male BMSCs. At 4 weeks, cells with Y-chromosomes were distributed in the new bone matrix throughout the BCP granule implant. At 6 weeks, cells with Y chromosomes were present in newly mineralized woven bone. TRAP positive osteoclast-like cells were observed in 4-week implants, and the number of such cells decreased from 4 to 6 weeks. These results show that osteoprogenitors were recruited from bone marrow and homed to ectopic site to serve as a cell source for calcium phosphate-induced bone formation. In conclusion, BMSCs were demonstrated to migrate from bone marrow through blood circulation to non-osseous bioceramic implant site to contribute to ectopic bone formation in a canine model. BCP induced new bone in muscles without growth factor delivery, showing excellent osteoinductivity that could be useful for bone tissue engineering. PMID:23298780

  3. Measurement of tributyl phosphate (TBP) in groundwater at a legacy radioactive waste site and its possible role in contaminant mobilisation.

    PubMed

    Rowling, Brett; Kinsela, Andrew S; Comarmond, M Josick; Hughes, Catherine E; Harrison, Jennifer J; Johansen, Mathew P; Payne, Timothy E

    2017-07-04

    At many legacy radioactive waste sites, organic compounds have been co-disposed, which may be a factor in mobilisation of radionuclides at these sites. Tri-butyl phosphate (TBP) is a component of waste streams from the nuclear fuel cycle, where it has been used in separating actinides during processing of nuclear fuels. Analyses of ground waters from the Little Forest Legacy Site (LFLS) in eastern Australia were undertaken using solid-phase extraction (SPE) followed by gas chromatographic mass spectrometry (GCMS). The results indicate the presence of TBP several decades after waste disposal, with TBP only being detected in the immediate vicinity of the main disposal area. TBP is generally considered to degrade in the environment relatively rapidly. Therefore, it is likely that its presence is due to relatively recent releases of TBP, possibly stemming from leakage due to container degradation. The ongoing presence and solubility of TBP has the potential to provide a mechanism for nuclide mobilisation, with implications for long term management of LFLS and similar legacy waste sites. Crown Copyright © 2017. Published by Elsevier Ltd. All rights reserved.

  4. Multiple phosphate positions in the catalytic site of glycogen phosphorylase: structure of the pyridoxal-5'-pyrophosphate coenzyme-substrate analog.

    PubMed Central

    Sprang, S. R.; Madsen, N. B.; Withers, S. G.

    1992-01-01

    The three-dimensional structure of an R-state conformer of glycogen phosphorylase containing the coenzyme-substrate analog pyridoxal-5'-diphosphate at the catalytic site (PLPP-GPb) has been refined by X-ray crystallography to a resolution of 2.87 A. The molecule comprises four subunits of phosphorylase related by approximate 222 symmetry. Whereas the quaternary structure of R-state PLPP-GPb is similar to that of phosphorylase crystallized in the presence of ammonium sulfate (Barford, D. & Johnson, L.N., 1989, Nature 340, 609-616), the tertiary structures differ in that the two domains of the PLPP-GPb subunits are rotated apart by 5 degrees relative to the T-state conformation. Global differences among the four subunits suggest that the major domains of the phosphorylase subunit are connected by a flexible hinge. The two different positions observed for the terminal phosphate of the PLPP are interpreted as distinct phosphate subsites that may be occupied at different points along the reaction pathway. The structural basis for the unique ability of R-state dimers to form tetramers results from the orientation of subunits with respect to the dyad axis of the dimer. Residues in opposing dimers are in proper registration to form tetramers only in the R-state. PMID:1304389

  5. The structure of sedoheptulose-7-phosphate isomerase from Burkholderia pseudomallei reveals a zinc binding site at the heart of the active site.

    PubMed

    Harmer, Nicholas J

    2010-07-16

    Heptoses are found in the surface polysaccharides of most bacteria, contributing to structures that are essential for virulence and antibiotic resistance. Consequently, the biosynthetic enzymes for these sugars are attractive targets for novel antibiotics. The best characterized biosynthetic enzyme is GmhA, which catalyzes the conversion of sedoheptulose-7-phosphate into D-glycero-D-manno-heptopyranose-7-phosphate, the first step in the biosynthesis of heptose. Here, the structure of GmhA from Burkholderia pseudomallei is reported. This enzyme contains a zinc ion at the heart of its active site: this ion stabilizes the active, closed form of the enzyme and presents coordinating side chains as a potential acid and base to drive catalysis. A complex with the product demonstrates that the enzyme retains activity in the crystal and thus suggests that the closed conformation is catalytically relevant and is an excellent target for the development of therapeutics. A revised mechanism for the action of GmhA is postulated on the basis of this structure and the activity of B. pseudomallei GmhA mutants.

  6. Small-molecule inhibition of pyruvate phosphate dikinase targeting the nucleotide binding site

    PubMed Central

    Minges, Alexander

    2017-01-01

    Pyruvate phosphate dikinase (PPDK) is an essential enzyme of C4 photosynthesis in plants, catalyzing the ATP-driven conversion of pyruvate to phosphoenolpyruvate (PEP). It is further used by some bacteria and unicellular protists in the reverse, ATP-forming direction. Many weed species use C4 photosynthesis in contrast to world’s major crops, which are C3 plants. Hence inhibitors of PPDK may be used as C4-specific herbicides. By screening a library of 80 commercially available kinase inhibitors, we identified compounds derived from bisindolylmaleimide (bisindolylmaleimide IV, IC50 = 0.76 ± 0.13 μM) and indirubin (indirubin-3’-monoxime, IC50 = 4.2 ± 0.9 μM) that showed high inhibitory potency towards PPDK and are among the most effective PPDK inhibitors described today. Physiological studies on leaf tissues of a C4 model plant confirmed in vivo inhibition of C4-driven photosynthesis by these substances. Moreover, comparative docking studies of non-inhibitory bisindolylmaleimide derivatives suggest that the selectivity towards PPDK may be increased by addition of functional groups to the core structure. PMID:28700696

  7. Small-molecule inhibition of pyruvate phosphate dikinase targeting the nucleotide binding site.

    PubMed

    Minges, Alexander; Groth, Georg

    2017-01-01

    Pyruvate phosphate dikinase (PPDK) is an essential enzyme of C4 photosynthesis in plants, catalyzing the ATP-driven conversion of pyruvate to phosphoenolpyruvate (PEP). It is further used by some bacteria and unicellular protists in the reverse, ATP-forming direction. Many weed species use C4 photosynthesis in contrast to world's major crops, which are C3 plants. Hence inhibitors of PPDK may be used as C4-specific herbicides. By screening a library of 80 commercially available kinase inhibitors, we identified compounds derived from bisindolylmaleimide (bisindolylmaleimide IV, IC50 = 0.76 ± 0.13 μM) and indirubin (indirubin-3'-monoxime, IC50 = 4.2 ± 0.9 μM) that showed high inhibitory potency towards PPDK and are among the most effective PPDK inhibitors described today. Physiological studies on leaf tissues of a C4 model plant confirmed in vivo inhibition of C4-driven photosynthesis by these substances. Moreover, comparative docking studies of non-inhibitory bisindolylmaleimide derivatives suggest that the selectivity towards PPDK may be increased by addition of functional groups to the core structure.

  8. Does phosphate enhance the natural attenuation of crude oil in groundwater under defined redox conditions?

    PubMed

    Ponsin, Violaine; Mouloubou, Olsen Raïnness; Prudent, Pascale; Höhener, Patrick

    2014-11-15

    After a crude oil spill caused by a broken pipeline in 2009 to a gravel aquifer in southern France, degradation processes under various redox conditions progressively established, but at rates that predict a long life-time of the source under natural attenuation after partial source removal. In this study, we aimed at identifying the rate-limiting factors for each redox condition, with special emphasis on phosphate as limiting nutrient. The study was conducted in laboratory microcosms assembled with material collected on site: sediments, water from monitoring wells, oil and microbial sludge. Redox conditions were promoted by adding electron acceptors (either oxygen, nitrate, limonite (FeO(OH)), cryptomelane (K(Mn(4+),Mn(2+))8O16), or sulfate). For each condition, the role of phosphate was studied by repeated additions for up to 290days. The results showed a very strong stimulation of aerobic and denitrifying rates of oil degradation by phosphate, provided that oxygen and nitrate were repeatedly supplied. Phosphate caused also a marked stimulation of methanogenic degradation, and a relatively small stimulation of metal reduction. These anaerobic processes started only after marked lag phases, and phosphate shortened the lag phase for methanogenic degradation. Degradation of aromatic and aliphatic hydrocarbons with less than 8 carbons, including benzene, was confirmed even under unstimulated conditions. It is concluded that degradation rates at the site are limited by both, availability of electron acceptors and availability of phosphate needed for promoting microbial growth. Copyright © 2014 Elsevier B.V. All rights reserved.

  9. Does phosphate enhance the natural attenuation of crude oil in groundwater under defined redox conditions?

    NASA Astrophysics Data System (ADS)

    Ponsin, Violaine; Mouloubou, Olsen Raïnness; Prudent, Pascale; Höhener, Patrick

    2014-11-01

    After a crude oil spill caused by a broken pipeline in 2009 to a gravel aquifer in southern France, degradation processes under various redox conditions progressively established, but at rates that predict a long life-time of the source under natural attenuation after partial source removal. In this study, we aimed at identifying the rate-limiting factors for each redox condition, with special emphasis on phosphate as limiting nutrient. The study was conducted in laboratory microcosms assembled with material collected on site: sediments, water from monitoring wells, oil and microbial sludge. Redox conditions were promoted by adding electron acceptors (either oxygen, nitrate, limonite (FeO(OH)), cryptomelane (K(Mn4 +,Mn2 +)8O16), or sulfate). For each condition, the role of phosphate was studied by repeated additions for up to 290 days. The results showed a very strong stimulation of aerobic and denitrifying rates of oil degradation by phosphate, provided that oxygen and nitrate were repeatedly supplied. Phosphate caused also a marked stimulation of methanogenic degradation, and a relatively small stimulation of metal reduction. These anaerobic processes started only after marked lag phases, and phosphate shortened the lag phase for methanogenic degradation. Degradation of aromatic and aliphatic hydrocarbons with less than 8 carbons, including benzene, was confirmed even under unstimulated conditions. It is concluded that degradation rates at the site are limited by both, availability of electron acceptors and availability of phosphate needed for promoting microbial growth.

  10. An Aberrant Splice Acceptor Site Due to a Novel Intronic Nucleotide Substitution in MSX1 Gene Is the Cause of Congenital Tooth Agenesis in a Japanese Family

    PubMed Central

    Tatematsu, Tadashi; Kimura, Masashi; Nakashima, Mitsuko; Machida, Junichiro; Yamaguchi, Seishi; Shibata, Akio; Goto, Hiroki; Nakayama, Atsuo; Higashi, Yujiro; Miyachi, Hitoshi; Shimozato, Kazuo; Matsumoto, Naomichi; Tokita, Yoshihito

    2015-01-01

    Congenital tooth agenesis is caused by mutations in the MSX1, PAX9, WNT10A, or AXIN2 genes. Here, we report a Japanese family with nonsyndromic tooth agenesis caused by a novel nucleotide substitution in the intronic region between exons 1 and 2 of the MSX1 gene. Because the mutation is located 9 bp before exon 2 (c.452-9G>A), we speculated that the nucleotide substitution would generate an abnormal splice site. Using cDNA analysis of an immortalized patient blood cell, we confirmed that an additional 7-nucleotide sequence was inserted at the splice junction between exons 1 and 2 (c.451_452insCCCTCAG). The consequent frameshift generated a homeodomain-truncated MSX1 (p.R151fsX20). We then studied the subcellular localization of truncated MSX1 protein in COS cells, and observed that it had a whole cell distribution more than a nuclear localization, compared to that of wild-type protein. This result suggests a deletion of the nuclear localization signal, which is mapped to the MSX1 homeodomain. These results indicate that this novel intronic nucleotide substitution is the cause of tooth agenesis in this family. To date, most MSX1 variants isolated from patients with tooth agenesis involve single amino acid substitutions in the highly conserved homeodomain or deletion mutants caused by frameshift or nonsense mutations. We here report a rare case of an intronic mutation of the MSX1 gene responsible for human tooth agenesis. In addition, the missing tooth patterns were slightly but significantly different between an affected monozygotic twin pair of this family, showing that epigenetic or environmental factors also affect the phenotypic variations of missing teeth among patients with nonsyndromic tooth agenesis caused by an MSX1 haploinsufficiency. PMID:26030286

  11. A{sup -2} {yields} G transition at the 3{prime} acceptor splice site of IVS17 characterizes the COL2A1 gene mutation in the original Stickler syndrome kindred

    SciTech Connect

    Williams, C.J.; Ganguly, A.; Considine, E.

    1996-06-14

    Hereditary progressive arthro-ophthalmopathy, or {open_quotes}Stickler syndrome,{close_quotes} is an autosomal dominant osteochondrodysplasia characterized by a variety of ocular and skeletal anomalies which frequently lead to retinal detachment and precocious osteoarthritis. A variety of mutations in the COL2A1 gene have been identified in {open_quotes}Stickler{close_quotes} families; in most cases studied thus far, the consequence of mutation is the premature generation of a stop codon. We report here the characterization of a COL2A1 gene mutation in the original kindred described by Stickler et al. Conformational sensitive gel electrophoresis (CSGE) was used to screen for mutations in the entire COL2A1 gene in an affected member from the kindred. A prominent heteroduplex species was noted in the polymerase chain reaction (PCR) product from a region of the gene including exons 17 to 20. Direct sequencing of PCR-amplified genomic DNA resulted in the identification of a base substitution at the A{sup -2} position of the 3{prime} splice acceptor site of IVS17. Sequencing of DNA from affected and unaffected family members confirmed that the mutation segregated with the disease phenotype. Reverse transcriptase-PCR analysis of poly A+ RNA demonstrated that the mutant allele utilized a cryptic splice site in exon 18 of the gene, eliminating 16 bp at the start of exon 18. This frameshift eventually results in a premature termination codon. These findings are the first report of a splice site mutation in classical Stickler syndrome and they provide a satisfying historical context in which to view COL2A1 mutations in this dysplasia. 25 refs., 3 figs., 1 tab.

  12. Site-Specific Protein Bioconjugation via a Pyridoxal 5'-Phosphate-Mediated N-Terminal Transamination Reaction.

    PubMed

    Witus, Leah S; Francis, Matthew

    2010-06-01

    The covalent attachment of chemical groups to proteins is a critically important tool for the study of protein function and the creation of protein-based materials. Methods of site-specific protein modification are necessary for the generation of well defined bioconjugates possessing a new functional group in a single position in the amino acid sequence. This article describes a pyridoxal 5'-phosphate (PLP)-mediated transamination reaction that is specific for the N-terminus of a protein. The reaction oxidizes the N-terminal amine to a ketone or an aldehyde, which can form a stable oxime linkage with an alkoxyamine reagent of choice. Screening studies have identified the most reactive N-terminal residues, facilitating the use of site-directed mutagenesis to achieve high levels of conversion. Additionally, this reaction has been shown to be effective for a number of targets that are not easily accessed through heterologous expression, such as monoclonal antibodies. Curr. Protoc. Chem. Biol. 2:125-134 © 2010 by John Wiley & Sons, Inc.

  13. Distance between two active-site lysines of ribulosebis-phosphate carboxylase/oxygenase

    SciTech Connect

    Lee, E.H.; Hartman, F.C.

    1986-05-01

    Previous affinity labeling studies and comparative sequence analyses have identified two different lysines at the active site of the title enzyme (Lys-166 and Lys-329 in the Rhodospirillum rubrum enzyme and Lys-175 and Lys-334 in the spinach enzyme). Because the two lysines are mutually exclusive to various reagents, they appear to be in proximity. To challenge this postulate, the authors have explored the reactions of the R. rubrum enzyme (a homodimer) with chemical cross-linking agents. 4,4'-Diisothiocyano-2,2'-disulfonate stilbene, which spans 12 A, rapidly inactivates the enzyme with protection afforded by the competitive inhibitor 2-carboxyribitol-1,5-bisphosphate. The inactivated enzyme was subjected to gel filtration in the presence of urea to remove material arising from intersubunit or intermolecular cross-linking. The monomeric fraction was digested with trypsin; inspection of the digest by HPLC revealed that over-half of the incorporated reagent was associated with a single peptide. This peptide was purified by successive ion-exchange chromatography and gel filtration. The amino acid composition and sequence of the purified peptide demonstrated that it is comprised of two chains, encompassing position 149-168 and 314-337 of the original protein subunit and connected by a cross-link between Lys-166 and Lys-329. Thus, the two active-site lysines can be juxtaposed only 12 A apart.

  14. Kinetic analysis of Escherichia coli 2-C-methyl-D-erythritol-4-phosphate cytidyltransferase, wild type and mutants, reveals roles of active site amino acids.

    PubMed

    Richard, Stéphane B; Lillo, Antonietta M; Tetzlaff, Charles N; Bowman, Marianne E; Noel, Joseph P; Cane, David E

    2004-09-28

    Escherichia coli 2-C-methyl-D-erythritol-4-phosphate cytidyltransferase (YgbP or IspD) catalyzes the conversion of 2-C-methyl-D-erythritol 4-phosphate (MEP) and cytidine triphosphate (CTP) to 4-diphosphocytidyl-2-C-methylerythritol (CDPME). Pulse chase experiments established that the reaction involves an ordered sequential mechanism with mandatory initial binding of CTP. On the basis of analysis of the previously reported crystal structures of apo-YgbP as well as YgbP complexed with both CTP.Mg(2+) and CDPME.Mg(2+) [Richard, S. B., Bowman, M. E., Kwiatkowski, W., Kang, I., Chow, C., Lillo, A. M., Cane, D. E., and Noel, J. P. (2001) Nat. Struct. Biol. 8, 641-648], a group of active site residues were selected for site-directed mutagenesis and steady-state kinetic analysis. Both Lys27 and Lys213 were shown to be essential to catalytic activity, consistent with their proposed role in stabilization of a pentacoordinate phosphate transition state resulting from in-line attack of the MEP phosphate on the alpha-phosphate of CTP. In addition, Thr140, Arg109, Asp106, and Thr165 were all shown to play critical roles in the binding and proper orientation of the MEP substrate.

  15. The 1974 National Acceptors Survey.

    PubMed

    Laing, J; Phillips, J; Zablan, Z; Llorente, R; Cabigon, J

    1976-01-01

    The 1974 National Acceptors Survey in the Philippines studied 4 methods of contraception: pill, IUD, rhythm, and condom. After 1 year, 72% of IUD acceptors had an IUD in place but only 29% of condom acceptors were still using condoms. Pills and rhythm were equally effective in terms of continuation and pregnancy rates. Continuation rates were higher among acceptors at postpartum clinics than at other clnics, higher among urban respondents than rural, and higher among older respondents. Those with more children had higher continuation rates, whereas those who wanted more children had lower continuation rates. Continuation rates also increased 1) as the duration of marriage lengthened; 2) with a later age at marriage; 3) with higher educational attainment; 4) among income-contributing respondents with higher incomes; 5) among previous contraceptive users; and 6) when physicians provided the services rather than nonmedical personnel, including medical screenings. Clinic attendance, husband's occupation, whether or not there was payment, and husband's support are other factors that seemed to affect continuation rates. Contraceptive effectiveness values were higher among pill and IUD acceptors. The percentage of reduction in fertility following acceptance of a method was 74% for IUDs and 27% for condoms. Fertility reduction was great among acceptors at postpartum clinics, acceptors in central visayas, and the highly educated. Future births averted ranged, for every 100 acceptors, 208 with the IUD, 32 with the condom, and 1 each pill and rhythm. Factors affecting method selection were administrative, beliefs, and preferences. The most common complaint about provision of clinical services was that the staff should spend more time in home visits (86%).

  16. Site-directed mutagenesis of serine 158 demonstrates its role in spinach leaf sucrose-phosphate synthase modulation

    NASA Technical Reports Server (NTRS)

    Toroser, D.; McMichael, R. Jr; Krause, K. P.; Kurreck, J.; Sonnewald, U.; Stitt, M.; Huber, S. C.; Davies, E. (Principal Investigator)

    1999-01-01

    Site-directed mutagenesis of spinach sucrose-phosphate synthase (SPS) was performed to investigate the role of Ser158 in the modulation of spinach leaf SPS. Tobacco plants expressing the spinach wild-type (WT), S158A, S158T and S157F/S158E SPS transgenes were produced. Expression of transgenes appeared not to reduce expression of the tobacco host SPS. SPS activity in the WT and the S158T SPS transgenics showed light/dark modulation, whereas the S158A and S157F/S158E mutants were not similarly light/dark modulated: the S158A mutant enzyme was not inactivated in the dark, and the S157F/S158E was not activated in the light. The inability to modulate the activity of the S158A mutant enzyme by protein phosphorylation was demonstrated in vitro. The WT spinach enzyme immunopurified from dark transgenic tobacco leaves had a low initial activation state, and could be activated by PP2A and subsequently inactivated by SPS-kinase plus ATP. Rapid purification of the S158A mutant enzyme from dark leaves of transgenic plants using spinach-specific monoclonal antibodies yielded enzyme that had a high initial activation state, and pre-incubation with leaf PP2A or ATP plus SPS-kinase (the PKIII enzyme) caused little modulation of activity. The results demonstrate the regulatory significance of Ser158 as the major site responsible for dark inactivation of spinach SPS in vivo, and indicate that the significance of phosphorylation is the introduction of a negative charge at the Ser158 position.

  17. Novel mode of inhibition by D-tagatose 6-phosphate through a Heyns rearrangement in the active site of transaldolase B variants.

    PubMed

    Stellmacher, Lena; Sandalova, Tatyana; Schneider, Sarah; Schneider, Gunter; Sprenger, Georg A; Samland, Anne K

    2016-04-01

    Transaldolase B (TalB) and D-fructose-6-phosphate aldolase A (FSAA) from Escherichia coli are C-C bond-forming enzymes. Using kinetic inhibition studies and mass spectrometry, it is shown that enzyme variants of FSAA and TalB that exhibit D-fructose-6-phosphate aldolase activity are inhibited covalently and irreversibly by D-tagatose 6-phosphate (D-T6P), whereas no inhibition was observed for wild-type transaldolase B from E. coli. The crystal structure of the variant TalB(F178Y) with bound sugar phosphate was solved to a resolution of 1.46 Å and revealed a novel mode of covalent inhibition. The sugar is bound covalently via its C2 atom to the ℇ-NH2 group of the active-site residue Lys132. It is neither bound in the open-chain form nor as the closed-ring form of D-T6P, but has been converted to β-D-galactofuranose 6-phosphate (D-G6P), a five-membered ring structure. The furanose ring of the covalent adduct is formed via a Heyns rearrangement and subsequent hemiacetal formation. This reaction is facilitated by Tyr178, which is proposed to act as acid-base catalyst. The crystal structure of the inhibitor complex is compared with the structure of the Schiff-base intermediate of TalB(E96Q) formed with the substrate D-fructose 6-phosphate determined to a resolution of 2.20 Å. This comparison highlights the differences in stereochemistry at the C4 atom of the ligand as an essential determinant for the formation of the inhibitor adduct in the active site of the enzyme.

  18. Total Phosphate Influences the Rate of Hydrocarbon Degradation but Phosphate Mineralogy Shapes Microbial Community Composition in Cold-Region Calcareous Soils.

    PubMed

    Siciliano, Steven D; Chen, Tingting; Phillips, Courtney; Hamilton, Jordan; Hilger, David; Chartrand, Blaine; Grosskleg, Jay; Bradshaw, Kris; Carlson, Trevor; Peak, Derek

    2016-05-17

    Managing phosphorus bioaccessibility is critical for the bioremediation of hydrocarbons in calcareous soils. This paper explores how soil mineralogy interacts with a novel biostimulatory solution to both control phosphorus bioavailability and influence bioremediation. Two large bore infiltrators (1 m diameter) were installed at a PHC contaminated site and continuously supplied with a solution containing nutrients and an electron acceptor. Soils from eight contaminated sites were prepared and pretreated, analyzed pretrial, spiked with diesel, placed into nylon bags into the infiltrators, and removed after 3 months. From XAS, we learned that three principal phosphate phases had formed: adsorbed phosphate, brushite, and newberyite. All measures of biodegradation in the samples (in situ degradation estimates, mineralization assays, culturable bacteria, catabolic genes) varied depending upon the soil's phosphate speciation. Notably, adsorbed phosphate increased anaerobic phenanthrene degradation and bzdN catabolic gene prevalence. The dominant mineralogical constraints on community composition were the relative amounts of adsorbed phosphate, brushite, and newberyite. Overall, this study finds that total phosphate influences microbial community phenotypes whereas relative percentages of phosphate minerals influences microbial community genotype composition.

  19. Photo-oxidation of 5-enolpyruvoylshikimate-3-phosphate synthase from Escherichia coli: evidence for a reactive imidazole group (His385) at the herbicide glyphosate-binding site.

    PubMed

    Huynh, Q K

    1993-03-01

    Photo-oxidation of Escherichia coli 5-enolpyruvoylshikimate-3-phosphate synthase, a target for the non-selective herbicide glyphosate (N-phosphonomethylglycine), in the presence of pyridoxal 5'-phosphate resulted in irreversible inactivation of the enzyme. The inactivation followed pseudo-first-order and saturation kinetics with a Kinact. of 50 microM. The inactivation is specifically prevented by preincubation of the enzyme with the combination of shikimate 3-phosphate and glyphosate. Increasing glyphosate concentration during preincubation resulted in a decreasing rate of inactivation. On 95% inactivation, approximately one histidine per molecule of enzyme was oxidized. Tryptic mapping of the enzyme modified in the absence and presence of shikimate 3-phosphate and glyphosate as well as analyses of the histidine content in the isolated peptides indicated that His385, in the peptide Asn383-Asp-His-Arg386, was the site of oxidation. These results suggest that His385 is the most accessible reactive imidazole group under these conditions and is located close to the glyphosate-binding site.

  20. Probing the location and function of the conserved histidine residue of phosphoglucose isomerase by using an active site directed inhibitor N-bromoacetylethanolamine phosphate.

    PubMed Central

    Meng, M.; Chane, T. L.; Sun, Y. J.; Hsiao, C. D.

    1999-01-01

    Phosphoglucose isomerase (EC 5.3.1.9) catalyzes the interconversion of D-glucopyranose-6-phosphate and D-fructofuranose-6-phosphate by promoting an intrahydrogen transfer between C1 and C2. A conserved histidine exists throughout all phosphoglucose isomerases and was hypothesized to be the base catalyzing the isomerization reaction. In the present study, this conserved histidine, His311, of the enzyme from Bacillus stearothermophilus was subjected to mutational analysis, and the mutational effect on the inactivation kinetics by N-bromoacetylethanolamine phosphate was investigated. The substitution of His311 with alanine, asparagine, or glutamine resulted in the decrease of activity, in k(cat)/K(M), by a factor of 10(3), indicating the importance of this residue. N-bromoacetylethanolamine phosphate inactivated irreversibly the activity of wild-type phosphoglucose isomerase; however, His311 --> Ala became resistant to this inhibitor, indicating that His311 is located in the active site and is responsible for the inactivation of the enzyme by this active site-directed inhibitor. The pKa of His311 was estimated to be 6.31 according to the pH dependence of the inactivation. The proximity of this value with the pKa value of 6.35, determined from the pH dependence of k(cat)/K(M), supports a role of His311 as a general base in the catalysis. PMID:10595547

  1. Active site cysteine-null glyceraldehyde-3-phosphate dehydrogenase (GAPDH) rescues nitric oxide-induced cell death.

    PubMed

    Kubo, Takeya; Nakajima, Hidemitsu; Nakatsuji, Masatoshi; Itakura, Masanori; Kaneshige, Akihiro; Azuma, Yasu-Taka; Inui, Takashi; Takeuchi, Tadayoshi

    2016-02-29

    Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a homotetrameric enzyme involved in a key step of glycolysis, also has a role in mediating cell death under nitrosative stress. Our previous reports suggest that nitric oxide-induced intramolecular disulfide-bonding GAPDH aggregation, which occurs through oxidation of the active site cysteine (Cys-152), participates in a mechanism to account for nitric oxide-induced death signaling in some neurodegenerative/neuropsychiatric disorders. Here, we demonstrate a rescue strategy for nitric oxide-induced cell death accompanied by GAPDH aggregation in a mutant with a substitution of Cys-152 to alanine (C152A-GAPDH). Pre-incubation of purified wild-type GAPDH with C152A-GAPDH under exposure to nitric oxide inhibited wild-type GAPDH aggregation in a concentration-dependent manner in vitro. Several lines of structural analysis revealed that C152A-GAPDH extensively interfered with nitric oxide-induced GAPDH-amyloidogenesis. Overexpression of doxycycline-inducible C152A-GAPDH in SH-SY5Y neuroblastoma significantly rescued nitric oxide-induced death, concomitant with the decreased formation of GAPDH aggregates. Further, both co-immunoprecipitation assays and simulation models revealed a heterotetramer composed of one dimer each of wild-type GAPDH and C152A-GAPDH. These results suggest that the C152A-GAPDH mutant acts as a dominant-negative molecule against GAPDH aggregation via the formation of this GAPDH heterotetramer. This study may contribute to a new therapeutic approach utilizing C152A-GAPDH against brain damage in nitrosative stress-related disorders.

  2. Galactosemia caused by a point mutation that activates cryptic donor splice site in the galactose-1-phosphate uridyltransferase gene

    SciTech Connect

    Wadelius, C.; Lagerkvist, A. Uppsala Univ. ); Molin, A.K.; Larsson, A. ); Von Doebeln, U. )

    1993-08-01

    Galactosemia affects 1/84,000 in Sweden and is manifested in infancy when the child is exposed to galactose in the diet. If untreated there is a risk of severe early symptoms and, even with a lactose-free diet, late symptoms such as mental retardation and ovarial dysfunction may develop. In classical galactosemia, galactose-1-phosphate uridyltransferase (GALT) (EC 2.7.7.12) is defective and the normal cDNA sequence of this enzyme has been characterized. Recently eight mutations leading to galactosemia were published. Heparinized venous blood was drawn from a patient with classical galactosemia. In the cDNA from the patient examined, an insertion of 54 bp was found at position 1087. Amplification of the relevant genomic region of the patient's DNA was performed. Exon-intron boundaries and intronic sequences thus determined revealed that the 54-bp insertion was located immediately downstream of exon 10. It was further found that the patient was heterozygous for a point mutation, changing a C to a T (in 5 of 9 clones) at the second base in the intron downstream of the insertion. This alteration creates a sequence which, as well as the ordinary splice site, differs in only two positions from the consensus sequence. It was found that the mutation occurred in only one of the 20 alleles from galactosemic patients and in none of the 200 alleles from normal controls. The mutation is inherited from the mother, who also was found to express the 54-bp-long insertion at the mRNA level. Sequences from the 5[prime] end of the coding region were determined after genomic amplification, revealing a sequence identical to that reported. The mutation on the paternal allele has not been identified. 9 refs., 1 fig.

  3. Effects of pH and phosphate on metal distribution with emphasis on As speciation and mobilization in soils from a lead smelting site.

    PubMed

    Impellitteri, Christopher A

    2005-06-01

    Arsenic in soils from the Asarco lead smelter in East Helena, Montana was characterized by X-ray absorption spectroscopy (XAS). Arsenic oxidation state and geochemical speciation were analyzed as a function of depth (two sampling sites) and surface distribution. These results were compared with intensive desorption/dissolution experiments performed in a pH stat reactor for samples from the site with the highest degree of As heterogeneity. The objectives of the study were to investigate the solid-phase geochemical As speciation, assess the speciation of As in solutions equilibrated with the solids under controlled pH (pH=4 or 6) and Eh (using hydrogen or air) environments, observe the effects of phosphate on the release of As into solution, and examine the effects of phosphate on metal mobility in the systems. Arsenic was predominantly found in the As(V) valence state, though there was evidence that As(III) and As(0) were present also. The dominant geochemical phase was scorodite (FeAsO4.2H2O). The pH was controlled in the pH stat experiments by the addition of equinormal solutions of monoprotic (HNO3), diprotic (H2SO4), or triprotic (H3PO4) acids. For many of the divalent metal cations, solution concentrations greatly decreased in the presence of phosphate. Solutions were also analyzed for anions. Evidence exists for sulfate release into solution. More As was released into solution at lower pH. A slight increase in solution arsenate occurs with the addition of phosphate, but the risk posed from the increased desorption/dissolution of As must be weighed against the decrease in solution concentrations of many metals especially Pb. If tailings from this site underwent acidification (e.g., acid mine drainage), in situ sequestration of metals by phosphate could be combined with placement of subsurface permeable reactive barriers for capture of As to reduce the risk associated with arsenic and trace metal mobilization. Results from this study could be used in risk

  4. Acceptors in ZnO

    SciTech Connect

    McCluskey, Matthew D. Corolewski, Caleb D.; Lv, Jinpeng; Tarun, Marianne C.; Teklemichael, Samuel T.; Walter, Eric D.; Norton, M. Grant; Harrison, Kale W.; Ha, Su

    2015-03-21

    Zinc oxide (ZnO) has potential for a range of applications in the area of optoelectronics. The quest for p-type ZnO has focused much attention on acceptors. In this paper, Cu, N, and Li acceptor impurities are discussed. Experimental evidence indicates these point defects have acceptor levels 3.2, 1.4, and 0.8 eV above the valence-band maximum, respectively. The levels are deep because the ZnO valence band is quite low compared to conventional, non-oxide semiconductors. Using MoO{sub 2} contacts, the electrical resistivity of ZnO:Li was measured and showed behavior consistent with bulk hole conduction for temperatures above 400 K. A photoluminescence peak in ZnO nanocrystals is attributed to an acceptor, which may involve a Zn vacancy. High field (W-band) electron paramagnetic resonance measurements on the nanocrystals revealed an axial center with g{sub ⊥} = 2.0015 and g{sub //} = 2.0056, along with an isotropic center at g = 2.0035.

  5. Acceptors in ZnO

    SciTech Connect

    Mccluskey, Matthew D.; Corolewski, Caleb; Lv, Jinpeng; Tarun, Marianne C.; Teklemichael, Samuel T.; Walter, Eric D.; Norton, M. G.; Harrison, Kale W.; Ha, Su Y.

    2015-03-21

    Zinc oxide (ZnO) has potential for a range of applications in the area of optoelectronics. The quest for p-type ZnO has focused much attention on acceptors. In this paper, Cu, N, and Li acceptor impurities are discussed. Experimental evidence shows that these point defects have acceptor levels 3.2, 1.5, and 0.8 eV above the valence-band maximum, respectively. The levels are deep because the ZnO valence band is quite low compared to conventional, non-oxide semiconductors. Using MoO2 contacts, the electrical resistivity of ZnO:Li was measured and showed behavior consistent with bulk hole conduction for temperatures above 400 K. A photoluminescence peak in ZnO nanocrystals has been attributed to an acceptor, which may involve a zinc vacancy. High field (W-band) electron paramagnetic resonance measurements on the nanocrystals revealed an axial center with g = 2.0033 and g = 2.0075, along with an isotropic center at g = 2.0053.

  6. ATP binding and hydrolysis steps of the uni-site catalysis by the mitochondrial F(1)-ATPase are affected by inorganic phosphate.

    PubMed

    Milgrom, Yakov M

    2010-10-01

    The effect of inorganic phosphate (P(i)) on uni-site ATP binding and hydrolysis by the nucleotide-depleted F(1)-ATPase from beef heart mitochondria (ndMF(1)) has been investigated. It is shown for the first time that P(i) decreases the apparent rate constant of uni-site ATP binding by ndMF(1) 3-fold with the K(d) of 0.38+/-0.14mM. During uni-site ATP hydrolysis, P(i) also shifts equilibrium between bound ATP and ADP+P(i) in the direction of ATP synthesis with the K(d) of 0.17+/-0.03mM. However, 10mM P(i) does not significantly affect ATP binding during multi-site catalysis.

  7. Evidence for a reactive gamma-carboxyl group (Glu-418) at the herbicide glyphosate binding site of 5-enolpyruvylshikimate-3-phosphate synthase from Escherichia coli.

    PubMed

    Huynh, Q K

    1988-08-25

    Incubation of 5-enolpyruvylshikimate-3-phosphate synthase, a target for the nonselective herbicide glyphosate (N-(phosphonomethyl)glycine), with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide in the presence of glycine ethyl ester resulted in a time-dependent loss of enzyme activity. The inactivation followed pseudo-first order kinetics, with a second order rate constant of 2.2 M-1 min-1 at pH 5.5 and 25 degrees C. The inactivation is prevented by preincubation of the enzyme with a combination of the substrate shikimate 3-phosphate plus glyphosate, but not by shikimate 3-phosphate, phosphoenolpyruvate, or glyphosate alone. Increasing the concentration of glyphosate during preincubation resulted in decreasing the rate of inactivation of the enzyme. Complete inactivation of the enzyme required the modification of 4 carboxyl groups per molecule of the enzyme. However, statistical analysis of the residual activity and the extent of modification showed that among the 4 modifiable carboxyl groups, only 1 is critical for activity. Tryptic mapping of the enzyme modified in the absence of shikimate 3-phosphate and glyphosate by reverse phase chromatography resulted in the isolation of a [14C]glycine ethyl ester-containing peptide that was absent in the enzyme modified in the presence of shikimate 3-phosphate and glyphosate. By amino acid sequencing of this labeled peptide, the modified critical carboxyl group was identified as Glu-418. The above results suggest that Glu-418 is the most accessible reactive carboxyl group under these conditions and is located at or close to the glyphosate binding site.

  8. MINE WASTE TECHNOLOGY PROGRAM; PHOSPHATE STABILIZATION OF HEAVY METALS CONTAMINATED MINE WASTE YARD SOILS, JOPLIN, MISSOURI NPL SITE

    EPA Science Inventory

    This document summarizes the results of Mine Waste Technology Project 22-Phosphate Stabilization of Heavy Metals-Contaminated Mine Waste Yard Soils. Mining, milling, and smelting of ores near Joplin, Missouri, have resulted in heavy metal contamination of the area. The Joplin s...

  9. MINE WASTE TECHNOLOGY PROGRAM; PHOSPHATE STABILIZATION OF HEAVY METALS CONTAMINATED MINE WASTE YARD SOILS, JOPLIN, MISSOURI NPL SITE

    EPA Science Inventory

    This document summarizes the results of Mine Waste Technology Project 22-Phosphate Stabilization of Heavy Metals-Contaminated Mine Waste Yard Soils. Mining, milling, and smelting of ores near Joplin, Missouri, have resulted in heavy metal contamination of the area. The Joplin s...

  10. [Acceptor activity of 4-N-acetylcytidine in the synthesis of (3'-5')-internucleotide bond catalyzed by pancreatic nuclease].

    PubMed

    Kavunenko, A P; Piaĭvinen, E A; Tikhomirova-Sidorova, N S

    1976-04-01

    Cytidine and 4-N-acetylcytidine were compared as phosphate acceptors in dinucleoside monophosphate synthesis catalyzed by pancreatic ribonuclease with uridine-2',3'-cyclophosphate and cytidine-2',3'-cyclo phosphate as phosphate donors. Because of low solubility of 4-N-acetylcytidine in water, the synthesis was carried out in aqueus-organic media. The results obtained indicate that acetylation of the exoaminogroup of cytidine decreases its acceptor activity. For the first time uridilyl-(3'-5')-4-N-acetylcytidine and cytidilyl-(3'-5')-4-N-acetylcytidine are prepared enzymatically by pancreatic ribonuclease.

  11. The structure and bonding of iron-acceptor pairs in silicon

    SciTech Connect

    Zhao, S.; Assali, L.V.C.; Kimerling, L.C.

    1995-08-01

    The highly mobile interstitial iron and Group III impurities (B, Al, Ga, In) form iron-acceptor pairs in silicon. Based on the migration kinetics and taking host silicon as a dielectric medium, we have simulated the pairing process in a static silicon lattice. Different from the conventional point charge ionic model, our phenomenological calculations include (1) a correction that takes into account valence electron cloud polarization which adds a short range, attractive interaction in the iron-acceptor pair bonding; and (2) silicon lattice relaxation due to the atomic size difference which causes a local strain field. Our model explains qualitatively (1) trends among the iron-acceptor pairs revealing an increase of the electronic state hole emission energy with increasing principal quantum number of acceptor and decreasing pair separation distance; and (2) the stable and metastable sites and configurational symmetries of the iron-acceptor pairs. The iron-acceptor pairing and bonding mechanism is also discussed.

  12. Site-Directed Mutagenesis from Arg195 to His of a Microalgal Putatively Chloroplastidial Glycerol-3-Phosphate Acyltransferase Causes an Increase in Phospholipid Levels in Yeast

    PubMed Central

    Ouyang, Long-Ling; Li, Hui; Yan, Xiao-Jun; Xu, Ji-Lin; Zhou, Zhi-Gang

    2016-01-01

    To analyze the contribution of glycerol-3-phosphate acyltransferase (GPAT) to the first acylation of glycerol-3-phosphate (G-3-P), the present study focused on a functional analysis of the GPAT gene from Lobosphaera incisa (designated as LiGPAT). A full-length cDNA of LiGPAT consisting of a 1,305-bp ORF, a 1,652-bp 5′-UTR, and a 354-bp 3′-UTR, was cloned. The ORF encoded a 434-amino acid peptide, of which 63 residues at the N-terminus defined a chloroplast transit peptide. Multiple sequence alignment and phylogeny analysis of GPAT homologs provided the convincible bioinformatics evidence that LiGPAT was localized to chloroplasts. Considering the conservation of His among the G-3-P binding sites from chloroplastidial GPATs and the substitution of His by Arg at position 195 in the LiGPAT mature protein (designated mLiGPAT), we established the heterologous expression of either mLiGPAT or its mutant (Arg195His) (sdmLiGPAT) in the GPAT-deficient yeast mutant gat1Δ. Lipid profile analyses of these transgenic yeasts not only validated the acylation function of LiGPAT but also indicated that the site-directed mutagenesis from Arg195 to His led to an increase in the phospholipid level in yeast. Semi-quantitative analysis of mLiGPAT and sdmLiGPAT, together with the structural superimposition of their G-3-P binding sites, indicated that the increased enzymatic activity was caused by the enlarged accessible surface of the phosphate group binding pocket when Arg195 was mutated to His. Thus, the potential of genetic manipulation of GPAT to increase the glycerolipid level in L. incisa and other microalgae would be of great interest. PMID:27014309

  13. Defining critical residues for substrate binding to 1-deoxy-d-xylulose 5-phosphate synthase: Active site substitutions stabilize the pre-decarboxylation intermediate C2α-lactylthiamin diphosphate

    PubMed Central

    Kakalis, Lazaros; Jordan, Frank; Meyers, Caren L. Freel

    2014-01-01

    1-Deoxy-d-xylulose 5-phosphate (DXP) synthase catalyzes formation of DXP from pyruvate and d-glyceraldehyde 3-phosphate (d-GAP) in a thiamin diphosphate (ThDP)-dependent manner, and is the first step in the essential pathway to isoprenoids in human pathogens. Understanding the mechanism of this unique enzyme is critical for developing new anti-infective agents that selectively target isoprenoid biosynthesis. The present study uses mutagenesis and a combination of protein fluorescence, circular dichroism and kinetics experiments to investigate the roles of Arg-420, Arg-478 and Tyr-392 in substrate binding and catalysis. The results support a random sequential, preferred order mechanism and predict Arg-420 and Arg-478 are involved in binding of the acceptor substrate, d-GAP. d-Glyceraldehyde, an alternative acceptor substrate lacking the phosphoryl group predicted to interact with Arg-420 and Arg-478, also accelerates decarboxylation of the pre-decarboxylation intermediate C2α-lactylthiamin diphosphate (LThDP) on DXP synthase, indicating this binding interaction is not absolutely required, and the hydroxyaldehyde sufficiently triggers decarboxylation. Unexpectedly, Tyr-392 contributes to d-GAP affinity and is not required for LThDP formation or its d-GAP-promoted decarboxylation. Time-resolved CD spectroscopy and NMR experiments indicate LThDP is significantly stabilized on R420A and Y392F variants compared to wild type DXP synthase in the absence of acceptor substrate, yet these substitutions do not appear to impact the rate of d-GAP-promoted LThDP decarboxylation in the presence of high d-GAP, and LThDP formation remains the rate-limiting step. These results suggest a role of these residues to promote d-GAP binding which in turn facilitates decarboxylation, and further highlight interesting differences between DXP synthase and other ThDP-dependent enzymes. PMID:24767541

  14. Ribose 5-phosphate isomerase type B from Trypanosoma cruzi: kinetic properties and site-directed mutagenesis reveal information about the reaction mechanism

    PubMed Central

    Stern, Ana L.; Burgos, Emmanuel; Salmon, Laurent; Cazzulo, Juan J.

    2006-01-01

    Trypanosoma cruzi, the human parasite that causes Chagas disease, contains a functional pentose phosphate pathway, probably essential for protection against oxidative stress and also for R5P (ribose 5-phosphate) production for nucleotide synthesis. The haploid genome of the CL Brener clone of the parasite contains one gene coding for a Type B Rpi (ribose 5-phosphate isomerase), but genes encoding Type A Rpis, most frequent in eukaryotes, seem to be absent. The RpiB enzyme was expressed in Escherichia coli as a poly-His tagged active dimeric protein, which catalyses the reversible isomerization of R5P to Ru5P (ribulose 5-phos-phate) with Km values of 4 mM (R5P) and 1.4 mM (Ru5P). 4-Phospho-D-erythronohydroxamic acid, an analogue to the reaction intermediate when the Rpi acts via a mechanism involving the formation of a 1,2-cis-enediol, inhibited the enzyme competi-tively, with an IC50 value of 0.7 mM and a Ki of 1.2 mM. Site-directed mutagenesis allowed the demonstration of a role for His102, but not for His138, in the opening of the ribose furanosic ring. A major role in catalysis was confirmed for Cys69, since the C69A mutant was inactive in both forward and reverse directions of the reaction. The present paper contributes to the know-ledge of the mechanism of the Rpi reaction; in addition, the absence of RpiBs in the genomes of higher animals makes this enzyme a possible target for chemotherapy of Chagas disease. PMID:16981853

  15. Electron acceptor dependence of electron shuttle secretion and extracellular electron transfer by Shewanella oneidensis MR-1.

    PubMed

    Wu, Chao; Cheng, Yuan-Yuan; Li, Bing-Bing; Li, Wen-Wei; Li, Dao-Bo; Yu, Han-Qing

    2013-05-01

    Shewanella oneidensis MR-1 is an extensively studied dissimilatory metal-reducing bacterium with a great potential for bioremediation and electricity generation. It secretes flavins as electron shuttles which play an important role in extracellular electron transfer. However, the influence of various environmental factors on the secretion of flavins is largely unknown. Here, the effects of electron acceptors, including fumarate, ferrihydrite, Fe(III)-nitrilotriacetic acid (NTA), nitrate and trimethylamine oxide (TMAO), on the secretion of flavins were investigated. The level of riboflavin and riboflavin-5'-phosphate (FMN) secreted by S. oneidensis MR-1 varied considerably with different electron acceptors. While nitrate and ferrihydrite suppressed the secretion of flavins in relative to fumarate, Fe(III)-NTA and TMAO promoted such a secretion and greatly enhanced ferrihydrite reduction and electricity generation. This work clearly demonstrates that electron acceptors could considerably affect the secretion of flavins and consequent microbial EET. Such impacts of electron acceptors in the environment deserve more attention.

  16. Selection of the acceptor medium in in vitro measurements of drug release from dermatological ointments.

    PubMed

    Gloor, M; Shabafrouz, H

    1983-01-01

    Comparative measurements of in vitro agent release using hydrophilic, intermediate, and lipophilic acceptor phases and in vivo measurements of the blanching effect with triamcinolone acetonide are reported. White petrolatum, wool alcohols ointment, and polyethylene glycol ointment served as donator phases. The results demonstrate that the lipophilic acceptor phase (isopropyl palmitate) is most representative for the in vivo acceptor phase. Conclusions cannot be drawn regarding in vivo effectiveness from measurements of agent release to the hydrophilic (phosphate buffer, pH 6) and intermediate (n-octanol) acceptor phases. In vitro measurements of agent release have a screening character and must usually be supplemented by very elaborate penetration models of the human skin for a definitive evaluation of an ointment.

  17. Phosphate salts

    MedlinePlus

    ... taken by mouth or used as enemas. Indigestion. Aluminum phosphate and calcium phosphate are FDA-permitted ingredients ... Phosphate salts containing sodium, potassium, aluminum, or calcium are LIKELY SAFE for most people when taken by mouth short-term, when sodium phosphate is inserted into the ...

  18. On the multiple functional roles of the active site histidine in catalysis and allosteric regulation of Escherichia coli glucosamine 6-phosphate deaminase.

    PubMed

    Montero-Morán, G M; Lara-González, S; Alvarez-Añorve, L I; Plumbridge, J A; Calcagno, M L

    2001-08-28

    The active site of glucosamine-6-phosphate deaminase (EC 3.5.99.6, formerly 5.3.1.10) from Escherichia coli was first characterized on the basis of the crystallographic structure of the enzyme bound to the competitive inhibitor 2-amino-2-deoxy-glucitol 6-phosphate. The structure corresponds to the R allosteric state of the enzyme; it shows the side-chain of His143 in close proximity to the O5 atom of the inhibitor. This arrangement suggests that His143 could have a role in the catalysis of the ring-opening step of glucosamine 6-phosphate whose alpha-anomer is the true substrate. The imidazole group of this active-site histidine contacts the carboxy groups from Glu148 and Asp141, via its Ndelta1 atom [Oliva et al. (1995) Structure 3, 1323-1332]. These interactions change in the T state because the side chain of Glu148 moves toward the allosteric site, leaving at the active site the dyad Asp141-His143 [Horjales et al. (1999) Structure 7, 527-536]. In this research, a dual approach using site-directed mutagenesis and controlled chemical modification of histidine residues has been used to investigate the role of the active-site histidine. Our results support a multifunctional role of His143; in the forward reaction, it is involved in the catalysis of the ring-opening step of the substrate, glucosamine 6-P. In the reverse reaction, the substrate fructose 6-P binds in its open chain, carbonylic form. The role of His143 in the binding of both glucosamine 6-P and reaction intermediates in their extended-chain forms was demonstrated by binding experiments using the reaction intermediate analogue, 2-amino-2-deoxy-D-glucitol 6-phosphate. His143 was also shown to be a critical residue for the conformational coupling between active and allosteric sites. From the pH dependence of the reactivity of the active site histidine to diethyl dicarbonate, we observed a pK(a) change of 1.2 units to the acid side when the enzyme undergoes the allosteric T to R transition during which the

  19. Evidence for the coupling of Gq protein to D1-like dopamine sites in rat striatum: possible role in dopamine-mediated inositol phosphate formation.

    PubMed

    Wang, H Y; Undie, A S; Friedman, E

    1995-12-01

    The role of G proteins in mediating the coupling of D1 dopamine receptors to inositol phosphate formation was investigated in rat brain striatum. Pertussis toxin-activated ADP-ribosylation ( > or = 95%) did not affect the ability of the D1 agonist SKF38393 to stimulate the generation of inositol phosphates in striatal slices. Stimulation of striatal membranes with dopamine in the presence of [35S]GTP gamma S or [alpha-32P]GTP increased guanine nucleotide binding to G alpha s, G alpha i, and G alpha q in a concentration-dependent fashion. The activation of G alpha s and G alpha q was mimicked by the D1 agonist SKF38393 and blocked by the D1 antagonist SCH23390. In contrast, the D2/3 dopamine receptor agonist quinpirole stimulated guanine nucleotide binding to G alpha i, and dopamine-stimulated activation of G alpha i was attenuated by the D2 antagonist I-sulpiride. Furthermore, antisera directed against G alpha s or G alpha q but not G alpha i, G alpha o, or G alpha z precipitated specific D1-like binding sites labeled with [3H]SCH23390. The D1-like receptors that coprecipitated with G alpha s-but not with G alpha q can be recognized by a specific D1 dopamine receptor antibody. The data provide evidence to suggest that in addition to coupling to Gs/adenylyl cyclase, D1-like dopamine sites that couple to Gq may mediate dopamine-stimulated formation of inositol phosphates in the rat striatum.

  20. Substitution of glutamine for lysine at the pyridoxal phosphate binding site of bacterial D-amino acid transaminase. Effects of exogenous amines on the slow formation of intermediates.

    PubMed

    Futaki, S; Ueno, H; Martinez del Pozo, A; Pospischil, M A; Manning, J M; Ringe, D; Stoddard, B; Tanizawa, K; Yoshimura, T; Soda, K

    1990-12-25

    In bacterial D-amino acid transaminase, Lys-145, which binds the coenzyme pyridoxal 5'-phosphate in Schiff base linkage, was changed to Gln-145 by site-directed mutagenesis (K145Q). The mutant enzyme had 0.015% the activity of the wild-type enzyme and was capable of forming a Schiff base with D-alanine; this external aldimine was formed over a period of minutes depending upon the D-alanine concentration. The transformation of the pyridoxal-5'-phosphate form of the enzyme to the pyridoxamine-5'-phosphate form (i.e. the half-reaction of transamination) occurred over a period of hours with this mutant enzyme. Thus, information on these two steps in the reaction and on the factors that influence them can readily be obtained with this mutant enzyme. In contrast, these reactions with the wild-type enzyme occur at much faster rates and are not easily studied separately. The mutant enzyme shows distinct preference for D- over L-alanine as substrates but it does so about 50-fold less effectively than the wild-type enzyme. Thus, Lys-145 probably acts in concert with the coenzyme and other functional side chain(s) to lead to efficient and stereochemically precise transamination in the wild-type enzyme. The addition of exogenous amines, ethanolamine or methyl amine, increased the rate of external aldimine formation with D-alanine and the mutant enzyme but the subsequent transformation to the pyridoxamine-5'-phosphate form of the enzyme was unaffected by exogenous amines. The wild-type enzyme displayed a large negative trough in the circular dichroic spectrum at 420 nm, which was practically absent in the mutant enzyme. However, addition of D-alanine to the mutant enzyme generated this negative Cotton effect (due to formation of the external aldimine with D-alanine). This circular dichroism band gradually collapsed in parallel with the transformation to the pyridoxamine-5'-phosphate enzyme. Further studies on this mutant enzyme, which displays the characteristics of the wild

  1. Absence of Substrate Channeling between Active Sites in the Agrobacterium tumefaciens IspDF and IspE Enzymes of the Methyl Erythritol Phosphate Pathway†

    PubMed Central

    Lherbet, Christian; Pojer, Florence; Richard, Stéphane B.; Noel, Joseph P.; Poulter, C. D.

    2008-01-01

    The conversion of 2C-methyl-d-erythritol 4-phosphate (MEP) to 2C-methyl-d-erythritol 2,4-cyclodiphosphate (cMEDP) in the MEP entry into the isoprenoid biosynthetic pathway occurs in three consecutive steps catalyzed by the IspD, IspE, and IspF enzymes, respectively. In Agrobacterium tumefaciens the ispD and ispF genes are fused to encode a bifunctional enzyme that catalyzes the first (synthesis of 4-diphosphocytidyl-2-C-methyl d-erythritol) and third (synthesis of 2C-methyl-d-erythritol 2,4-cyclodiphosphate) steps. Sedimentation velocity experiments indicate that the bifunctional IspDF enzyme and the IspE protein associate in solution raising the possibility of substrate channeling among the active sites in these two proteins. Kinetic evidence for substrate channeling was sought by measuring the time courses for product formation during incubations of MEP, CTP, and ATP with the IspDF and IspE proteins with and without an excess of the inactive IspE (D152A) mutant in presence or absence of 30% (v/v) glycerol. The time dependencies indicate that the enzyme-generated intermediates are not transferred from the IspD active site in IspDF to the active site of IspE or from the active site in IspE to the active site in the IspF module of IspDF. PMID:16533036

  2. Absence of substrate channeling between active sites in the Agrobacterium tumefaciens IspDF and IspE enzymes of the methyl erythritol phosphate pathway.

    PubMed

    Lherbet, Christian; Pojer, Florence; Richard, Stéphane B; Noel, Joseph P; Poulter, C D

    2006-03-21

    The conversion of 2-C-methyl-d-erythritol 4-phosphate (MEP) to 2-C-methyl-d-erythritol 2,4-cyclodiphosphate (cMEDP) in the MEP entry into the isoprenoid biosynthetic pathway occurs in three consecutive steps catalyzed by the IspD, IspE, and IspF enzymes, respectively. In Agrobacterium tumefaciens the ispD and ispF genes are fused to encode a bifunctional enzyme that catalyzes the first (synthesis of 4-diphosphocytidyl-2-C-methyl d-erythritol) and third (synthesis of 2-C-methyl-d-erythritol 2,4-cyclodiphosphate) steps. Sedimentation velocity experiments indicate that the bifunctional IspDF enzyme and the IspE protein associate in solution, raising the possibility of substrate channeling among the active sites in these two proteins. Kinetic evidence for substrate channeling was sought by measuring the time courses for product formation during incubations of MEP, CTP, and ATP with the IspDF and IspE proteins with and without an excess of the inactive IspE(D152A) mutant in the presence or absence of 30% (v/v) glycerol. The time dependencies indicate that the enzyme-generated intermediates are not transferred from the IspD active site in IspDF to the active site of IspE or from the active site in IspE to the active site of the IspF module of IspDF.

  3. Site-specific regulatory interaction between spinach leaf sucrose-phosphate synthase and 14-3-3 proteins

    NASA Technical Reports Server (NTRS)

    Toroser, D.; Athwal, G. S.; Huber, S. C.; Davies, E. (Principal Investigator)

    1998-01-01

    We report an Mg2+-dependent interaction between spinach leaf sucrose-phosphate synthase (SPS) and endogenous 14-3-3 proteins, as evidenced by co-elution during gel filtration and co-immunoprecipitation. The content of 14-3-3s associated with an SPS immunoprecipitate was inversely related to activity, and was specifically reduced when tissue was pretreated with 5-aminoimidazole-4-carboxamide riboside, suggesting metabolite control in vivo. A synthetic phosphopeptide based on Ser-229 was shown by surface plasmon resonance to bind a recombinant plant 14-3-3, and addition of the phosphorylated SPS-229 peptide was found to stimulate the SPS activity of an SPS:14-3-3 complex. Taken together, the results suggest a regulatory interaction of 14-3-3 proteins with Ser-229 of SPS.

  4. Site-specific regulatory interaction between spinach leaf sucrose-phosphate synthase and 14-3-3 proteins

    NASA Technical Reports Server (NTRS)

    Toroser, D.; Athwal, G. S.; Huber, S. C.; Davies, E. (Principal Investigator)

    1998-01-01

    We report an Mg2+-dependent interaction between spinach leaf sucrose-phosphate synthase (SPS) and endogenous 14-3-3 proteins, as evidenced by co-elution during gel filtration and co-immunoprecipitation. The content of 14-3-3s associated with an SPS immunoprecipitate was inversely related to activity, and was specifically reduced when tissue was pretreated with 5-aminoimidazole-4-carboxamide riboside, suggesting metabolite control in vivo. A synthetic phosphopeptide based on Ser-229 was shown by surface plasmon resonance to bind a recombinant plant 14-3-3, and addition of the phosphorylated SPS-229 peptide was found to stimulate the SPS activity of an SPS:14-3-3 complex. Taken together, the results suggest a regulatory interaction of 14-3-3 proteins with Ser-229 of SPS.

  5. Engineering of Recombinant Poplar Deoxy-D-Xylulose-5-Phosphate Synthase (PtDXS) by Site-Directed Mutagenesis Improves Its Activity.

    PubMed

    Banerjee, Aparajita; Preiser, Alyssa L; Sharkey, Thomas D

    2016-01-01

    Deoxyxylulose 5-phosphate synthase (DXS), a thiamine diphosphate (ThDP) dependent enzyme, plays a regulatory role in the methylerythritol 4-phosphate (MEP) pathway. Isopentenyl diphosphate (IDP) and dimethylallyl diphosphate (DMADP), the end products of this pathway, inhibit DXS by competing with ThDP. Feedback inhibition of DXS by IDP and DMADP constitutes a significant metabolic regulation of this pathway. The aim of this work was to experimentally test the effect of key residues of recombinant poplar DXS (PtDXS) in binding both ThDP and IDP. This work also described the engineering of PtDXS to improve the enzymatic activity by reducing its inhibition by IDP and DMADP. We have designed and tested modifications of PtDXS in an attempt to reduce inhibition by IDP. This could possibly be valuable by removing a feedback that limits the usefulness of the MEP pathway in biotechnological applications. Both ThDP and IDP use similar interactions for binding at the active site of the enzyme, however, ThDP being a larger molecule has more anchoring sites at the active site of the enzyme as compared to the inhibitors. A predicted enzyme structure was examined to find ligand-enzyme interactions, which are relatively more important for inhibitor-enzyme binding than ThDP-enzyme binding, followed by their modifications so that the binding of the inhibitors can be selectively affected compared to ThDP. Two alanine residues important for binding ThDP and the inhibitors were mutated to glycine. In two of the cases, both the IDP inhibition and the overall activity were increased. In another case, both the IDP inhibition and the overall activity were reduced. This provides proof of concept that it is possible to reduce the feedback from IDP on DXS activity.

  6. Engineering of Recombinant Poplar Deoxy-D-Xylulose-5-Phosphate Synthase (PtDXS) by Site-Directed Mutagenesis Improves Its Activity

    PubMed Central

    Banerjee, Aparajita; Preiser, Alyssa L.

    2016-01-01

    Deoxyxylulose 5-phosphate synthase (DXS), a thiamine diphosphate (ThDP) dependent enzyme, plays a regulatory role in the methylerythritol 4-phosphate (MEP) pathway. Isopentenyl diphosphate (IDP) and dimethylallyl diphosphate (DMADP), the end products of this pathway, inhibit DXS by competing with ThDP. Feedback inhibition of DXS by IDP and DMADP constitutes a significant metabolic regulation of this pathway. The aim of this work was to experimentally test the effect of key residues of recombinant poplar DXS (PtDXS) in binding both ThDP and IDP. This work also described the engineering of PtDXS to improve the enzymatic activity by reducing its inhibition by IDP and DMADP. We have designed and tested modifications of PtDXS in an attempt to reduce inhibition by IDP. This could possibly be valuable by removing a feedback that limits the usefulness of the MEP pathway in biotechnological applications. Both ThDP and IDP use similar interactions for binding at the active site of the enzyme, however, ThDP being a larger molecule has more anchoring sites at the active site of the enzyme as compared to the inhibitors. A predicted enzyme structure was examined to find ligand-enzyme interactions, which are relatively more important for inhibitor-enzyme binding than ThDP-enzyme binding, followed by their modifications so that the binding of the inhibitors can be selectively affected compared to ThDP. Two alanine residues important for binding ThDP and the inhibitors were mutated to glycine. In two of the cases, both the IDP inhibition and the overall activity were increased. In another case, both the IDP inhibition and the overall activity were reduced. This provides proof of concept that it is possible to reduce the feedback from IDP on DXS activity. PMID:27548482

  7. Characterization and site-directed mutagenesis of a novel class II 5-enopyruvylshikimate-3-phosphate (EPSP) synthase from the deep-sea bacterium Alcanivorax sp. L27.

    PubMed

    Zhang, Yi; Yi, Licong; Lin, Yongjun; Zhang, Lili; Shao, Zongze; Liu, Ziduo

    2014-09-01

    The 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) is a key enzyme in the aromatic amino acid biosynthetic pathway in microorganisms and plants, which catalyzes the formation of 5-enolpyruvylshikimate-3-phosphate (EPSP) from shikimate-3-phosphate (S3P) and phosphoenolpyruvate (PEP). In this study, a novel AroA-encoding gene was identified from the deep sea bacterium Alcanivorax sp. L27 through screening the genomic library and termed as AroAA.sp. A phylogenetic analysis revealed that AroAA.sp (1317 bp and 438 amino acids) is a class II AroA. This enzyme exhibited considerable activity between pH 5.5 and pH 8.0 and notable activity at low temperatures. The KM for PEP and IC50 [glyphosate] values (the concentration of glyphosate that inhibited enzyme activity by 50%) of AroAA.sp were 78 μM and 1.5 mM, respectively. Furthermore, site-directed mutagenesis revealed that the G100A mutant had a 30-fold increase in the IC50 [glyphosate] value; while the L105P mutant showed only 20% catalytic activity compared to wild-type AroAA.sp. The specific activity of the wild-type AroAA.sp, the G100A mutant and the L105P mutant were 7.78 U/mg, 7.26 U/mg and 1.76 U/mg, respectively. This is the first report showing that the G100A mutant of AroA displays considerably improved glyphosate resistance and demonstrates that Leu105 is essential for the enzyme's activity.

  8. On the role of the conformational flexibility of the active-site lid on the allosteric kinetics of glucosamine-6-phosphate deaminase.

    PubMed

    Bustos-Jaimes, Ismael; Sosa-Peinado, Alejandro; Rudiño-Piñera, Enrique; Horjales, Eduardo; Calcagno, Mario L

    2002-05-24

    The active site of glucosamine-6-phosphate deaminase from Escherichia coli (GlcN6P deaminase, EC 3.5.99.6) has a complex lid formed by two antiparallel beta-strands connected by a helix-loop segment (158-187). This motif contains Arg172, which is a residue involved in binding the substrate in the active-site, and three residues that are part of the allosteric site, Arg158, Lys160 and Thr161. This dual binding role of the motif forming the lid suggests that it plays a key role in the functional coupling between active and allosteric sites. Previous crystallographic work showed that the temperature coefficients of the active-site lid are very large when the enzyme is in its T allosteric state. These coefficients decrease in the R state, thus suggesting that this motif changes its conformational flexibility as a consequence of the allosteric transition. In order to explore the possible connection between the conformational flexibility of the lid and the function of the deaminase, we constructed the site-directed mutant Phe174-Ala. Phe174 is located at the C-end of the lid helix and its side-chain establishes hydrophobic interactions with the remainder of the enzyme. The crystallographic structure of the T state of Phe174-Ala deaminase, determined at 2.02 A resolution, shows no density for the segment 162-181, which is part of the active-site lid (PDB 1JT9). This mutant form of the enzyme is essentially inactive in the absence of the allosteric activator, N-acetylglucosamine-6-P although it recovers its activity up to the wild-type level in the presence of this ligand. Spectrometric and binding studies show that inactivity is due to the inability of the active-site to bind ligands when the allosteric site is empty. These data indicate that the conformational flexibility of the active-site lid critically alters the binding properties of the active site, and that the occupation of the allosteric site restores the lid conformational flexibility to a functional state.

  9. Replacement of water molecules in a phosphate binding site by furanoside-appended lin-benzoguanine ligands of tRNA-guanine transglycosylase (TGT).

    PubMed

    Barandun, Luzi J; Ehrmann, Frederik R; Zimmerli, Daniel; Immekus, Florian; Giroud, Maude; Grünenfelder, Claudio; Schweizer, W Bernd; Bernet, Bruno; Betz, Michael; Heine, Andreas; Klebe, Gerhard; Diederich, François

    2015-01-02

    The enzyme tRNA-guanine transglycosylase has been identified as a drug target for the foodborne illness shigellosis. A key challenge in structure-based design for this enzyme is the filling of the polar ribose-34 pocket. Herein, we describe a novel series of ligands consisting of furanoside-appended lin-benzoguanines. They were designed to replace a conserved water cluster and differ by the functional groups at C(2) and C(3) of the furanosyl moiety being either OH or OMe. The unfavorable desolvation of Asp102 and Asp280, which are located close to the ribose-34 pocket, had a significant impact on binding affinity. While the enzyme has tRNA as its natural substrate, X-ray co-crystal structures revealed that the furanosyl moieties of the ligands are not accommodated in the tRNA ribose-34 site, but at the location of the adjacent phosphate group. A remarkable similarity of the position of the oxygen atoms in these two structures suggests furanosides as a potential phosphate isoster. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. The phosphorylation pattern of oligosaccharides in secreted procathepsin D is glycosylation site-specific and independent of the expression of mannose 6-phosphate receptors.

    PubMed

    Dittmer, F; Pohlmann, R; von Figura, K

    1997-01-10

    Mammalian cells contain two types of mannose 6-phosphate receptors (MPR), MPRs 46 and 300, that contribute with variable efficiency to the sorting of individual lysosomal proteins. To evaluate the role of phosphorylated oligosaccharides for the sorting efficiency by either of the two receptors, the structure of phosphorylated oligosaccharides on lysosomal proteins escaping sorting in cells lacking MPR 46 and/or MPR 300 was analyzed. Procathepsin D was chosen as a model because it is sorted efficiently via MPR 300 and poorly via MPR 46 and contains a distinct and highly heterogenous mixture of phosphorylated oligosaccharides at either of its two N-glycosylation sites. Both MPRs 46 and 300 were found to have a minor but distinct preference for forms of procathepsin D and other lysosomal proteins containing oligosaccharides with two phosphomonoesters. However, the phosphorylation of oligosaccharides in procathepsin D and other lysosomal proteins that escape sorting in control cells or in cells lacking MPR 46 and/or MPR 300 was strikingly similar, and oligosaccharides with two phosphomonoesters represented the major oligosaccharide species. We conclude from these results that the position of the position of the phosphate groups, the structure of the underlying oligosaccharide, and/or the polypeptide backbone of lysosomal proteins have major roles in determining the affinity to MPRs.

  11. Evaluation of the expression of collagen type I in porous calcium phosphate ceramics implanted in an extra-osseous site.

    PubMed

    Qu, S X; Guo, X; Weng, J; Cheng, J C Y; Feng, B; Yeung, H Y; Zhang, X D

    2004-02-01

    The aim of the present study is to demonstrate the newly formed tissue in calcium phosphate (Ca/P) ceramics after extra-osseous implantation by histological and immunohistochemistry (IHC) methods. Synthesis porous Ca/P ceramics without adding any growth factor and living cell were implanted in the dorsal muscle of dogs for 1 and 2 months. Undecalcified and decalcified sections were stained by hematoxylin and eosin (H&E), and IHC, respectively. The histological results showed the beginning of osteogenesis and angiogenesis after being implanted for 1 month and the obvious new bone formation after being implanted for 2 months. IHC were conducted via the avidin-biotin peroxidase complex (ABC) method and the primary antibody was collagen type I. IHC results indicated that collagen type I was expressed within osteoblast-like cells and newly formed bone-like tissue in Ca/P ceramics after 1 month, and in the mineralized matrix of newly formed bone and osteoblasts, some osteocytes and some lacunae after 2 months. No cartilage and chondrocytes were observed in the histological and IHC-stained sections. Evidence of intramembranous osteogenesis was confirmed.

  12. Transglucosylation potential of six sucrose phosphorylases toward different classes of acceptors.

    PubMed

    Aerts, Dirk; Verhaeghe, Tom F; Roman, Bart I; Stevens, Christian V; Desmet, Tom; Soetaert, Wim

    2011-09-27

    In this study, the transglucosylation potential of six sucrose phosphorylase (SP) enzymes has been compared using eighty putative acceptors from different structural classes. To increase the solubility of hydrophobic acceptors, the addition of various co-solvents was first evaluated. All enzymes were found to retain at least 50% of their activity in 25% dimethylsulfoxide, with the enzymes from Bifidobacterium adolescentis and Streptococcus mutans being the most stable. Screening of the enzymes' specificity then revealed that the vast majority of acceptors are transglucosylated very slowly by SP, at a rate that is comparable to the contaminating hydrolytic reaction. The enzyme from S. mutans displayed the narrowest acceptor specificity and the one from Leuconostoc mesenteroides NRRL B1355 the broadest. However, high activity could only be detected on l-sorbose and l-arabinose, besides the native acceptors d-fructose and phosphate. Improving the affinity for alternative acceptors by means of enzyme engineering will, therefore, be a major challenge for the commercial exploitation of the transglucosylation potential of sucrose phosphorylase.

  13. Glucansucrase acceptor reactions with D-mannose

    USDA-ARS?s Scientific Manuscript database

    The main acceptor product of glucansucrases with D-mannose has not previously been identified. We used glucansucrases that form water-insoluble a-D-glucans to produce increased yields of acceptor products from D-mannose, and identified the major product as 6-O-a-D-glucopyranosyl-D-mannose. Glucansuc...

  14. Anaerobic electron acceptor chemotaxis in Shewanella putrefaciens

    NASA Technical Reports Server (NTRS)

    Nealson, K. H.; Moser, D. P.; Saffarini, D. A.

    1995-01-01

    Shewanella putrefaciens MR-1 can grow either aerobically or anaerobically at the expense of many different electron acceptors and is often found in abundance at redox interfaces in nature. Such redox interfaces are often characterized by very strong gradients of electron acceptors resulting from rapid microbial metabolism. The coincidence of S. putrefaciens abundance with environmental gradients prompted an examination of the ability of MR-1 to sense and respond to electron acceptor gradients in the laboratory. In these experiments, taxis to the majority of the electron acceptors that S. putrefaciens utilizes for anaerobic growth was seen. All anaerobic electron acceptor taxis was eliminated by the presence of oxygen, nitrate, nitrite, elemental sulfur, or dimethyl sulfoxide, even though taxis to the latter was very weak and nitrate and nitrite respiration was normal in the presence of dimethyl sulfoxide. Studies with respiratory mutants of MR-1 revealed that several electron acceptors that could not be used for anaerobic growth nevertheless elicited normal anaerobic taxis. Mutant M56, which was unable to respire nitrite, showed normal taxis to nitrite, as well as the inhibition of taxis to other electron acceptors by nitrite. These results indicate that electron acceptor taxis in S. putrefaciens does not conform to the paradigm established for Escherichia coli and several other bacteria. Carbon chemo-taxis was also unusual in this organism: of all carbon compounds tested, the only positive response observed was to formate under anaerobic conditions.

  15. Anaerobic electron acceptor chemotaxis in Shewanella putrefaciens.

    PubMed

    Nealson, K H; Moser, D P; Saffarini, D A

    1995-04-01

    Shewanella putrefaciens MR-1 can grow either aerobically or anaerobically at the expense of many different electron acceptors and is often found in abundance at redox interfaces in nature. Such redox interfaces are often characterized by very strong gradients of electron acceptors resulting from rapid microbial metabolism. The coincidence of S. putrefaciens abundance with environmental gradients prompted an examination of the ability of MR-1 to sense and respond to electron acceptor gradients in the laboratory. In these experiments, taxis to the majority of the electron acceptors that S. putrefaciens utilizes for anaerobic growth was seen. All anaerobic electron acceptor taxis was eliminated by the presence of oxygen, nitrate, nitrite, elemental sulfur, or dimethyl sulfoxide, even though taxis to the latter was very weak and nitrate and nitrite respiration was normal in the presence of dimethyl sulfoxide. Studies with respiratory mutants of MR-1 revealed that several electron acceptors that could not be used for anaerobic growth nevertheless elicited normal anaerobic taxis. Mutant M56, which was unable to respire nitrite, showed normal taxis to nitrite, as well as the inhibition of taxis to other electron acceptors by nitrite. These results indicate that electron acceptor taxis in S. putrefaciens does not conform to the paradigm established for Escherichia coli and several other bacteria. Carbon chemo-taxis was also unusual in this organism: of all carbon compounds tested, the only positive response observed was to formate under anaerobic conditions.

  16. Site-directed fluorescence labeling reveals differences on the R-conformer of glucosamine 6-phosphate deaminase of Escherichia coli induced by active or allosteric site ligands at steady state.

    PubMed

    Sosa-Peinado, Alejandro; González-Andrade, Martín

    2005-11-22

    Engineered glucosamine 6-phosphate deaminase of Escherichia coli with unique reactive cysteines at positions 164 or 206 was created by site-directed mutagenesis to monitor the allosteric transition in solution by the fluorescence emission of the bimane or dansyl-amidoethyl groups attached to the indicated residues. The selection of both positions was due to the differential interaction of these residues between T- and R-conformers at the interface of two trimers that form the hexameric structure; in the T-conformer, residue 164 or 206 presents only intrasubunit contacts, but in the R-conformer, new intersubunit contacts are established. As in the wild-type enzyme, fluorescent-labeled mutants show no modification on the allosteric activation of the K-system, only the kcat was reduced to a value of 72 s(-1) (approximately 50% of wild-type). With these preparations, conformational changes were detected by the fluorescence emission spectra at steady state when the active site or the allosteric site ligands were titrated. Despite the similar changes in the fluorescence spectra that were correlated with the induction of the R-state, differences were observed at the maximal change in the fluorescence spectra and in the relative solvent polarities at the positions labeled. These data suggested structural differences in the conformation of the R-state when it is induced from the active site or from the allosteric site, which is not consistent with the two-state structural model proposed by previous crystallographic studies of this enzyme.

  17. Active site mapping of MraY, a member of the polyprenyl-phosphate N-acetylhexosamine 1-phosphate transferase superfamily, catalyzing the first membrane step of peptidoglycan biosynthesis.

    PubMed

    Al-Dabbagh, Bayan; Henry, Xavier; El Ghachi, Meriem; Auger, Geneviève; Blanot, Didier; Parquet, Claudine; Mengin-Lecreulx, Dominique; Bouhss, Ahmed

    2008-08-26

    The MraY transferase is an integral membrane protein that catalyzes an essential step of peptidoglycan biosynthesis, namely the transfer of the phospho-N-acetylmuramoyl-pentapeptide motif onto the undecaprenyl phosphate carrier lipid. It belongs to a large superfamily of eukaryotic and prokaryotic prenyl sugar transferases. No 3D structure has been reported for any member of this superfamily, and to date MraY is the only protein that has been successfully purified to homogeneity. Nineteen polar residues located in the five cytoplasmic segments of MraY appeared as invariants in the sequences of MraY orthologues. A certain number of these invariant residues were found to be conserved in the whole superfamily. To assess the importance of these residues in the catalytic process, site-directed mutagenesis was performed using the Bacillus subtilis MraY as a model. Fourteen residues were shown to be essential for MraY activity by an in vivo functional complementation assay using a constructed conditional mraY mutant strain. The corresponding mutant proteins were purified and biochemically characterized. None of these mutations did significantly affect the binding of the nucleotidic and lipidic substrates, but the k cat was dramatically reduced in almost all cases. The important residues for activity therefore appeared to be distributed in all the cytoplasmic segments, indicating that these five regions contribute to the structure of the catalytic site. Our data show that the D98 residue that is invariant in the whole superfamily should be involved in the deprotonation of the lipid substrate during the catalytic process.

  18. Transcription of lncRNA prt, clustered prt RNA sites for Mmi1 binding, and RNA polymerase II CTD phospho-sites govern the repression of pho1 gene expression under phosphate-replete conditions in fission yeast.

    PubMed

    Chatterjee, Debashree; Sanchez, Ana M; Goldgur, Yehuda; Shuman, Stewart; Schwer, Beate

    2016-07-01

    Expression of fission yeast Pho1 acid phosphatase is repressed during growth in phosphate-rich medium. Repression is mediated by transcription of the prt locus upstream of pho1 to produce a long noncoding (lnc) prt RNA. Repression is also governed by RNA polymerase II CTD phosphorylation status, whereby inability to place a Ser7-PO4 mark (as in S7A) derepresses Pho1 expression, and inability to place a Thr4-PO4 mark (as in T4A) hyper-represses Pho1 in phosphate replete cells. Here we find that basal pho1 expression from the prt-pho1 locus is inversely correlated with the activity of the prt promoter, which resides in a 110-nucleotide DNA segment preceding the prt transcription start site. CTD mutations S7A and T4A had no effect on the activity of the prt promoter or the pho1 promoter, suggesting that S7A and T4A affect post-initiation events in prt lncRNA synthesis that make it less and more repressive of pho1, respectively. prt lncRNA contains clusters of DSR (determinant of selective removal) sequences recognized by the YTH-domain-containing protein Mmi1. Altering the nucleobase sequence of two DSR clusters in the prt lncRNA caused hyper-repression of pho1 in phosphate replete cells, concomitant with increased levels of the prt transcript. The isolated Mmi1 YTH domain binds to RNAs with single or tandem DSR elements, to the latter in a noncooperative fashion. We report the 1.75 Å crystal structure of the Mmi1 YTH domain and provide evidence that Mmi1 recognizes DSR RNA via a binding mode distinct from that of structurally homologous YTH proteins that recognize m(6)A-modified RNA.

  19. Selective Plasmon-Exciton Coupling in Nonradiative Energy Transfer: Donor-Selective versus Acceptor-Selective

    NASA Astrophysics Data System (ADS)

    Hernandez-Martinez, Pedro Ludwig; Ozel, Tuncay; Mutlugun, Evren; Akin, Onur; Nizamoglu, Sedat; Ozel, Ilkem Ozge; Zhang, Qing; Xiong, Qihua; Demir, Hilmi Volkan

    2014-03-01

    We report selectively plasmon-mediated nonradiative energy transfer between quantum dot (QD) emitters interacting with each other via Förster-type resonance energy transfer (FRET) under controlled plasmon coupling either to only the donor QDs or to only the acceptor QDs. The comparative results of theoretical modelling of the donor- and acceptor selective plasmon-exciton coupling of nonradiative energy transfer is presented. Here, we demonstrate the ability to enable/disable the coupled plasmon-exciton formation distinctly at the donor site or at the acceptor site of our choice. In the case of donor-selective plasmon-exciton coupling, we observed a substantial shortening in the donor QD lifetime from 1.33 to 0.29 ns as a result of plasmon-coupling to the donors and the FRET-assisted exciton transfer from the donors to the acceptors. This enhances the acceptor emission by a factor of 1.93. In the complementary case, we observed a 2.70-fold emission enhancement in the acceptor QDs as a result of the combined effects of the acceptor plasmon coupling and the FRET-assisted exciton feeding. Our theoretical results are in good agreement with the systematic experimental characterization. Bilkent University.

  20. Bright Solid-State Emission of Disilane-Bridged Donor-Acceptor-Donor and Acceptor-Donor-Acceptor Chromophores.

    PubMed

    Shimada, Masaki; Tsuchiya, Mizuho; Sakamoto, Ryota; Yamanoi, Yoshinori; Nishibori, Eiji; Sugimoto, Kunihisa; Nishihara, Hiroshi

    2016-02-24

    The development of disilane-bridged donor-acceptor-donor (D-Si-Si-A-Si-Si-D) and acceptor-donor-acceptor (A-Si-Si-D-Si-Si-A) compounds is described. Both types of compound showed strong emission (λem =ca. 500 and ca. 400 nm, respectively) in the solid state with high quantum yields (Φ: up to 0.85). Compound 4 exhibited aggregation-induced emission enhancement in solution. X-ray diffraction revealed that the crystal structures of 2, 4, and 12 had no intermolecular π-π interactions to suppress the nonradiative transition in the solid state.

  1. Differences in gene expression of human xylosyltransferases and determination of acceptor specificities for various proteoglycans

    SciTech Connect

    Roch, Christina; Kuhn, Joachim; Kleesiek, Knut; Goetting, Christian

    2010-01-01

    The xylosyltransferase (XT) isoforms XT-I and XT-II initiate the posttranslational glycosaminoglycan (GAG) synthesis. Here, we determined the relative expression of both isoforms in 33 human cell lines. The majority of tested cell lines showed dominant XYLT2 gene expression, while only in 23132/87, JAR, NCI-H510A and THP-1 was the XT-I mRNA expression higher. Nearly equal expression levels were detected in six cell lines. Additionally, to shed light on putative differences in acceptor specificities the acceptor properties of potential acceptor sequences were determined. Peptides were expressed as glutathione-S-transferase fusion proteins containing putative or known GAG attachment sites of in vivo proteoglycans. Kinetic analysis showed that K{sub m} and V{sub max} values for XT-I mediated xylosylation were slightly higher than those for XT-II, and that XT-I showed a lesser stringency concerning the acceptor sequence. Mutagenesis of the bikunin peptide sequence in the G-S-G attachment site and flanking regions generated potential acceptor molecules. Here, mutations on the N-terminal side and the attachment site were found to be more susceptible to a loss of acceptor function than mutations in the C-terminus. Altogether the known consensus sequence a-a-a-a-G-S-G-a-a/G-a ('a' representing Asp or Glu) for XT-I mediated xylosylation could be approved and additionally extended to apply to XT-II as well.

  2. Functional characterization of the phosphorylating D-glyceraldehyde 3-phosphate dehydrogenase from the archaeon Methanothermus fervidus by comparative molecular modelling and site-directed mutagenesis.

    PubMed

    Talfournier, F; Colloc'h, N; Mornon, J P; Branlant, G

    1999-10-01

    Phosphorylating archaeal D-glyceraldehyde 3-phosphate dehydrogenases (GraP-DHs) share only 15-20% identity with their glycolytic bacterial and eukaryotic counterparts. Unlike the latter which are NAD-specific, archaeal GraP-DHs exhibit a dual-cofactor specificity with a marked preference for NADP. In the present study, we have constructed a three-dimensional model of the Methanothermus fervidus GraP-DH based upon the X-ray structures of the Bacillus stearothermophilus and Escherichia coli GraP-DHs. The overall structure of the archaeal enzyme is globally similar to homology modelling-derived structures, in particular for the cofactor binding domain, which might adopt a classical Rossmann fold. M. fervidus GraP-DH can be considered as a dimer of dimers which exhibits negative and positive cooperativity in binding the coenzymes NAD and NADP, respectively. As expected, the differences between the model and the templates are located mainly within the loops. Based on the predictions derived from molecular modelling, site-directed mutagenesis was performed to characterize better the cofactor binding pocket and the catalytic domain. The Lys32Ala, Lys32Glu and Lys32Asp mutants led to a drastic increase in the Km value for NADP (i.e. 165-, 500- and 1000-fold, respectively), thus demonstrating that the invariant Lys32 residue is one of the most important determinants favouring the adenosine 2'-PO42- binding of NADP. The involvement of the side chain of Asn281, which was postulated to play a role equivalent to that of the Asn313 of bacterial and eukaryotic GraP-DHs in fixing the position of the nicotinamide ring in a syn orientation [Fabry, S. & Hensel, R. (1988) Gene 64, 189-197], was ruled out. Most of the amino acids involved in catalysis and in substrate recognition in bacterial and eukaryotic GraP-DHs are not conserved in the archaeal enzyme except for the essential Cys149. Inspection of our model suggests that side chains of invariant residues Asn150, Arg176, Arg177 and

  3. Synthetic CO.sub.2 acceptor

    DOEpatents

    Lancet, Michael S.; Curran, George P.

    1981-08-18

    A synthetic CO.sub.2 acceptor consisting essentially of at least one compound selected from the group consisting of calcium oxide and calcium carbonate supported in a refractory carrier matrix, the carrier having the general formula Ca.sub.5 (SiO.sub.4).sub.2 CO.sub.3. A method for producing the synthetic CO.sub.2 acceptor is also disclosed.

  4. Mechanisms of electron acceptor utilization: Implications for simulating anaerobic biodegradation

    USGS Publications Warehouse

    Schreiber, M.E.; Carey, G.R.; Feinstein, D.T.; Bahr, J.M.

    2004-01-01

    Simulation of biodegradation reactions within a reactive transport framework requires information on mechanisms of terminal electron acceptor processes (TEAPs). In initial modeling efforts, TEAPs were approximated as occurring sequentially, with the highest energy-yielding electron acceptors (e.g. oxygen) consumed before those that yield less energy (e.g., sulfate). Within this framework in a steady state plume, sequential electron acceptor utilization would theoretically produce methane at an organic-rich source and Fe(II) further downgradient, resulting in a limited zone of Fe(II) and methane overlap. However, contaminant plumes often display much more extensive zones of overlapping Fe(II) and methane. The extensive overlap could be caused by several abiotic and biotic processes including vertical mixing of byproducts in long-screened monitoring wells, adsorption of Fe(II) onto aquifer solids, or microscale heterogeneity in Fe(III) concentrations. Alternatively, the overlap could be due to simultaneous utilization of terminal electron acceptors. Because biodegradation rates are controlled by TEAPs, evaluating the mechanisms of electron acceptor utilization is critical for improving prediction of contaminant mass losses due to biodegradation. Using BioRedox-MT3DMS, a three-dimensional, multi-species reactive transport code, we simulated the current configurations of a BTEX plume and TEAP zones at a petroleum- contaminated field site in Wisconsin. Simulation results suggest that BTEX mass loss due to biodegradation is greatest under oxygen-reducing conditions, with smaller but similar contributions to mass loss from biodegradation under Fe(III)-reducing, sulfate-reducing, and methanogenic conditions. Results of sensitivity calculations document that BTEX losses due to biodegradation are most sensitive to the age of the plume, while the shape of the BTEX plume is most sensitive to effective porosity and rate constants for biodegradation under Fe(III)-reducing and

  5. A specific variant of the PHR1 binding site is highly enriched in the Arabidopsis phosphate-responsive phospholipase DZ2 coexpression network.

    PubMed

    Acevedo-Hernández, Gustavo; Oropeza-Aburto, Araceli; Herrera-Estrella, Luis

    2012-08-01

    PLDZ2 is a member of the Arabidopsis phospholipase D gene family that is induced in both shoot and root in response to phosphate (Pi) starvation. Recently, through deletion and gain-of-function analyses of the PLDZ2 promoter, we identified a 65 bp region (denominated enhancer EZ2) capable of conferring tissue-specific and low-Pi responses to a minimal inactive promoter. The EZ2 element contains two P1BS motifs, each of which is the binding site for PHR1 and related transcription factors. This structural organization is evolutionarily conserved in orthologous promoters within the rosid clade. To determine whether EZ2 is significantly over-represented in Arabidopsis genes coexpressed with PLDZ2, we constructed a PLDZ2 coexpression network containing 26 genes, almost half of them encoding enzymes or regulatory proteins involved in Pi recycling. A variant of the P1BS motif was found to be highly enriched in the promoter regions of these coexpressed genes, showing an EZ2-like arrangement in seven of them. No other motifs were significantly enriched. The over-representation of the EZ2 arrangement of P1BS motifs in the promoters of genes coexpressed with PLDZ2, suggests this unit has a particularly important role as a regulatory element in a coexpression network involved in the release of Pi from phospholipids and other molecules under Pi-limiting conditions.

  6. A specific variant of the PHR1 binding site is highly enriched in the Arabidopsis phosphate-responsive phospholipase DZ2 coexpression network

    PubMed Central

    Acevedo-Hernández, Gustavo; Oropeza-Aburto, Araceli; Herrera-Estrella, Luis

    2012-01-01

    PLDZ2 is a member of the Arabidopsis phospholipase D gene family that is induced in both shoot and root in response to phosphate (Pi) starvation. Recently, through deletion and gain-of-function analyses of the PLDZ2 promoter, we identified a 65 bp region (denominated enhancer EZ2) capable of conferring tissue-specific and low-Pi responses to a minimal inactive promoter. The EZ2 element contains two P1BS motifs, each of which is the binding site for PHR1 and related transcription factors. This structural organization is evolutionarily conserved in orthologous promoters within the rosid clade. To determine whether EZ2 is significantly over-represented in Arabidopsis genes coexpressed with PLDZ2, we constructed a PLDZ2 coexpression network containing 26 genes, almost half of them encoding enzymes or regulatory proteins involved in Pi recycling. A variant of the P1BS motif was found to be highly enriched in the promoter regions of these coexpressed genes, showing an EZ2-like arrangement in seven of them. No other motifs were significantly enriched. The over-representation of the EZ2 arrangement of P1BS motifs in the promoters of genes coexpressed with PLDZ2, suggests this unit has a particularly important role as a regulatory element in a coexpression network involved in the release of Pi from phospholipids and other molecules under Pi-limiting conditions. PMID:22836502

  7. Mutational analysis of the catalytic and feedback sites of the tryptophan-sensitive 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase of Escherichia coli.

    PubMed Central

    Ray, J M; Yanofsky, C; Bauerle, R

    1988-01-01

    The nucleotide sequence of aroH, the structural gene for the tryptophan-sensitive 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase [DAHPS(Trp)], is presented, and the deduced amino acid sequence of AroH is compared with that of the tyrosine-sensitive (AroF) and phenylalanine-sensitive (AroG) DAHPS isoenzymes. The high degree of sequence similarity among the three isoenzymes strongly indicates that they have a common evolutionary origin. In vitro chemical mutagenesis of the cloned aroH gene was used to identify residues and regions of the polypeptide essential for catalytic activity and for tryptophan feedback regulation. Missense mutations leading either to loss of catalytic activity or to feedback resistance were found interspersed throughout the polypeptide, suggesting overlapping catalytic and regulatory sites in DAHPS(Trp). We conclude that the specificity of feedback regulation of the isoenzymes was probably acquired by the duplication and divergent evolution of an ancestral gene, rather than by domain recruitment. PMID:2903857

  8. A Comparison of the Process of Remodeling of Hydroxyapatite/Poly-D/L-Lactide and Beta-Tricalcium Phosphate in a Loading Site

    PubMed Central

    Akagi, Hiroyuki; Ochi, Hiroki; Soeta, Satoshi; Kanno, Nobuo; Yoshihara, Megumi; Okazaki, Kenshi; Yogo, Takuya; Harada, Yasuji; Amasaki, Hajime; Hara, Yasushi

    2015-01-01

    Currently, the most commonly used bioresorbable scaffold is made of beta-tricalcium phosphate (β-TCP); it is hoped that scaffolds made of a mixture of hydroxyapatite (HA) and poly-D/L-lactide (PDLLA) will be able to act as novel bioresorbable scaffolds. The aim of this study was to evaluate the utility of a HA/PDLLA scaffold compared to β-TCP, at a loading site. Dogs underwent surgery to replace a section of tibial bone with a bioresorbable scaffold. After the follow-up period, the scaffold was subjected to histological analysis. The HA/PDLLA scaffold showed similar bone formation and superior cell and tissue infiltration compared to the β-TCP scaffold, as seen after Villanueva Goldner staining. Moreover, silver staining and immunohistochemistry for Von Willebrand factor and cathepsin K demonstrated better cell infiltration in the HA/PDLLA scaffold. The fibrous tissue and cells that had infiltrated into the HA/PDLLA scaffold tested positive for collagen type I and RUNX2, respectively, indicating that the tissue and cells that had infiltrated into the HA/PDLLA scaffold had the potential to differentiate into bone. The HA/PDLLA scaffold is therefore likely to find clinical application as a new bioresorbable scaffold. PMID:26504825

  9. Structural-functional characterization of the cathodic haemoglobin of the conger eel Conger conger: molecular modelling study of an additional phosphate-binding site.

    PubMed Central

    Pellegrini, Mariagiuseppina; Giardina, Bruno; Verde, Cinzia; Carratore, Vito; Olianas, Alessandra; Sollai, Luigi; Sanna, Maria T; Castagnola, Massimo; di Prisco, Guido

    2003-01-01

    The protein sequence data for the alpha- and beta-chains have been deposited in the SWISS-PROT and TrEMBL protein knowledgebase under the accession numbers P83479 and P83478 respectively. The Conger conger (conger eel) haemoglobin (Hb) system is made of three components, one of which, the so-called cathodic Hb, representing approx. 20% of the total pigment, has been purified and characterized from both a structural and functional point of view. Stripped Hb showed a reverse Bohr effect, high oxygen affinity and slightly low cooperativity in the absence of any effector. Addition of saturating GTP strongly influences the pH dependence of the oxygen affinity, since the reverse Bohr effect, observed under stripped conditions, is converted into a small normal Bohr effect. A further investigation of the GTP effect on oxygen affinity, carried out by fitting its titration curve, demonstrated the presence of two independent binding sites. Therefore, on the basis of the amino acid sequence of the alpha- and beta-chains, which have been determined, a computer modelling study has been performed. The data suggest that C. conger cathodic Hb may bind organic phosphates at two distinct binding sites located along the central cavity of the tetramer by hydrogen bonds and/or electrostatic interactions with amino acid residues of both chains, which have been identified. Among these residues, the two Lys-alpha(G6) (where the letter refers to the haemoglobin helix and the number to the amino acid position in the helix) appear to have a key role in the GTP movement from the external binding region to the internal central cavity of the tetrameric molecule. PMID:12646043

  10. Designing of a novel dextransucrase efficient in acceptor reactions.

    PubMed

    Parlak, Mahmut; Ustek, Duran; Tanriseven, Aziz

    2014-03-11

    Dextransucrase is produced by Leuconostoc, Streptococcus and Lactobacillus Species. The enzyme synthesizes dextran and acceptor products some of which act as prebiotics that are increasingly used in such industries as food, medicine, and cosmetics. B-512F Leuconostoc mesenteroides dextransucrase (DSR-S) is the preferred enzyme in commercial production of dextran and prebiotics. In the present work, a novel dextransucrase which is efficient in prebiotics production was designed. The enzyme was produced at optimal conditions in Escherichia coli by truncation and fusion to glutathione S-transferase (GST) in the gene from Leuconostoc mesenteroides B-512 FMC. The novel enzyme (MW: 119 kDa) was active and carried out dextran biosynthesis and acceptor reactions effectively. The novel dextransucrase (fTDSR-S) was produced by truncating signal, variable, and the glucan-binding regions in the gene and fusion of gst gene at the 5' end. fTDSR-S was characterized in detail and compared to the DSR-S. Truncation and fusion resulted in an increase in fTDSR-S biosynthesis in E. coli BL21 (DE3) by 35 fold. fTDSR-S leads to production of dextran as well as increased acceptor reactions. Due to GST fusion, it was possible to immobilize fTDSR-S covalently onto Eupergit C successfully. It was also found that the size of the active site of dextransucrase is 49 amino acids shorter than that reported previously in the literature. Copyright © 2014 Elsevier Ltd. All rights reserved.

  11. Statistical analysis of mammalian pre-mRNA splicing sites.

    PubMed Central

    Gelfand, M S

    1989-01-01

    222 donor and 222 acceptor (including 206 pairs) non-homologous splicing sites were studied. Well known features of these were confirmed and some novel observations were made. It is (1) cCAGGGag signal in (-60)-(-58) region of acceptor sites; (2) strong complementarity between regions (-69)-(-55) and (-36)-(-22) of some of the acceptor sites, and (3) small but statistically significant correlation between discrimination energies of corresponding donor and acceptor sites. PMID:2528123

  12. Electron paramagnetic resonance study of neutral Mg acceptors in β-Ga2O3 crystals

    NASA Astrophysics Data System (ADS)

    Kananen, B. E.; Halliburton, L. E.; Scherrer, E. M.; Stevens, K. T.; Foundos, G. K.; Chang, K. B.; Giles, N. C.

    2017-08-01

    Electron paramagnetic resonance (EPR) is used to directly observe and characterize neutral Mg acceptors ( M gGa0 ) in a β-Ga2O3 crystal. These acceptors, best considered as small polarons, are produced when the Mg-doped crystal is irradiated at or near 77 K with x rays. During the irradiation, neutral acceptors are formed when holes are trapped at singly ionized Mg acceptors ( M gGa- ). Unintentionally present Fe3+ (3d5) and Cr3+ (3d3) transition-metal ions serve as the corresponding electron traps. The hole is localized in a nonbonding p orbital on a threefold-coordinated oxygen ion adjacent to an Mg ion at a sixfold-coordinated Ga site. These M gGa0 acceptors (S = 1/2) have a slightly anisotropic g matrix (principal values are 2.0038, 2.0153, and 2.0371). There is also partially resolved 69Ga and 71Ga hyperfine structure resulting from unequal interactions with the two Ga ions adjacent to the hole. With the magnetic field along the a direction, hyperfine parameters are 2.61 and 1.18 mT for the 69Ga nuclei at the two inequivalent neighboring Ga sites. The M gGa0 acceptors thermally convert back to their nonparamagnetic M gGa- charge state when the temperature of the crystal is raised above approximately 250 K.

  13. S-glutathionylation of glyceraldehyde-3-phosphate dehydrogenase induces formation of C150-C154 intrasubunit disulfide bond in the active site of the enzyme.

    PubMed

    Barinova, K V; Serebryakova, M V; Muronetz, V I; Schmalhausen, E V

    2017-09-19

    Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a glycolytic protein involved in numerous non-glycolytic functions. S-glutathionylated GAPDH was revealed in plant and animal tissues. The role of GAPDH S-glutathionylation is not fully understood. Rabbit muscle GAPDH was S-glutathionylated in the presence of H2O2 and reduced glutathione (GSH). The modified protein was assayed by MALDI-MS analysis, differential scanning calorimetry, dynamic light scattering, and ultracentrifugation. Incubation of GAPDH in the presence of H2O2 together with GSH resulted in the complete inactivation of the enzyme. In contrast to irreversible oxidation of GAPDH by H2O2, this modification could be reversed in the excess of GSH or dithiothreitol. By data of MALDI-MS analysis, the modified protein contained both mixed disulfide between Cys150 and GSH and the intrasubunit disulfide bond between Cys150 and Cys154 (different subunits of tetrameric GAPDH may contain different products). S-glutathionylation results in loosening of the tertiary structure of GAPDH, decreases its affinity to NAD(+) and thermal stability. The mixed disulfide between Cys150 and GSH is an intermediate product of S-glutathionylation: its subsequent reaction with Cys154 results in the intrasubunit disulfide bond in the active site of GAPDH. The mixed disulfide and the C150-C154 disulfide bond protect GAPDH from irreversible oxidation and can be reduced in the excess of thiols. Conformational changes that were observed in S-glutathionylated GAPDH may affect interactions between GAPDH and other proteins (ligands), suggesting the role of S-glutathionylation in the redox signaling. The manuscript considers one of the possible mechanisms of redox regulation of cell functions. Copyright © 2017 Elsevier B.V. All rights reserved.

  14. Donor acceptor complexes of noble gases.

    PubMed

    Mück, Leonie Anna; Timoshkin, Alexey Y; von Hopffgarten, Moritz; Frenking, Gernot

    2009-03-25

    Donor-acceptor (DA) complexes of noble gases (Ng) of the general type A <-- Ng <-- D (A = Lewis acid, D = Lewis base) have been theoretically studied using ab initio and DFT methods. Chemical bonding in these compounds is realized via a 3-center 4-electron bond, which is formed by a lone pair of the noble gas, a lone pair of the donor molecule and a vacant orbital of the acceptor molecule. Detailed bonding analysis of the model compounds F(3)Al-Ng-NH(3) reveals that Ng-ammonia interaction is repulsive due to Pauli repulsion. Bonding interaction between Ng and N is mostly electrostatic. In contrast, strong orbital interactions are responsible for the attractive interactions between Ng and AlF(3). Due to the repulsive interactions with the donor molecule and a sizable reorganization energy of the acceptor molecule, optimization attempts of the A <-- Ng <-- D compounds, which feature individual donor and acceptor molecules, always lead to the dissociation of the complex and eventual formation of free Ng. To overcome this obstacle, the concept of a rigid C(3v) symmetric cryptand-type ligand, which features spacially separated pyramidalized donor and acceptor fragments, is introduced. Such "push-pull" ligands are predicted to exothermically form complexes with noble gases. These are the first examples of the thermodynamically stable Ar and Kr compounds. Application of the push-pull cryptand ligands featuring multiple (two and three) donor-acceptor induced chemical bonds is expected to yield stable complexes with virtually any electron-rich element in the periodic table.

  15. Electron Donor Acceptor Interactions. Final Progress Report

    SciTech Connect

    2002-08-16

    The Gordon Research Conference (GRC) on Electron Donor Acceptor Interactions was held at Salve Regina University, Newport, Rhode Island, 8/11-16/02. Emphasis was placed on current unpublished research and discussion of the future target areas in this field.

  16. Hydration effects on the photoionization energy of 2‧-deoxyguanosine 5‧-phosphate and activation barriers for guanine methylation by carcinogenic methane diazonium ions

    NASA Astrophysics Data System (ADS)

    Eichler, Daniel R.; Hamann, Haley A.; Harte, Katherine A.; Papadantonakis, George A.

    2017-07-01

    Results from DFT calculations indicate that states originating from gas-phase ionization of the phosphate and the base are degenerate in syn-5‧-dGMP- and that bulk hydration lowers the base-localized ionization energy by <0.5 eV. Local ionization maps show that micro-hydration leads to the formation of donor and acceptor hydrogen bonds and the ionization energy decreases or increases in each case respectively. The SN2 transition states of the methylation reactions of guanine with methane diazonium ions are lower at the N7 than at the O6 sites and they are influenced by local ionization energy and steric interference.

  17. Vaccine perception among acceptors and non-acceptors in Sokoto State, Nigeria.

    PubMed

    Murele, Bola; Vaz, Rui; Gasasira, Alex; Mkanda, Pascal; Erbeto, Tesfaye; Okeibunor, Joseph

    2014-05-30

    Vaccine perceptions among acceptors and non-acceptors of childhood vaccination were explored. Seventy-two care givers, among them, acceptors and non-acceptors were interviewed in-depth with an interview guide that assessed vaccine acceptance, social and personality factors, and health belief model (HBM) categories in relation to oral polio vaccine (perceived susceptibility, severity, cost barriers, general barriers, benefits, knowledge, and engagement in preventative health behaviours). Community leaders were purposively selected while parents were selected on the basis of availability while ensuring the different attitude to vaccines was covered. Results showed that the HBM framework was found to be appropriate for identifying and distinguishing vaccine acceptors and non-acceptors. In addition, the HBM categories of benefits and susceptibility were found to influence oral polio vaccine acceptance. Second, the opinion of family members about the oral polio vaccine moderated the relationship between number of social ties and vaccine acceptance. Further, oral polio vaccine acceptance was related to outbreaks of paralysis of any sort, but not aggregate scores of other preventative health behaviours. Implications of this study include the investigation of vaccine acceptance in a high risk population. Research was done to investigate vaccine acceptance. Copyright © 2014 Elsevier Ltd. All rights reserved.

  18. Studies of endogenous UDP-glucose: glycoprotein glucose-1-phosphotransferase acceptors in embryonic chick neural tissues

    SciTech Connect

    Hiller, A.M.S.

    1986-01-01

    UPD-glucose: glycoprotein glucose-1-phosphotransferase (GlcPTase) catalyzes the transfer of a Glc-1-P from UDP-Glc to high mannose-type oligosaccharides on a class of embryonic chick neutral retinal glycoproteins. The primary acceptors for this glycosylphosphotransferase were determined by incubating embryonic chick tissue sonicates with (B-/sup 32/P)UDP-Glc followed by SDS-polyacrylamine gel electrophoresis and autoradiography. The primary GlcPT ase acceptors in brain tissue have apparent subunit molecular weights of 66 and 62 kilodaltons (kd). /sup 32/P incorporation into these peptides was eliminated by excess levels of unlabeled UDP-Glc and unaffected by the inclusion of other phosphate-containing compounds, with the exception of UDP-galactose which can be converted to UDP-Glc by an endogenous epimerase.

  19. Structural analysis of substrate-mimicking inhibitors in complex with Neisseria meningitidis 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase - The importance of accommodating the active site water.

    PubMed

    Heyes, Logan C; Reichau, Sebastian; Cross, Penelope J; Jameson, Geoffrey B; Parker, Emily J

    2014-12-01

    3-Deoxy-d-arabino-heptulosonate 7-phosphate synthase (DAH7PS) catalyses the first committed step of the shikimate pathway, which produces the aromatic amino acids as well as many other aromatic metabolites. DAH7PS catalyses an aldol-like reaction between phosphoenolpyruvate and erythrose 4-phosphate. Three phosphoenolpyruvate mimics, (R)-phospholactate, (S)-phospholactate and vinyl phosphonate [(E)-2-methyl-3-phosphonoacrylate], were found to competitively inhibit DAH7PS from Neisseria meningitidis, which is the pathogen responsible for bacterial meningitis. The most potent inhibitor was the vinyl phosphonate with a Ki value of 3.9±0.4μM. We report for the first time crystal structures of these compounds bound in the active site of a DAH7PS enzyme which reveals that the inhibitors bind to the active site of the enzyme in binding modes that mimic those of the predicted oxocarbenium and tetrahedral intermediates of the enzyme-catalysed reaction. Furthermore, the inhibitors accommodate the binding of a key active site water molecule. Together, these observations provide strong evidence that this active site water participates directly in the DAH7PS reaction, enabling the facial selectivity of the enzyme-catalysed reaction sequence to be delineated.

  20. High Performance Magazine Acceptor Threshold Criteria

    DTIC Science & Technology

    1994-08-01

    detonation transition (DDT). To account for unknown mechanisms the term XDT is also used. Development of a design procedure to prevent SD requires...propagation walls are used to prevent sympathetic detonation between munitions stored in adjacent cells. Design of the walls, and their mitigation...effects, requires sympathetic detonation threshold criteria for acceptor munitions. This paper outlines the procedures being used to develop SD threshold

  1. Fundamentals of phosphate transfer.

    PubMed

    Kirby, Anthony J; Nome, Faruk

    2015-07-21

    Historically, the chemistry of phosphate transfer-a class of reactions fundamental to the chemistry of Life-has been discussed almost exclusively in terms of the nucleophile and the leaving group. Reactivity always depends significantly on both factors; but recent results for reactions of phosphate triesters have shown that it can also depend strongly on the nature of the nonleaving or "spectator" groups. The extreme stabilities of fully ionised mono- and dialkyl phosphate esters can be seen as extensions of the same effect, with one or two triester OR groups replaced by O(-). Our chosen lead reaction is hydrolysis-phosphate transfer to water: because water is the medium in which biological chemistry takes place; because the half-life of a system in water is an accepted basic index of stability; and because the typical mechanisms of hydrolysis, with solvent H2O providing specific molecules to act as nucleophiles and as general acids or bases, are models for reactions involving better nucleophiles and stronger general species catalysts. Not least those available in enzyme active sites. Alkyl monoester dianions compete with alkyl diester monoanions for the slowest estimated rates of spontaneous hydrolysis. High stability at physiological pH is a vital factor in the biological roles of organic phosphates, but a significant limitation for experimental investigations. Almost all kinetic measurements of phosphate transfer reactions involving mono- and diesters have been followed by UV-visible spectroscopy using activated systems, conveniently compounds with good leaving groups. (A "good leaving group" OR* is electron-withdrawing, and can be displaced to generate an anion R*O(-) in water near pH 7.) Reactivities at normal temperatures of P-O-alkyl derivatives-better models for typical biological substrates-have typically had to be estimated: by extended extrapolation from linear free energy relationships, or from rate measurements at high temperatures. Calculation is free

  2. Contact effects on electronic transport in donor-bridge-acceptor complexes interacting with a thermal bath.

    PubMed

    Volkovich, Roie; Peskin, Uri

    2006-12-28

    A model for electron transfer in donor-bridge-acceptor complexes with electronic coupling to nuclear bridge modes is studied using the Redfield formulation. We demonstrate that the transport mechanism through the molecular bridge is controlled by the location of the electronic-nuclear coupling term along the bridge. As the electronic-nuclear coupling term is shifted from the donor/acceptor-bridge contact sites into the bridge, the mechanism changes from kinetic transport (incoherent, thermally activated, and bridge-length independent) to coherent tunneling oscillations. This study joins earlier works aiming to explore the factors which control the mechanism of electronic transport through molecular bridges and molecular wires.

  3. Observation of selective plasmon-exciton coupling in nonradiative energy transfer: donor-selective versus acceptor-selective plexcitons.

    PubMed

    Ozel, Tuncay; Hernandez-Martinez, Pedro Ludwig; Mutlugun, Evren; Akin, Onur; Nizamoglu, Sedat; Ozel, Ilkem Ozge; Zhang, Qing; Xiong, Qihua; Demir, Hilmi Volkan

    2013-07-10

    We report selectively plasmon-mediated nonradiative energy transfer between quantum dot (QD) emitters interacting with each other via Förster-type resonance energy transfer (FRET) under controlled plasmon coupling either to only the donor QDs (i.e., donor-selective) or to only the acceptor QDs (i.e., acceptor-selective). Using layer-by-layer assembled colloidal QD nanocrystal solids with metal nanoparticles integrated at carefully designed spacing, we demonstrate the ability to enable/disable the coupled plasmon-exciton (plexciton) formation distinctly at the donor (exciton departing) site or at the acceptor (exciton feeding) site of our choice, while not hindering the donor exciton-acceptor exciton interaction but refraining from simultaneous coupling to both sites of the donor and the acceptor in the FRET process. In the case of donor-selective plexciton, we observed a substantial shortening in the donor QD lifetime from 1.33 to 0.29 ns as a result of plasmon-coupling to the donors and the FRET-assisted exciton transfer from the donors to the acceptors, both of which shorten the donor lifetime. This consequently enhanced the acceptor emission by a factor of 1.93. On the other hand, in the complementary case of acceptor-selective plexciton we observed a 2.70-fold emission enhancement in the acceptor QDs, larger than the acceptor emission enhancement of the donor-selective plexciton, as a result of the combined effects of the acceptor plasmon coupling and the FRET-assisted exciton feeding. Here we present the comparative results of theoretical modeling of the donor- and acceptor-selective plexcitons of nonradiative energy transfer developed here for the first time, which are in excellent agreement with the systematic experimental characterization. Such an ability to modify and control energy transfer through mastering plexcitons is of fundamental importance, opening up new applications for quantum dot embedded plexciton devices along with the development of new

  4. Imprinting of molecular recognition sites combined with π-donor-acceptor interactions using bis-aniline-crosslinked Au-CdSe/ZnS nanoparticles array on electrodes: Development of electrochemiluminescence sensor for the ultrasensitive and selective detection of 2-methyl-4-chlorophenoxyacetic acid.

    PubMed

    Yang, Yukun; Fang, Guozhen; Wang, Xiaomin; Liu, Guiyang; Wang, Shuo

    2016-03-15

    A novel strategy is reported for the fabrication of bis-aniline-crosslinked Au nanoparticles (NPs)-CdSe/ZnS quantum dots (QDs) array composite by facil one-step co-electropolymerization of thioaniline-functionalized AuNPs and thioaniline-functionalized CdSe/ZnS QDs onto thioaniline-functionalized Au elctrodes (AuE). Stable and enhanced cathodic electrochemiluminescence (ECL) of CdSe/ZnS QDs is observed on the modified electrode in neutral solution, suggesting promising applications in ECL sensing. An advanced ECL sensor is explored for detection of 2-methyl-4-chlorophenoxyacetic acid (MCPA) which quenches the ECL signal through electron-transfer pathway. The sensitive determination of MCPA with limit of detection (LOD) of 2.2 nmolL(-1) (S/N=3) is achieved by π-donor-acceptor interactions between MCPA and the bis-aniline bridging units. Impressively, the imprinting of molecular recognition sites into the bis-aniline-crosslinked AuNPs-CdSe/ZnS QDs array yields a functionalized electrode with an extremely sensitive response to MCPA in a linear range of 10 pmolL(-1)-50 μmolL(-1) with a LOD of 4.3 pmolL(-1 ()S/N=3). The proposed ECL sensor with high sensitivity, good selectivity, reproducibility and stability has been successfully applied for the determination of MCPA in real samples with satisfactory recoveries. In this study, ECL sensor combined the merits of QDs-ECL and molecularly imprinting technology is reported for the first time. The developed ECL sensor holds great promise for the fabrication of QDs-based ECL sensors with improved sensitivity and furthermore opens the door to wide applications of QDs-based ECL in food safety and environmental monitoring.

  5. Ultrafast Non-Förster Intramolecular Donor-Acceptor Excitation Energy Transfer.

    PubMed

    Athanasopoulos, Stavros; Alfonso Hernandez, Laura; Beljonne, David; Fernandez-Alberti, Sebastian; Tretiak, Sergei

    2017-04-06

    Ultrafast intramolecular electronic energy transfer in a conjugated donor-acceptor system is simulated using nonadiabatic excited-state molecular dynamics. After initial site-selective photoexcitation of the donor, transition density localization is monitored throughout the S2 → S1 internal conversion process, revealing an efficient unidirectional donor → acceptor energy-transfer process. Detailed analysis of the excited-state trajectories uncovers several salient features of the energy-transfer dynamics. While a weak temperature dependence is observed during the entire electronic energy relaxation, an ultrafast initially temperature-independent process allows the molecular system to approach the S2-S1 potential energy crossing seam within the first ten femtoseconds. Efficient energy transfer occurs in the absence of spectral overlap between the donor and acceptor units and is assisted by a transient delocalization phenomenon of the excited-state wave function acquiring Frenkel-exciton character at the moment of quantum transition.

  6. Identification of a Deep Acceptor Level in ZnO Due to Silver Doping

    NASA Astrophysics Data System (ADS)

    Chai, J.; Mendelsberg, R. J.; Reeves, R. J.; Kennedy, J.; von Wenckstern, H.; Schmidt, M.; Grundmann, M.; Doyle, K.; Myers, T. H.; Durbin, S. M.

    2010-05-01

    There remains considerable interest in the behavior of acceptors in ZnO, the ultimate goal being the realization of device grade p-type material. Silver is a candidate acceptor, and, in this study, in situ doping of silver was performed during plasma-assisted molecular beam epitaxy. Silver concentrations, as determined by ion beam analysis, ranged between 1018 cm-3and 1020 cm-3, with as much as 94% incorporated substitutionally on Zn lattice sites. Variable magnetic field Hall effect measurements detected no evidence of holes, and 4 K photoluminescence was dominated by donor bound excitons. Transient capacitance measurements, however, suggested that incorporated silver had led to the formation of an acceptor, located approximately 320 meV above the valence band edge, indicating that compensation remains a significant issue in determining the conductivity of ZnO.

  7. Enhanced biodegradation of cyclotetramethylenetetranitramine (HMX) under mixed electron-acceptor condition.

    PubMed

    Boopathy, R

    2001-02-01

    The biodegradation of cyclotetramethylenetetranitramine, commonly known as 'high melting explosive' (HMX), under various electron-acceptor conditions was investigated using enrichment cultures developed from the anaerobic digester sludge of Thibodaux sewage treatment plant. The results indicated that the HMX was biodegraded under sulfate reducing, nitrate reducing, fermenting, methanogenic, and mixed electron accepting conditions. However, the rates of degradation varied among the various conditions studied. The fastest removal of HMX (from 22 ppm on day 0 to < 0.05 ppm on day 11) was observed under mixed electron-acceptor conditions, followed in order by sulfate reducing, fermenting, methanogenic, and nitrate reducing conditions. Under aerobic conditions, HMX was not biodegraded, which indicated that HMX degradation takes place under anaerobic conditions via reduction. HMX was converted to methanol and chloroform under mixed electron-acceptor conditions. This study showed evidence for HMX degradation under anaerobic conditions in a mixed microbial population system similar to any contaminated field sites, where a heterogeneous population exists.

  8. Molecular nitrogen acceptors in ZnO nanowires induced by nitrogen plasma annealing

    NASA Astrophysics Data System (ADS)

    Ton-That, C.; Zhu, L.; Lockrey, M. N.; Phillips, M. R.; Cowie, B. C. C.; Tadich, A.; Thomsen, L.; Khachadorian, S.; Schlichting, S.; Jankowski, N.; Hoffmann, A.

    2015-07-01

    X-ray absorption near-edge spectroscopy, photoluminescence, cathodoluminescence, and Raman spectroscopy have been used to investigate the chemical states of nitrogen dopants in ZnO nanowires. It is found that nitrogen exists in multiple states: NO,NZn, and loosely bound N2 molecule. The results establish a direct link between a donor-acceptor pair emission at 3.232 eV and the concentration of loosely bound N2. This work confirms that N2 at Zn site is a potential candidate for producing a shallow acceptor state in N-doped ZnO as theoretically predicted by Lambrecht and Boonchun [Phys. Rev. B 87, 195207 (2013), 10.1103/PhysRevB.87.195207]. Additionally, shallow acceptor states arising from NO complexes have been ruled out in this paper.

  9. Vibrational-mode theory of acceptor-hydrogen complexes in silicon

    NASA Astrophysics Data System (ADS)

    da Silva, E. C. F.; Assali, L. V. C.; Leite, J. R.; dal Pino, A., Jr.

    1988-02-01

    The vibrational properties of the acceptor-hydrogen complexes, for the acceptors B, Al, and Ga, in Si have been investigated within the framework of the Assali and Leite model proposed for the microscopic structure of the complexes [Phys. Rev. Lett. 55, 980 (1985)]. The A1 and E vibrational modes of the complexes were studied by using a molecular cluster embedded in a rigid Si lattice, where H at an interstitial site is connected to its three Si and the acceptor nearest neighbors by spring force constants of variable strength. It is shown that the model reproduces all the vibrational energies of the hydrogen- and deuterium-related complexes measured so far. Indeed, the model is used to predict several new values of vibrational energies associated to these complexes.

  10. Photoinduced Electron Transfer within Supramolecular Donor-Acceptor Peptide Nanostructures under Aqueous Conditions.

    PubMed

    Sanders, Allix M; Magnanelli, Timothy J; Bragg, Arthur E; Tovar, John D

    2016-03-16

    We report the synthesis, self-assembly, and electron transfer capabilities of peptide-based electron donor-acceptor molecules and supramolecular nanostructures. These modified peptides contain π-conjugated oligothiophene electron donor cores that are peripherally substituted with naphthalene diimide electron acceptors installed via imidation of site-specific lysine residues. These molecules self-assemble into one-dimensional nanostructures in aqueous media, as shown through steady-state absorption, photoluminescence, and circular dichroism spectra, as well as transmission electron microscopy. Excitation of the oligothiophene donor moieties results in electron transfer to the acceptor units, ultimately creating polar, charge-separated states that persist for over a nanosecond as observed with transient absorption spectroscopy. This study demonstrates how transient electric fields can be engineered into aqueous nanomaterials of biomedical relevance through external, temporally controlled photonic inputs.

  11. Photoionization in micelles: Addition of charged electron acceptors

    NASA Astrophysics Data System (ADS)

    Stenland, Chris; Kevan, Larry

    The relative photoyield of the electron donor N, N, N', N'-tetramethylbenzidine (TMB), solubilized in sodium and lithium dodecyl sulfate micelles with added charged electron acceptors was investigated. It was attempted to control the acceptor distance from a charged micellar interface by differently charged acceptors, cationic dimethyl viologen and anionic ferricyanide. However, back electron transfer from both cationic and anionic acceptors was found to be efficient. Thus simple electrostatic arguments for control of the photoyield do not seem applicable. Salt effects associated with the added ionic acceptors which partially neutralize the ionic micellar interface are suggested to be an important factor.

  12. Prediction of the Intrinsic Hydrogen Bond Acceptor Strength of Chemical Substances from Molecular Structure

    NASA Astrophysics Data System (ADS)

    Schwöbel, Johannes; Ebert, Ralf-Uwe; Kühne, Ralph; Schüürmann, Gerrit

    2009-08-01

    Hydrogen bonding affects the partitioning of organic compounds between environmental and biological compartments as well as the three-dimensional shape of macromolecules. Using the semiempirical quantum chemical AM1 level of calculation, we have developed a model to predict the site-specific hydrogen bond (HB) acceptor strength from ground-state properties of the individual compounds. At present, the model parametrization is confined to compounds with one HB acceptor site of the following atom types: N, O, S, F, Cl, and Br that act as lone-pair HB acceptors, and π-electron (aromatic or conjugated) systems with the associated C atoms as particularly weak HB acceptors. The HB acceptor strength is expressed in terms of the Abraham parameter B and calculated from local molecular parameters, taking into account electrostatic, polarizability, and charge transfer contributions according to the Morokuma concept. For a data set of 383 compounds, the squared correlation coefficient r2 is 0.97 when electrostatic potential (ESP) derived net atomic charges are employed, and the root-mean-square (rms) error is 0.04 that is in the range of experimental uncertainty. The model is validated using an extended leave-50%-out approach, and its performance is comparatively analyzed with the ones of earlier introduced ab initio (HF/6-31G**) and density functional theory (B3LYP/6-31G**) models as well as of two increment methods with respect to the total compound set as well as HB acceptor type subsets. The discussion includes an explorative model application to amides and organophosphates that demonstrates the robustness of the approach, and further opportunities for model extensions.

  13. Binomial distribution-based quantitative measurement of multiple-acceptors fluorescence resonance energy transfer by partially photobleaching acceptor

    NASA Astrophysics Data System (ADS)

    Zhang, Lili; Yu, Huaina; Zhang, Jianwei; Chen, Tongsheng

    2014-06-01

    We report that binomial distribution depending on acceptor photobleaching degree can be used to characterize the proportions of various kinds of FRET (Fluorescence Resonance Energy Transfer) constructs resulted from partial acceptor photobleaching of multiple-acceptors FRET system. On this basis, we set up a rigorous quantitation theory for multiple-acceptors FRET construct named as Mb-PbFRET which is not affected by the imaging conditions and fluorophore properties. We experimentally validate Mb-PbFRET with FRET constructs consisted of one donor and two or three acceptors inside living cells on confocal and wide-field microscopes.

  14. Donor-acceptor pair recombination in gallium sulfide

    NASA Astrophysics Data System (ADS)

    Aydinli, A.; Gasanly, N. M.; Gökşen, K.

    2000-12-01

    Low temperature photoluminescence of GaS single crystals shows three broad emission bands below 2.4 eV. Temperature and excitation light intensity dependencies of these bands reveal that all of them originate from close donor-acceptor pair recombination processes. Temperature dependence of the peak energies of two of these bands in the visible range follow, as expected, the band gap energy shift of GaS. However, the temperature dependence of the peak energy of the third band in the near infrared shows complex behavior by blueshifting at low temperatures followed by a redshift at intermediate temperatures and a second blueshift close to room temperature, which could only be explained via a configuration coordinate model. A simple model calculation indicates that the recombination centers are most likely located at the nearest neighbor lattice or interstitial sites.

  15. Alkyl Chlorides as Hydrogen Bond Acceptors

    SciTech Connect

    Nadas, Janos I; Vukovic, Sinisa; Hay, Benjamin

    2012-01-01

    To gain an understanding of the role of an alkyl chloride as a hydrogen bond acceptor, geometries and interaction energies were calculated at the MP2/aug-cc-pVDZ level of theory for complexes between ethyl chloride and representative hydrogen donor groups. The results establish that these donors, which include hydrogen cyanide, methanol, nitrobenzene, pyrrole, acetamide, and N-methylurea, form X-H {hor_ellipsis} Cl hydrogen bonds (X = C, N, O) of weak to moderate strength, with {Delta}E values ranging from -2.8 to -5.3 kcal/mol.

  16. Ga(III) complexes as models for the M(III) site of purple acid phosphatase: ligand effects on the hydrolytic reactivity toward bis(2,4-dinitrophenyl) phosphate.

    PubMed

    Coleman, Fergal; Hynes, Michael J; Erxleben, Andrea

    2010-07-19

    The effects of a series of Ga(III) complexes with tripodal ligands on the hydrolysis rate of the activated phosphate diester bis(2,4-dinitrophenyl)phosphate (BDNPP) have been investigated. In particular, the influence of the nature of the ligand donor sites on the reactivity of Ga(III) which represents a mimic of the Fe(III) ion in purple acid phosphatase has been evaluated. It has been shown that replacing neutral nitrogen donor atoms and carboxylate groups by phenolate groups enhanced the reactivity of the Ga complexes. Bell-shaped pH-rate profiles and the measured solvent deuterium isotope effects are indicative of a mechanism that involves nucleophilic attack on the coordinated substrate by Ga-OH. The trend in reactivity found for the different Ga complexes reveals that of the two effects of the metal, Lewis acid activation of the substrate and nucleophile activation, the latter one is more important in determining the intrinsic reactivity of the metal catalyst. The relevance of the present findings for the modulation of the activity of the M(III) ion in purple acid phosphatase whose active site contains a phenolate (tyrosine side chain) is discussed.

  17. Effects of kinase inhibitors and potassium phosphate (KPi) on site-specific phosphorylation of branched chain. cap alpha. -ketoacid dehydrogenase (BCKDH)

    SciTech Connect

    Kuntz, M.J.; Shimomura, Y.; Ozawa, T.; Harris, R.A.

    1987-05-01

    BCKDH is phosphorylated by a copurifying kinase at two serine residues on the El..cap alpha.. subunit. Phosphorylation of both sites occurs at about the same rate initially, but inactivation is believed associated only with site 1 phosphorylation. The effects of KPi and known inhibitors of BCKDH kinase, ..cap alpha..-chloroisocaproate (CIC) and branched chain ..cap alpha..-ketoacids (BCKA), on the phosphorylation of purified rat liver BCKDH were studied. Site-specific phosphorylation was quantitated by thin-layer electrophoresis of tryptic peptides followed by densitometric scanning of autoradiograms. Addition of 5 mM KPi was found necessary to stabilize the BCKDH activity at 37/sup 0/C. Increasing the KPi to 50 mM dramatically increased the CIC and BCKA inhibition of site 1 and site 2 phosphorylation. The finding of enhanced sensitivity of inhibitors with 50 mM KPi may facilitate identification of physiologically important kinase effectors. Regardless of the KPi concentration, CIC and the BCKA showed much more effective inhibition of site 2 than site 1 phosphorylation. Although site 1 is the primary inactivating site, predominant inhibition of site 2 phosphorylation may provide a means of modulating kinase/phosphatase control of BCKDH activity under steady state conditions.

  18. Towards building artificial light harvesting complexes: enhanced singlet-singlet energy transfer between donor and acceptor pairs bound to albumins.

    PubMed

    Kumar, Challa V; Duff, Michael R

    2008-12-01

    Specific donor and acceptor pairs have been assembled in bovine serum albumin (BSA), at neutral pH and room temperature, and these dye-protein complexes indicated efficient donor to acceptor singlet-singlet energy transfer. For example, pyrene-1-butyric acid served as the donor and Coumarin 540A served as the acceptor. Both the donor and the acceptor bind to BSA with affinity constants in excess of 2x10(5) M(-1), as measured in absorption and circular dichroism (CD) spectral titrations. Simultaneous binding of both the donor and the acceptor chromophores was supported by CD spectra and one chromophore did not displace the other from the protein host, even when limited concentrations of the host were used. For example, a 1:1:1 complex between the donor, acceptor and the host can be readily formed, and spectral data clearly show that the binding sites are mutually exclusive. The ternary complexes (two different ligands bound to the same protein molecule) provided opportunities to examine singlet-singlet energy transfer between the protein-bound chromophores. Donor emission was quenched by the addition of the acceptor, in the presence of limited amounts of BSA, while no energy transfer was observed in the absence of the protein host, under the same conditions. The excitation spectra of the donor-acceptor-host complexes clearly show the sensitization of acceptor emission by the donor. Protein denaturation, as induced by the addition of urea or increasing the temperature to 360 K, inhibited energy transfer, which indicate that protein structure plays an important role. Sensitization also proceeded at low temperature (77 K) and diffusion of the donor or the acceptor is not required for energy transfer. Stern-Volmer quenching plots show that the quenching constant is (3.1+/-0.2)x10(4) M(-1), at low acceptor concentrations (<35 microM). Other albumins such as human and porcine proteins also served as good hosts for the above experiments. For the first time, non

  19. The reaction of choline dehydrogenase with some electron acceptors.

    PubMed Central

    Barrett, M C; Dawson, A P

    1975-01-01

    1. The choline dehydrogenase (EC 1.1.99.1) WAS SOLUBILIZED FROM ACETONE-DRIED POWDERS OF RAT LIVER MITOCHONDRIA BY TREATMENT WITH Naja naja venom. 2. The kinetics of the reaction of enzyme with phenazine methosulphate and ubiquinone-2 as electron acceptors were investigated. 3. With both electron acceptors the reaction mechanism appears to involve a free, modified-enzyme intermediate. 4. With some electron acceptors the maximum velocity of the reaction is independent of the nature of the acceptor. With phenazine methosulphate and ubiquinone-2 as acceptors the Km value for choline is also independent of the nature of the acceptor molecule. 5. The mechanism of the Triton X-100-solubilized enzyme is apparently the smae as that for the snake venom solubilized enzyme. PMID:1218095

  20. The reaction of choline dehydrogenase with some electron acceptors.

    PubMed

    Barrett, M C; Dawson, A P

    1975-12-01

    1. The choline dehydrogenase (EC 1.1.99.1) WAS SOLUBILIZED FROM ACETONE-DRIED POWDERS OF RAT LIVER MITOCHONDRIA BY TREATMENT WITH Naja naja venom. 2. The kinetics of the reaction of enzyme with phenazine methosulphate and ubiquinone-2 as electron acceptors were investigated. 3. With both electron acceptors the reaction mechanism appears to involve a free, modified-enzyme intermediate. 4. With some electron acceptors the maximum velocity of the reaction is independent of the nature of the acceptor. With phenazine methosulphate and ubiquinone-2 as acceptors the Km value for choline is also independent of the nature of the acceptor molecule. 5. The mechanism of the Triton X-100-solubilized enzyme is apparently the smae as that for the snake venom solubilized enzyme.

  1. [Relations between the retinoic acid acceptor and teratogenesis of retinoids].

    PubMed

    Li, Zeng-Gang; Sun, Kai-Lai

    2004-09-01

    Retinoic acid can induce teratogenesis of the fetus of many animals including human, and its biological activities are induced by a serious of different retinoic acid accepters and their ligands. The retinoic acid acceptor RAR plays key roles in the teratogenesis, and the ligands of RAR are strong teratogens. The intensity sequence of the relative teratogenesis is ligandalpha, ligandbeta and ligandgamma. The ligands of the retinoic acid acceptor RXR cannot induce teratogenesis, but they can enhance the teratogenesis of the RAR stimulus. The retinoic acid acceptors can also affect the development of the fetus by adjusting the expression of the other genes. The relations between the gene mutation of the retinoic acid acceptor, various retinoic acid acceptors and their ligands and teratogenesis of retinoic acid are summarized in this article. In addition, the regulations of the retinoic acid acceptors to the other genes are also discussed.

  2. Intramolecular donor-acceptor cyclopropane ring-opening cyclizations.

    PubMed

    Cavitt, Marchello A; Phun, Lien H; France, Stefan

    2014-02-07

    Cyclization reactions of donor-acceptor (D-A) cyclopropanes are recognized as versatile methods for construction of carbocyclic and heterocyclic scaffolds. In the literature, many examples of these polarized cyclopropanes' reactivity with nucleophiles, electrophiles, and radicals are prevalent. Although intermolecular reactivity of donor-acceptor cyclopropanes is widely reported, reviews that center on their intramolecular chemistry are rare. Thereupon, this tutorial review focalizes on new intramolecular transformations of donor-acceptor cyclopropanes for cycloisomerizations, formal cycloadditions, umpolung reactions, rearrangements and ring-opening lactonizations/lactamizations from 2009 to 2013. Furthermore, the role of D-A acceptor cyclopropanes as reactive subunits in natural product synthesis is underscored.

  3. New shallow acceptor levels in GaAs

    NASA Astrophysics Data System (ADS)

    Skromme, B. J.; Bose, S. S.; Stillman, G. E.

    1986-11-01

    Two previously unreported shallow acceptor levels with ionization energies of 25.2 and 43.2 meV, respectively, have been observed in a number of vapor phase epitaxial and metalorganic chemical vapor deposited GaAs samples grown in several different laboratories. The corresponding donor-to-acceptor and conduction band-to-acceptor transitions are identified in low temperature photoluminescence spectra by means of their temperature and excitation intensity-dependence. These levels are present as residual acceptors in high purity material, but their chemical and/or metallurgical nature has not yet been determined.

  4. Effects of electron acceptors on sulphate reduction activity in activated sludge processes.

    PubMed

    Rubio-Rincón, Francisco; Lopez-Vazquez, Carlos; Welles, Laurens; van den Brand, Tessa; Abbas, Ben; van Loosdrecht, Mark; Brdjanovic, Damir

    2017-08-01

    The concentration of sulphate present in wastewater can vary from 10 to 500 mg SO4(2-)/L. During anaerobic conditions, sulphate is reduced to sulphide by sulphate-reducing bacteria (SRB). Sulphide generation is undesired in wastewater treatment plants (WWTPs). Previous research indicated that SRB are inhibited by the presence of electron acceptors (such as O2, NO3 and NO2). However, the contact times and concentrations used in those studies are by far higher than occur in WWTPs. Since sulphide can influence the biological nitrogen and phosphorus removal processes, this research aimed to understand how the different electron acceptors commonly present in biological nutrient removal (BNR) systems can affect the proliferation of SRB. For this purpose, a culture of SRB was enriched in a sequencing batch reactor (approx. 88% of the total bacteria population). Once enriched, the SRB were exposed for 2 h to typical concentrations of electron acceptors like those observed in BNR systems. Their activity was assessed using three different types of electron donors (acetate, propionate and lactate). Oxygen was the most inhibiting electron acceptor regardless the carbon source used. After exposure to oxygen and when feeding acetate, an inactivation time in the sulphate reduction activity was observed for 1.75 h. Once the sulphate reduction activity resumed, only 60% of the original activity was recovered. It is suggested that the proliferation of SRB is most likely to occur in BNR plants with an anaerobic fraction higher than 15% and operating at sludge retention times higher than 20 days (at a temperature of 20 °C). These results can be used to implement strategies to control the growth of sulphate reducers that might compete for organic carbon with phosphate-accumulating organisms.

  5. Preparation of porous lanthanum phosphate with templates

    SciTech Connect

    Onoda, Hiroaki; Ishima, Yuya; Takenaka, Atsushi; Tanaka, Isao

    2009-08-05

    Malonic acid, propionic acid, glycine, n-butylamine, and urea were added to the preparation of lanthanum phosphate from lanthanum nitrate and phosphoric acid solutions. All additives were taken into lanthanum phosphate particles. The additives that have a basic site were easy to contain in precipitates. The addition of templates improved the specific surface area of lanthanum phosphate. The amount of pore, with radius smaller than 4 nm, increased with the addition of templates. The remained additives had influence on the acidic properties of lanthanum phosphate.

  6. Ligand-bound structures of 3-deoxy-D-manno-octulosonate 8-phosphate phosphatase from Moraxella catarrhalis reveal a water channel connecting to the active site for the second step of catalysis.

    PubMed

    Dhindwal, Sonali; Priyadarshini, Priyanka; Patil, Dipak N; Tapas, Satya; Kumar, Pramod; Tomar, Shailly; Kumar, Pravindra

    2015-02-01

    KdsC, the third enzyme of the 3-deoxy-D-manno-octulosonic acid (KDO) biosynthetic pathway, catalyzes a substrate-specific reaction to hydrolyze 3-deoxy-D-manno-octulosonate 8-phosphate to generate a molecule of KDO and phosphate. KdsC is a phosphatase that belongs to the C0 subfamily of the HAD superfamily. To understand the molecular basis for the substrate specificity of this tetrameric enzyme, the crystal structures of KdsC from Moraxella catarrhalis (Mc-KdsC) with several combinations of ligands, namely metal ion, citrate and products, were determined. Various transition states of the enzyme have been captured in these crystal forms. The ligand-free and ligand-bound crystal forms reveal that the binding of ligands does not cause any specific conformational changes in the active site. However, the electron-density maps clearly showed that the conformation of KDO as a substrate is different from the conformation adopted by KDO when it binds as a cleaved product. Furthermore, structural evidence for the existence of an intersubunit tunnel has been reported for the first time in the C0 subfamily of enzymes. A role for this tunnel in transferring water molecules from the interior of the tetrameric structure to the active-site cleft has been proposed. At the active site, water molecules are required for the formation of a water bridge that participates as a proton shuttle during the second step of the two-step phosphoryl-transfer reaction. In addition, as the KDO biosynthesis pathway is a potential antibacterial target, pharmacophore-based virtual screening was employed to identify inhibitor molecules for the Mc-KdsC enzyme.

  7. Metal-catalyzed oxidation of phenylalanine-sensitive 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase from Escherichia coli: inactivation and destabilization by oxidation of active-site cysteines.

    PubMed

    Park, O K; Bauerle, R

    1999-03-01

    The in vitro instability of the phenylalanine-sensitive 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase [DAHPS(Phe)] from Escherichia coli has been found to be due to a metal-catalyzed oxidation mechanism. DAHPS(Phe) is one of three differentially feedback-regulated isoforms of the enzyme which catalyzes the first step of aromatic biosynthesis, the formation of DAHP from phosphoenolpyruvate and D-erythrose-4-phosphate. The activity of the apoenzyme decayed exponentially, with a half-life of about 1 day at room temperature, and the heterotetramer slowly dissociated to the monomeric state. The enzyme was stabilized by the presence of phosphoenolpyruvate or EDTA, indicating that in the absence of substrate, a trace metal(s) was the inactivating agent. Cu2+ and Fe2+, but none of the other divalent metals that activate the enzyme, greatly accelerated the rate of inactivation and subunit dissociation. Both anaerobiosis and the addition of catalase significantly reduced Cu2+-catalyzed inactivation. In the spontaneously inactivated enzyme, there was a net loss of two of the seven thiols per subunit; this value increased with increasing concentrations of added Cu2+. Dithiothreitol completely restored the enzymatic activity and the two lost thiols in the spontaneously inactivated enzyme but was only partially effective in reactivation of the Cu2+-inactivated enzyme. Mutant enzymes with conservative replacements at either of the two active-site cysteines, Cys61 or Cys328, were insensitive to the metal attack. Peptide mapping of the Cu2+-inactivated enzyme revealed a disulfide linkage between these two cysteine residues. All results indicate that DAHPS(Phe) is a metal-catalyzed oxidation system wherein bound substrate protects active-site residues from oxidative attack catalyzed by bound redox metal cofactor. A mechanism of inactivation of DAHPS is proposed that features a metal redox cycle that requires the sequential oxidation of its two active-site cysteines.

  8. Vanguard family planning acceptors in Senegal.

    PubMed

    Nichols, D; Ndiaye, S; Burton, N; Janowitz, B; Gueye, L; Gueye, M

    1985-01-01

    This study examines contraceptive use among clients at the three clinics providing family planning services in Dakar, Senegal in early 1983. Most clients first became interested in family planning following the birth of a child, and most are interested in spacing future pregnancies, although one-third state that they want no more children. The clinic itself was found to be an important determinant of the type of contraceptive used, with only the government-operated clinic providing a balance between IUDs, oral contraceptives, and barrier methods. Nearly half of the clients interviewed said that a lack of knowledge about contraception is the reason for the low contraceptive prevalence rates among Senegalese women; another frequently cited reason was the opposition of the husband. Most clients reported the broadcast media to be the best means of providing family planning information to potential acceptors.

  9. Quantum computing with acceptor spins in silicon

    NASA Astrophysics Data System (ADS)

    Salfi, Joe; Tong, Mengyang; Rogge, Sven; Culcer, Dimitrie

    2016-06-01

    The states of a boron acceptor near a Si/SiO2 interface, which bind two low-energy Kramers pairs, have exceptional properties for encoding quantum information and, with the aid of strain, both heavy hole and light hole-based spin qubits can be designed. Whereas a light-hole spin qubit was introduced recently (arXiv:1508.04259), here we present analytical and numerical results proving that a heavy-hole spin qubit can be reliably initialised, rotated and entangled by electrical means alone. This is due to strong Rashba-like spin-orbit interaction terms enabled by the interface inversion asymmetry. Single qubit rotations rely on electric-dipole spin resonance (EDSR), which is strongly enhanced by interface-induced spin-orbit terms. Entanglement can be accomplished by Coulomb exchange, coupling to a resonator, or spin-orbit induced dipole-dipole interactions. By analysing the qubit sensitivity to charge noise, we demonstrate that interface-induced spin-orbit terms are responsible for sweet spots in the dephasing time {T}2* as a function of the top gate electric field, which are close to maxima in the EDSR strength, where the EDSR gate has high fidelity. We show that both qubits can be described using the same starting Hamiltonian, and by comparing their properties we show that the complex interplay of bulk and interface-induced spin-orbit terms allows a high degree of electrical control and makes acceptors potential candidates for scalable quantum computation in Si.

  10. Quantum computing with acceptor spins in silicon.

    PubMed

    Salfi, Joe; Tong, Mengyang; Rogge, Sven; Culcer, Dimitrie

    2016-06-17

    The states of a boron acceptor near a Si/SiO2 interface, which bind two low-energy Kramers pairs, have exceptional properties for encoding quantum information and, with the aid of strain, both heavy hole and light hole-based spin qubits can be designed. Whereas a light-hole spin qubit was introduced recently (arXiv:1508.04259), here we present analytical and numerical results proving that a heavy-hole spin qubit can be reliably initialised, rotated and entangled by electrical means alone. This is due to strong Rashba-like spin-orbit interaction terms enabled by the interface inversion asymmetry. Single qubit rotations rely on electric-dipole spin resonance (EDSR), which is strongly enhanced by interface-induced spin-orbit terms. Entanglement can be accomplished by Coulomb exchange, coupling to a resonator, or spin-orbit induced dipole-dipole interactions. By analysing the qubit sensitivity to charge noise, we demonstrate that interface-induced spin-orbit terms are responsible for sweet spots in the dephasing time [Formula: see text] as a function of the top gate electric field, which are close to maxima in the EDSR strength, where the EDSR gate has high fidelity. We show that both qubits can be described using the same starting Hamiltonian, and by comparing their properties we show that the complex interplay of bulk and interface-induced spin-orbit terms allows a high degree of electrical control and makes acceptors potential candidates for scalable quantum computation in Si.

  11. Binding characteristics of homogeneous molecularly imprinted polymers for acyclovir using an (acceptor-donor-donor)-(donor-acceptor-acceptor) hydrogen-bond strategy, and analytical applications for serum samples.

    PubMed

    Wu, Suqin; Tan, Lei; Wang, Ganquan; Peng, Guiming; Kang, Chengcheng; Tang, Youwen

    2013-04-12

    This paper demonstrates a novel approach to assembling homogeneous molecularly imprinted polymers (MIPs) based on mimicking multiple hydrogen bonds between nucleotide bases by preparing acyclovir (ACV) as a template and using coatings grafted on silica supports. (1)H NMR studies confirmed the AAD-DDA (A for acceptor, D for donor) hydrogen-bond array between template and functional monomer, while the resultant monodisperse molecularly imprinted microspheres (MIMs) were evaluated using a binding experiment, high performance liquid chromatography (HPLC), and solid phase extraction. The Langmuir isothermal model and the Langmuir-Freundlich isothermal model suggest that ACV-MIMs have more homogeneous binding sites than MIPs prepared through normal imprinting. In contrast to previous MIP-HPLC columns, there were no apparent tailings for the ACV peaks, and ACV-MIMs had excellent specific binding properties with a Ka peak of 3.44 × 10(5)M(-1). A complete baseline separation is obtained for ACV and structurally similar compounds. This work also successfully used MIMs as a specific sorbent for capturing ACV from serum samples. The detection limit and mean recovery of ACV was 1.8 ng/mL(-1) and 95.6%, respectively, for molecularly imprinted solid phase extraction coupled with HPLC. To our knowledge, this was the first example of MIPs using AAD-DDA hydrogen bonds.

  12. New acceptor-donor-acceptor (A-D-A) type copolymers for efficient organic photovoltaic devices

    NASA Astrophysics Data System (ADS)

    Ghomrasni, S.; Ayachi, S.; Alimi, K.

    2015-01-01

    Three new conjugated systems alternating acceptor-donor-acceptor (A-D-A) type copolymers have been investigated by means of Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) at the 6-31g (d) level of theory. 4,4‧-Dimethoxy-chalcone, also called the 1,3-bis(4-methoxyphenyl)prop-2-en-1-one (BMP), has been used as a common acceptor moiety. It forced intra-molecular S⋯O interactions through alternating oligo-thiophene derivatives: 4-AlkylThiophenes (4-ATP), 4-AlkylBithiophenes (4-ABTP) and 4-Thienylene Vinylene (4-TEV) as donor moieties. The band gap, HOMO and LUMO electron distributions as well as optical properties were analyzed for each molecule. The fully optimized resulting copolymers showed low band gaps (2.2-2.8 eV) and deep HOMO energy levels ranging from -4.66 to -4.86 eV. A broad absorption [300-900 nm] covering the solar spectrum and absorption maxima ranges from 486 to 604 nm. In addition, organic photovoltaic cells (OPCs) based on alternating copolymers in bulk heterojunction (BHJ) composites with the 1-(3-methoxycarbonyl) propyl-1-phenyl-[6,6]-C61 (PCBM), as an acceptor, have been optimized. Thus, the band gap decreased to 1.62 eV, the power conversion efficiencies (PCEs) were about 3-5% and the open circuit voltage Voc of the resulting molecules decreased from 1.50 to 1.27 eV.

  13. Efficient organic dye-sensitized solar cells: molecular engineering of donor-acceptor-acceptor cationic dyes.

    PubMed

    Cheng, Ming; Yang, Xichuan; Zhao, Jianghua; Chen, Cheng; Tan, Qin; Zhang, Fuguo; Sun, Licheng

    2013-12-01

    Three metal-free donor-acceptor-acceptor sensitizers with ionized pyridine and a reference dye were synthesized, and a detailed investigation of the relationship between the dye structure and the photophysical and photoelectrochemical properties and the performance of dye-sensitized solar cells (DSSCs) is described. The ionization of pyridine results in a red shift of the absorption spectrum in comparison to that of the reference dye. This is mainly attributable to the ionization of pyridine increasing the electron-withdrawing ability of the total acceptor part. Incorporation of the strong electron-withdrawing units of pyridinium and cyano acrylic acid gives rise to optimized energy levels, resulting in a large response range of wavelengths. When attached to TiO2 film, the conduction band of TiO2 is negatively shifted to a different extent depending on the dye. This is attributed to the electron recombination rate between the TiO2 film and the electrolyte being efficiently suppressed by the introduction of long alkyl chains and thiophene units. DSSCs assembled using these dyes show efficiencies as high as 8.8 %.

  14. Impact of Thermal Annealing on Organic Photovoltaic Cells Using Regioisomeric Donor-Acceptor-Acceptor Molecules.

    PubMed

    Zhang, Tao; Han, Han; Zou, Yunlong; Lee, Ying-Chi; Oshima, Hiroya; Wong, Ken-Tsung; Holmes, Russell J

    2017-08-02

    We report a promising set of donor-acceptor-acceptor (D-A-A) electron-donor materials based on coplanar thieno[3,2-b]/[2,3-b]indole, benzo[c][1,2,5]thiadiazole, and dicyanovinylene, which are found to show broadband absorption with high extinction coefficients. The role of the regioisomeric electron-donating thienoindole moiety on the physical and structural properties is examined. Bulk heterojunction (BHJ) organic photovoltaic cells (OPVs) based on the thieno[2,3-b]indole-based electron donor NTU-2, using C70 as an electron acceptor, show a champion power conversion efficiency of 5.2% under AM 1.5G solar simulated illumination. This efficiency is limited by a low fill factor (FF), as has previously been the case in D-A-A systems. In order to identify the origin of the limited FF, further insight into donor layer charge-transport behavior is realized by examining planar heterojunction OPVs, with emphasis on the evolution of film morphology with thermal annealing. Compared to as-deposited OPVs that exhibit insufficient donor crystallinity, crystalline OPVs based on annealed thin films show an increase in the short-circuit current density, FF, and power conversion efficiency. These results suggest that that the crystallization of D-A-A molecules might not be realized spontaneously at room temperature and that further processing is needed to realize efficient charge transport in these materials.

  15. π-Extended rigid triptycene-trisaroylenimidazoles as electron acceptors.

    PubMed

    Menke, Elisabeth H; Lami, Vincent; Vaynzof, Yana; Mastalerz, Michael

    2016-01-18

    Two soluble isomeric acceptor molecules based on a triptycene core, which is connected to three aroylenimidazole units are described. Due to the inherent threefold axis, the molecules are soluble and thus could be fully photophysically characterized in solution and film. Additionally, the preliminary results of these acceptors in organic photovoltaic devices with two different donor materials are reported.

  16. The role of deep acceptor centers in the oxidation of acceptor-doped wide-band-gap perovskites ABO3

    NASA Astrophysics Data System (ADS)

    Putilov, L. P.; Tsidilkovski, V. I.

    2017-03-01

    The impact of deep acceptor centers on defect thermodynamics and oxidation of wide-band-gap acceptor-doped perovskites without mixed-valence cations is studied. These deep centers are formed by the acceptor-bound small hole polarons whose stabilization energy can be high enough (significantly higher than the hole-acceptor Coulomb interaction energy). It is shown that the oxidation enthalpy ΔHox of oxide is determined by the energy εA of acceptor-bound states along with the formation energy EV of oxygen vacancies. The oxidation reaction is demonstrated to be either endothermic or exothermic, and the regions of εA and EV values corresponding to the positive or negative ΔHox are determined. The contribution of acceptor-bound holes to the defect thermodynamics strongly depends on the acceptor states depth εA: it becomes negligible at εA less than a certain value (at which the acceptor levels are still deep). With increasing εA, the concentration of acceptor-bound small hole polarons can reach the values comparable to the dopant content. The results are illustrated with the acceptor-doped BaZrO3 as an example. It is shown that the experimental data on the bulk hole conductivity of barium zirconate can be described both in the band transport model and in the model of hopping small polarons localized on oxygen ions away from the acceptor centers. Depending on the εA magnitude, the oxidation reaction can be either endothermic or exothermic for both mobility mechanisms.

  17. Inhibition of the respiratory chain reactions in denitrifying EBPR biomass under simultaneous presence of acetate and electron acceptor.

    PubMed

    Zafiriadis, Ilias; Kapagiannidis, Anastasios G; Ntougias, Spyridon; Aivasidis, Alexander

    2017-05-25

    In this study, the deterioration of the typical EBPR (Enhanced Biological Phosphorus Removal) process due to the simultaneous presence of electron donor (external substrate) and electron acceptor (oxygen or nitrate) was investigated by using a PAOs (Polyphosphate Accumulating Organisms)-enriched biomass grown in a modified DEPHANOX system. Intracellular and extracellular constituents were monitored in batch tests under different electron donor and acceptor conditions and specific oxygen and nitrogen uptake rates were evaluated. Results showed that phosphorus uptake was inhibited during the simultaneous presence of electron donor (acetate) and acceptor (O2/NO3(-)) in the mixed liquor. In the presence of acetate, PHAs and glycogen were produced under both aerobic and anoxic conditions irrespectively to the PHAs amount already stored intracellularly. The Krebs cycle reactions and oxidative phosphorylation provided the reduced coenzymes and energy required for PHAs synthesis when biomass polyphosphate content was low. On the contrary, polyphosphate cleavage provided the ATP required for PHAs synthesis in the presence of high biomass polyphosphate content. Inhibition of the respiratory chain reactions was observed when biomass with high polyphosphate and low PHAs content was subjected to simultaneous presence of electron donor and acceptor. PHAs utilization rather than glycogen degradation appears to favor phosphate accumulation since no polyphosphate synthesis occurred in the absence of PHAs reserves. Copyright © 2017 Elsevier B.V. All rights reserved.

  18. Re-evaluation of the glycerol-3-phosphate dehydrogenase/L-lactate dehydrogenase enzyme system. Evidence against the direct transfer of NADH between active sites.

    PubMed Central

    Brooks, S P; Storey, K B

    1991-01-01

    An investigation of the direct transfer of metabolites from rabbit muscle L-lactate dehydrogenase (LDH, EC 1.1.1.27) to glycerol-3-phosphate dehydrogenase (GPDH, EC 1.1.1.8) revealed discrepancies between theoretical predictions and experimental results. Measurements of the GPDH reaction rate at a fixed NADH concentration and in the presence of increasing LDH concentrations gave experimental results similar to those previously obtained by Srivastava, Smolen, Betts, Fukushima, Spivey & Bernhard [(1989) Proc. Natl. Acad. Sci. U.S.A. 86, 6464-6468]. However, a mathematical solution of the direct-transfer-mechanism equations as described by Srivastava et al. (1989) showed that the direct-transfer model did not adequately describe the experimental behaviour of the reaction rate at increasing LDH concentrations. In addition, experiments designed to measure the formation of an LDH4.NADH.GPDH2 complex, predicted by the direct-transfer model, indicated that no significant formation of tertiary complex occurred. An examination of other kinetic models, developed to describe the LDH/GPDH/NADH system better, revealed that the experimental results may be best explained by assuming that free NADH, and not E1.NADH, is the sole substrate for GPDH. These results suggest that direct transfer of NADH between rabbit muscle LDH and GPDH does not occur in vitro. PMID:1898374

  19. Acceptor impurity activation in III-nitride light emitting diodes

    SciTech Connect

    Römer, Friedhard Witzigmann, Bernd

    2015-01-12

    In this work, the role of the acceptor doping and the acceptor activation and its impact on the internal quantum efficiency (IQE) of a Gallium Nitride (GaN) based multi-quantum well light emitting diode is studied by microscopic simulation. Acceptor impurities in GaN are subject to a high activation energy which depends on the presence of proximate dopant atoms and the electric field. A combined model for the dopant ionization and activation barrier reduction has been developed and implemented in a semiconductor carrier transport simulator. By model calculations, we demonstrate the impact of the acceptor activation mechanisms on the decay of the IQE at high current densities, which is known as the efficiency droop. A major contributor to the droop is the electron leakage which is largely affected by the acceptor doping.

  20. Acceptor impurity activation in III-nitride light emitting diodes

    NASA Astrophysics Data System (ADS)

    Römer, Friedhard; Witzigmann, Bernd

    2015-01-01

    In this work, the role of the acceptor doping and the acceptor activation and its impact on the internal quantum efficiency (IQE) of a Gallium Nitride (GaN) based multi-quantum well light emitting diode is studied by microscopic simulation. Acceptor impurities in GaN are subject to a high activation energy which depends on the presence of proximate dopant atoms and the electric field. A combined model for the dopant ionization and activation barrier reduction has been developed and implemented in a semiconductor carrier transport simulator. By model calculations, we demonstrate the impact of the acceptor activation mechanisms on the decay of the IQE at high current densities, which is known as the efficiency droop. A major contributor to the droop is the electron leakage which is largely affected by the acceptor doping.

  1. Regulation of serum phosphate

    PubMed Central

    Lederer, Eleanor

    2014-01-01

    The regulation of serum phosphate, an acknowledged risk factor for chronic kidney disease and cardiovascular mortality, is poorly understood. The discovery of fibroblast growth factor 23 (FGF23) as a key regulator of renal phosphate handling and activation of vitamin D has revolutionized our comprehension of phosphate homeostasis. Through as yet undetermined mechanisms, circulating and dietary phosphate appear to have a direct effect on FGF23 release by bone cells that, in turn, causes renal phosphate excretion and decreases intestinal phosphate absorption through a decrease in vitamin D production. Thus, the two major phosphaturic hormones, PTH and FGF23, have opposing effects on vitamin D production, placing vitamin D at the nexus of phosphate homeostasis. While our understanding of phosphate homeostasis has advanced, the factors determining regulation of serum phosphate level remain enigmatic. Diet, time of day, season, gender, age and genetics have all been identified as significant contributors to serum phosphate level. The effects of these factors on serum phosphate have major implications for what is understood as ‘normal’ and for studies of phosphate homeostasis and metabolism. Moreover, other hormonal mediators such as dopamine, insulin-like growth factor, and angiotensin II also affect renal handling of phosphate. How the major hormone effects on phosphate handling are regulated and how the effect of these other factors are integrated to yield the measurable serum phosphate are only now beginning to be studied. PMID:24973411

  2. Acceptor and Excitation Density Dependence of the Ultrafast Polaron Absorption Signal in Donor-Acceptor Organic Solar Cell Blends.

    PubMed

    Zarrabi, Nasim; Burn, Paul L; Meredith, Paul; Shaw, Paul E

    2016-07-21

    Transient absorption spectroscopy on organic semiconductor blends for solar cells typically shows efficient charge generation within ∼100 fs, accounting for the majority of the charge carriers. In this Letter, we show using transient absorption spectroscopy on blends containing a broad range of acceptor content (0.01-50% by weight) that the rise of the polaron signal is dependent on the acceptor concentration. For low acceptor content (<10% by weight), the polaron signal rises gradually over ∼1 ps with most polarons generated after 200 fs, while for higher acceptor concentrations (>10%) most polarons are generated within 200 fs. The rise time in blends with low acceptor content was also found to be sensitive to the pump fluence, decreasing with increasing excitation density. These results indicate that the sub-100 fs rise of the polaron signal is a natural consequence of both the high acceptor concentrations in many donor-acceptor blends and the high excitation densities needed for transient absorption spectroscopy, which results in a short average distance between the exciton and the donor-acceptor interface.

  3. Synthetic inositol phosphate analogs reveal that PPIP5K2 has a surface-mounted substrate capture site that is a target for drug discovery.

    PubMed

    Wang, Huanchen; Godage, Himali Y; Riley, Andrew M; Weaver, Jeremy D; Shears, Stephen B; Potter, Barry V L

    2014-05-22

    Diphosphoinositol pentakisphosphate kinase 2 (PPIP5K2) is one of the mammalian PPIP5K isoforms responsible for synthesis of diphosphoinositol polyphosphates (inositol pyrophosphates; PP-InsPs), regulatory molecules that function at the interface of cell signaling and organismic homeostasis. The development of drugs that inhibit PPIP5K2 could have both experimental and therapeutic applications. Here, we describe a synthetic strategy for producing naturally occurring 5-PP-InsP4, as well as several inositol polyphosphate analogs, and we study their interactions with PPIP5K2 using biochemical and structural approaches. These experiments uncover an additional ligand-binding site on the surface of PPIP5K2, adjacent to the catalytic pocket. This site facilitates substrate capture from the bulk phase, prior to transfer into the catalytic pocket. In addition to demonstrating a "catch-and-pass" reaction mechanism in a small molecule kinase, we demonstrate that binding of our analogs to the substrate capture site inhibits PPIP5K2. This work suggests that the substrate-binding site offers new opportunities for targeted drug design.

  4. EFFECTS OF PH AND PHOSPHATE ON METAL DISTRIBUTION WITH EMPHASIS ON AS SPECIATION AND MOBILIZATION IN SOILS FROM A LEAD SMELTING SITE

    EPA Science Inventory

    Arsenic in soils from the Asarco Lead Smelter in East Helena, Montana was characterized by X-ray absorption spectroscopy (XAS). As oxidation state and geochemical speciation were analyzed as a function of depth (two sampling sites) and surface distribution. These results were c...

  5. Active and regulatory sites of cytosolic 5'-nucleotidase.

    PubMed

    Pesi, Rossana; Allegrini, Simone; Careddu, Maria Giovanna; Filoni, Daniela Nicole; Camici, Marcella; Tozzi, Maria Grazia

    2010-12-01

    Cytosolic 5'-nucleotidase (cN-II), which acts preferentially on 6-hydroxypurine nucleotides, is essential for the survival of several cell types. cN-II catalyses both the hydrolysis of nucleotides and transfer of their phosphate moiety to a nucleoside acceptor through formation of a covalent phospho-intermediate. Both activities are regulated by a number of phosphorylated compounds, such as diadenosine tetraphosphate (Ap₄A), ADP, ATP, 2,3-bisphosphoglycerate (BPG) and phosphate. On the basis of a partial crystal structure of cN-II, we mutated two residues located in the active site, Y55 and T56. We ascertained that the ability to catalyse the transfer of phosphate depends on the presence of a bulky residue in the active site very close to the aspartate residue that forms the covalent phospho-intermediate. The molecular model indicates two possible sites at which adenylic compounds may interact. We mutated three residues that mediate interaction in the first activation site (R144, N154, I152) and three in the second (F127, M436 and H428), and found that Ap₄A and ADP interact with the same site, but the sites for ATP and BPG remain uncertain. The structural model indicates that cN-II is a homotetrameric protein that results from interaction through a specific interface B of two identical dimers that have arisen from interaction of two identical subunits through interface A. Point mutations in the two interfaces and gel-filtration experiments indicated that the dimer is the smallest active oligomerization state. Finally, gel-filtration and light-scattering experiments demonstrated that the native enzyme exists as a tetramer, and no further oligomerization is required for enzyme activation.

  6. Phosphate Uptake by Phosphate-Starved Euglena

    PubMed Central

    BLUM, J. J.

    1966-01-01

    Phosphate-deprived Euglena acquire the ability to rapidly in-corporate added phosphate and, also, synthesize an induced acid phosphatase localized in the pellicle. The phosphate uptake system is saturated at low concentrations of phosphate and is inhibited by dinitrophenol, by low temperature, by K+, Li+, and Na+ ions, and competitively by arsenate. The orthophosphate incorporated into the cell is rapidly converted into organic forms but enough remains unesterified to suggest that the uptake is an active transport process. The data do not rule out the possibility that the induced phosphatase is involved in the transport process. PMID:5924104

  7. Phosphate homeostasis and disorders.

    PubMed

    Manghat, P; Sodi, R; Swaminathan, R

    2014-11-01

    Recent studies of inherited disorders of phosphate metabolism have shed new light on the understanding of phosphate metabolism. Phosphate has important functions in the body and several mechanisms have evolved to regulate phosphate balance including vitamin D, parathyroid hormone and phosphatonins such as fibroblast growth factor-23 (FGF23). Disorders of phosphate homeostasis leading to hypo- and hyperphosphataemia are common and have clinical and biochemical consequences. Notably, recent studies have linked hyperphosphataemia with an increased risk of cardiovascular disease. This review outlines the recent advances in the understanding of phosphate homeostasis and describes the causes, investigation and management of hypo- and hyperphosphataemia.

  8. Microbial solubilization of phosphate

    DOEpatents

    Rogers, R.D.; Wolfram, J.H.

    1993-10-26

    A process is provided for solubilizing phosphate from phosphate containing ore by treatment with microorganisms which comprises forming an aqueous mixture of phosphate ore, microorganisms operable for solubilizing phosphate from the phosphate ore and maintaining the aqueous mixture for a period of time and under conditions operable to effect the microbial solubilization process. An aqueous solution containing soluble phosphorus can be separated from the reacted mixture by precipitation, solvent extraction, selective membrane, exchange resin or gravity methods to recover phosphate from the aqueous solution. 6 figures.

  9. Microbial solubilization of phosphate

    DOEpatents

    Rogers, Robert D.; Wolfram, James H.

    1993-01-01

    A process is provided for solubilizing phosphate from phosphate containing ore by treatment with microorganisms which comprises forming an aqueous mixture of phosphate ore, microorganisms operable for solubilizing phosphate from the phosphate ore and maintaining the aqueous mixture for a period of time and under conditions operable to effect the microbial solubilization process. An aqueous solution containing soluble phosphorous can be separated from the reacted mixture by precipitation, solvent extraction, selective membrane, exchange resin or gravity methods to recover phosphate from the aqueous solution.

  10. Donor-Acceptor Properties of a Single-Molecule Altered by On-Surface Complex Formation.

    PubMed

    Meier, Tobias; Pawlak, Rémy; Kawai, Shigeki; Geng, Yan; Liu, Xunshan; Decurtins, Silvio; Hapala, Prokop; Baratoff, Alexis; Liu, Shi-Xia; Jelínek, Pavel; Meyer, Ernst; Glatzel, Thilo

    2017-08-22

    Electron donor-acceptor molecules are of outstanding interest in molecular electronics and organic solar cells for their intramolecular charge transfer controlled via electrical or optical excitation. The preservation of their electronic character in the ground state upon adsorption on a surface is cardinal for their implementation in such single-molecule devices. Here, we investigate by atomic force microscopy and scanning tunneling microscopy a prototypical system consisting of a π-conjugated tetrathiafulvalene-fused dipyridophenazine molecule adsorbed on thin NaCl films on Cu(111). Depending on the adsorption site, the molecule is found either in a nearly undisturbed free state or in a bound state. In the latter case, the molecule adopts a specific adsorption site, leading to the formation of a chelate complex with a single Na(+) alkali cation pulled out from the insulating film. Although expected to be electronically decoupled, the charge distribution of the complex is drastically modified, leading to the loss of the intrinsic donor-acceptor character. The chelate complex formation is reversible with respect to lateral manipulations, enabling tunable donor-acceptor molecular switches activated by on-surface coordination.

  11. Intramolecular charge transfer in donor-acceptor molecules

    SciTech Connect

    Slama-Schwok, A.; Blanchard-Desce, M.; Lehn, J.M. )

    1990-05-17

    The photophysical properties of donor-acceptor molecules, push-pull polyenes and carotenoids, have been studied by absorption and fluorescence spectroscopy. The compounds bear various acceptor and donor groups, linked together by chains of different length and structure. The position of the absorption and fluorescence maxima and their variation in solvents of increasing polarity are in agreement with long-distance intramolecular charge-transfer processes, the linker acting as a molecular wire. The effects of the linker length and structure and of the nature of acceptor and donor are presented.

  12. Three holes bound to a double acceptor - Be(+) in germanium

    NASA Technical Reports Server (NTRS)

    Haller, E. E.; Mcmurray, R. E., Jr.; Falicov, L. M.; Haegel, N. M.; Hansen, W. L.

    1983-01-01

    A double acceptor binding three holes has been observed for the first time with photoconductive far-infrared spectroscopy in beryllium-doped germanium single crystals. This new center, Be(+), has a hole binding energy of about 5 meV and is only present when free holes are generated by ionization of either neutral shallow acceptors or neutral Be double acceptors. The Be(+) center thermally ionizes above 4 K. It disappears at a uniaxial stress higher than about a billion dyn/sq cm parallel to (111) as a result of the lifting of the valence-band degeneracy.

  13. Efficient organic solar cells with helical perylene diimide electron acceptors.

    PubMed

    Zhong, Yu; Trinh, M Tuan; Chen, Rongsheng; Wang, Wei; Khlyabich, Petr P; Kumar, Bharat; Xu, Qizhi; Nam, Chang-Yong; Sfeir, Matthew Y; Black, Charles; Steigerwald, Michael L; Loo, Yueh-Lin; Xiao, Shengxiong; Ng, Fay; Zhu, X-Y; Nuckolls, Colin

    2014-10-29

    We report an efficiency of 6.1% for a solution-processed non-fullerene solar cell using a helical perylene diimide (PDI) dimer as the electron acceptor. Femtosecond transient absorption spectroscopy revealed both electron and hole transfer processes at the donor-acceptor interfaces, indicating that charge carriers are created from photogenerated excitons in both the electron donor and acceptor phases. Light-intensity-dependent current-voltage measurements suggested different recombination rates under short-circuit and open-circuit conditions.

  14. Donor–Acceptor Oligorotaxanes Made to Order

    SciTech Connect

    Basu, Subhadeep; Coskun, Ali; Friedman, Douglas C.; Olson, Mark A.; Benitez, Diego; Tkatchouk, Ekaterina; Barin, Gokhan; Yang, Jeffrey; Fahrenbach, Albert C.; Goddard, William A.; Stoddart, J. Fraser

    2011-01-01

    Five donor–acceptor oligorotaxanes made up of dumbbells composed of tetraethylene glycol chains, interspersed with three and five 1,5-dioxynaphthalene units, and terminated by 2,6-diisopropylphenoxy stoppers, have been prepared by the threading of discrete numbers of cyclobis(paraquat-p-phenylene) rings, followed by a kinetically controlled stoppering protocol that relies on click chemistry. The well-known copper(I)-catalyzed alkyne–azide cycloaddition between azide functions placed at the ends of the polyether chains and alkyne-bearing stopper precursors was employed during the final kinetically controlled template-directed synthesis of the five oligorotaxanes, which were characterized subsequently by ¹H NMR spectroscopy at low temperature (233 K) in deuterated acetonitrile. The secondary structures, as well as the conformations, of the five oligorotaxanes were unraveled by spectroscopic comparison with the dumbbell and ring components. By focusing attention on the changes in chemical shifts of some key probe protons, obtained from a wide range of low-temperature spectra, a picture emerges of a high degree of folding within the thread protons of the dumbbells of four of the five oligorotaxanes—the fifth oligorotaxane represents a control compound in effect—brought about by a combination of C[BOND]H···O and π–π stacking interactions between the π-electron-deficient bipyridinium units in the rings and the π-electron-rich 1,5-dioxynaphthalene units and polyether chains in the dumbbells. The secondary structures of a foldamer-like nature have received further support from a solid-state superstructure of a related [3]pseudorotaxane and density functional calculations performed thereon.

  15. Structure of the catalytic chain of Methanococcus jannaschii aspartate transcarbamoylase in a hexagonal crystal form: Insights into the path of carbamoyl phosphate to the active site of the enzyme

    SciTech Connect

    Vitali J.; Soares A.; Singh, A. K.; Colaneri, M. J.

    2012-05-01

    Crystals of the catalytic chain of Methanococcus jannaschii aspartate transcarbamoylase (ATCase) grew in the presence of the regulatory chain in the hexagonal space group P6{sub 3}22, with one monomer per asymmetric unit. This is the first time that crystals with only one monomer in the asymmetric unit have been obtained; all known structures of the catalytic subunit contain several crystallographically independent monomers. The symmetry-related chains form the staggered dimer of trimers observed in the other known structures of the catalytic subunit. The central channel of the catalytic subunit contains a sulfate ion and a K{sup +} ion as well as a glycerol molecule at its entrance. It is possible that it is involved in channeling carbamoyl phosphate (CP) to the active site of the enzyme. A second sulfate ion near Arg164 is near the second CP position in the wild-type Escherichia coli ATCase structure complexed with CP. It is suggested that this position may also be in the path that CP takes when binding to the active site in a partial diffusion process at 310 K. Additional biochemical studies of carbamoylation and the molecular organization of this enzyme in M. jannaschii will provide further insight into these points.

  16. C vs N: which end of the cyanide anion is a better hydrogen bond acceptor?

    PubMed

    Ramabhadran, Raghunath O; Hua, Yuran; Flood, Amar H; Raghavachari, Krishnan

    2014-09-04

    The ability of the C and N ends of the cyanide anion (CN(-)) as acceptors of hydrogen bonds, an experimentally difficult problem, has been computationally examined in this study. Structures obtained in our previous work involving cyanide binding within the cavity of a triazolophane macrocycle (Chem.-Eur. J. 2011, 17, 9123-9129) were used to analyze the problem. Three different approaches involving (a) breakdown of the triazolophane into smaller components, (b) population analyses, and (c) ion-dipole analyses helped demonstrate that the N terminus of cyanide is a slightly better hydrogen bond acceptor than the C terminus even though it is not the site of protonation or covalent bond formation. This outcome reflects a competition between the preference for noncovalent interactions at the nitrogen and covalent bond formation at the carbon.

  17. Electron transfer in donor-acceptor systems: Many-particle effects and influence of electronic correlations

    NASA Astrophysics Data System (ADS)

    Tornow, S.; Tong, N.-H.; Bulla, R.

    2006-03-01

    We investigate electron transfer processes in donor-acceptor systems with a coupling of the electronic degrees of freedom to a common bosonic bath. The model allows to study many-particle effects and the influence of the local Coulomb interaction U between electrons on donor and acceptor sites. Using the non-perturbative numerical renormalization group approach we find distinct differences between the electron transfer characteristics in the single- and two-particle subspaces. We calculate the critical electron-boson coupling αc as a function of U and show results for density-density correlation functions in the whole parameter space. The possibility of many-particle (bipolaronic) and Coulomb-assisted transfer is discussed.

  18. Glucose-6-phosphate dehydrogenase

    MedlinePlus

    ... this page: //medlineplus.gov/ency/article/003671.htm Glucose-6-phosphate dehydrogenase test To use the sharing features on this page, please enable JavaScript. Glucose-6-phosphate dehydrogenase (G6PD) is a protein that ...

  19. BIOREMEDIATION AT WOOD-PRESERVING SITES

    EPA Science Inventory

    The removal of organic compounds from ground water during bioremediation at wood-preserving sites is a function of the stoichiometric demand for electron acceptors (oxygen, nitrate, and sulfate) to metabolize the organic contaminants and the supply of the electron acceptors in th...

  20. BIOREMEDIATION AT WOOD-PRESERVING SITES

    EPA Science Inventory

    The removal of organic compounds from ground water during bioremediation at wood-preserving sites is a function of the stoichiometric demand for electron acceptors (oxygen, nitrate, and sulfate) to metabolize the organic contaminants and the supply of the electron acceptors in th...

  1. Nitrogen is a deep acceptor in ZnO

    SciTech Connect

    Tarun, M. C.; Iqbal, M. Zafar; McCluskey, M. D.

    2011-04-14

    Zinc oxide is a promising material for blue and UV solid-state lighting devices, among other applications. Nitrogen has been regarded as a potential p-type dopant for ZnO. However, recent calculations indicate that nitrogen is a deep acceptor. This paper presents experimental evidence that nitrogen is, in fact, a deep acceptor and therefore cannot produce p-type ZnO. A broad photoluminescence (PL) emission band near 1.7 eV, with an excitation onset of ~2.2 eV, was observed, in agreement with the deep-acceptor model of the nitrogen defect. Thus the deep-acceptor behavior can be explained by the low energy of the ZnO valence band relative to the vacuum level.

  2. Nitrogen is a deep acceptor in ZnO

    DOE PAGES

    Tarun, M. C.; Iqbal, M. Zafar; McCluskey, M. D.

    2011-04-14

    Zinc oxide is a promising material for blue and UV solid-state lighting devices, among other applications. Nitrogen has been regarded as a potential p-type dopant for ZnO. However, recent calculations indicate that nitrogen is a deep acceptor. This paper presents experimental evidence that nitrogen is, in fact, a deep acceptor and therefore cannot produce p-type ZnO. A broad photoluminescence (PL) emission band near 1.7 eV, with an excitation onset of ~2.2 eV, was observed, in agreement with the deep-acceptor model of the nitrogen defect. Thus the deep-acceptor behavior can be explained by the low energy of the ZnO valence bandmore » relative to the vacuum level.« less

  3. 2. PHOSPHATE UNLOADING BUILDING. VIEW IS TO THE NORTH. THIS ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. PHOSPHATE UNLOADING BUILDING. VIEW IS TO THE NORTH. THIS STRUCTURE WAS RELOCATED TO THE SOUTH OF ITS ORIGINAL SITE IN 1993 FOR USE AS A DECONTAMINATION FACILITY WITHIN THE BUNKER HILL SUPERFUND SITE. - North Idaho Phosphate Company, Silver King Community, Kellogg, Shoshone County, ID

  4. An Overview of Electron Acceptors in Microbial Fuel Cells

    PubMed Central

    Ucar, Deniz; Zhang, Yifeng; Angelidaki, Irini

    2017-01-01

    Microbial fuel cells (MFC) have recently received increasing attention due to their promising potential in sustainable wastewater treatment and contaminant removal. In general, contaminants can be removed either as an electron donor via microbial catalyzed oxidization at the anode or removed at the cathode as electron acceptors through reduction. Some contaminants can also function as electron mediators at the anode or cathode. While previous studies have done a thorough assessment of electron donors, cathodic electron acceptors and mediators have not been as well described. Oxygen is widely used as an electron acceptor due to its high oxidation potential and ready availability. Recent studies, however, have begun to assess the use of different electron acceptors because of the (1) diversity of redox potential, (2) needs of alternative and more efficient cathode reaction, and (3) expanding of MFC based technologies in different areas. The aim of this review was to evaluate the performance and applicability of various electron acceptors and mediators used in MFCs. This review also evaluated the corresponding performance, advantages and disadvantages, and future potential applications of select electron acceptors (e.g., nitrate, iron, copper, perchlorate) and mediators. PMID:28469607

  5. Fullerene-bisadduct acceptors for polymer solar cells.

    PubMed

    Li, Yongfang

    2013-10-01

    Polymer solar cells (PSCs) have drawn great attention in recent years for their simple device structure, light weight, and low-cost fabrication in comparison with inorganic semiconductor solar cells. However, the power-conversion efficiency (PCE) of PSCs needs to be increased for their future application. The key issue for improving the PCE of PSCs is the design and synthesis of high-efficiency conjugated polymer donors and fullerene acceptors for the photovoltaic materials. For the acceptor materials, several fullerene-bisadduct acceptors with high LUMO energy levels have demonstrated excellent photovoltaic performance in PSCs with P3HT as a donor. In this Focus Review, recent progress in high-efficiency fullerene-bisadduct acceptors is discussed, including the bisadduct of PCBM, indene-C60 bisadduct (ICBA), indene-C70 bisadduct (IC70BA), DMPCBA, NCBA, and bisTOQC. The LUMO levels and photovoltaic performance of these bisadduct acceptors with P3HT as a donor are summarized and compared. In addition, the applications of an ICBA acceptor in new device structures and with other conjugated polymer donors than P3HT are also introduced and discussed.

  6. An Overview of Electron Acceptors in Microbial Fuel Cells.

    PubMed

    Ucar, Deniz; Zhang, Yifeng; Angelidaki, Irini

    2017-01-01

    Microbial fuel cells (MFC) have recently received increasing attention due to their promising potential in sustainable wastewater treatment and contaminant removal. In general, contaminants can be removed either as an electron donor via microbial catalyzed oxidization at the anode or removed at the cathode as electron acceptors through reduction. Some contaminants can also function as electron mediators at the anode or cathode. While previous studies have done a thorough assessment of electron donors, cathodic electron acceptors and mediators have not been as well described. Oxygen is widely used as an electron acceptor due to its high oxidation potential and ready availability. Recent studies, however, have begun to assess the use of different electron acceptors because of the (1) diversity of redox potential, (2) needs of alternative and more efficient cathode reaction, and (3) expanding of MFC based technologies in different areas. The aim of this review was to evaluate the performance and applicability of various electron acceptors and mediators used in MFCs. This review also evaluated the corresponding performance, advantages and disadvantages, and future potential applications of select electron acceptors (e.g., nitrate, iron, copper, perchlorate) and mediators.

  7. Peptidyl transferase centre of bacterial ribosomes: substrate specificity and binding sites.

    PubMed Central

    Krayevsky, A A; Kukhanova, M K; Gottikh, B P

    1975-01-01

    A detailed scheme of the Peptidyl Transferase Centre of bacterial ribosomes is proposed by summarizing the literature data on the substrate specificity of the acceptor and donor sites. According to the proposed scheme only the elements of the donor and acceptor having a stable structure bind with the ribosome. The present paper proposes such main elements for the donor and acceptor. PMID:802510

  8. The Impact of Heterogeneity and Dark Acceptor States on FRET: Implications for Using Fluorescent Protein Donors and Acceptors

    PubMed Central

    Vogel, Steven S.; Nguyen, Tuan A.; van der Meer, B. Wieb; Blank, Paul S.

    2012-01-01

    Förster resonance energy transfer (FRET) microscopy is widely used to study protein interactions in living cells. Typically, spectral variants of the Green Fluorescent Protein (FPs) are incorporated into proteins expressed in cells, and FRET between donor and acceptor FPs is assayed. As appreciable FRET occurs only when donors and acceptors are within 10 nm of each other, the presence of FRET can be indicative of aggregation that may denote association of interacting species. By monitoring the excited-state (fluorescence) decay of the donor in the presence and absence of acceptors, dual-component decay analysis has been used to reveal the fraction of donors that are FRET positive (i.e., in aggregates)._However, control experiments using constructs containing both a donor and an acceptor FP on the same protein repeatedly indicate that a large fraction of these donors are FRET negative, thus rendering the interpretation of dual-component analysis for aggregates between separately donor-containing and acceptor-containing proteins problematic. Using Monte-Carlo simulations and analytical expressions, two possible sources for such anomalous behavior are explored: 1) conformational heterogeneity of the proteins, such that variations in the distance separating donor and acceptor FPs and/or their relative orientations persist on time-scales long in comparison with the excited-state lifetime, and 2) FP dark states. PMID:23152925

  9. Acceptor Specificity of Amylosucrase from Deinococcus radiopugnans and Its Application for Synthesis of Rutin Derivatives.

    PubMed

    Kim, Myo-Deok; Jung, Dong-Hyun; Seo, Dong-Ho; Jung, Jong-Hyun; Seo, Ean-Jeong; Baek, Nam-In; Yoo, Sang-Ho; Park, Cheon-Seok

    2016-11-28

    The transglycosylation activity of amylosucrase (ASase) has received significant attention owing to its use of an inexpensive donor, sucrose, and broad acceptor specificity, including glycone and aglycone compounds. The transglycosylation reaction of recombinant ASase from Deinococcus radiopugnans (DRpAS) was investigated using various phenolic compounds, and quercetin-3-O-rutinoside (rutin) was found to be the most suitable acceptor molecule used by DRpAS. Two amino acid residues in DRpAS variants (DRpAS Q299K and DRpAS Q299R), assumed to be involved in acceptor binding, were constructed by site-directed mutagenesis. Intriguingly, DRpAS Q299K and DRpAS Q299R produced 10-fold and 4-fold higher levels of rutin transglycosylation product than did the wild-type (WT) DRpAS, respectively. According to in silico molecular docking analysis, the lysine residue at position 299 in the mutants enables rutin to more easily position inside the active pocket of the mutant enzyme than in that of the WT, due to conformational changes in loop 4.

  10. His166 is the Schiff base proton acceptor in attractant phototaxis receptor sensory rhodopsin I.

    PubMed

    Sasaki, Jun; Takahashi, Hazuki; Furutani, Yuji; Sineshchekov, Oleg A; Spudich, John L; Kandori, Hideki

    2014-09-23

    Photoactivation of attractant phototaxis receptor sensory rhodopsin I (SRI) in Halobacterium salinarum entails transfer of a proton from the retinylidene chromophore's Schiff base (SB) to an unidentified acceptor residue on the cytoplasmic half-channel, in sharp contrast to other microbial rhodopsins, including the closely related repellent phototaxis receptor SRII and the outward proton pump bacteriorhodopsin, in which the SB proton acceptor is an aspartate residue salt-bridged to the SB in the extracellular (EC) half-channel. His166 on the cytoplasmic side of the SB in SRI has been implicated in the SB proton transfer reaction by mutation studies, and mutants of His166 result in an inverted SB proton release to the EC as well as inversion of the protein's normally attractant phototaxis signal to repellent. Here we found by difference Fourier transform infrared spectroscopy the appearance of Fermi-resonant X-H stretch modes in light-minus-dark difference spectra; their assignment with (15)N labeling and site-directed mutagenesis demonstrates that His166 is the SB proton acceptor during the photochemical reaction cycle of the wild-type SRI-HtrI complex.

  11. Why nature chose phosphates.

    PubMed

    Westheimer, F H

    1987-03-06

    Phosphate esters and anhydrides dominate the living world but are seldom used as intermediates by organic chemists. Phosphoric acid is specially adapted for its role in nucleic acids because it can link two nucleotides and still ionize; the resulting negative charge serves both to stabilize the diesters against hydrolysis and to retain the molecules within a lipid membrane. A similar explanation for stability and retention also holds for phosphates that are intermediary metabolites and for phosphates that serve as energy sources. Phosphates with multiple negative charges can react by way of the monomeric metaphosphate ion PO3- as an intermediate. No other residue appears to fulfill the multiple roles of phosphate in biochemistry. Stable, negatively charged phosphates react under catalysis by enzymes; organic chemists, who can only rarely use enzymatic catalysis for their reactions, need more highly reactive intermediates than phosphates.

  12. Anaerobic Mineralization of Toluene by Enriched Sediments with Quinones and Humus as Terminal Electron Acceptors

    PubMed Central

    Cervantes, Francisco J.; Dijksma, Wouter; Duong-Dac, Tuan; Ivanova, Anna; Lettinga, Gatze; Field, Jim A.

    2001-01-01

    The anaerobic microbial oxidation of toluene to CO2 coupled to humus respiration was demonstrated by use of enriched anaerobic sediments from the Amsterdam petroleum harbor (APH) and the Rhine River. Both highly purified soil humic acids (HPSHA) and the humic quinone moiety model compound anthraquinone-2,6-disulfonate (AQDS) were utilized as terminal electron acceptors. After 2 weeks of incubation, 50 and 85% of added uniformly labeled [13C]toluene were recovered as 13CO2 in HPSHA- and AQDS-supplemented APH sediment enrichment cultures, respectively; negligible recovery occurred in unsupplemented cultures. The conversion of [13C]toluene agreed with the high level of recovery of electrons as reduced humus or as anthrahydroquinone-2,6-disulfonate. APH sediment was also able to use nitrate and amorphous manganese dioxide as terminal electron acceptors to support the anaerobic biodegradation of toluene. The addition of substoichiometric amounts of humic acids to bioassay reaction mixtures containing amorphous ferric oxyhydroxide as a terminal electron acceptor led to more than 65% conversion of toluene (1 mM) after 11 weeks of incubation, a result which paralleled the partial recovery of electron equivalents as acid-extractable Fe(II). Negligible conversion of toluene and reduction of Fe(III) occurred in these bioassay reaction mixtures when humic acids were omitted. The present study provides clear quantitative evidence for the mineralization of an aromatic hydrocarbon by humus-respiring microorganisms. The results indicate that humic substances may significantly contribute to the intrinsic bioremediation of anaerobic sites contaminated with priority pollutants by serving as terminal electron acceptors. PMID:11571145

  13. L-allo-threonine aldolase from Aeromonas jandaei DK-39: gene cloning, nucleotide sequencing, and identification of the pyridoxal 5'-phosphate-binding lysine residue by site-directed mutagenesis.

    PubMed Central

    Liu, J Q; Dairi, T; Kataoka, M; Shimizu, S; Yamada, H

    1997-01-01

    We have isolated the gene encoding L-allo-threonine aldolase (L-allo-TA) from Aeromonas jandaei DK-39, a pyridoxal 5'-phosphate (PLP)-dependent enzyme that stereospecifically catalyzes the interconversion of L-allo-threonine and glycine. The gene contains an open reading frame consisting of 1,014 nucleotides corresponding to 338 amino acid residues. The protein molecular weight was estimated to be 36,294, which is in good agreement with the subunit molecular weight of the enzyme determined by polyacrylamide gel electrophoresis. The enzyme was overexpressed in recombinant Escherichia coli cells and purified to homogeneity by one hydrophobic column chromatography step. The predicted amino acid sequence showed no significant similarity to those of the currently known PLP-dependent enzymes but displayed 40 and 41% identity with those of the hypothetical GLY1 protein of Saccharomyces cerevisiae and the GLY1-like protein of Caenorhabditis elegans, respectively. Accordingly, L-allo-TA might represent a new type of PLP-dependent enzyme. To determine the PLP-binding site of the enzyme, all of the three conserved lysine residues of L-allo-TA were replaced by alanine by site-directed mutagenesis. The purified mutant enzymes, K51A and K224A, showed properties similar to those of the wild type, while the mutant enzyme K199A was catalytically inactive, with corresponding disappearance of the absorption maximum at 420 nm. Thus, Lys199 of L-allo-TA probably functions as an essential catalytic residue forming an internal Schiff base with PLP of the enzyme to catalyze the reversible aldol reaction. PMID:9171400

  14. Truncated forms of the insulin-like growth factor II (IGF-II)/mannose 6-phosphate receptor encompassing the IGF-II binding site: characterization of a point mutation that abolishes IGF-II binding.

    PubMed

    Garmroudi, F; Devi, G; Slentz, D H; Schaffer, B S; MacDonald, R G

    1996-06-01

    Complete understanding of the functional significance of insulin-like growth factor II (IGF-II) binding by the IGF-II/mannose-6-phosphate (Man-6-P) receptor requires mapping and ultimately mutational analysis of the receptor's IGF-II binding domain. Recent advances have localized the IGF-II binding site to extracytoplasmic repeats 10-11. To improve resolution of the binding site map, a nested set of epitope-tagged, truncated forms of the human IGF-II/Man-6-P receptor were transiently expressed in COS-7 cells. The IGF-II binding properties of truncated receptors immunoprecipitated from cell lysates and conditioned media were determined by affinity cross-linking. From the largest truncated receptor, encompassing extracytoplasmic repeats 8-11 (M(r) 68 K), through the smallest, comprised primarily of repeat 11 (M(r) 23 K), all were able to bind and cross-link to IGF-II. As a group, the truncated receptors had similar affinities for IGF-II, but with relative binding affinities 5-to 10-fold lower than those of full-length receptors. A point mutation substituting threonine for isoleucine at residue 1572, located in the NH2-terminal half of repeat 11, completely abolished IGF-II binding. We conclude that repeat 11 of the IGF-II/Man-6-P receptor's extracytoplasmic domain contains the minimal elements required for binding and cross-linking to IGF-II, and that lle1572 and other residues within the NH2-terminal half of repeat 11 are particularly important for IGF-II interaction.

  15. Phosphate, inositol and polyphosphates.

    PubMed

    Livermore, Thomas M; Azevedo, Cristina; Kolozsvari, Bernadett; Wilson, Miranda S C; Saiardi, Adolfo

    2016-02-01

    Eukaryotic cells have ubiquitously utilized the myo-inositol backbone to generate a diverse array of signalling molecules. This is achieved by arranging phosphate groups around the six-carbon inositol ring. There is virtually no biological process that does not take advantage of the uniquely variable architecture of phosphorylated inositol. In inositol biology, phosphates are able to form three distinct covalent bonds: phosphoester, phosphodiester and phosphoanhydride bonds, with each providing different properties. The phosphoester bond links phosphate groups to the inositol ring, the variable arrangement of which forms the basis of the signalling capacity of the inositol phosphates. Phosphate groups can also form the structural bridge between myo-inositol and diacylglycerol through the phosphodiester bond. The resulting lipid-bound inositol phosphates, or phosphoinositides, further expand the signalling potential of this family of molecules. Finally, inositol is also notable for its ability to host more phosphates than it has carbons. These unusual organic molecules are commonly referred to as the inositol pyrophosphates (PP-IPs), due to the presence of high-energy phosphoanhydride bonds (pyro- or diphospho-). PP-IPs themselves constitute a varied family of molecules with one or more pyrophosphate moiety/ies located around the inositol. Considering the relationship between phosphate and inositol, it is no surprise that members of the inositol phosphate family also regulate cellular phosphate homoeostasis. Notably, the PP-IPs play a fundamental role in controlling the metabolism of the ancient polymeric form of phosphate, inorganic polyphosphate (polyP). Here we explore the intimate links between phosphate, inositol phosphates and polyP, speculating on the evolution of these relationships. © 2016 Authors; published by Portland Press Limited.

  16. Transition dynamics for Mu acceptor states in Si{sub 1–x}Ge{sub x} alloys

    SciTech Connect

    Jayarathna, G.; Lichti, R. L.; Mengyan, P. W.; Baker, B. B.; Celebi, Y. G.; Carroll, B. R.; Yonenaga, I.

    2014-02-21

    We use the longitudinal field muon spin relaxation technique to observe charge-state and site-change transitions of muonium in Si{sub 1–x}Ge{sub x} alloys. In this project, we examine the temperature and magnetic field dependences of the relaxation rates for Si{sub 1–x}Ge{sub x} samples (x = 0.77, 0.81, and 0.84), in the composition range where the acceptor level lies within the band gap. This study particularly focuses on the relaxation rates for Si{sub 0.19}Ge{sub 0.81} to identify various cyclic charge-state and site-change processes as a function of both temperature and magnetic field. We extract the paramagnetic hyperfine constant and the relevant transition rate parameters for site changes and charge-state transitions involving Mu acceptor states for this sample. At small x, a site change dominates the transition out of the neutral T-site acceptor state, while in higher Ge content alloys hole ionization becomes the dominant transition out of the Mu{sub T}{sup 0}.

  17. Structural basis for acceptor-substrate recognition of UDP-glucose: anthocyanidin 3-O-glucosyltransferase from Clitoria ternatea

    PubMed Central

    Hiromoto, Takeshi; Honjo, Eijiro; Noda, Naonobu; Tamada, Taro; Kazuma, Kohei; Suzuki, Masahiko; Blaber, Michael; Kuroki, Ryota

    2015-01-01

    UDP-glucose: anthocyanidin 3-O-glucosyltransferase (UGT78K6) from Clitoria ternatea catalyzes the transfer of glucose from UDP-glucose to anthocyanidins such as delphinidin. After the acylation of the 3-O-glucosyl residue, the 3′- and 5′-hydroxyl groups of the product are further glucosylated by a glucosyltransferase in the biosynthesis of ternatins, which are anthocyanin pigments. To understand the acceptor-recognition scheme of UGT78K6, the crystal structure of UGT78K6 and its complex forms with anthocyanidin delphinidin and petunidin, and flavonol kaempferol were determined to resolutions of 1.85 Å, 2.55 Å, 2.70 Å, and 1.75 Å, respectively. The enzyme recognition of unstable anthocyanidin aglycones was initially observed in this structural determination. The anthocyanidin- and flavonol-acceptor binding details are almost identical in each complex structure, although the glucosylation activities against each acceptor were significantly different. The 3-hydroxyl groups of the acceptor substrates were located at hydrogen-bonding distances to the Nε2 atom of the His17 catalytic residue, supporting a role for glucosyl transfer to the 3-hydroxyl groups of anthocyanidins and flavonols. However, the molecular orientations of these three acceptors are different from those of the known flavonoid glycosyltransferases, VvGT1 and UGT78G1. The acceptor substrates in UGT78K6 are reversely bound to its binding site by a 180° rotation about the O1–O3 axis of the flavonoid backbones observed in VvGT1 and UGT78G1; consequently, the 5- and 7-hydroxyl groups are protected from glucosylation. These substrate recognition schemes are useful to understand the unique reaction mechanism of UGT78K6 for the ternatin biosynthesis, and suggest the potential for controlled synthesis of natural pigments. PMID:25556637

  18. Structural basis for acceptor-substrate recognition of UDP-glucose: anthocyanidin 3-O-glucosyltransferase from Clitoria ternatea.

    PubMed

    Hiromoto, Takeshi; Honjo, Eijiro; Noda, Naonobu; Tamada, Taro; Kazuma, Kohei; Suzuki, Masahiko; Blaber, Michael; Kuroki, Ryota

    2015-03-01

    UDP-glucose: anthocyanidin 3-O-glucosyltransferase (UGT78K6) from Clitoria ternatea catalyzes the transfer of glucose from UDP-glucose to anthocyanidins such as delphinidin. After the acylation of the 3-O-glucosyl residue, the 3'- and 5'-hydroxyl groups of the product are further glucosylated by a glucosyltransferase in the biosynthesis of ternatins, which are anthocyanin pigments. To understand the acceptor-recognition scheme of UGT78K6, the crystal structure of UGT78K6 and its complex forms with anthocyanidin delphinidin and petunidin, and flavonol kaempferol were determined to resolutions of 1.85 Å, 2.55 Å, 2.70 Å, and 1.75 Å, respectively. The enzyme recognition of unstable anthocyanidin aglycones was initially observed in this structural determination. The anthocyanidin- and flavonol-acceptor binding details are almost identical in each complex structure, although the glucosylation activities against each acceptor were significantly different. The 3-hydroxyl groups of the acceptor substrates were located at hydrogen-bonding distances to the Nε2 atom of the His17 catalytic residue, supporting a role for glucosyl transfer to the 3-hydroxyl groups of anthocyanidins and flavonols. However, the molecular orientations of these three acceptors are different from those of the known flavonoid glycosyltransferases, VvGT1 and UGT78G1. The acceptor substrates in UGT78K6 are reversely bound to its binding site by a 180° rotation about the O1-O3 axis of the flavonoid backbones observed in VvGT1 and UGT78G1; consequently, the 5- and 7-hydroxyl groups are protected from glucosylation. These substrate recognition schemes are useful to understand the unique reaction mechanism of UGT78K6 for the ternatin biosynthesis, and suggest the potential for controlled synthesis of natural pigments.

  19. l-Glyceraldehyde 3-Phosphate, a Bactericidal Agent

    PubMed Central

    Tang, Chu-Tay; Engel, Robert; Tropp, Burton E.

    1977-01-01

    At a concentration of 2.5 mM, dl-glyceraldehyde 3-phosphate has a bactericidal effect upon Escherichia coli. The glycerol 3-phosphate transport system is required for the entry of the biologically active l-enantiomer. l-Glyceraldehyde must be phosphorylated by the cell to exert its full effect upon growth. The addition of dl-glyceraldehyde 3-phosphate to a culture of E. coli caused no preferential inhibition of the accumulation of deoxyribonucleic acid, ribonucleic acid, or phosphoglycerides, although protein accumulation was less affected. Studies with mutant strains ruled out catabolic glycerol 3-phosphate dehydrogenase, anabolic nicotinamide adenine dinucleotide (phosphate):sn-glycerol 3-phosphate oxidoreductase, and fructose 1,6-diphosphate aldolase as the primary sites of action. l-Glyceraldehyde 3-phosphate is a competitive inhibitor of sn-glycerol 3-phosphate in the reactions catalyzed by acyl coenzyme A:sn-glycerol 3-phosphate acyltransferase (Ki of 1.8 mM) and cytidine 5′-diphosphate-diglyceride:sn-glycerol 3-phosphate phosphatidyltransferase (Ki of 2.7 mM). A Km mutant for the former enzyme was susceptible to the inhibitor. l-Glyceraldehyde 3-phosphate does not affect acyl coenzyme A:lysophosphatidate acyltransferase activity. In vivo, phosphatidylethanolamine and phosphatidylglycerol accumulation are inhibited to the same extent by the addition of dl-glyceraldehyde 3-phosphate to a culture of E. coli. PMID:319747

  20. Substitution of calcium by strontium within selected calcium phosphates

    NASA Astrophysics Data System (ADS)

    Rokita, E.; Hermes, C.; Nolting, H.-F.; Ryczek, J.

    1993-06-01

    Sr incorporation in the molecules of amorphous calcium phosphate, apatitic tricalcium phosphate, hydroxyapatite, octacalcium phosphate and dicalcium phosphate dihydrate was investigated. The concentration of Sr ranged from 225 to 1010 μ g / g, i.e. it overlapped with the physiological range of Sr concentrations in human bone. The leading experimental technique was extended X-ray absorption fine structure (EXAFS) at the Sr K edge. Results of these studies demonstrated the following: (1) Sr incorporation in the calcium phosphates is compound-dependent, (2) the coordination of incorporated Sr atoms in the Ca-P molecules is similar to that of Ca atoms, but interatomic distances are ≈0.015 nm larger, (3) in apatitic tricalcium phosphate, hydroxyapatite and octacalcium phosphate lattices Sr atoms may occupy selected Ca sites, which was not the case for dicalcium phosphate dihydrate, (4) in the apatite lattice Sr atoms are coordinated by 6 PO 4 tetrahedrals and (5) EXAFS spectra at the K edge of the incorporated Sr may be used to distinguish the structures of amorphous calcium phosphate, dicalcium phosphate dihydrate as well as apatite and its derivatives (apatitic tricalcium phosphate, octacalcium phosphate).

  1. Designer Metallic Acceptor-Containing Halogen Bonding: General Strategies.

    PubMed

    Zhang, Xinxing; Bowen, Kit H

    2017-03-13

    Being electrostatic interactions in nature, hydrogen bonding (HB) and halogen bonding (XB) are considered to be two parallel worlds. In principle, all the applications that HB has could also be applied to XB. However, there has been no report on a metallic XB acceptor but metal anions have been observed to be good HB acceptors. This missing mosaic piece of XB is because common metal anions are reactive for XB donors. In view of this, we propose two strategies for designing metallic acceptor-containing XB using ab initio calculations. The first one is to utilize a metal cluster anion with a high electron detachment energy, such as the superatom, Al13- as the XB acceptor. The second strategy is to design a ligand passivated/protected metal core while it still can maintain the negative charge; several exotic clusters, such as PtH5-, PtZnH5- and PtMgH5-, are utilized as examples. Based on these two strategies, we anticipate that more metallic acceptor-containing XB will be discovered.

  2. Electron acceptor-dependent respiratory and physiological stratifications in biofilms.

    PubMed

    Yang, Yonggang; Xiang, Yinbo; Sun, Guoping; Wu, Wei-Min; Xu, Meiying

    2015-01-06

    Bacterial respiration is an essential driving force in biogeochemical cycling and bioremediation processes. Electron acceptors respired by bacteria often have solid and soluble forms that typically coexist in the environment. It is important to understand how sessile bacteria attached to solid electron acceptors respond to ambient soluble alternative electron acceptors. Microbial fuel cells (MFCs) provide a useful tool to investigate this interaction. In MFCs with Shewanella decolorationis, azo dye was used as an alternative electron acceptor in the anode chamber. Different respiration patterns were observed for biofilm and planktonic cells, with planktonic cells preferred to respire with azo dye while biofilm cells respired with both the anode and azo dye. The additional azo respiration dissipated the proton accumulation within the anode biofilm. There was a large redox potential gap between the biofilms and anode surface. Changing cathodic conditions caused immediate effects on the anode potential but not on the biofilm potential. Biofilm viability showed an inverse and respiration-dependent profile when respiring with only the anode or azo dye and was enhanced when respiring with both simultaneously. These results provide new insights into the bacterial respiration strategies in environments containing multiple electron acceptors and support an electron-hopping mechanism within Shewanella electrode-respiring biofilms.

  3. Phosphate taxis in Pseudomonas aeruginosa.

    PubMed

    Kato, J; Ito, A; Nikata, T; Ohtake, H

    1992-08-01

    Pseudomonas aeruginosa was shown to be attracted to phosphate. The chemotactic response was induced by phosphate starvation. The specificity of chemoreceptors for phosphate was high so that no other tested phosphorus compounds elicited a chemotactic response as strong as that elicited by phosphate. Competition experiments showed that the chemoreceptors for phosphate appeared to be different from those for the common amino acids. Mutants constitutive for alkaline phosphatase showed the chemotactic response to phosphate regardless of whether the cells were starved for phosphate.

  4. Role of Pr segregation in acceptor-state formation at ZnO grain boundaries.

    PubMed

    Sato, Yukio; Buban, James P; Mizoguchi, Teruyasu; Shibata, Naoya; Yodogawa, Masatada; Yamamoto, Takahisa; Ikuhara, Yuichi

    2006-09-08

    The role of Pr doping on double Schottky barrier formations at ZnO single grain boundaries was investigated by the combination of current-voltage measurements, atomic-resolution Z-contrast scanning transmission electron microscopy, and first-principles calculations. Although Pr segregated to the specific atomic site along the boundaries, it was found not to be the direct cause of nonlinear current-voltage properties. Instead, under appropriate annealing conditions, Pr enhances formations of acceptor-type native defects that are essential for the creation of double Schottky barriers in ZnO.

  5. Recent advances in renal phosphate handling.

    PubMed

    Farrow, Emily G; White, Kenneth E

    2010-04-01

    Phosphate is critical for the maintenance of skeletal integrity, is a necessary component of important biomolecules, and is central to signal transduction and cell metabolism. It is becoming clear that endocrine communication between the skeleton, kidney, and the intestine is involved in maintaining appropriate serum phosphate concentrations, and that the kidney is the primary site for minute-to-minute regulation of phosphate levels. The identification of genetic alterations in Mendelian disorders of hypophosphatemia and hyperphosphatemia has led to the isolation of novel genes and the identification of new roles for existing proteins--such as fibroblast growth factor 23 and its processing systems, the co-receptor alpha-klotho, and phosphate transporters--in the control of renal phosphate handling. Recent findings also indicate that fibroblast growth factor 23 has feedback mechanisms involving parathyroid hormone and vitamin D that control phosphate homeostasis. This Review will highlight genetic, in vitro and in vivo findings, and will discuss how these clinical and experimental discoveries have uncovered novel aspects of renal phosphate handling and opened new research and therapeutic avenues.

  6. A kinetic study of the effects of phosphate and organic phosphates on the activity of phosphoenolpyruvate carboxylase from Crassula argentea.

    PubMed

    Meyer, C R; Rustin, P; Wedding, R T

    1989-05-15

    The effects of phosphate and several phosphate-containing compounds on the activity of purified phosphoenolpyruvate carboxylase (PEPC) from the crassulacean acid metabolism plant, Crassula argentea, were investigated. When assayed at subsaturating phosphoenolpyruvate (PEP) concentrations, low concentrations of most of the compounds tested were found to stimulate PEPC activity. This activation, variable in extent, was found in all cases to be competitive with glucose 6-phosphate (Glc-6-P) stimulation, suggesting that these effectors bind to the Glc-6-P site. At higher concentrations, depending upon the effector molecule studied, deactivation, inhibition, or no response was observed. More detailed studies were performed with Glc-6-P, AMP, phosphoglycolate, and phosphate. AMP had previously been shown to be a specific ligand for the Glc-6-P site. The main effect of Glc-6-P and AMP on the kinetic parameters was to decrease the apparent Km and increase Vmax/Km. AMP also caused a decrease in the Vmax of the reaction. In contrast, phosphoglycolate acted essentially as a competitive inhibitor increasing the apparent Km for PEP and decreasing Vmax/Km. Inorganic phosphate had a biphasic effect on the kinetic parameters, resulting in a transient decrease in Km followed by an increase of the apparent Km for PEP with increasing concentration of phosphate. The Vmax also was decreased with increasing phosphate concentrations. Further, the enzyme appeared to respond to the complex of phosphate with magnesium. In the presence of a saturating concentration of AMP, no activation but rather inhibition was observed with increasing phosphate concentration. This is consistent with the binding of phosphate to two separate sites--the Glc-6-P activation site and an inhibitory site, a phenomenon that may be occurring with other phosphate containing compounds. High concentrations of phosphate with magnesium were found to protect enzyme activity when PEPC, previously shown to contain an

  7. Gut inflammation provides a respiratory electron acceptor for Salmonella

    PubMed Central

    Winter, Sebastian E.; Thiennimitr, Parameth; Winter, Maria G.; Butler, Brian P.; Huseby, Douglas L.; Crawford, Robert W.; Russell, Joseph M.; Bevins, Charles L.; Adams, L. Garry; Tsolis, Renée M.; Roth, John R.; Bäumler, Andreas J.

    2010-01-01

    Salmonella enterica serotype Typhimurium (S. Typhimurium) causes acute gut inflammation by using its virulence factors to invade the intestinal epithelium and survive in mucosal macrophages. The inflammatory response enhances the transmission success of S. Typhimurium by promoting its outgrowth in the gut lumen through unknown mechanisms. Here we show that reactive oxygen species generated during inflammation reacted with endogenous, luminal sulphur compounds (thiosulfate) to form a new respiratory electron acceptor, tetrathionate. The genes conferring the ability to utilize tetrathionate as an electron acceptor produced a growth advantage for S. Typhimurium over the competing microbiota in the lumen of the inflamed gut. We conclude that S. Typhimurium virulence factors induce host-driven production of a new electron acceptor that allows the pathogen to use respiration to compete with fermenting gut microbes. Thus, the ability to trigger intestinal inflammation is crucial for the biology of this diarrhoeal pathogen. PMID:20864996

  8. Improving Photoconductance of Fluorinated Donors with Fluorinated Acceptors

    SciTech Connect

    Garner, Logan E.; Larson, Bryon; Oosterhout, Stefan; Owczarczyk, Zbyslaw; Olson, Dana C.; Kopidakis, Nikos; Boltalina, Olga V.; Strauss, Steven H.; Braunecker, Wade A.

    2016-11-21

    This work investigates the influence of fluorination of both donor and acceptor materials on the generation of free charge carriers in small molecule donor/fullerene acceptor BHJ OPV active layers. A fluorinated and non-fluorinated small molecule analogue were synthesized and their optoelectronic properties characterized. The intrinsic photoconductance of blends of these small molecule donors was investigated using time-resolved microwave conductivity. Blends of the two donor molecules with a traditional non-fluorinated fullerene (PC70BM) as well as a fluorinated fullerene (C60(CF3)2-1) were investigated using 5% and 50% fullerene loading. We demonstrate for the first time that photoconductance in a 50:50 donor:acceptor BHJ blend using a fluorinated fullerene can actually be improved relative to a traditional non-fluorinated fullerene by fluorinating the donor molecule as well.

  9. Theory of Primary Photoexcitations in Donor-Acceptor Copolymers.

    PubMed

    Aryanpour, Karan; Dutta, Tirthankar; Huynh, Uyen N V; Vardeny, Zeev Valy; Mazumdar, Sumit

    2015-12-31

    We present a generic theory of primary photoexcitations in low band gap donor-acceptor conjugated copolymers. Because of the combined effects of strong electron correlations and broken symmetry, there is considerable mixing between a charge-transfer exciton and an energetically proximate triplet-triplet state with an overall spin singlet. The triplet-triplet state, optically forbidden in homopolymers, is allowed in donor-acceptor copolymers. For an intermediate difference in electron affinities of the donor and the acceptor, the triplet-triplet state can have a stronger oscillator strength than the charge-transfer exciton. We discuss the possibility of intramolecular singlet fission from the triplet-triplet state, and how such fission can be detected experimentally.

  10. Donor-acceptor semiconducting polymers for organic photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Kularatne, Ruvini S.

    Organic solar cells hold the key for future energy demand due to their unique properties such as low cost, light weight and flexibility. A remarkable amount of effort has been done to improve the power conversion efficiencies in bulk heterojunction solar cells (BHJ). Considerable effort has been done to develop novel donor-acceptor copolymers to improve the absorbance of the copolymer in the visible to near Infrared (IR) regions and to lower the highest occupied molecular orbital (HOMO) energy level of the conjugated polymer as these properties improve the short circuit current density (J SC) and the open circuit voltage (VOC) and hence the power conversion efficiency (PCE) of the BHJ solar cells. In this dissertation, Chapter 1 describes the synthesis and photovoltaic performance of donor-acceptor semiconducting polymers that have been reported during the last decade. 9,9-Dialkyl-2,7-fluorene (FL), 2,7-carbazole (CZ), cyclopenta[2,1-b:3,4-b']dithiophene (CPDT), dithieno[3,2-b:2',3'-d]silole (DTS), dithieno[3,2- b:2',3'-d]pyrrole (DTP), benzo[1,2-b:4,5- b']dithiophene (BDT), benzo[1,2-b:4,5- b']difurane (BDF) building blocks and their donor-acceptor copolymers and their photovoltaic properties have been discussed in this chapter. Chapter 2 describes the synthesis and photovoltaic properties of two novel donor-acceptor polymers P1 and P2 containing benzodithiophene with 3,3',5-trihexylbithienyl substituents as the donor unit with Benzo[c][1,2,5]thiadiazole and 5-hexylthieno[3,4- c]pyrrole-4,6-dione as acceptor building blocks. The photovoltaic properties of the synthesized donor-acceptor polymers were investigated in bulk heterojunction solar cells with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) acceptor. Chapter 3 describes the synthesis of three novel donor-acceptor copolymers P3, P4 and P5 via Stille coupling polymerization with bithienyl substituted BDT as the donor with three different acceptors; 5,6-difluorobenzo[c][1,2,5]thiadiazole, 4,7-di(thiophen-2

  11. An overview of molecular acceptors for organic solar cells

    NASA Astrophysics Data System (ADS)

    Hudhomme, Piétrick

    2013-07-01

    Organic solar cells (OSCs) have gained serious attention during the last decade and are now considered as one of the future photovoltaic technologies for low-cost power production. The first dream of attaining 10% of power coefficient efficiency has now become a reality thanks to the development of new materials and an impressive work achieved to understand, control and optimize structure and morphology of the device. But most of the effort devoted to the development of new materials concerned the optimization of the donor material, with less attention for acceptors which to date remain dominated by fullerenes and their derivatives. This short review presents the progress in the use of non-fullerene small molecules and fullerene-based acceptors with the aim of evaluating the challenge for the next generation of acceptors in organic photovoltaics.

  12. Electron acceptor taxis and blue light effect on bacterial chemotaxis.

    PubMed

    Taylor, B L; Miller, J B; Warrick, H M; Koshland, D E

    1979-11-01

    Salmonella typhimurium and Escherichia coli from anaerobic cultures displayed tactic responses to gradients of nitrate, fumarate, and oxygen when the appropriate electron transport pathway was present. Such responses were named "electron acceptor taxis" because they are elicited by terminal electron acceptors. Mutant strains of S. typhimurium and E. coli were used to establish that functioning electron transport pathways to nitrate and fumarate are required for taxis to these compounds. Aerotaxis in S. typhimurium was blocked by 1.0 mM KCN, which inhibited oxygen uptake. Similarly, a functioning electron transport pathway was shown to be essential for the tumbling response of S. typhimurium and E. coli to intense light (290 to 530 nm). Some inhibitors and uncouplers of respiration were repellents of S. typhimurium. We propose that behavioral responses to light or electron acceptors involve electron transport-mediated perturbations of the proton motive force.

  13. The crystal structure of a ternary complex of betaine aldehyde dehydrogenase from Pseudomonas aeruginosa Provides new insight into the reaction mechanism and shows a novel binding mode of the 2'-phosphate of NADP+ and a novel cation binding site.

    PubMed

    González-Segura, Lilian; Rudiño-Piñera, Enrique; Muñoz-Clares, Rosario A; Horjales, Eduardo

    2009-01-16

    In the human pathogen Pseudomonas aeruginosa, the NAD(P)(+)-dependent betaine aldehyde dehydrogenase (PaBADH) may play the dual role of assimilating carbon and nitrogen from choline or choline precursors--abundant at infection sites--and producing glycine betaine and NADPH, potentially protective against the high-osmolarity and oxidative stresses prevalent in the infected tissues. Disruption of the PaBADH gene negatively affects the growth of bacteria, suggesting that this enzyme could be a target for antibiotic design. PaBADH is one of the few ALDHs that efficiently use NADP(+) and one of the even fewer that require K(+) ions for stability. Crystals of PaBADH were obtained under aerobic conditions in the presence of 2-mercaptoethanol, glycerol, NADP(+) and K(+) ions. The three-dimensional structure was determined at 2.1-A resolution. The catalytic cysteine (C286, corresponding to C302 of ALDH2) is oxidized to sulfenic acid or forms a mixed disulfide with 2-mercaptoethanol. The glutamyl residue involved in the deacylation step (E252, corresponding to E268 of ALDH2) is in two conformations, suggesting a proton relay system formed by two well-conserved residues (E464 and K162, corresponding to E476 and K178, respectively, of ALDH2) that connects E252 with the bulk water. In some active sites, a bound glycerol molecule mimics the thiohemiacetal intermediate; its hydroxyl oxygen is hydrogen bonded to the nitrogen of the amide groups of the side chain of the conserved N153 (N169 of ALDH2) and those of the main chain of C286, which form the "oxyanion hole." The nicotinamide moiety of the nucleotide is not observed in the crystal, and the adenine moiety binds in the usual way. A salt bridge between E179 (E195 of ALDH2) and R40 (E53 of ALDH2) moves the carboxylate group of the former away from the 2'-phosphate of the NADP(+), thus avoiding steric clashes and/or electrostatic repulsion between the two groups. Finally, the crystal shows two K(+) binding sites per subunit

  14. The Crystal Structure of a Ternary Complex of Betaine Aldehyde Dehydrogenase from Pseudomonas aeruginosa Provides New Insight Into the Reaction Mechansim and Shows A Novel Binding Mode of the 2'-Phosphate of NADP+ and A Novel Cation Binding Site

    SciTech Connect

    Gonzalez-Segura, L.; Rudino-Pinera, E; Munoz-Clares, R; Horjales, E

    2009-01-01

    In the human pathogen Pseudomonas aeruginosa, the NAD(P)+-dependent betaine aldehyde dehydrogenase (PaBADH) may play the dual role of assimilating carbon and nitrogen from choline or choline precursors-abundant at infection sites-and producing glycine betaine and NADPH, potentially protective against the high-osmolarity and oxidative stresses prevalent in the infected tissues. Disruption of the PaBADH gene negatively affects the growth of bacteria, suggesting that this enzyme could be a target for antibiotic design. PaBADH is one of the few ALDHs that efficiently use NADP+ and one of the even fewer that require K+ ions for stability. Crystals of PaBADH were obtained under aerobic conditions in the presence of 2-mercaptoethanol, glycerol, NADP+ and K+ ions. The three-dimensional structure was determined at 2.1-A resolution. The catalytic cysteine (C286, corresponding to C302 of ALDH2) is oxidized to sulfenic acid or forms a mixed disulfide with 2-mercaptoethanol. The glutamyl residue involved in the deacylation step (E252, corresponding to E268 of ALDH2) is in two conformations, suggesting a proton relay system formed by two well-conserved residues (E464 and K162, corresponding to E476 and K178, respectively, of ALDH2) that connects E252 with the bulk water. In some active sites, a bound glycerol molecule mimics the thiohemiacetal intermediate; its hydroxyl oxygen is hydrogen bonded to the nitrogen of the amide groups of the side chain of the conserved N153 (N169 of ALDH2) and those of the main chain of C286, which form the 'oxyanion hole.' The nicotinamide moiety of the nucleotide is not observed in the crystal, and the adenine moiety binds in the usual way. A salt bridge between E179 (E195 of ALDH2) and R40 (E53 of ALDH2) moves the carboxylate group of the former away from the 2?-phosphate of the NADP+, thus avoiding steric clashes and/or electrostatic repulsion between the two groups. Finally, the crystal shows two K+ binding sites per subunit. One is in an

  15. Hybrid Functional Calculations of Acceptor Doping in Protonic Conductor SrZrO3

    NASA Astrophysics Data System (ADS)

    Weston, Leigh; Janotti, Anderson; Cui, Xiangyuan; Stampfl, Catherine; van de Walle, Chris

    2015-03-01

    Perovskite oxides such as SrZrO3 (SZO), which exhibit high temperature proton conductivity, are promising electrolyte materials for use in solid oxide fuel cells (SOFCs). Proton conductivity in SZO is typically achieved via acceptor doping with trivalent cations substituting at the Zr site, where the formation of charge compensating oxygen vacancies facilitates proton solvation. We present a detailed study of Sc and Y dopants in SZO based on first-principles, hybrid density functional calculations. When substituting at the Zr site, both dopants form deep acceptors, where the neutral charge state forms a localized hole polaron state. Under certain growth conditions Sc and Y will form auto-compensating donor species by substituting at the Sr site, which would inhibit proton solubility. Moreover, the proton - dopant association was found to be strong, with proton binding energies of -0.41 eV and -0.31 eV for Sc Zr- and Y Zr- respectively, indicating that proton transport is limited by trapping. These new results will be useful in the development of zirconate based proton conducting electrolyte materials for solid oxide fuel cells.

  16. Zinc phosphate conversion coatings

    DOEpatents

    Sugama, T.

    1997-02-18

    Zinc phosphate conversion coatings for producing metals which exhibit enhanced corrosion prevention characteristics are prepared by the addition of a transition-metal-compound promoter comprising a manganese, iron, cobalt, nickel, or copper compound and an electrolyte such as polyacrylic acid, polymethacrylic acid, polyitaconic acid and poly-L-glutamic acid to a phosphating solution. These coatings are further improved by the incorporation of Fe ions. Thermal treatment of zinc phosphate coatings to generate {alpha}-phase anhydrous zinc phosphate improves the corrosion prevention qualities of the resulting coated metal. 33 figs.

  17. Zinc phosphate conversion coatings

    DOEpatents

    Sugama, Toshifumi

    1997-01-01

    Zinc phosphate conversion coatings for producing metals which exhibit enhanced corrosion prevention characteristics are prepared by the addition of a transition-metal-compound promoter comprising a manganese, iron, cobalt, nickel, or copper compound and an electrolyte such as polyacrylic acid, polymethacrylic acid, polyitaconic acid and poly-L-glutamic acid to a phosphating solution. These coatings are further improved by the incorporation of Fe ions. Thermal treatment of zinc phosphate coatings to generate .alpha.-phase anhydrous zinc phosphate improves the corrosion prevention qualities of the resulting coated metal.

  18. Donor-acceptor chemistry in the main group.

    PubMed

    Rivard, Eric

    2014-06-21

    This Perspective article summarizes recent progress from our laboratory in the isolation of reactive main group species using a general donor-acceptor protocol. A highlight of this program is the use of carbon-based donors in combination with suitable Lewis acidic acceptors to yield stable complexes of parent Group 14 element hydrides (e.g. GeH2 and H2SiGeH2). It is anticipated that this strategy could be extended to include new synthetic targets from throughout the Periodic Table with possible applications in bottom-up materials synthesis and main group element catalysis envisioned.

  19. Acceptor specificity in the transglycosylation reaction using Endo-M.

    PubMed

    Tomabechi, Yusuke; Odate, Yuki; Izumi, Ryuko; Haneda, Katsuji; Inazu, Toshiyuki

    2010-11-22

    To determine the structural specificity of the glycosyl acceptor of the transglycosylation reaction using endo-β-N-acetylglucosaminidase (ENGase) (EC 3.2.1.96) from Mucor hiemalis (Endo-M), several acceptor derivatives were designed and synthesized. The narrow regions of the 1,3-diol structure from the 4- to 6-hydroxy functions of GlcNAc were found to be essential for the transglycosylation reaction using Endo-M. Furthermore, it was determined that Endo-M strictly recognizes a 1,3-diol structure consisting of primary and secondary hydroxyl groups.

  20. Characterization of the Dynamics in the Protonic Conductor CsH2PO4 by 17O Solid-State NMR Spectroscopy and First-Principles Calculations: Correlating Phosphate and Protonic Motion

    PubMed Central

    2015-01-01

    17O NMR spectroscopy combined with first-principles calculations was employed to understand the local structure and dynamics of the phosphate ions and protons in the paraelectric phase of the proton conductor CsH2PO4. For the room-temperature structure, the results confirm that one proton (H1) is localized in an asymmetric H-bond (between O1 donor and O2 acceptor oxygen atoms), whereas the H2 proton undergoes rapid exchange between two sites in a hydrogen bond with a symmetric double potential well at a rate ≥107 Hz. Variable-temperature 17O NMR spectra recorded from 22 to 214 °C were interpreted by considering different models for the rotation of the phosphate anions. At least two distinct rate constants for rotations about four pseudo C3 axes of the phosphate ion were required in order to achieve good agreement with the experimental data. An activation energy of 0.21 ± 0.06 eV was observed for rotation about the P–O1 axis, with a higher activation energy of 0.50 ± 0.07 eV being obtained for rotation about the P–O2, P–O3d, and P–O3a axes, with the superscripts denoting, respectively, dynamic donor and acceptor oxygen atoms of the H-bond. The higher activation energy of the second process is most likely associated with the cost of breaking an O1–H1 bond. The activation energy of this process is slightly lower than that obtained from the 1H exchange process (0.70 ± 0.07 eV) (Kim, G.; Blanc, F.; Hu, Y.-Y.; Grey, C. P. J. Phys. Chem. C2013, 117, 6504−6515) associated with the translational motion of the protons. The relationship between proton jumps and phosphate rotation was analyzed in detail by considering uncorrelated motion, motion of individual PO4 ions and the four connected/H-bonded protons, and concerted motions of adjacent phosphate units, mediated by proton hops. We conclude that, while phosphate rotations aid proton motion, not all phosphate rotations result in proton jumps. PMID:25732257

  1. Hydration of the phosphate group in double-helical DNA.

    PubMed Central

    Schneider, B; Patel, K; Berman, H M

    1998-01-01

    Water distributions around phosphate groups in 59 B-, A-, and Z-DNA crystal structures were analyzed. It is shown that the waters are concentrated in six hydration sites per phosphate and that the positions and occupancies of these sites are dependent on the conformation and type of nucleotide. The patterns of hydration that are characteristic of the backbone of the three DNA helical types can be attributed in part to the interactions of these hydration sites. PMID:9788937

  2. Phosphate import at the arbuscule: just a nutrient?

    PubMed

    Yang, Shu-Yi; Paszkowski, Uta

    2011-11-01

    Central to the mutualistic arbuscular mycorrhizal symbiosis is the arbuscule, the site where symbiotic phosphate is delivered. Initial investigations in legumes have led to the exciting observation that symbiotic phosphate uptake not only enhances plant growth but also regulates arbuscule dynamics and is, furthermore, required for maintenance of the symbiosis. This review evaluates the possible role of the phosphate ion, not only as a nutrient but also as a signal that is necessary for reprogramming the host cortex cell for symbiosis.

  3. Dual mechanism of ion permeation through VDAC revealed with inorganic phosphate ions and phosphate metabolites.

    PubMed

    Krammer, Eva-Maria; Vu, Giang Thi; Homblé, Fabrice; Prévost, Martine

    2015-01-01

    In the exchange of metabolites and ions between the mitochondrion and the cytosol, the voltage-dependent anion channel (VDAC) is a key element, as it forms the major transport pathway for these compounds through the mitochondrial outer membrane. Numerous experimental studies have promoted the idea that VDAC acts as a regulator of essential mitochondrial functions. In this study, using a combination of molecular dynamics simulations, free-energy calculations, and electrophysiological measurements, we investigated the transport of ions through VDAC, with a focus on phosphate ions and metabolites. We showed that selectivity of VDAC towards small anions including monovalent phosphates arises from short-lived interactions with positively charged residues scattered throughout the pore. In dramatic contrast, permeation of divalent phosphate ions and phosphate metabolites (AMP and ATP) involves binding sites along a specific translocation pathway. This permeation mechanism offers an explanation for the decrease in VDAC conductance measured in the presence of ATP or AMP at physiological salt concentration. The binding sites occur at similar locations for the divalent phosphate ions, AMP and ATP, and contain identical basic residues. ATP features a marked affinity for a central region of the pore lined by two lysines and one arginine of the N-terminal helix. This cluster of residues together with a few other basic amino acids forms a "charged brush" which facilitates the passage of the anionic metabolites through the pore. All of this reveals that VDAC controls the transport of the inorganic phosphates and phosphate metabolites studied here through two different mechanisms.

  4. Tetrathiafulvalene-based mixed-valence acceptor-donor-acceptor triads: a joint theoretical and experimental approach.

    PubMed

    Calbo, Joaquín; Aragó, Juan; Otón, Francisco; Lloveras, Vega; Mas-Torrent, Marta; Vidal-Gancedo, José; Veciana, Jaume; Rovira, Concepció; Ortí, Enrique

    2013-12-02

    This work presents a joint theoretical and experimental characterisation of the structural and electronic properties of two tetrathiafulvalene (TTF)-based acceptor-donor-acceptor triads (BQ-TTF-BQ and BTCNQ-TTF-BTCNQ; BQ is naphthoquinone and BTCNQ is benzotetracyano-p-quinodimethane) in their neutral and reduced states. The study is performed with the use of electrochemical, electron paramagnetic resonance (EPR), and UV/Vis/NIR spectroelectrochemical techniques guided by quantum-chemical calculations. Emphasis is placed on the mixed-valence properties of both triads in their radical anion states. The electrochemical and EPR results reveal that both BQ-TTF-BQ and BTCNQ-TTF-BTCNQ triads in their radical anion states behave as class-II mixed-valence compounds with significant electronic communication between the acceptor moieties. Density functional theory calculations (BLYP35/cc-pVTZ), taking into account the solvent effects, predict charge-localised species (BQ(.-)-TTF-BQ and BTCNQ(.-)-TTF-BTCNQ) as the most stable structures for the radical anion states of both triads. A stronger localisation is found both experimentally and theoretically for the BTCNQ-TTF-BTCNQ anion, in accordance with the more electron-withdrawing character of the BTCNQ acceptor. CASSCF/CASPT2 calculations suggest that the low-energy, broad absorption bands observed experimentally for the BQ-TTF-BQ and BTCNQ-TTF-BTCNQ radical anions are associated with the intervalence charge transfer (IV-CT) electronic transition and two nearby donor-to-acceptor CT excitations. The study highlights the molecular efficiency of the electron-donor TTF unit as a molecular wire connecting two acceptor redox centres. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Calcium Phosphate Nanoparticle Adjuvant

    PubMed Central

    He, Qing; Mitchell, Alaina R.; Johnson, Stacy L.; Wagner-Bartak, Claus; Morcol, Tulin; Bell, Steve J. D.

    2000-01-01

    Vaccination to protect against human infectious diseases may be enhanced by using adjuvants that can selectively stimulate immunoregulatory responses. In a murine model, a novel nanoparticulate adjuvant composed of calcium phosphate (CAP) was compared with the commonly used aluminum (alum) adjuvants for its ability to induce immunity to herpes simplex virus type 2 (HSV-2) and Epstein-Barr virus (EBV) infections. Results indicated that CAP was more potent as an adjuvant than alum, elicited little or no inflammation at the site of administration, induced high titers of immunoglobulin G2a (IgG2a) antibody and neutralizing antibody, and facilitated a high percentage of protection against HSV-2 infection. Additional benefits of CAP include (i) an insignificant IgE response, which is an important advantage over injection of alum compounds, and (ii) the fact that CAP is a natural constituent of the human body. Thus, CAP is very well tolerated and absorbed. These studies were performed with animal models. By virtue of the potency of this CAP adjuvant and the relative absence of side effects, we believe that this new CAP formulation has great potential for use as an adjuvant in humans. PMID:11063495

  6. Three Redox States of a Diradical Acceptor-Donor-Acceptor Triad: Gating the Magnetic Coupling and the Electron Delocalization.

    PubMed

    Souto, Manuel; Lloveras, Vega; Vela, Sergi; Fumanal, Maria; Ratera, Imma; Veciana, Jaume

    2016-06-16

    The diradical acceptor-donor-acceptor triad 1(••), based on two polychlorotriphenylmethyl (PTM) radicals connected through a tetrathiafulvalene(TTF)-vinylene bridge, has been synthesized. The generation of the mixed-valence radical anion, 1(•-), and triradical cation species, 1(•••+), obtained upon electrochemical reduction and oxidation, respectively, was monitored by optical and ESR spectroscopy. Interestingly, the modification of electron delocalization and magnetic coupling was observed when the charged species were generated and the changes have been rationalized by theoretical calculations.

  7. Improvement of DNA adenylation using T4 DNA ligase with a template strand and a strategically mismatched acceptor strand

    PubMed Central

    Patel, Maha P.; Baum, Dana A.; Silverman, Scott K.

    2008-01-01

    DNA with a 5′-adenylpyrophosphoryl cap (5′-adenylated DNA; AppDNA) is an activated form of DNA that is the biochemical intermediate of the reactions catalyzed by DNA ligase, RNA ligase, polynucleotide kinase, and other nucleic acid modifying enzymes. 5′-Adenylated DNA is also useful for in vitro selection experiments. Efficient preparation of 5′-adenylated DNA is therefore desirable for several biochemical applications. Here we have developed a DNA adenylation procedure that uses T4 DNA ligase and is more reliable than a previously reported approach that used the 5′-phosphorylated donor DNA substrate to be adenylated, a DNA template, and ATP but no acceptor strand. Our improved DNA adenylation procedure uses the above components as well as an acceptor strand that has a strategically chosen C-T acceptor-template mismatch directly adjacent to the adenylation site. This mismatch permits adenylation of the donor DNA substrate but largely suppresses subsequent ligation of the donor with the acceptor, as assayed on nine different DNA substrates that collectively have all four DNA nucleotides represented at each of the first two positions. The new DNA adenylation procedure is successful using either laboratory-prepared or commercial T4 DNA ligase and works well on the preparative (2 nmol) scale for all nine of the test DNA substrates. PMID:18022669

  8. EXAFS study of dopant ions with different charges in nanocrystalline anatase: evidence for space-charge segregation of acceptor ions.

    PubMed

    Knauth, Philippe; Chadwick, Alan V; Lippens, Pierre E; Auer, Gerhard

    2009-06-02

    Nanocrystalline TiO(2) (anatase) is an essential oxide for environment and energy applications. A combination of EXAFS spectroscopy and DFT calculations on a series of dopants with quite similar ion radius, but increasing ion charge, show boundary space charge segregation of acceptor cations. The picture illustrates the Fourier-transformed EXAFS spectrum for Sn(4+)-doped TiO(2).A series of dopants, including acceptor ions (Zn(2+), Y(3+)), isovalent ions (Zr(4+), Sn(4+)) as well as a donor ion (Nb(5+)), were studied by EXAFS spectroscopy in nanocrystalline TiO(2) anatase powders and nanoceramics. Similar results were found for nanocrystalline powders and nanocrystalline ceramics, made by hot-pressing the powders. Boundary segregation was observed for the acceptor ions yttrium and zinc, whereas tin, zirconium and niobium ions were placed on substitutional bulk sites and did not segregate, whatever their concentration. These results can be interpreted based on defect thermodynamics, in the framework of a space charge segregation model with positive boundary core, due to excess oxide ion vacancies, and negative space charge regions, where ionized acceptors are segregated.

  9. Redesigning the active site of transaldolase TalB from Escherichia coli: new variants with improved affinity towards nonphosphorylated substrates.

    PubMed

    Schneider, Sarah; Gutiérrez, Mariana; Sandalova, Tatyana; Schneider, Gunter; Clapés, Pere; Sprenger, Georg A; Samland, Anne K

    2010-03-22

    Recently, we reported on a transaldolase B variant (TalB F178Y) that is able to use dihydroxyacetone (DHA) as donor in aldol reactions. In a second round of protein engineering, we aimed at improving the affinity of this variant towards nonphosphorylated acceptor aldehydes, that is, glyceraldehyde (GA). The anion binding site was identified in the X-ray structure of TalB F178Y where a sulfate ion from the buffer was bound in the active site. Therefore, we performed site-directed saturation mutagenesis at three residues forming the putative phosphate binding site, Arg181, Ser226 and Arg228. The focused libraries were screened for the formation of D-fructose from DHA and d,l-GA by using an adjusted colour assay. The best results with respect to the synthesis of D-fructose were achieved with the TalB F178Y/R181E variant, which exhibited an at least fivefold increase in affinity towards d,l-GA (K(M)=24 mM). We demonstrated that this double mutant can use D-GA, glycolaldehyde and the L-isomer, L-GA, as acceptor substrates. This resulted in preparative synthesis of D-fructose, D-xylulose and L-sorbose when DHA was used as donor. Hence, we engineered a DHA-dependent aldolase that can synthesise the formation of polyhydroxylated compounds from simple and cheap substrates at preparative scale.

  10. CADMIUM PHOSPHATE GLASS

    DOEpatents

    Carpenter, H.W.; Johnson, P.D.

    1963-04-01

    A method of preparing a cadmium phosphate glass that comprises providing a mixture of solid inorganic compounds of cadmuim and phosphate having vaporizable components and heating the resulting composition to a temperature of at least 850 un. Concent 85% C is presented. (AEC)

  11. Electron Acceptor-Electron Donor Interactions. XV and XVI.

    DTIC Science & Technology

    mixtures exhibit simple eutectic phase diagrams and the thermochromic effect is interpreted as a randomized structure in the liquid , whereas the solid is a...two-phase aggregate of isolated acceptor and onor crystals . The charge-transfer spectra of solutions of tungsten and molybdenum hexafluorides and iodine heptafluoride in n-hexane and cyclohexane were obtained.

  12. Resorbable calcium phosphate bone substitute.

    PubMed

    Knaack, D; Goad, M E; Aiolova, M; Rey, C; Tofighi, A; Chakravarthy, P; Lee, D D

    1998-01-01

    The in vitro and in vivo properties of a novel, fully resorbable, apatitic calcium phosphate bone substitute (ABS) are described. The ABS was prepared from calcium phosphate precursors that were hydrated to form an injectable paste that hardens endothermically at 37 degrees C to form a poorly crystalline apatitic calcium phosphate (PCA). The PCA reaction product is stable in vivo as determined by FTIR and XRD analysis of rabbit intramuscular implants of ABS retrieved 4, 7, and 14 days postimplantation. Bone formation and resorption characteristics of the ABS material were characterized in a canine femoral slot defect model. Femoral slot defects in dogs were filled with either autologous bone implants or the ABS material. Sections of femoral bone defect site from animals sacrificed at 3, 4, 12, 26, and 52 weeks demonstrated that new bone formation proceeded similarly in both autograft and ABS filled slots. Defects receiving either material were filled with trabecular bone in the first 3 to 4 weeks after implantation; lamellar or cortical bone formation was well established by week 12. New bone formation in ABS filled defects followed a time course comparable to autologous bone graft filled defects. Histomorphometric evaluation of ABS resorption and new bone formation indicated that the ABS material was greater than 99% resorbed within 26 weeks; residual ABS occupied 0.36+/-0.36% (SEM, n = 4) of the original defect area at 26 weeks. Quantitatively and qualitatively, the autograft and ABS were associated with similar new bone growth and defect filling characteristics.

  13. Development of imide- and imidazole-containing electron acceptors for use in donor-acceptor conjugated compounds and polymers

    NASA Astrophysics Data System (ADS)

    Li, Duo

    Conjugated organic compounds and polymers have attracted significant attention due to their potential application in electronic devices as semiconducting materials, such as organic solar cells (OSCs). In order to tune band gaps, donor-acceptor (D-A) structure is widely used, which has been proved to be one of the most effective strategies. This thesis consists of three parts: 1) design, syntheses and characterization of new weak acceptors based on imides and the systematic study of the structure-property relationship; (2) introduction of weak and strong acceptors in one polymer to achieve a broad coverage of light absorption and improve the power conversion efficiency (PCE); (3) modification of benzothiadiazole (BT) acceptor in order to increase the electron withdrawing ability. Imide-based electron acceptors, 4-(5-bromothiophen-2-y1)-2-(2-ethylhexyl)-9- phenyl- 1H-benzo[f]isoindole-1,3(2H)-dione (BIDO-1) and 4,9-bis(5-bromothiophen-2-yl)-2-(2-ethylhexyl)-benzo[f]isoindole-1,3-dione (BIDO-2), were designed and synthesized. In this design, naphthalene is selected as its main core to maintain a planar structure, and thienyl groups are able to facilitate the bromination reaction and lower the band gap. BIDO-1 and BIDO-2 were successfully coupled with different donors by both Suzuki cross-coupling and Stille cross-coupling reactions. Based on the energy levels and band gaps of the BIDO-containing compounds and polymers, BIDO-1 and BIDO-2 are proved to be weak electron acceptors. Pyromellitic diimide (PMDI) was also studied and found to be a stronger electron acceptor than BIDO . In order to obtain broad absorption coverage, both weak acceptor ( BIDO-2) and strong acceptor diketopyrrolopyrrole (DPP) were introduced in the same polymer. The resulting polymers show two absorption bands at 400 and 600 nm and two emission peaks at 500 and 680 nm. The band gaps of the polymers are around 1.6 eV, which is ideal for OSC application. The PCE of 1.17% was achieved. Finally

  14. Anaerobic methanotrophy in tidal wetland: Effects of electron acceptors

    NASA Astrophysics Data System (ADS)

    Lin, Li-Hung; Yu, Zih-Huei; Wang, Pei-Ling

    2016-04-01

    Wetlands have been considered to represent the largest natural source of methane emission, contributing substantially to intensify greenhouse effect. Despite in situ methanogenesis fueled by organic degradation, methanotrophy also plays a vital role in controlling the exact quantity of methane release across the air-sediment interface. As wetlands constantly experience various disturbances of anthropogenic activities, biological burrowing, tidal inundation, and plant development, rapid elemental turnover would enable various electron acceptors available for anaerobic methanotrophy. The effects of electron acceptors on stimulating anaerobic methanotrophy and the population compositions involved in carbon transformation in wetland sediments are poorly explored. In this study, sediments recovered from tidally influenced, mangrove covered wetland in northern Taiwan were incubated under the static conditions to investigate whether anaerobic methanotrophy could be stimulated by the presence of individual electron acceptors. Our results demonstrated that anaerobic methanotrophy was clearly stimulated in incubations amended with no electron acceptor, sulfate, or Fe-oxyhydroxide. No apparent methane consumption was observed in incubations with nitrate, citrate, fumarate or Mn-oxides. Anaerobic methanotrophy in incubations with no exogenous electron acceptor appears to proceed at the greatest rates, being sequentially followed by incubations with sulfate and Fe-oxyhydroxide. The presence of basal salt solution stimulated methane oxidation by a factor of 2 to 3. In addition to the direct impact of electron acceptor and basal salts, incubations with sediments retrieved from low tide period yielded a lower rate of methane oxidation than from high tide period. Overall, this study demonstrates that anaerobic methanotrophy in wetland sediments could proceed under various treatments of electron acceptors. Low sulfate content is not a critical factor in inhibiting methane

  15. Acceptor conductivity in bulk zinc oxide (0001) crystals

    NASA Astrophysics Data System (ADS)

    Adekore, Bababunmi Tolu

    ZnO is a promising wide bandgap semiconductor. Its renowned and prominent properties as its bandgap of 3.37eV at 4.2K; its very high excitonic binding energy, 60meV; its high melting temperature, 2248K constitute the basis for the recently renewed and sustained scientific interests in the material. In addition to the foregoing, the availability of bulk substrates of industrially relevant sizes provides important opportunities such as homoepitaxial deposition of the material which is a technological asset in the production of efficient optoelectronic and electronic devices. The nemesis of wide bandgap materials cannot be more exemplified than in ZnO. The notorious limitation of asymmetric doping and the haunting plague of electrically active point defects dim the bright future of the material. In this case, the search for reliable and consistent acceptor conductivity in bulk substrates has been hitherto, unsuccessful. In the dissertation that now follows, our efforts have been concerted in the search for a reliable acceptor. We have carefully investigated the science of point defects in the material, especially those responsible for the high donor conductivity. We also investigated and herein report variety of techniques of introducing acceptors into the material. We employ the most relevant and informative characterization techniques in verifying both the intended conductivity and the response of intrinsic crystals to variation in temperature and strain. And finally we explain deviations, where they exist, from ideal acceptor characteristics. Our work on reliable acceptor has been articulated in four papers. The first establishing capacitance based methods of monitoring electrically active donor defects. The second investigates the nature of anion acceptors on the oxygen sublattice. A study similar to the preceding study was conducted for cation acceptors on the zinc sublattice and reported in the third paper. Finally, an analysis of the response of the crystal to

  16. Polaronic Hole Localization and Multiple Hole Binding of Acceptors in Oxide Wide-Gap Semiconductors

    SciTech Connect

    Lany, S.; Zunger, A.

    2009-01-01

    Acceptor-bound holes in oxides often localize asymmetrically at one out of several equivalent oxygen ligands. Whereas Hartree-Fock (HF) theory overly favors such symmetry-broken polaronic hole localization in oxides, standard local-density (LD) calculations suffer from spurious delocalization among several oxygen sites. These opposite biases originate from the opposite curvatures of the energy as a function of the fractional occupation number n, i.e., d{sup 2}E/dn{sup 2}<0 in HF and d{sup 2}E/dn{sup 2}>0 in LD. We recover the correct linear behavior, d{sup 2}E/dn{sup 2}=0, that removes the (de)localization bias by formulating a generalized Koopmans condition. The correct description of oxygen hole localization reveals that the cation-site nominal single acceptors in ZnO, In{sub 2}O{sub 3}, and SnO{sub 2} can bind multiple holes.

  17. Crystal Structures of a Poplar Xyloglucan Endotransglycosylase Reveal Details of Transglycosylation Acceptor Binding

    PubMed Central

    Johansson, Patrik; Brumer, Harry; Baumann, Martin J.; Kallas, Åsa M.; Henriksson, Hongbin; Denman, Stuart E.; Teeri, Tuula T.; Jones, T. Alwyn

    2004-01-01

    Xyloglucan endotransglycosylases (XETs) cleave and religate xyloglucan polymers in plant cell walls via a transglycosylation mechanism. Thus, XET is a key enzyme in all plant processes that require cell wall remodeling. To provide a basis for detailed structure–function studies, the crystal structure of Populus tremula x tremuloides XET16A (PttXET16A), heterologously expressed in Pichia pastoris, has been determined at 1.8-Å resolution. Even though the overall structure of PttXET16A is a curved β-sandwich similar to other enzymes in the glycoside hydrolase family GH16, parts of its substrate binding cleft are more reminiscent of the distantly related family GH7. In addition, XET has a C-terminal extension that packs against the conserved core, providing an additional β-strand and a short α-helix. The structure of XET in complex with a xyloglucan nonasaccharide, XLLG, reveals a very favorable acceptor binding site, which is a necessary but not sufficient prerequisite for transglycosylation. Biochemical data imply that the enzyme requires sugar residues in both acceptor and donor sites to properly orient the glycosidic bond relative to the catalytic residues. PMID:15020748

  18. Subunit Interactions and Glutamine Utilization by Escherichia coli Imidazole Glycerol Phosphate Synthase

    PubMed Central

    Klem, Thomas J.; Chen, Yuan; Davisson, V. Jo

    2001-01-01

    A selection strategy has been developed to identify amino acid residues involved in subunit interactions that coordinate the two half-reactions catalyzed by glutamine amidotransferases. The protein structures known for this class of enzymes have revealed that ammonia is shuttled over long distances and that each amidotransferase evolved different molecular tunnels for this purpose. The heterodimeric Escherichia coli imidazole glycerol phosphate (IGP) synthase was probed to assess if residues in the substrate amination subunit (HisF) are critical for the glutaminase activity in the HisH subunit. The activity of the HisH subunit is dependent upon binding of the nucleotide substrate at the HisF active site. This regulatory function has been exploited as a biochemical selection of mutant HisF subunits that retain full activity with ammonia as a substrate but, when constituted as a holoenzyme with wild-type HisH, impair the glutamine-dependent activity of IGP synthase. The steady-state kinetic constants for these IGP synthases with HisF alleles showed three distinct effects depending upon the site of mutation. For example, mutation of the R5 residue has similar effects on the glutamine-dependent amidotransfer reaction; however, kcat/Km for the glutaminase half-reaction was increased 10-fold over that for the wild-type enzyme with nucleotide substrate. This site appears essential for coupling of the glutamine hydrolysis and ammonia transfer steps and is the first example of a site remote to the catalytic triad that modulates the process. The results are discussed in the context of recent X-ray crystal structures of glutamine amidotransferases that relate the glutamine binding and acceptor binding sites. PMID:11208798

  19. Phosphate Sorption in Water by Several cationic Polyer flocculants

    USDA-ARS?s Scientific Manuscript database

    Although inorganic phosphate is an essential plant nutrient, elevated levels in surface waters may lead to adverse effects in the environment. These effects are attributed to runoff from rain or irrigation events that may cause the sorbed phosphate to move away from the application sites and move i...

  20. PHOSPHATE MANAGEMENT: FY2010 RESULTS OF PHOSPHATE PRECIPITATION TESTS

    SciTech Connect

    Hay, M.; King, W.

    2011-04-04

    The Phosphate Management program seeks to develop treatment options for caustic phosphate solutions resulting from the caustic leaching of the bismuth phosphate sludge. The SRNL subtask investigated the precipitation of phosphate salts from caustic solutions through addition of fluoride and by crystallization. The scoping tests examined the: precipitation of phosphate by the addition of sodium fluoride to form the sodium fluorophosphate double salt, Na{sub 7}F(PO{sub 4}){sub 2} {center_dot} 19H{sub 2}O, crystallization of phosphate by reducing the temperature of saturated phosphate solutions, and combinations of precipitation and crystallization. A simplified leachate simulant was used in the study produced by dissolving sodium phosphate in 1 M to 3.5 M sodium hydroxide solutions. The results show that all three processes; precipitation with sodium fluoride, crystallization, and combined precipitation/crystallization can be effective for removing large amounts of phosphate from solution. The combined process of precipitation/crystallization showed >90% removal of phosphate at all hydroxide concentrations when cooling a non-saturated phosphate solution from 65 C to 25 C. Based on the measured solubility of sodium phosphate, pH adjustment/caustic addition will also remove large amounts of phosphate from solution (>80%). For all three processes, the phosphate concentration in the caustic solution must be managed to keep the phosphate from becoming too concentrated and thereby potentially forming a solid mass of sodium phosphate after an effective phosphate removal process.

  1. Superconducting oxides containing sulphate and phosphate groups

    NASA Astrophysics Data System (ADS)

    Dominguez, Angel Bustamante; Scorzelli, R. B.; Baggio-Saitovitch, E.; Giordanengo, B.; Elmassalami, M.

    1994-12-01

    The effects of partial substitution of Sr and Ca in YBaCuO related materials containing sulphate and phosphate groups have been investigated. 57Fe Mössbauer measurements were performed on samples doped with lat.% 57Fe and the spectral components related to different Cu sites and oxygen vacancies.

  2. Superconducting oxides containing sulphate and phosphate groups

    NASA Astrophysics Data System (ADS)

    Scorzelli, R. B.; Baggio-Saitovitch, E.; Giordanengo, B.; Elmassalami, M.; Dominguez, A. B.; Bustamante Dominguez, A.

    1994-12-01

    The effects of partial substitution of Sr and Ca in Y-Ba-Cu-O related materials containing sulphate and phosphate groups have been investigated. e57Fe Mössbauer measurements were performed on samples doped with lat. % e57Fe and the spectral components related to different Cu sites and oxygen vacancies.

  3. Fragment charge difference method for estimating donor-acceptor electronic coupling: Application to DNA π-stacks

    NASA Astrophysics Data System (ADS)

    Voityuk, Alexander A.; Rösch, Notker

    2002-09-01

    The purpose of this communication is two-fold. We introduce the fragment charge difference (FCD) method to estimate the electron transfer matrix element HDA between a donor D and an acceptor A, and we apply this method to several aspects of hole transfer electronic couplings in π-stacks of DNA, including systems with several donor-acceptor sites. Within the two-state model, our scheme can be simplified to recover a convenient estimate of the electron transfer matrix element HDA=(1-Δq2)1/2(E2-E1)/2 based on the vertical excitation energy E2-E1 and the charge difference Δq between donor and acceptor. For systems with strong charge separation, Δq≳0.95, one should resort to the FCD method. As favorable feature, we demonstrate the stability of the FCD approach for systems which require an approach beyond the two-state model. On the basis of ab initio calculations of various DNA related systems, we compared three approaches for estimating the electronic coupling: the minimum splitting method, the generalized Mulliken-Hush (GMH) scheme, and the FCD approach. We studied the sensitivity of FCD and GMH couplings to the donor-acceptor energy gap and found both schemes to be quite robust; they are applicable also in cases where donor and acceptor states are off resonance. In the application to π-stacks of DNA, we demonstrated for the Watson-Crick pair dimer [(GC),(GC)] how structural changes considerably affect the coupling strength of electron hole transfer. For models of three Watson-Crick pairs, we showed that the two-state model significantly overestimates the hole transfer coupling whereas simultaneous treatment of several states leads to satisfactory results.

  4. Temperature- and acceptor-specificity of cell-free vesicular transfer from transitional endoplasmic reticulum to the cis Golgi apparatus.

    PubMed Central

    Dunkle, S; Reust, T; Nowack, D D; Waits, L; Paulik, M; Morre, D M; Morre, D J

    1992-01-01

    The temperature dependence and specificity of transfer of membrane constituents from donor transitional endoplasmic reticulum to the cis Golgi apparatus were investigated using a cell-free system from rat liver. The radiolabelled transitional endoplasmic reticulum donors were prepared from slices of rat liver prelabelled with [14C]leucine. The acceptor Golgi apparatus elements were unlabelled and immobilized on nitrocellulose. When Golgi apparatus stacks were separated by preparative free-flow electrophoresis into subfractions enriched in cisternae derived from the cis, medial and trans portions of the stack respectively, efficient specific transfer was observed only to cis elements. Trans elements were devoid of specific acceptor capacity. Similarly, when transfer was determined as a function of temperature, a transition was observed in transfer activity between 12 degrees C and 18 degrees C similar to that seen in vivo for formation of the so-called 16 degrees C cis Golgi-located membrane compartment. Transfer at temperatures below 16 degrees C and transfer to trans Golgi apparatus compartments at temperatures either above or below 16 degrees C was similar and unspecific. The unspecific transfer at low temperature was pH independent, whereas specific transfer was greatest at the physiological pH of 7, and was reduced to 10% and 18% of that occurring at pH 8 and pH 5.5 respectively. These findings show that the cell-free system derived from rat liver exhibits a high degree of fidelity to transfer in vivo, an efficiency approaching that observed in vivo, and a nearly absolute acceptor specificity for cis Golgi apparatus. The acceptor-, temperature- and pH-specificity of the cell-free transfer, as well as the saturation kinetics exhibited with respect to acceptor Golgi apparatus, support the concept of transition-vesicle-specific docking sites of finite number associated with cis Golgi apparatus cisternae. Images Fig. 4. PMID:1472010

  5. Cascade energy transfer and tunable emission from nanosheet hybrids: locating acceptor molecules through chiral doping.

    PubMed

    Goudappagouda; Wakchaure, Vivek Chandrakant; Ranjeesh, Kayaramkodath Chandran; Abhai, Chalona Antony Ralph; Babu, Sukumaran Santhosh

    2017-06-27

    Light harvesting donor-acceptor assemblies are indispensable to efficiently tap photons. In an attempt to improve the light harvesting efficiency of an acceptor doped assembly, we design and synthesize a donor-acceptor-donor triad which exhibits an exceptional intramolecular energy transfer with excellent efficiency. Moreover, a facile cascade energy transfer (energy funnelling) is observed in the presence of a series of second acceptors (63-91% efficiency) with tunable emission colours. Self-assembled nanosheets formed by the triad in the presence of acceptors exhibit cascade energy transfer assisted tunable emission. In addition, use of chiral acceptors induces chirality to the triad and results in the formation of chiral nanosheets along with cascade energy transfer. Here chiral induction, nanosheet formation and cascade energy transfer in the presence of chiral acceptors are used as tools to probe the intercalation of acceptor molecules in the donor scaffold.

  6. Gelatin powders accelerate the resorption of calcium phosphate cement and improve healing in the alveolar ridge.

    PubMed

    Matsumoto, Goichi; Sugita, Yoshihiko; Kubo, Katsutoshi; Yoshida, Waka; Ikada, Yoshito; Sobajima, Satoshi; Neo, Masashi; Maeda, Hatsuhiko; Kinoshita, Yukihiko

    2014-05-01

    The aim of this study was to show the effectiveness of combining calcium phosphate cement and gelatin powders to promote bone regeneration in the canine mandible. We mixed gelatin powders with calcium phosphate cement to create a macroporous composite. In four beagle dogs, two saddle-type bone defects were created on each side of the mandible, and calcium phosphate cement alone or calcium phosphate cement containing composite gelatin powders was implanted in each of the defects. After a healing period of six months, mandibles were removed for µCT and histological analyses. The µCT and histological analyses showed that at experimental sites at which calcium phosphate cement alone had been placed new bone had formed only around the periphery of the residual calcium phosphate cement and that there had been little or no ingrowth into the calcium phosphate cement. On the other hand, at experimental sites at which calcium phosphate cement containing composite gelatin powders had been placed, we observed regenerated new bone in the interior of the residual calcium phosphate cement as well as around its periphery. The amount of resorption of calcium phosphate cement and bone regeneration depended on the mixing ratio of gelatin powders to calcium phosphate cement. New bone replacement was significantly better in the sites treated with calcium phosphate cement containing composite gelatin powders than in those treated with calcium phosphate cement alone.

  7. Acute phosphate nephropathy.

    PubMed

    Monfared, Ali; Habibzadeh, Seyed Mahmoud; Mesbah, Seyed Alireza

    2014-05-01

    We present acute phosphate nephropathy in a 28-year-old man, which was developed after a car accident due to rhabdomyolysis. Treatment of acute kidney injury was done with administration of sodium bicarbonate.

  8. Phosphate Mines, Jordan

    NASA Image and Video Library

    2008-04-21

    Jordan leading industry and export commodities are phosphate and potash, ranked in the top three in the world. These are used to make fertilizer. This image was acquired by NASA Terra satellite on September 17, 2005.

  9. Metal-phosphate binders

    DOEpatents

    Howe, Beth Ann [Lewistown, IL; Chaps-Cabrera, Jesus Guadalupe [Coahuila, MX

    2009-05-12

    A metal-phosphate binder is provided. The binder may include an aqueous phosphoric acid solution, a metal-cation donor including a metal other than aluminum, an aluminum-cation donor, and a non-carbohydrate electron donor.

  10. Cross-conjugated chromophores: synthesis of iso-polydiacetylenes with Donor/Acceptor substitution

    PubMed

    Ciulei; Tykwinski

    2000-11-16

    The iterative construction of cross-conjugated donor (D), acceptor (A), and donor-acceptor (D-A) substituted iso-polydiacetylene (iso-PDA) oligomers has been achieved utilizing palladium-catalyzed cross-coupling techniques. Structure-property relationships for these compounds have been analyzed for cross-conjugated pi-electronic communication as a result of contributions from donor, acceptor, or donor-acceptor functionalization.

  11. Phosphate control in dialysis

    PubMed Central

    Cupisti, Adamasco; Gallieni, Maurizio; Rizzo, Maria Antonietta; Caria, Stefania; Meola, Mario; Bolasco, Piergiorgio

    2013-01-01

    Prevention and correction of hyperphosphatemia is a major goal of chronic kidney disease–mineral and bone disorder (CKD–MBD) management, achievable through avoidance of a positive phosphate balance. To this aim, optimal dialysis removal, careful use of phosphate binders, and dietary phosphate control are needed to optimize the control of phosphate balance in well-nourished patients on a standard three-times-a-week hemodialysis schedule. Using a mixed diffusive–convective hemodialysis tecniques, and increasing the number and/or the duration of dialysis tecniques are all measures able to enhance phosphorus (P) mass removal through dialysis. However, dialytic removal does not equal the high P intake linked to the high dietary protein requirement of dialysis patients; hence, the use of intestinal P binders is mandatory to reduce P net intestinal absorption. Unfortunately, even a large dose of P binders is able to bind approximately 200–300 mg of P on a daily basis, so it is evident that their efficacy is limited in the case of an uncontrolled dietary P load. Hence, limitation of dietary P intake is needed to reach the goal of neutral phosphate balance in dialysis, coupled to an adequate protein intake. To this aim, patients should be informed and educated to avoid foods that are naturally rich in phosphate and also processed food with P-containing preservatives. In addition, patients should preferentially choose food with a low P-to-protein ratio. For example, patients could choose egg white or protein from a vegetable source. Finally, boiling should be the preferred cooking procedure, because it induces food demineralization, including phosphate loss. The integrated approach outlined in this article should be actively adapted as a therapeutic alliance by clinicians, dieticians, and patients for an effective control of phosphate balance in dialysis patients. PMID:24133374

  12. Phosphate control in dialysis.

    PubMed

    Cupisti, Adamasco; Gallieni, Maurizio; Rizzo, Maria Antonietta; Caria, Stefania; Meola, Mario; Bolasco, Piergiorgio

    2013-10-04

    Prevention and correction of hyperphosphatemia is a major goal of chronic kidney disease-mineral and bone disorder (CKD-MBD) management, achievable through avoidance of a positive phosphate balance. To this aim, optimal dialysis removal, careful use of phosphate binders, and dietary phosphate control are needed to optimize the control of phosphate balance in well-nourished patients on a standard three-times-a-week hemodialysis schedule. Using a mixed diffusive-convective hemodialysis tecniques, and increasing the number and/or the duration of dialysis tecniques are all measures able to enhance phosphorus (P) mass removal through dialysis. However, dialytic removal does not equal the high P intake linked to the high dietary protein requirement of dialysis patients; hence, the use of intestinal P binders is mandatory to reduce P net intestinal absorption. Unfortunately, even a large dose of P binders is able to bind approximately 200-300 mg of P on a daily basis, so it is evident that their efficacy is limited in the case of an uncontrolled dietary P load. Hence, limitation of dietary P intake is needed to reach the goal of neutral phosphate balance in dialysis, coupled to an adequate protein intake. To this aim, patients should be informed and educated to avoid foods that are naturally rich in phosphate and also processed food with P-containing preservatives. In addition, patients should preferentially choose food with a low P-to-protein ratio. For example, patients could choose egg white or protein from a vegetable source. Finally, boiling should be the preferred cooking procedure, because it induces food demineralization, including phosphate loss. The integrated approach outlined in this article should be actively adapted as a therapeutic alliance by clinicians, dieticians, and patients for an effective control of phosphate balance in dialysis patients.

  13. Chemical synthesis of long RNAs with terminal 5'-phosphate groups.

    PubMed

    Pradère, Ugo; Halloy, François; Hall, Jonathan

    2017-03-12

    Long structured RNAs are useful biochemical and biological tools. They are usually prepared enzymatically, but this precludes their site-specific modification with functional groups for chemical biology studies. One solution is to perform solid-phase synthesis of multiple RNAs loaded with 5'-terminal phosphate groups, so that RNAs can be concatenated using template ligation reactions. However, there are currently no readily available reagents suitable for the incorporation of the phosphate group into long RNAs by solid-phase synthesis. Here we describe an easy-to-prepare phosphoramidite reagent suitable for the chemical introduction of 5'-terminal phosphate groups into long RNAs. The phosphate is protected by a dinitrobenzhydryl group that serves as an essential lipophilic group for the separation of oligonucleotide by-products. The phosphate is unmasked quantitatively by brief UV irradiation. We demonstrate the value of this reagent in the preparation of a library of long structured RNAs that are site-specifically modified with functional groups.

  14. Fused Nonacyclic Electron Acceptors for Efficient Polymer Solar Cells.

    PubMed

    Dai, Shuixing; Zhao, Fuwen; Zhang, Qianqian; Lau, Tsz-Ki; Li, Tengfei; Liu, Kuan; Ling, Qidan; Wang, Chunru; Lu, Xinhui; You, Wei; Zhan, Xiaowei

    2017-01-25

    We design and synthesize four fused-ring electron acceptors based on 6,6,12,12-tetrakis(4-hexylphenyl)-indacenobis(dithieno[3,2-b;2',3'-d]thiophene) as the electron-rich unit and 1,1-dicyanomethylene-3-indanones with 0-2 fluorine substituents as the electron-deficient units. These four molecules exhibit broad (550-850 nm) and strong absorption with high extinction coefficients of (2.1-2.5) × 10(5) M(-1) cm(-1). Fluorine substitution downshifts the LUMO energy level, red-shifts the absorption spectrum, and enhances electron mobility. The polymer solar cells based on the fluorinated electron acceptors exhibit power conversion efficiencies as high as 11.5%, much higher than that of their nonfluorinated counterpart (7.7%). We investigate the effects of the fluorine atom number and position on electronic properties, charge transport, film morphology, and photovoltaic properties.

  15. Defect Donor and Acceptor in GaN

    SciTech Connect

    Look, D.C.; Reynolds, D.C.; Hemsky, J.W.; Sizelove, J.R.; Jones, R.L.

    1997-09-01

    High-energy (0.7{endash}1MeV) electron irradiation in GaN grown on sapphire produces shallow donors and deep or shallow acceptors at equal rates, 1{plus_minus}0.2 cm{sup {minus}1}. The data, in conjunction with theory, are consistent only with the shallow donor being the N vacancy, and the acceptor the N interstitial. The N-vacancy donor energy is 64{plus_minus}10 meV, much larger than the value of 18meV found for the residual donor (probably Si) in this material. The Hall-effect measurements also reveal a degenerate n -type layer at the GaN/sapphire interface which must be accounted for to get the proper donor activation energy. {copyright} {ital 1997} {ital The American Physical Society}

  16. An organic donor/acceptor lateral superlattice at the nanoscale.

    PubMed

    Otero, Roberto; Ecija, David; Fernandez, Gustavo; Gallego, José María; Sanchez, Luis; Martín, Nazario; Miranda, Rodolfo

    2007-09-01

    A precise control of the nanometer-scale morphology in systems containing mixtures of donor/acceptor molecules is a key factor to improve the efficiency of organic photovoltaic devices. Here we report on a scanning tunneling microscopy study of the first stages of growth of 2-[9-(1,3-dithiol-2-ylidene)anthracen-10(9H)-ylidene]-1,3-dithiole, as electron donor, and phenyl-C61-butyric acid methyl ester, as electron acceptor, on a Au(111) substrate under ultrahigh vacuum conditions. Due to differences in bonding strength with the substrate and different interactions with the Au(111) herringbone surface reconstruction, mixed thin films spontaneously segregate into a lateral superlattice of interdigitated nanoscale stripes with a characteristic width of about 10-20 nm, a morphology that has been predicted to optimize the efficiency of organic solar cells.

  17. Free Carrier Generation in Organic Photovoltaic Bulk Heterojunctions of Conjugated Polymers with Molecular Acceptors: Planar versus Spherical Acceptors

    SciTech Connect

    Nardes, Alexandre M.; Ferguson, Andrew J.; Wolfer, Pascal; Gui, Kurt; Burn, Paul L.; Meredith, Paul; Kopidakis, Nikos

    2014-03-05

    We present a comparative study of the photophysical performance of the prototypical fullerene derivative PC61BM with a planar small-molecule acceptor in an organic photovoltaic device. The small-molecule planar acceptor is 2-[{7-(9,9-di-n-propyl-9H-fluoren-2-yl)benzo[c][1,2,5]thiadiazol-4-yl}methylene]malononitrile, termed K12. We discuss photoinduced free charge-carrier generation and transport in blends of PC61BM or K12 with poly(3-n-hexylthiophene) (P3HT), surveying literature results for P3HT:PC61BM and presenting new results on P3HT:K12. For both systems we also review previous work on film structure and correlate the structural and photophysical results. In both cases, a disordered mixed phase is formed between P3HT and the acceptor, although the photophysical properties of this mixed phase differ markedly for PC61BM and K12. In the case of PC61BM the mixed phase acts as a free carrier generation region that can efficiently shuttle carriers to the pure polymer and fullerene domains. As a result, the vast majority of excitons quenched in P3HT:PC61BM blends yield free carriers detected by the contactless time-resolved microwave conductivity (TRMC) method. In contrast, approximately 85 % of the excitons quenched in P3HT:K12 do not result in free carriers over the nanosecond timescale of the TRMC experiment. We attribute this to poor electron-transport properties in the mixed P3HT:K12 phase. Here, we propose that the observed differences can be traced to the respective shapes of PC61BM and K12: the three-dimensional nature of the fullerene cage facilitates coupling between PC61BM molecules irrespective of their relative orientation, whereas for K12 strong electronic coupling is only expected for molecules oriented with their π systems parallel to each other. Comparison between the eutectic compositions of the P3HT:PC61BM and P3HT:K12 shows that the former contains enough fullerene to form a percolation pathway for electrons, whereas the latter contains a sub

  18. Current advances in fused tetrathiafulvalene donor-acceptor systems.

    PubMed

    Bergkamp, Jesse J; Decurtins, Silvio; Liu, Shi-Xia

    2015-02-21

    Electron donor (D) and acceptor (A) systems have been studied extensively. Among them, fused D-A systems have attracted much attention during the past decades. Herein, we will present the evolution of tetrathiafulvalene (TTF) fused D-A systems and their potential applications in areas such as solar cells, OFETs, molecular wires and optoelectronics just to name a few. The synthesis and electrochemical, photophysical and intrinsic properties of fused D-A systems will be described as well.

  19. 2012 ELECTRON DONOR-ACCEPTOR INTERACTIONS GORDON RESEARCH CONFERENCE, AUGUST 5-10, 2012

    SciTech Connect

    McCusker, James

    2012-08-10

    The upcoming incarnation of the Gordon Research Conference on Electron Donor Acceptor Interactions will feature sessions on classic topics including proton-coupled electron transfer, dye-sensitized solar cells, and biological electron transfer, as well as emerging areas such as quantum coherence effects in donor-acceptor interactions, spintronics, and the application of donor-acceptor interactions in chemical synthesis.

  20. Fullerene derivatives as electron acceptors for organic photovoltaic cells.

    PubMed

    Mi, Dongbo; Kim, Ji-Hoon; Kim, Hee Un; Xu, Fei; Hwang, Do-Hoon

    2014-02-01

    Energy is currently one of the most important problems humankind faces. Depletion of traditional energy sources such as coal and oil results in the need to develop new ways to create, transport, and store electricity. In this regard, the sun, which can be considered as a giant nuclear fusion reactor, represents the most powerful source of energy available in our solar system. For photovoltaic cells to gain widespread acceptance as a source of clean and renewable energy, the cost per watt of solar energy must be decreased. Organic photovoltaic cells, developed in the past two decades, have potential as alternatives to traditional inorganic semiconductor photovoltaic cells, which suffer from high environmental pollution and energy consumption during production. Organic photovoltaic cells are composed of a blended film of a conjugated-polymer donor and a soluble fullerene-derivative acceptor sandwiched between a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)-coated indium tin oxide positive electrode and a low-work-function metal negative electrode. Considerable research efforts aim at designing and synthesizing novel fullerene derivatives as electron acceptors with up-raised lowest unoccupied molecular orbital energy, better light-harvesting properties, higher electron mobility, and better miscibility with the polymer donor for improving the power conversion efficiency of the organic photovoltaic cells. In this paper, we systematically review novel fullerene acceptors synthesized through chemical modification for enhancing the photovoltaic performance by increasing open-circuit voltage, short-circuit current, and fill factor, which determine the performance of organic photovoltaic cells.

  1. Dimethyl sulfoxide as an electron acceptor for anaerobic growth.

    PubMed

    Zinder, S H; Brock, T D

    1978-01-23

    The isolation from lake mud of a bacterium which can use dimethyl sulfoxide (DMSO) as an electron acceptor for growth is described. The isolate, called strain DL-1, was a small, gram negative, non-motile spiral. The sole product of DMSO reduction was dimethyl sulfide (DMS). Other electron acceptors used by the isolate included sulfite, thiosulfate, elemental sulfur, methionine sulfoxide, tetramethylene sulfoxide, nitrate, and oxygen (microaerophilically). Sulfate was not reduced and could not even be assimilated. Lactate or succinate could serve as electron donors, with acetate as the main product. Hydrogen could be used as an electron donor if acetate was present in the medium as a carbon source. The organism has a c-type cytochrome, and most likely uses electron transport phosphorylation during DMSO reduction. Cultures of Desulfovibrio sp., Escherichia coli, Pseudomonas aeruginosa, and Proteus vulgaris were tested for growth using DMSO as an electron acceptor, and only the Proteus strain grew. Both Proteus and strain DL-1 are versatile at coupling reductions with energy generation. There is a marked resemblance between strain DL-1 and the recently described sulfur-reducing spirillum of Wolfe and Pfennig.

  2. Design directed self-assembly of donor-acceptor polymers.

    PubMed

    Marszalek, Tomasz; Li, Mengmeng; Pisula, Wojciech

    2016-09-21

    Donor-acceptor polymers with an alternating array of donor and acceptor moieties have gained particular attention during recent years as active components of organic electronics. By implementation of suitable subunits within the conjugated backbone, these polymers can be made either electron-deficient or -rich. Additionally, their band gap and light absorption can be precisely tuned for improved light-harvesting in solar cells. On the other hand, the polymer design can also be modified to encode the desired supramolecular self-assembly in the solid-state that is essential for an unhindered transport of charge carriers. This review focuses on three major factors playing a role in the assembly of donor-acceptor polymers on surfaces which are (1) nature, geometry and substitution position of solubilizing alkyl side chains, (2) shape of the conjugated polymer defined by the backbone curvature, and (3) molecular weight which determines the conjugation length of the polymer. These factors adjust the fine balance between attractive and repulsive forces and ensure a close polymer packing important for an efficient charge hopping between neighboring chains. On the microscopic scale, an appropriate domain formation with a low density of structural defects in the solution deposited thin film is crucial for the charge transport. The charge carrier transport through such thin films is characterized by field-effect transistors as basic electronic elements.

  3. Income-generating activities for family planning acceptors.

    PubMed

    1989-07-01

    The Income Generating Activities program for Family Planning Acceptors was introduced in Indonesia in 1979. Capital input by the Indonesian National Family Planning Coordination Board and the UN Fund for Population Activities was used to set up small businesses by family planning acceptors. In 2 years, when the businesses become self-sufficient, the loans are repaid, and the money is used to set up new family planning acceptors in business. The program strengthens family planning acceptance, improves the status of women, and enhances community self-reliance. The increase in household income generated by the program raises the standards of child nutrition, encourages reliance on the survival of children, and decreases the value of large families. Approximately 18,000 Family Planning-Income Generating Activities groups are now functioning all over Indonesia, with financial assistance from the central and local governments, the World Bank, the US Agency for International Development, the UN Population Fund, the Government of the Netherlands, and the Government of Australia through the Association of South East Asian Nations.

  4. Microbial arsenite oxidation with oxygen, nitrate, or an electrode as the sole electron acceptor.

    PubMed

    Nguyen, Van Khanh; Tran, Huong T; Park, Younghyun; Yu, Jaecheul; Lee, Taeho

    2017-02-09

    The purpose of this study was to identify bacteria that can perform As(III) oxidation for environmental bioremediation. Two bacterial strains, named JHS3 and JHW3, which can autotrophically oxidize As(III)-As(V) with oxygen as an electron acceptor, were isolated from soil and water samples collected in the vicinity of an arsenic-contaminated site. According to 16S ribosomal RNA sequence analysis, both strains belong to the ɤ-Proteobacteria class and share 99% sequence identity with previously described strains. JHS3 appears to be a new strain of the Acinetobacter genus, whereas JHW3 is likely to be a novel strain of the Klebsiella genus. Both strains possess the aioA gene encoding an arsenite oxidase and are capable of chemolithoautotrophic growth in the presence of As(III) up to 10 mM as a primary electron donor. Cell growth and As(III) oxidation rate of both strains were significantly enhanced during cultivation under heterotrophic conditions. Under anaerobic conditions, only strain JHW3 oxidized As(III) using nitrate or a solid-state electrode of a bioelectrochemical system as a terminal electron acceptor. Kinetic studies of As(III) oxidation under aerobic condition demonstrated a higher V max and K m from strain JHW3 than strain JHS3. This study indicated the potential application of strain JHW3 for remediation of subsurface environments contaminated with arsenic.

  5. Spectrophotometric and electrical studies of charge-transfer complexes of sodium flucloxacillin with π-acceptors

    NASA Astrophysics Data System (ADS)

    Refat, Moamen S.; El-Didamony, Akram M.

    2006-11-01

    The present study is interested to develop a simple, rapid and accurate spectrophotometric method for determination of sodium flucloxacillin (fluc) in pure form and pharmaceutical formulations. The charge-transfer (CT) interactions between sodium flucloxacillin as electron donor and chloranilic acid (CLA), dichloroquinone 4-chloroimide (DCQ), 2,3-dichloro-5,6-dicyano- p-benzoquinone (DDQ) and 7,7,8,8 tetracyano- p-quinodimethane (TCNQ), as π-electron acceptors have been investigated spectrophotometrically. Different variables affecting the reaction were studied and optimized. Under the optimum conditions, linear relationships with good correlation coefficients (0.9979-0.9995) were found between the absorbance and the concentration of the drug in the range 16-880 μg ml -1. The proposed methods were applied successfully to the determination of the examined drug either in pure or pharmaceutical dosage forms with good accuracy and precision. The formation of the CT-complexes and the sites of interaction were confirmed by elemental analysis CHN, UV-vis, IR, 1H NMR and mass spectra techniques. Based on Job's method of continuous variation plots, the obtained results indicate the formation of 1:1 charge-transfer complexes with the general formula [(fluc)(acceptor)]. Statistical analysis of the obtained results showed no significant difference between the proposed method and official method.

  6. Cholesterol acceptor capacity is preserved by different mechanisms in preterm and term fetuses.

    PubMed

    Pecks, Ulrich; Mohaupt, Markus G; Hütten, Matthias C; Maass, Nicolai; Rath, Werner; Escher, Geneviève

    2014-02-01

    Fetal serum cholesterol and lipoprotein concentrations differ between preterm and term born neonates. An imbalance of the flow of cholesterol from the sites of synthesis or efflux from cells of peripheral organs to the liver, the reverse cholesterol transport (RCT), is linked to atherosclerosis and cardiovascular disease (CVD). Preterm delivery is a risk factor for the development of CVD. Thus, we hypothesized that RCT is affected by a diminished cholesterol acceptor capacity in preterm as compared to term fetuses. Cholesterol efflux assays were performed in RAW264.7, HepG2, and HUVEC cell lines. In the presence and absence of ABC transporter overexpression by TO-901317, umbilical cord sera of preterm and term born neonates (n = 28 in both groups) were added. Lipid components including high density lipoprotein (HDL), low density lipoprotein (LDL), apolipoprotein A1, and apolipoprotein E were measured and related to fractional cholesterol efflux values. We found overall, fractional cholesterol efflux to remain constant between the study groups, and over gestational ages at delivery, respectively. However, correlation analysis revealed cholesterol efflux values to be predominantly related to HDL concentration at term, while in preterm neonates, cholesterol efflux was mainly associated with LDL In conclusion cholesterol acceptor capacity during fetal development is kept in a steady state with different mechanisms and lipid fractions involved at distinct stages during the second half of fetal development. However, RCT mechanisms in preterm neonates seem not to be involved in the development of CVD later in life suggesting rather changes in the lipoprotein pattern causative.

  7. Whole Exome Sequencing Reveals Novel PHEX Splice Site Mutations in Patients with Hypophosphatemic Rickets

    PubMed Central

    Gillies, Christopher; Sampson, Matthew G.; Kher, Vijay; Sethi, Sidharth K.; Otto, Edgar A.

    2015-01-01

    Objective Hypophosphatemic rickets (HR) is a heterogeneous genetic phosphate wasting disorder. The disease is most commonly caused by mutations in the PHEX gene located on the X-chromosome or by mutations in CLCN5, DMP1, ENPP1, FGF23, and SLC34A3. The aims of this study were to perform molecular diagnostics for four patients with HR of Indian origin (two independent families) and to describe their clinical features. Methods We performed whole exome sequencing (WES) for the affected mother of two boys who also displayed the typical features of HR, including bone malformations and phosphate wasting. B-lymphoblast cell lines were established by EBV transformation and subsequent RT-PCR to investigate an uncommon splice site variant found by WES. An in silico analysis was done to obtain accurate nucleotide frequency occurrences of consensus splice positions other than the canonical sites of all human exons. Additionally, we applied direct Sanger sequencing for all exons and exon/intron boundaries of the PHEX gene for an affected girl from an independent second Indian family. Results WES revealed a novel PHEX splice acceptor mutation in intron 9 (c.1080-3C>A) in a family with 3 affected individuals with HR. The effect on splicing of this mutation was further investigated by RT-PCR using RNA obtained from a patient’s EBV-transformed lymphoblast cell line. RT-PCR revealed an aberrant splice transcript skipping exons 10-14 which was not observed in control samples, confirming the diagnosis of X-linked dominant hypophosphatemia (XLH). The in silico analysis of all human splice sites adjacent to all 327,293 exons across 81,814 transcripts among 20,345 human genes revealed that cytosine is, with 64.3%, the most frequent nucleobase at the minus 3 splice acceptor position, followed by thymidine with 28.7%, adenine with 6.3%, and guanine with 0.8%. We generated frequency tables and pictograms for the extended donor and acceptor splice consensus regions by analyzing all human

  8. Spectral, thermal and kinetic studies of charge-transfer complexes formed between the highly effective antibiotic drug metronidazole and two types of acceptors: σ- and π-acceptors

    NASA Astrophysics Data System (ADS)

    Refat, Moamen S.; Saad, Hosam A.; Adam, Abdel Majid A.

    2015-04-01

    Understanding the interaction between drugs and small inorganic or organic molecules is critical in being able to interpret the drug-receptor interactions and acting mechanism of these drugs. A combined solution and solid state study was performed to describe the complexation chemistry of drug metronidazole (MZ) which has a broad-spectrum antibacterial activity with two types of acceptors. The acceptors include, σ-acceptor (i.e., iodine) and π-acceptors (i.e., dichlorodicyanobenzoquinone (DDQ), chloranil (CHL) and picric acid (PA)). The molecular structure, spectroscopic characteristics, the binding modes as well as the thermal stability were deduced from IR, UV-vis, 1H NMR and thermal studies. The binding ratio of complexation (MZ: acceptor) was determined to be 1:2 for the iodine acceptor and 1:1 for the DDQ, CHL or PA acceptor, according to the CHN elemental analyses and spectrophotometric titrations. It has been found that the complexation with CHL and PA acceptors increases the values of enthalpy and entropy, while the complexation with DDQ and iodine acceptors decreases the values of these parameters compared with the free MZ donor.

  9. Spectral, thermal and kinetic studies of charge-transfer complexes formed between the highly effective antibiotic drug metronidazole and two types of acceptors: σ- and π-acceptors.

    PubMed

    Refat, Moamen S; Saad, Hosam A; Adam, Abdel Majid A

    2015-04-15

    Understanding the interaction between drugs and small inorganic or organic molecules is critical in being able to interpret the drug-receptor interactions and acting mechanism of these drugs. A combined solution and solid state study was performed to describe the complexation chemistry of drug metronidazole (MZ) which has a broad-spectrum antibacterial activity with two types of acceptors. The acceptors include, σ-acceptor (i.e., iodine) and π-acceptors (i.e., dichlorodicyanobenzoquinone (DDQ), chloranil (CHL) and picric acid (PA)). The molecular structure, spectroscopic characteristics, the binding modes as well as the thermal stability were deduced from IR, UV-vis, (1)H NMR and thermal studies. The binding ratio of complexation (MZ: acceptor) was determined to be 1:2 for the iodine acceptor and 1:1 for the DDQ, CHL or PA acceptor, according to the CHN elemental analyses and spectrophotometric titrations. It has been found that the complexation with CHL and PA acceptors increases the values of enthalpy and entropy, while the complexation with DDQ and iodine acceptors decreases the values of these parameters compared with the free MZ donor.

  10. Reduction of Uranium(VI) Phosphate during Growth of the Thermophilic Bacterium Thermoterrabacterium ferrireducens

    PubMed Central

    Khijniak, T. V.; Slobodkin, A. I.; Coker, V.; Renshaw, J. C.; Livens, F. R.; Bonch-Osmolovskaya, E. A.; Birkeland, N.-K.; Medvedeva-Lyalikova, N. N.; Lloyd, J. R.

    2005-01-01

    The thermophilic, gram-positive bacterium Thermoterrabacterium ferrireducens coupled organotrophic growth to the reduction of sparingly soluble U(VI) phosphate. X-ray powder diffraction and X-ray absorption spectroscopy analysis identified the electron acceptor in a defined medium as U(VI) phosphate [uramphite; (NH4)(UO2)(PO4) · 3H2O], while the U(IV)-containing precipitate formed during bacterial growth was identified as ningyoite [CaU(PO4)2 · H2O]. This is the first report of microbial reduction of a largely insoluble U(VI) compound. PMID:16204572

  11. Magnetite nanoparticles facilitate methane production from ethanol via acting as electron acceptors.

    PubMed

    Yang, Zhiman; Shi, Xiaoshuang; Wang, Chuanshui; Wang, Lin; Guo, Rongbo

    2015-11-12

    Potential for interspecies hydrogen transfer within paddy soil enrichments obtained via addition of magnetite nanoparticles and ethanol (named as PEM) was investigated. To do this, PEM derived from rice field of Hangzhou (named as PEM-HZ) was employed, because it offered the best methane production performance. Methane production and Fe (III) reduction proceeded in parallel in the presence of magnetite. Inhibition experiments with 2-bromoethane sulfonate (BES) or phosphate showed that interspecies hydrogen transfer and Fe (III) reduction also occurred in methane production from ethanol. 16S rRNA-based Illumina sequencing results showed that Dechloromonas, Thauera, Desulfovibrio and Clostridium were the dominant putative Fe (III) -reducers, and that hydrogenotrophic Methanobacterium accounted for about 88% of the total archaeal community. These results indicated that magnetite nanoparticles that acted as electron acceptor could facilitate rapid oxidation of ethanol by members of the Fe (III) -reducers in PEM-HZ and establishment of the syntrophic relationship of Fe (III) -reducers with Methanobacterium via interspecies hydrogen transfer. Our results could offer a model to understand the microbial interaction with magnetite from a novel angle during methanogenesis.

  12. Magnetite nanoparticles facilitate methane production from ethanol via acting as electron acceptors

    PubMed Central

    Yang, Zhiman; Shi, Xiaoshuang; Wang, Chuanshui; Wang, Lin; Guo, Rongbo

    2015-01-01

    Potential for interspecies hydrogen transfer within paddy soil enrichments obtained via addition of magnetite nanoparticles and ethanol (named as PEM) was investigated. To do this, PEM derived from rice field of Hangzhou (named as PEM-HZ) was employed, because it offered the best methane production performance. Methane production and Fe (III) reduction proceeded in parallel in the presence of magnetite. Inhibition experiments with 2-bromoethane sulfonate (BES) or phosphate showed that interspecies hydrogen transfer and Fe (III) reduction also occurred in methane production from ethanol. 16S rRNA-based Illumina sequencing results showed that Dechloromonas, Thauera, Desulfovibrio and Clostridium were the dominant putative Fe (III) -reducers, and that hydrogenotrophic Methanobacterium accounted for about 88% of the total archaeal community. These results indicated that magnetite nanoparticles that acted as electron acceptor could facilitate rapid oxidation of ethanol by members of the Fe (III) -reducers in PEM-HZ and establishment of the syntrophic relationship of Fe (III) -reducers with Methanobacterium via interspecies hydrogen transfer. Our results could offer a model to understand the microbial interaction with magnetite from a novel angle during methanogenesis. PMID:26559132

  13. Magnetite nanoparticles facilitate methane production from ethanol via acting as electron acceptors

    NASA Astrophysics Data System (ADS)

    Yang, Zhiman; Shi, Xiaoshuang; Wang, Chuanshui; Wang, Lin; Guo, Rongbo

    2015-11-01

    Potential for interspecies hydrogen transfer within paddy soil enrichments obtained via addition of magnetite nanoparticles and ethanol (named as PEM) was investigated. To do this, PEM derived from rice field of Hangzhou (named as PEM-HZ) was employed, because it offered the best methane production performance. Methane production and Fe (III) reduction proceeded in parallel in the presence of magnetite. Inhibition experiments with 2-bromoethane sulfonate (BES) or phosphate showed that interspecies hydrogen transfer and Fe (III) reduction also occurred in methane production from ethanol. 16S rRNA-based Illumina sequencing results showed that Dechloromonas, Thauera, Desulfovibrio and Clostridium were the dominant putative Fe (III) -reducers, and that hydrogenotrophic Methanobacterium accounted for about 88% of the total archaeal community. These results indicated that magnetite nanoparticles that acted as electron acceptor could facilitate rapid oxidation of ethanol by members of the Fe (III) -reducers in PEM-HZ and establishment of the syntrophic relationship of Fe (III) -reducers with Methanobacterium via interspecies hydrogen transfer. Our results could offer a model to understand the microbial interaction with magnetite from a novel angle during methanogenesis.

  14. Engineering the specificity of trehalose phosphorylase as a general strategy for the production of glycosyl phosphates.

    PubMed

    Chen, Chao; Van der Borght, Jef; De Vreese, Rob; D'hooghe, Matthias; Soetaert, Wim; Desmet, Tom

    2014-07-25

    A two-step process is reported for the anomeric phosphorylation of galactose, using trehalose phosphorylase as biocatalyst. The monosaccharide enters this process as acceptor but can subsequently be released from the donor side, thanks to the non-reducing nature of the disaccharide intermediate. A key development was the creation of an optimized enzyme variant that displays a strict specificity (99%) for β-galactose 1-phosphate as product.

  15. Dynamics of iron-acceptor-pair formation in co-doped silicon

    NASA Astrophysics Data System (ADS)

    Bartel, T.; Gibaja, F.; Graf, O.; Gross, D.; Kaes, M.; Heuer, M.; Kirscht, F.; Möller, C.; Lauer, K.

    2013-11-01

    The pairing dynamics of interstitial iron and dopants in silicon co-doped with phosphorous and several acceptor types are presented. The classical picture of iron-acceptor pairing dynamics is expanded to include the thermalization of iron between different dopants. The thermalization is quantitatively described using Boltzmann statistics and different iron-acceptor binding energies. The proper understanding of the pairing dynamics of iron in co-doped silicon will provide additional information on the electronic properties of iron-acceptor pairs and may become an analytical method to quantify and differentiate acceptors in co-doped silicon.

  16. Dynamics of iron-acceptor-pair formation in co-doped silicon

    SciTech Connect

    Bartel, T.; Gibaja, F.; Graf, O.; Gross, D.; Kaes, M.; Heuer, M.; Kirscht, F.; Möller, C.; Lauer, K.

    2013-11-11

    The pairing dynamics of interstitial iron and dopants in silicon co-doped with phosphorous and several acceptor types are presented. The classical picture of iron-acceptor pairing dynamics is expanded to include the thermalization of iron between different dopants. The thermalization is quantitatively described using Boltzmann statistics and different iron-acceptor binding energies. The proper understanding of the pairing dynamics of iron in co-doped silicon will provide additional information on the electronic properties of iron-acceptor pairs and may become an analytical method to quantify and differentiate acceptors in co-doped silicon.

  17. Method for producing and regenerating a synthetic CO.sub.2 acceptor

    DOEpatents

    Lancet, Michael S [Pittsburgh, PA; Curran, George P [Pittsburgh, PA; Gorin, Everett [San Rafael, CA

    1982-01-01

    A method for producing a synthetic CO.sub.2 acceptor by feeding a mixture of finely divided silica and at least one finely divided calcium compound selected from the group consisting of calcium oxide and calcium carbonate to a fluidized bed; operating the fluidized bed at suitable conditions to produce pellets of synthetic CO.sub.2 acceptor and recovering the pellets of synthetic CO.sub.2 acceptor from the fluidized bed. Optionally, spent synthetic CO.sub.2 acceptor can be charged to the fluidized bed to produce regenerated pellets of synthetic CO.sub.2 acceptor.

  18. Method for producing and regenerating a synthetic CO[sub 2] acceptor

    DOEpatents

    Lancet, M. S.; Curran, G. P.; Gorin, E.

    1982-05-18

    A method is described for producing a synthetic CO[sub 2] acceptor by feeding a mixture of finely divided silica and at least one finely divided calcium compound selected from the group consisting of calcium oxide and calcium carbonate to a fluidized bed; operating the fluidized bed at suitable conditions to produce pellets of synthetic CO[sub 2] acceptor and recovering the pellets of synthetic CO[sub 2] acceptor from the fluidized bed. Optionally, spent synthetic CO[sub 2] acceptor can be charged to the fluidized bed to produce regenerated pellets of synthetic CO[sub 2] acceptor. 1 fig.

  19. Sodium phosphate-derived calcium phosphate cements

    SciTech Connect

    Sugama, T.; Carciello, N.R. )

    1995-01-01

    Calcium phosphate cements (CPC) were synthesized by the acid-base reaction between sodium phosphate, NaH[sub 2]PO[sub 4] or -(-NaPO[sub 3]-)-[sub n], as the acid solution, and calcium aluminate cements (CAC) as the base reactant at 25 C. The extent of reactivity of -(-NaPO[sub 3]-)-[sub n] with CAC was much higher than that of NaH[sub 2]PO[sub 4], thereby resulting in a compressive strength of > 20 MPa. Sodium calcium orthophosphate (SCOP) salts as amorphous reaction products were responsible for the development of this strength. When this CPC specimen as exposed in an autoclave, in-situ amorphous [r arrow] crystal conversions, such as SCOP [r arrow] hydroxyapatite (HOAp), and Al[sub 2]O[sub 3] [center dot] xH[sub 2]O [r arrow] [gamma]-AlOOH, occurred at [approx] 100 C, while the rate of reaction of the residual CAC with the phosphate reactant was increasingly accelerated by hydrothermal catalysis. Based upon this information, the authors prepared lightweight CPC specimens by hydrothermally treating a low-density cement slurry (1.28 g/cc) consisting of CAC powder, -(-NaPO[sub 3]-)-[sub n] solution, and mullite-hollow microspheres. The characteristics of the autoclaved lightweight specimens were a compressive strength of > 9.0 MPa, water permeability of [approx] 5.0 [times] 10[sup [minus]3] milli darcy, and a low rate of alkali carbonation. The reasons for such a low carbonation rate reflected the presence of a minimum amount of residual CAC, in conjunction with the presence of HOAp and [gamma]-AlOOH phases that are unsusceptible to wet carbonation.

  20. Using oxygen isotopes of phosphate to investigate phosphate release from sediments and phosphate input from waste water treatment plants into Lake Erie

    NASA Astrophysics Data System (ADS)

    Roberts, K.; Klass, T.; Watson, S.; Mah, B.; Paytan, A.

    2010-12-01

    Phosphorus is often a limiting nutrient in freshwater systems; however increased inputs have been promoting eutrophication in many of these systems. Phosphate is one of the more bio-available forms of phosphate and it has been suggested by Elsbury et al., (2009) that in addition to riverin input some other yet unidentified phosphate source contributes to the phosphorous loading in Lake Erie. We are using the oxygen isotope of phosphate to identify two potential sources of phosphorus into Lake Erie. Specifically we determine the isotopic composition of oxygen in phosphate which is associated with various sedimentary phases at two sites in Lake Erie. The distinct sedimentary phases have different phosphate mobility and thus release potential to the lake. In addition we determine the isotopic signature of phosphate that is released into the lake from treated waste water effluent throughout the year. Results will be compared to the isotopic signature of phosphate in Lake water to evaluate the potential contribution form each of these sources.

  1. Improved Manganese Phosphate Coatings

    DTIC Science & Technology

    1975-04-01

    Conversion coatings 3 . Phosphating bath 20 AGrjC onln odd*. ta It .. c..soMV midP 1J.,alft. by block noc.mb) Work was conducted to determine the mechanism by...34 TABULAR DATA Table I Analyses of Solution and Coating for Phosphating Baths 4 of Di-ferlng Compositions 11 Atomic Absorption...manganese and iron phosphate coating: k * a. Mn(H 2PO4) 2 Nn-P0 4 + H3PO0 k2 k) b. 3MnHPO4 - Mn3 (P04) 2 + H3i’O4 k4 k5 c. Fe(H 2PO4) 2 -01 FeHPO4

  2. Codeine dihydrogen phosphate hemihydrate.

    PubMed

    Langes, Christoph; Gelbrich, Thomas; Griesser, Ulrich J; Kahlenberg, Volker

    2009-08-01

    The cation of the title structure [systematic name: (5alpha,6alpha)-6-hydroxy-7,8-didehydro-4,5-epoxy-3-methoxy-17-methylmorphinanium dihydrogen phosphate hemihydrate], C18H22NO3+.H2PO4-.0.5H2O, has a T-shaped conformation. The dihydrogen phosphate anions are linked by O-H...O hydrogen bonds to give an extended ribbon chain. The codeine cations are linked together by O-H...O hydrogen bonds into a zigzag chain. There are also N-H...O bonds between the two types of hydrogen-bonded units. Additionally, they are connected to one another via O...H-O-H...O bridging water molecules. The asymmetric unit contains two codeine hydrogen cations, two dihydrogen phosphate anions and one water molecule. This study shows that the water molecules are firmly bound within a complex three-dimensional hydrogen-bonded framework.

  3. Phosphate Mines, Jordan

    NASA Technical Reports Server (NTRS)

    2008-01-01

    Jordan's leading industry and export commodities are phosphate and potash, ranked in the top three in the world. These are used to make fertilizer. The Jordan Phosphate Mines Company is the sole producer, having started operations in 1935. In addition to mining activities, the company produces phosphoric acid (for fertilizers, detergents, pharmaceuticals), diammonium phosphate (for fertilizer), sulphuric acid (many uses), and aluminum fluoride (a catalyst to make aluminum and magnesium).

    The image covers an area of 27.5 x 49.4 km, was acquired on September 17, 2005, and is located near 30.8 degrees north latitude, 36.1 degrees east longitude.

    The U.S. science team is located at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate.

  4. Multisite inhibition of Pinus pinea isocitrate lyase by phosphate.

    PubMed

    Ranaldi, F; Vanni, P; Giachetti, E

    2000-11-01

    Our results show that the phosphate ion is a nonlinear competitive inhibitor of Pinus pinea isocitrate lyase. In addition, this compound induces a sigmoidal response of the enzyme, which usually exhibits standard Michaelis-Menten kinetics. This peculiar behavior of P. pinea isocitrate lyase could be explained by a dimer (two-site) model, in which phosphate binds cooperatively, but the affinity of the vacant site for substrate (the magnesium-isocitrate complex) remains the same. As a result, the interaction of phosphate with free enzyme produces an inhibitor-enzyme-inhibitor species that is of significant importance in determining reaction rate; a possible regulatory role of the glyoxylate cycle by inorganic phosphate is suggested. The mode of phosphate inhibition is consistent with both the mechanism for magnesium ion activation of P. pinea isocitrate lyase and its site heterogeneity. Our results explain the cooperative effects observed by some authors in kinetic studies of isocitrate lyase carried out in phosphate buffers and also account for the higher K(m) values determined by using such assay systems. Phosphate buffer should be avoided in performing isocitrate lyase kinetics.

  5. Dissipative exciton transfer in donor bridge acceptor systems: numerical renormalization group calculation of equilibrium properties

    NASA Astrophysics Data System (ADS)

    Tornow, Sabine; Tong, Ning-Hua; Bulla, Ralf

    2006-07-01

    We present a detailed model study of exciton transfer processes in donor-bridge-acceptor (DBA) systems. Using a model which includes the intermolecular Coulomb interaction and the coupling to a dissipative environment we calculate the phase diagram, the absorption spectrum as well as dynamic equilibrium properties with the numerical renormalization group. This method is non-perturbative and therefore allows one to cover the full parameter space, especially the case when the intermolecular Coulomb interaction is of the same order as the coupling to the environment and perturbation theory cannot be applied. For DBA systems with up to six sites we found a transition to the localized phase (self-trapping) depending on the coupling to the dissipative environment. We discuss various criteria which favour delocalized exciton transfer.

  6. Organic Donor-Acceptor Complexes as Novel Organic Semiconductors.

    PubMed

    Zhang, Jing; Xu, Wei; Sheng, Peng; Zhao, Guangyao; Zhu, Daoben

    2017-07-18

    Organic donor-acceptor (DA) complexes have attracted wide attention in recent decades, resulting in the rapid development of organic binary system electronics. The design and synthesis of organic DA complexes with a variety of component structures have mainly focused on metallicity (or even superconductivity), emission, or ferroelectricity studies. Further efforts have been made in high-performance electronic investigations. The chemical versatility of organic semiconductors provides DA complexes with a great number of possibilities for semiconducting applications. Organic DA complexes extend the semiconductor family and promote charge separation and transport in organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). In OFETs, the organic complex serves as an active layer across extraordinary charge pathways, ensuring the efficient transport of induced charges. Although an increasing number of organic semiconductors have been reported to exhibit good p- or n-type properties (mobilities higher than 1 or even 10 cm(2) V(-1) s(-1)), critical scientific challenges remain in utilizing the advantages of existing semiconductor materials for more and wider applications while maintaining less complicated synthetic or device fabrication processes. DA complex materials have revealed new insight: their unique molecular packing and structure-property relationships. The combination of donors and acceptors could offer practical advantages compared with their unimolecular materials. First, growing crystals of DA complexes with densely packed structures will reduce impurities and traps from the self-assembly process. Second, complexes based on the original structural components could form superior mixture stacking, which can facilitate charge transport depending on the driving force in the coassembly process. Third, the effective use of organic semiconductors can lead to tunable band structures, allowing the operation mode (p- or n-type) of the transistor to be

  7. Characterization of the phosphorylation sites of the squid (Loligo pealei) high-molecular-weight neurofilament protein from giant axon axoplasm.

    PubMed

    Jaffe, H; Sharma, P; Grant, P; Pant, H

    2001-02-01

    Axonal caliber in vertebrates is attributed, in part, to the extensive phosphorylation of NFM and NFH C-terminal tail domain KSP repeats by proline-directed kinases. The squid giant axon, primarily involved in rapid impulse conduction during jet propulsion motility, is enriched in squid-specific neurofilaments, particularly the highly phosphorylated NF-220. Of the 228 serine-threonine candidate phosphate acceptor sites in the NF-220 tail domain (residues 401-1220), 82 are found in numerous repeats of three different motifs SAR/K, SEK/R, K/RSP, with 62 of these tightly clustered in the C-terminal repeat segment (residues 840-1160). Characterization of the in vivo NF-220 phosphorylated sites should provide clues as to the relevant kinases. To characterize these sites, proteolytic digests of NF-220 were analyzed by a combination of HPLC, electrospray tandem mass spectrometry and database searching. A total of 53 phosphorylation sites were characterized, with 47 clustered in the C-terminal repeat segment (residues 840-1160), representing 76% (47/62) of the total acceptor sites in the region. As in mammalian NFH, approximately 64% of the K/RSP sites (14/22) in this region were found to be phosphorylated implicating proline-directed kinases. Significantly, 78% of serines (31/40) in the KAES*EK and EKS*ARSP motifs were also phosphorylated suggesting that non proline-directed kinases such as CKI may also be involved. This is consistent with previous studies showing that CKI is the principal kinase associated with axoplasmic NF preparations. It also suggests that phosphorylation of large macromolecules with multiple phospho-sites requires sequential phosphorylation by several kinases.

  8. Chemopreventive Agents from Physalis minima Function as Michael Reaction Acceptors.

    PubMed

    Men, Ruizhi; Li, Ning; Ding, Chihong; Tang, Yingzhan; Xing, Yachao; Ding, Wanjing; Ma, Zhongjun

    2016-05-01

    The fruits of some varieties of genus Physalis have been used as delicious fruits and functional food in the Northeast of China. To reveal the functional material basis, we performed bioactivity-guided phytochemical research and chemopreventive effect assay of the constituents from Physalis minima. It was demonstrated that the ethyl acetate extract of P. minima L. (EEPM) had potential quinone reductase (QR) inducing activity with induction ratio (IR, QR induction activity) value of 1.47 ± 0.24, and glutathione binding property as potential Michael reaction acceptors (with an α, β-unsaturated ketone moiety). Furthermore, bioactivity-guided phytochemical research led eight compounds (1-8), which were elucidated as 3-isopropyl-5-acetoxycyclohexene-2-one-1 (1), isophysalin B (2), physalin G (3), physalin D (4), physalin I (5), physordinose B (6), stigmasterol-3-O-β-D-glucopyranoside (7) and 5α-6β-dihydroxyphysalin R (8) on the basis of nuclear magnetic resonance spectroscopy analyses and HRESIMS. Then, isophysalin B (2) and physordinose B (6) showed significant QR inducing activity with IR value of 2.80 ± 0.19 and 2.38 ± 0.46, respectively. An ultra-performance liquid chromatographic method with glutathione as the substrate was used to detect the Michael reaction acceptors in extracts of Physalis minima (EPM)We investigated the chemical constituents of EPM guided by biological activity methodIsophysalin B (1) and physordinose B (6) showed strong quinone reductase inducing activity with induction ratio values of 2.80 ± 0.19 and 2.38 ± 0.46This study generated useful information for consumers and many encourage researchers to utilize edible fruits from Physalis as a source of phytochemicals Abbreviations used: EPM: Extracts of Physalis minima, EEPM: Ethyl acetate extract of Physalis minima L., GSH: Glutathione, MRAs: Michael reaction acceptors, QR: Quinone reductase.

  9. Chemopreventive Agents from Physalis minima Function as Michael Reaction Acceptors

    PubMed Central

    Men, Ruizhi; Li, Ning; Ding, Chihong; Tang, Yingzhan; Xing, Yachao; Ding, Wanjing; Ma, Zhongjun

    2016-01-01

    Background: The fruits of some varieties of genus Physalis have been used as delicious fruits and functional food in the Northeast of China. Materials and Methods: To reveal the functional material basis, we performed bioactivity-guided phytochemical research and chemopreventive effect assay of the constituents from Physalis minima. Results: It was demonstrated that the ethyl acetate extract of P. minima L. (EEPM) had potential quinone reductase (QR) inducing activity with induction ratio (IR, QR induction activity) value of 1.47 ± 0.24, and glutathione binding property as potential Michael reaction acceptors (with an α, β-unsaturated ketone moiety). Furthermore, bioactivity-guided phytochemical research led eight compounds (1–8), which were elucidated as 3-isopropyl-5-acetoxycyclohexene-2-one-1 (1), isophysalin B (2), physalin G (3), physalin D (4), physalin I (5), physordinose B (6), stigmasterol-3-O-β-D-glucopyranoside (7) and 5α-6β-dihydroxyphysalin R (8) on the basis of nuclear magnetic resonance spectroscopy analyses and HRESIMS. Then, isophysalin B (2) and physordinose B (6) showed significant QR inducing activity with IR value of 2.80 ± 0.19 and 2.38 ± 0.46, respectively. SUMMARY An ultra-performance liquid chromatographic method with glutathione as the substrate was used to detect the Michael reaction acceptors in extracts of Physalis minima (EPM)We investigated the chemical constituents of EPM guided by biological activity methodIsophysalin B (1) and physordinose B (6) showed strong quinone reductase inducing activity with induction ratio values of 2.80 ± 0.19 and 2.38 ± 0.46This study generated useful information for consumers and many encourage researchers to utilize edible fruits from Physalis as a source of phytochemicals Abbreviations used: EPM: Extracts of Physalis minima, EEPM: Ethyl acetate extract of Physalis minima L., GSH: Glutathione, MRAs: Michael reaction acceptors, QR: Quinone reductase. PMID:27279713

  10. A donor-acceptor pair for the real time study of vibrational energy transfer in proteins.

    PubMed

    Müller-Werkmeister, Henrike M; Bredenbeck, Jens

    2014-02-21

    Vibrational energy transfer (VET) is believed to play an important role in protein function. Theoretical studies predict highly directional, anisotropic VET in proteins. Distinct energy transfer pathways which connect distant functional sites in proteins have been proposed by simulations, indicating a function in allosteric communication. Experimental evidence for such pathways, however, is lacking. In small molecules, ultrafast vibrational pump-probe spectroscopy has been used to investigate VET between different parts of a molecule in great detail. Here, we address the requirements for extending this powerful approach to proteins and present a protein-compatible donor-acceptor pair for the real time investigation of VET. This VET pair consists of two non-native amino acids, β-(1-azulenyl)-alanine and azidohomoalanine, which can be positioned site-specifically and are found to be very well suited for spectroscopic studies of VET. Important for the study of proteins, co-translational incorporation of each of the amino acids has been demonstrated before using mutually independent approaches of protein engineering. We investigated the performance of the proposed VET pair in a model peptide which is designed to contain additional characteristic vibrational modes frequently used in infrared spectroscopy of proteins. Despite a larger inter-residue distance, we find that our VET acceptor generates a major signal that is easily observed compared to the other vibrational modes in the congested parts of the spectrum. We find sufficient signal size at concentrations compatible with proteins and over distances that will allow tracking of energy flow along predicted transfer pathways.

  11. Construction of an Artificial Ferrimagnetic Lattice by Lithium Ion Insertion into a Neutral Donor/Acceptor Metal-Organic Framework.

    PubMed

    Taniguchi, Kouji; Narushima, Keisuke; Mahin, Julien; Kosaka, Wataru; Miyasaka, Hitoshi

    2016-04-18

    Construction of a molecular system in which the magnetic lattice exhibits long-range order is one of the fundamental goals in materials science. In this study, we demonstrate the artificial construction of a ferrimagnetic lattice by doping electrons into acceptor sites of a neutral donor/acceptor metal-organic framework (D/A-MOF). This doping was achieved by the insertion of Li-ions into the D/A-MOF, which was used as the cathode of a Li-ion battery cell. The neutral D/A-MOF is a layered system composed of a carboxylate-bridged paddlewheel-type diruthenium(II,II) complex as the donor and a TCNQ derivative as the acceptor. The ground state of the neutral form was a magnetically disordered paramagnetic state. Upon discharge of the cell, spontaneous magnetization was induced; the transition temperature was variable. The stability of the magnetically ordered lattice depended on the equilibrium electric potential of the D/A-MOF cathode, which reflected the electron-filling level. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Dual Mechanism of Ion Permeation through VDAC Revealed with Inorganic Phosphate Ions and Phosphate Metabolites

    PubMed Central

    Krammer, Eva-Maria; Vu, Giang Thi; Homblé, Fabrice; Prévost, Martine

    2015-01-01

    In the exchange of metabolites and ions between the mitochondrion and the cytosol, the voltage-dependent anion channel (VDAC) is a key element, as it forms the major transport pathway for these compounds through the mitochondrial outer membrane. Numerous experimental studies have promoted the idea that VDAC acts as a regulator of essential mitochondrial functions. In this study, using a combination of molecular dynamics simulations, free-energy calculations, and electrophysiological measurements, we investigated the transport of ions through VDAC, with a focus on phosphate ions and metabolites. We showed that selectivity of VDAC towards small anions including monovalent phosphates arises from short-lived interactions with positively charged residues scattered throughout the pore. In dramatic contrast, permeation of divalent phosphate ions and phosphate metabolites (AMP and ATP) involves binding sites along a specific translocation pathway. This permeation mechanism offers an explanation for the decrease in VDAC conductance measured in the presence of ATP or AMP at physiological salt concentration. The binding sites occur at similar locations for the divalent phosphate ions, AMP and ATP, and contain identical basic residues. ATP features a marked affinity for a central region of the pore lined by two lysines and one arginine of the N-terminal helix. This cluster of residues together with a few other basic amino acids forms a “charged brush” which facilitates the passage of the anionic metabolites through the pore. All of this reveals that VDAC controls the transport of the inorganic phosphates and phosphate metabolites studied here through two different mechanisms. PMID:25860993

  13. Assessment of structural, optical and conduction properties of ZnO thin films in the presence of acceptor impurities

    NASA Astrophysics Data System (ADS)

    Plugaru, R.; Plugaru, N.

    2016-06-01

    The structural, optical and electrical conduction properties of (Li/Cu,N):ZnO codoped thin films synthesized by the sol-gel method were investigated by field emission scanning electron microscopy (FESEM), x-ray diffraction (XRD), transmission and absorption, photoluminescence (PL) and I-V measurements in order to bring evidence of the formation of acceptor centers by dual-acceptor codoping processes. The (Li 3%,N 5%):ZnO films consist of crystallites with average size of 15 nm, show 95% transmission in the visible region, and an optical band gap of 3.22 eV. The PL spectra show emission maxima at 3.21 and 2.96 eV which are related to the emission of acceptor centers and the presence of defects, respectively. Li occupies interstitial sites and may form Lii-N(O) defect complexes that act as acceptor centers. The (Cu 3%,N 5%):ZnO films consist of crystallites with average size of 12 nm, and exhibit 90% transmission in the visible region. The PL spectra reveal band edge emission at 3.23 eV and defect related emission at 2.74 eV. In the (Cu,N) codoped films, copper substitutes zinc and adopts mainly the Cu1+ state. A possible defect complex involving Cu and N determines the transition from n- to p-type conductivity. These findings are in agreement with results of electronic structure calculations at the GGA-PBE level.

  14. Domestic phosphate deposits

    USGS Publications Warehouse

    McKelvey, V.E.; Cathcart, J.B.; Altschuler, Z.S.; Swanson, R.W.; Lutz, Katherine

    1953-01-01

    Most of the worlds phosphate deposits can be grouped into six types: 1) igneous apatite deposits; 2) marine phosphorites; 3) residual phosphorites; 4) river pebble deposits; 5) phosphatized rock; and 6) guano. The igneous apatites and marine phosphorites form deposits measurable in millions or billions of tons; the residual deposits are measurable in thousands or millions; and the other types generally only in thousands of tons. Igneous apatite deposits have been mined on a small scale in New York, New Jersey, and Virginia. Marine phosphorites have been mined in Montana, Idaho, Utah, Wyoming, Arkansas, Tennessee, North Carolina, South Carolina, Georgia, and Florida. Residual phosphorites have been mined in Tennessee, Pennsylvania, and Florida. River pebble has been produced in South Carolina and Florida; phosphatized rock in Tennessee and Florida; and guano in New Mexico and Texas. Present production is limited almost entirely to Florida, Tennessee, Montana, Idaho, and Wyoming. Incomplete but recently partly revised estimates indicate the presence of about 5 billion tons of phosphate deposits in the United States that is minable under present economic conditions. Deposits too lean in quality or thickness to compete with those in the western and southeastern fields probably contain tens of billions of tons.

  15. 2-O-α-D-Glucosylglycerol Phosphorylase from Bacillus selenitireducens MLS10 Possessing Hydrolytic Activity on β-D-Glucose 1-Phosphate

    PubMed Central

    Nihira, Takanori; Saito, Yuka; Ohtsubo, Ken’ichi; Nakai, Hiroyuki; Kitaoka, Motomitsu

    2014-01-01

    The glycoside hydrolase family (GH) 65 is a family of inverting phosphorylases that act on α-glucosides. A GH65 protein (Bsel_2816) from Bacillus selenitireducens MLS10 exhibited inorganic phosphate (Pi)-dependent hydrolysis of kojibiose at the rate of 0.43 s−1. No carbohydrate acted as acceptor for the reverse phosphorolysis using β-d-glucose 1-phosphate (βGlc1P) as donor. During the search for a suitable acceptor, we found that Bsel_2816 possessed hydrolytic activity on βGlc1P with a kcat of 2.8 s−1; moreover, such significant hydrolytic activity on sugar 1-phosphate had not been reported for any inverting phosphorylase. The H218O incorporation experiment and the anomeric analysis during the hydrolysis of βGlc1P revealed that the hydrolysis was due to the glucosyl-transferring reaction to a water molecule and not a phosphatase-type reaction. Glycerol was found to be the best acceptor to generate 2-O-α-d-glucosylglycerol (GG) at the rate of 180 s−1. Bsel_2816 phosphorolyzed GG through sequential Bi-Bi mechanism with a kcat of 95 s−1. We propose 2-O-α-d-glucopyranosylglycerol: phosphate β-d-glucosyltransferase as the systematic name and 2-O-α-d-glucosylglycerol phosphorylase as the short name for Bsel_2816. This is the first report describing a phosphorylase that utilizes polyols, and not carbohydrates, as suitable acceptor substrates. PMID:24466148

  16. Perylene-Diimide Based Donor-Acceptor-Donor Type Small-Molecule Acceptors for Solution-Processable Organic Solar Cells

    NASA Astrophysics Data System (ADS)

    Ganesamoorthy, Ramasamy; Vijayaraghavan, Rajagopalan; Sakthivel, Pachagounder

    2017-08-01

    Development of nonfullerene acceptors plays an important role in the commercial availability of plastic solar cells. We report herein synthesis of bay-substituted donor-acceptor-donor (D-A-D)-type perylene diimide (PDI)-based small molecules (SM-1 to SM-4) by Suzuki coupling method and their use as acceptors in bulk heterojunction organic solar cells (BHJ-OSCs) with poly(3-hexylthiophene) (P3HT) polymer donor. We varied the number of electron-rich thiophene units and the solubilizing side chains and also evaluated the optical and electrochemical properties of the small molecules. The synthesized small molecules were confirmed by Fourier-transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and high-resolution mass spectroscopy (HR-MS). The small molecules showed extensive and strong absorption in the ultraviolet-visible (UV-Vis) region up to 750 nm, with bandgap (E_{{g}}^{{opt}} ) reduced below <2 eV. The energy levels of small molecules SM-1 to SM-4 were suitable for use as electron-accepting materials. The small molecules showed good thermal stability up to 300°C. BHJ-OSCs with SM-1 and P3HT polymer donor showed maximum power conversion efficiency (PCE) of 0.19% with V oc of 0.30 V, J sc of 1.72 mA cm-2, and fill factor (FF) of 37%. The PCE decreased with the number of thiophene units. The PCE of SM-2 was lower than that of SM-1. This difference in PCE can be explained by the higher aggregation tendency of the bithiophene compared with the thiophene unit. Introduction of the solubilizing group in the bay position increased the aggregation property, leading to much lower PCE than for the small molecules without solubilizing group.

  17. Donor-acceptor complexation and dehydrogenation chemistry of aminoboranes.

    PubMed

    Malcolm, Adam C; Sabourin, Kyle J; McDonald, Robert; Ferguson, Michael J; Rivard, Eric

    2012-12-03

    A series of formal donor-acceptor adducts of aminoborane (H(2)BNH(2)) and its N-substituted analogues (H(2)BNRR') were prepared: LB-H(2)BNRR'(2)-BH(3) (LB = DMAP, IPr, IPrCH(2) and PCy(3); R and R' = H, Me or tBu; IPr = [(HCNDipp)(2)C:] and Dipp = 2,6-iPr(2)C(6)H(3)). To potentially access complexes of molecular boron nitride, LB-BN-LA (LA = Lewis acid), preliminary dehydrogenation chemistry involving the parent aminoborane adducts LB-H(2)BNH(2)-BH(3) was investigated using [Rh(COD)Cl](2), CuBr, and NiBr(2) as dehydrogenation catalysts. In place of isolating the intended dehydrogenated BN donor-acceptor complexes, the formation of borazine was noted as a major product. Attempts to prepare the fluoroarylborane-capped aminoborane complexes, LB-H(2)BNH(2)-B(C(6)F(5))(3), are also described.

  18. Dissimilatory reduction of extracellular electron acceptors in anaerobic respiration.

    PubMed

    Richter, Katrin; Schicklberger, Marcus; Gescher, Johannes

    2012-02-01

    An extension of the respiratory chain to the cell surface is necessary to reduce extracellular electron acceptors like ferric iron or manganese oxides. In the past few years, more and more compounds were revealed to be reduced at the surface of the outer membrane of Gram-negative bacteria, and the list does not seem to have an end so far. Shewanella as well as Geobacter strains are model organisms to discover the biochemistry that enables the dissimilatory reduction of extracellular electron acceptors. In both cases, c-type cytochromes are essential electron-transferring proteins. They make the journey of respiratory electrons from the cytoplasmic membrane through periplasm and over the outer membrane possible. Outer membrane cytochromes have the ability to catalyze the last step of the respiratory chains. Still, recent discoveries provided evidence that they are accompanied by further factors that allow or at least facilitate extracellular reduction. This review gives a condensed overview of our current knowledge of extracellular respiration, highlights recent discoveries, and discusses critically the influence of different strategies for terminal electron transfer reactions.

  19. Glutathione Adduct Patterns of Michael-Acceptor Carbonyls.

    PubMed

    Slawik, Christian; Rickmeyer, Christiane; Brehm, Martin; Böhme, Alexander; Schüürmann, Gerrit

    2017-02-22

    Glutathione (GSH) has so far been considered to facilitate detoxification of soft organic electrophiles through covalent binding at its cysteine (Cys) thiol group, followed by stepwise catalyzed degradation and eventual elimination along the mercapturic acid pathway. Here we show that in contrast to expectation from HSAB theory, Michael-acceptor ketones, aldehydes and esters may form also single, double and triple adducts with GSH involving β-carbon attack at the much harder N-terminus of the γ-glutamyl (Glu) unit of GSH. In particular, formation of the GSH-N single adduct contradicts the traditional view that S alkylation always forms the initial reaction of GSH with Michael-acceptor carbonyls. To this end, chemoassay analyses of the adduct formation of GSH with nine α,β-unsaturated carbonyls employing high performance liquid chromatography and tandem mass spectrometry have been performed. Besides enriching the GSH adductome and potential biomarker applications, electrophilic N-terminus functio-nalization is likely to impair GSH homeostasis substantially through blocking the γ-glutamyl transferase catalysis of the first breakdown step of modified GSH, and thus its timely reconstitution. The discussion includes a comparison with cyclic adducts of GSH and furan metabolites as reported in literature, and quantum chemically calculated thermodynamics of hard-hard, hard-soft and soft-soft adducts.

  20. Conductivity of a Weyl semimetal with donor and acceptor impurities

    NASA Astrophysics Data System (ADS)

    Rodionov, Ya. I.; Syzranov, S. V.

    2015-05-01

    We study transport in a Weyl semimetal with donor and acceptor impurities. At sufficiently high temperatures transport is dominated by electron-electron interactions, while the low-temperature resistivity comes from the scattering of quasiparticles on screened impurities. Using the diagrammatic technique, we calculate the conductivity σ (T ,ω ,nA,nD) in the impurities-dominated regime as a function of temperature T , frequency ω , and the concentrations nA and nD of acceptors and donors and discuss the crossover behavior between the regimes of low and high temperatures and impurity concentrations. In a sufficiently compensated material [| nA-nD|≪ (nA+nD) ] with a small effective fine structure constant α ,σ (ω ,T ) ∝T2/(T-2-i ω .const) in a wide interval of temperatures. For very low temperatures, or in the case of an uncompensated material, the transport is effectively metallic. We discuss experimental conditions necessary for realizing each regime.

  1. Donator acceptor map for carotenoids, melatonin and vitamins.

    PubMed

    Martínez, Ana; Rodríguez-Gironés, Miguel A; Barbosa, Andrés; Costas, Miguel

    2008-09-25

    Bright yellow and red colors in animals and plants are assumed to be caused by carotenoids (CAR). In animals, these pigments are deposited in scales, skin and feathers. Together with other naturally occurring and colorless substances such as melatonin and vitamins, they are considered antioxidants due to their free-radical-scavenging properties. However, it would be better to refer to them as "antiradicals", an action that can take place either donating or accepting electrons. In this work we present quantum chemical calculations for several CAR and some colorless antioxidants, such as melatonin and vitamins A, C and E. The antiradical capacity of these substances is determined using vertical ionization energy (I), electron affinity (A), the electrodonating power (omega(-)) and the electroaccepting power (omega(+)). Using fluor and sodium as references, electron acceptance (R(a)) and electron donation (R(d)) indexes are defined. A plot of R(d) vs R(a) provides a donator acceptor map (DAM) useful to classify any substance regarding its electron donating-accepting capability. Using this DAM, a qualitative comparison among all the studied compounds is presented. According to R(d) values, vitamin E is the most effective antiradical in terms of its electron donor capacity, while the most effective antiradical in terms of its electron acceptor capacity, R(a), is astaxanthin, the reddest CAR. These results may be helpful for understanding the role played by naturally occurring pigments, acting as radical scavengers either donating or accepting electrons.

  2. Evaluation of Manganese Phosphate Coatings.

    DTIC Science & Technology

    1984-02-01

    84003 _____________ 4 . TTLE and -bitle)5. TYPE OF REPORT & PERIOD COVERED EVALUATION OF MANGANESE PHOSPHATE COATINGS Final 6. PERFORMING ORG. REPORT...rosion resistance of the Endurion phosphate was significantly superior to the 4 . basic manganese phosphate . Endurion phosphate with a Supplementary...OF CONTENTS Page STATEMENT OF THE PROBLEM 1 BACKGROUND 1 APPROACH TO THE PROBLEM 3 RESULTS 4 CONCLUSIONS 7 TABLES I. Falex Wear Life Test Procedure 8

  3. Phosphate Bonded Solidification of Radioactive Incinerator Wastes

    SciTech Connect

    Walker, B. W.

    1999-04-13

    The incinerator at the Department of Energy Savannah River Site burns low level radioactive and hazardous waste. Ash and scrubber system waste streams are generated during the incineration process. Phosphate Ceramic technology is being tested to verify the ash and scrubber waste streams can be stabilized using this solidification method. Acceptance criteria for the solid waste forms include leachability, bleed water, compression testing, and permeability. Other testing on the waste forms include x-ray diffraction and scanning electron microscopy.

  4. Structural basis for non-genuine phenolic acceptor substrate specificity of Streptomyces roseochromogenes prenyltransferase CloQ from the ABBA/PT-barrel superfamily

    PubMed Central

    Araya-Cloutier, Carla; Martens, Bianca; Schaftenaar, Gijs; Leipoldt, Franziska; Gruppen, Harry

    2017-01-01

    Acceptor substrate specificity of Streptomyces roseochromogenes prenyltransferase SrCloQ was investigated using different non-genuine phenolic compounds. RP-UHPLC-UV-MSn was used for the tentative annotation and quantification of the prenylated products. Flavonoids, isoflavonoids and stilbenoids with different types of substitution were prenylated by SrCloQ, although with less efficiency than the genuine substrate 4-hydroxyphenylpyruvate. The isoflavan equol, followed by the flavone 7,4’-dihydroxyflavone, were the best non-genuine acceptor substrates. B-ring C-prenylation was in general preferred over A-ring C-prenylation (ratio 5:1). Docking studies of non-genuine acceptor substrates with the B-ring oriented towards the donor substrate dimethylallyl pyrophosphate, showed that the carbonyl group of the C-ring was able to make stabilizing interactions with the residue Arg160, which might determine the preference observed for B-ring prenylation. No reaction products were formed when the acceptor substrate had no phenolic hydroxyl groups. This preference can be explained by the essential hydrogen bond needed between a phenolic hydroxyl group and the residue Glu281. Acceptor substrates with an additional hydroxyl group at the C3’ position (B-ring), were mainly O3’-prenylated (> 80% of the reaction products). This can be explained by the proximity of the C3’ hydroxyl group to the donor substrate at the catalytic site. Flavones were preferred over isoflavones by SrCloQ. Docking studies suggested that the orientation of the B-ring and of the phenolic hydroxyl group at position C7 (A-ring) of flavones towards the residue Tyr233 plays an important role in this observed preference. Finally, the insights obtained on acceptor substrate specificity and regioselectivity for SrCloQ were extended to other prenyltransferases from the CloQ/NhpB family. PMID:28355308

  5. Nicotinamide Adenine Dinucleotide Phosphate-Dependent Formate Dehydrogenase from Clostridium thermoaceticum: Purification and Properties

    PubMed Central

    Andreesen, Jan R.; Ljungdahl, Lars G.

    1974-01-01

    The nicotinamide adenine dinucleotide phosphate (NADP)-dependent formate dehydrogenase in Clostridium thermoaceticum used, in addition to its natural electron acceptor, methyl and benzyl viologen. The enzyme was purified to a specific activity of 34 (micromoles per minute per milligram of protein) with NADP as electron acceptor. Disc gel electrophoresis of the purified enzyme yielded two major and two minor protein bands, and during centrifugation in sucrose gradients two components of apparent molecular weights of 270,000 and 320,000 were obtained, both having formate dehydrogenase activity. The enzyme preparation catalyzed the reduction of riboflavine 5′-phosphate flavine adenine dinucleotide and methyl viologen by using reduced NADP as a source of electrons. It also had reduced NADP oxidase activity. The enzyme was strongly inhibited by cyanide and ethylenediaminetetraacetic acid. It was also inhibited by hypophosphite, an inhibition that was reversed by formate. Sulfite inhibited the activity with NADP but not with methyl viologen as acceptor. The apparent Km at 55 C and pH 7.5 for formate was 2.27 × 10−4 M with NADP and 0.83 × 10−4 with methyl viologen as acceptor. The apparent Km for NADP was 1.09 × 10−4 M and for methyl viologen was 2.35 × 10−3 M. NADP showed substrate inhibition at 5 × 10−3 M and higher concentrations. With NADP as electron acceptor, the enzyme had a broad pH optimum between 7 and 9.5. The apparent temperature optimum was 85 C. In the absence of substrates, the enzyme was stable at 70 C but was rapidly inactivated at temperatures above 73 C. The enzyme was very sensitive to oxygen but was stabilized by thiol-iron complexes and formate. PMID:4154039

  6. Structural Isosteres of Phosphate Groups in the Protein Data Bank.

    PubMed

    Zhang, Yuezhou; Borrel, Alexandre; Ghemtio, Leo; Regad, Leslie; Boije Af Gennäs, Gustav; Camproux, Anne-Claude; Yli-Kauhaluoma, Jari; Xhaard, Henri

    2017-03-13

    We developed a computational workflow to mine the Protein Data Bank for isosteric replacements that exist in different binding site environments but have not necessarily been identified and exploited in compound design. Taking phosphate groups as examples, the workflow was used to construct 157 data sets, each composed of a reference protein complexed with AMP, ADP, ATP, or pyrophosphate as well other ligands. Phosphate binding sites appear to have a high hydration content and large size, resulting in U-shaped bioactive conformations recurrently found across unrelated protein families. A total of 16 413 replacements were extracted, filtered for a significant structural overlap on phosphate groups, and sorted according to their SMILES codes. In addition to the classical isosteres of phosphate, such as carboxylate, sulfone, or sulfonamide, unexpected replacements that do not conserve charge or polarity, such as aryl, aliphatic, or positively charged groups, were found.

  7. Investigation of structural mimetics of natural phosphate ion binding motifs.

    PubMed

    Kataev, Evgeny A; Shumilova, Tatiana A

    2015-02-16

    Phosphates are ubiquitous in biology and nearly half of all proteins interact with their partners by means of recognition of phosphate residues. Therefore, a better understanding of the phosphate ion binding by peptidic structures is highly desirable. Two new receptors have been designed and synthesized and their anion binding properties in an acetonitrile solution have been determined. The structure of hosts mimics a part of the kinase active site that is responsible for the recognition of the phosphate residue. New hosts contain additional free amino groups with the aim to facilitate coordination of protonated anions, such as dihydrogen phosphate. According to spectrophotometric measurements, stepwise 1:1 and 1:2 binding modes have been observed for both receptors in the presence of acetate, hydrogen sulfate and dihydrogen phosphate. Compared with the acyclic receptor, the macrocyclic receptor has demonstrated a remarkably enhanced selectivity for dihydrogen phosphate over other anions. Fluorometric measurements have revealed different responses of the acyclic and macrocyclic receptors towards anions. However, in both cases, a 5-8 nm hypsochromic shift of fluorescence maximum has been observed upon interaction of acetate and dihydrogen phosphate with receptors.

  8. Engineering frontier energy levels in donor-acceptor fluoren-9-ylidene malononitriles versus fluorenones.

    PubMed

    Homnick, Paul J; Tinkham, Jonathan S; Devaughn, Raymond; Lahti, Paul M

    2014-01-16

    Donor-acceptor molecules incorporating fluoren-9-ylidene malononitrile acceptor units conjugated to trimethoxystyrene and/or diarylamine donor units were synthesized, and their electronic spectral properties and electrochemical behaviors were evaluated by comparison to those of the analogous fluorenones. Frontier energy level and optical transition energy trends are explained based on a quantitative, modular donor-acceptor interaction model. A connectivity effect on absorption transition moment strength is also described.

  9. Calcium Phosphates and Human Beings

    NASA Astrophysics Data System (ADS)

    Dorozhkin, Sergey V.

    2006-05-01

    This article describes the general importance of calcium phosphates for human beings. The basic information on the structure and chemical properties of the biologically relevant calcium phosphates is summarized. Basic facts on the natural occurrence and the industrial use of natural calcium phosphates are discussed. Fundamental details on the presence of calcium phosphates in major calcified tissues (bones and teeth) of humans and mammals, as well as on biomaterials made of calcium phosphates are discussed. The article will be of value for chemistry teachers for expansion of their general background and point the students' attention to the rapidly growing topic of bone-substituting biomaterials.

  10. Severe and mild phenotypes in Pfeiffer syndrome with splice acceptor mutations in exon IIIc of FGFR2.

    PubMed

    Teebi, Ahmad S; Kennedy, Shelley; Chun, Kathy; Ray, Peter N

    2002-01-01

    Pfeiffer syndrome is clinically and genetically heterogeneous. Three clinical subtypes have been delineated based on the severity of acrocephalysyndactyly and associated manifestations. Severe cases are usually sporadic and caused by a number of different mutations in exons IIIa and IIIc of the fibroblast growth factor receptor 2 (FGFR2) gene. Mild cases are either sporadic or familial and are caused by mutations in FGFR2 or FGFR1, respectively. We report on two individuals with different novel de novo mutations in FGFR2. The first is a 17-year-old male who has a severe phenotype, within the spectrum of subtype 1 including severe ocular proptosis, elbow ankylosis, visceral anomalies, and normal intelligence. This patient was found to have a novel complex mutation at the 3' acceptor site of exon IIIc of FGFR2, denoted as C952-3 del10insACC. The other patient, a 2-year-old female, has a mild phenotype, typical of the classic subtype 1 including brachycephaly with coronal synostosis and hypertelorism. She was also found to have a mutation at the 3' acceptor site (the same splice site) of exon IIIc of FGFR2, a point mutation designated as 952-1G-->A. Speculation on the molecular mechanisms that cause severe and mild phenotypes is presented in relation to these two cases.

  11. Influence of Coherent Tunneling and Incoherent Hopping on the Charge Transfer Mechanism in Linear Donor-Bridge-Acceptor Systems.

    PubMed

    Li, Guangqi; Govind, Niranjan; Ratner, Mark A; Cramer, Christopher J; Gagliardi, Laura

    2015-12-17

    The mechanism of charge transfer has been observed to change from tunneling to hopping with increasing numbers of DNA base pairs in polynucleotides and with the length of molecular wires. The aim of this paper is to investigate this transition by examining the population dynamics using a tight-binding Hamiltonian with model parameters to describe a linear donor-bridge-acceptor (D-B-A) system. The model includes a primary vibration and an electron-vibration coupling at each site. A further coupling of the primary vibration with a secondary phonon bath allows the system to dissipate energy to the environment and reach a steady state. We apply the quantum master equation (QME) approach, based on second-order perturbation theory in a quantum dissipative system, to examine the dynamical processes involved in charge-transfer and follow the population transfer rate at the acceptor, ka, to shed light on the transition from tunneling to hopping. With a small tunneling parameter, V, the on-site population tends to localize and form polarons, and the hopping mechanism dominates the transfer process. With increasing V, the population tends to be delocalized and the tunneling mechanism dominates. The competition between incoherent hopping and coherent tunneling governs the mechanism of charge transfer. By varying V and the total number of sites, we also examine the onset of the transition from tunneling to hopping with increasing length.

  12. 21 CFR 184.1434 - Magnesium phosphate.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Magnesium phosphate. 184.1434 Section 184.1434 Food... Specific Substances Affirmed as GRAS § 184.1434 Magnesium phosphate. (a) Magnesium phosphate includes both magnesium phosphate, dibasic, and magnesium phosphate, tribasic. Magnesium phosphate, dibasic (MgHPO4·3H2O...

  13. 21 CFR 184.1434 - Magnesium phosphate.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 3 2014-04-01 2014-04-01 false Magnesium phosphate. 184.1434 Section 184.1434... GRAS § 184.1434 Magnesium phosphate. (a) Magnesium phosphate includes both magnesium phosphate, dibasic, and magnesium phosphate, tribasic. Magnesium phosphate, dibasic (MgHPO4·3H2O, CAS Reg. No. 7782-0975...

  14. 21 CFR 184.1434 - Magnesium phosphate.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 3 2011-04-01 2011-04-01 false Magnesium phosphate. 184.1434 Section 184.1434... Listing of Specific Substances Affirmed as GRAS § 184.1434 Magnesium phosphate. (a) Magnesium phosphate includes both magnesium phosphate, dibasic, and magnesium phosphate, tribasic. Magnesium phosphate, dibasic...

  15. 21 CFR 184.1434 - Magnesium phosphate.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 3 2012-04-01 2012-04-01 false Magnesium phosphate. 184.1434 Section 184.1434... Listing of Specific Substances Affirmed as GRAS § 184.1434 Magnesium phosphate. (a) Magnesium phosphate includes both magnesium phosphate, dibasic, and magnesium phosphate, tribasic. Magnesium phosphate, dibasic...

  16. 21 CFR 184.1434 - Magnesium phosphate.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 3 2013-04-01 2013-04-01 false Magnesium phosphate. 184.1434 Section 184.1434... Listing of Specific Substances Affirmed as GRAS § 184.1434 Magnesium phosphate. (a) Magnesium phosphate includes both magnesium phosphate, dibasic, and magnesium phosphate, tribasic. Magnesium phosphate, dibasic...

  17. Tetrathiafulvalene-fused porphyrins via quinoxaline linkers: symmetric and asymmetric donor-acceptor systems.

    PubMed

    Jia, Hongpeng; Schmid, Belinda; Liu, Shi-Xia; Jaggi, Michael; Monbaron, Philippe; Bhosale, Sheshanath V; Rivadehi, Shadi; Langford, Steven J; Sanguinet, Lionel; Levillain, Eric; El-Khouly, Mohamed E; Morita, Ysushi; Fukuzumi, Shunichi; Decurtins, Silvio

    2012-10-08

    A tetrathiafulvalene (TTF) donor is annulated to porphyrins (P) via quinoxaline linkers to form novel symmetric P-TTF-P triads 1 a-c and asymmetric P-TTF dyads 2 a,b in good yields. These planar and extended π-conjugated molecules absorb light over a wide region of the UV/Vis spectrum as a result of additional charge-transfer excitations within the donor-acceptor assemblies. Quantum-chemical calculations elucidate the nature of the electronically excited states. The compounds are electrochemically amphoteric and primarily exhibit low oxidation potentials. Cyclic voltammetric and spectroelectrochemical studies allow differentiation between the TTF and porphyrin sites with respect to the multiple redox processes occurring within these molecular assemblies. Transient absorption measurements give insight into the excited-state events and deliver corresponding kinetic data. Femtosecond transient absorption spectra in benzonitrile may suggest the occurrence of fast charge separation from TTF to porphyrin in dyads 2 a,b but not in triads 1 a-c. Clear evidence for a photoinduced and relatively long lived charge-separated state (385 ps lifetime) is obtained for a supramolecular coordination compound built from the ZnP-TTF dyad and a pyridine-functionalized C(60) acceptor unit. This specific excited state results in a (ZnP-TTF)(⋅+) ⋅⋅⋅(C(60) py)(⋅-) state. The binding constant of Zn(II) ⋅⋅⋅py is evaluated by constructing a Benesi-Hildebrand plot based on fluorescence data. This plot yields a binding constant K of 7.20×10(4)  M(-1), which is remarkably high for bonding of pyridine to ZnP. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Two acceptor levels and hopping conduction in Mn-doped GaAs

    NASA Astrophysics Data System (ADS)

    Kajikawa, Yasutomo

    2017-01-01

    By analysing the experimental data of the temperature-dependent Hall-effect measurements, an additional acceptor level has been confirmed to exist in Mn-doped p-GaAs besides the isolated substitutional Mn acceptor level. It is found that, in most of the investigated samples, the room-temperature hole concentration is governed by the additional acceptor level rather than the isolated substitutional Mn acceptor level. The concentration of the additional acceptor level is found to increase almost in proportion to the square of the concentration of the isolated substitutional Mn acceptors, suggesting that the additional acceptor level is related to Mn dimers. This suggests that the ferromagnetism observed in more heavily Mn-doped GaAs may be attributed to Mn clusters. For some of the samples in which the characteristic of nearest-neighbour hopping conduction in the substitutional Mn acceptor impurity band is evident, the hopping activation energy is deduced and is proved to increase in proportion to the cube root of the concentration of the substitutional Mn acceptors.

  19. Protected sphingosine from phytosphingosine as an efficient acceptor in glycosylation reaction.

    PubMed

    Di Benedetto, Roberta; Zanetti, Luca; Varese, Monica; Rajabi, Mehdi; Di Brisco, Riccardo; Panza, Luigi

    2014-02-07

    A convenient, simple, and high-yielding five-step synthesis of a sphingosine acceptor from phytosphingosine is reported, and its behavior in glycosylation reactions is described. Different synthetic paths to sphingosine acceptors using tetrachlorophthalimide as a protecting group for the sphingosine amino function and different glycosylation methods have been explored. Among the acceptors tested, the easiest accessible acceptor, unprotected on the two hydroxyl groups in positions 1 and 3, was regioselectively glycosylated on the primary position, the regioselectivity depending on the donor used.

  20. Process for gasification using a synthetic CO/sub 2/ acceptor

    SciTech Connect

    Lancet, M.S.; Curran, G.P.

    1980-11-04

    Conoco's gasification process uses a synthetic CO/sub 2/ acceptor consisting essentially of at least one calcium compound (either calcium oxide or calcium carbonate) supported in a refractory carrier matrix having the general formula Ca/sub 5/(SiO/sub 4/)/sub 2/CO/sub 3/. The synthetic acceptor is more effective than a natural calcium oxide acceptor during the gasification process because the thermally stable matrix causes the calcium compounds to remain in discrete particles that tend to reactivate with each passage through the process. This eliminates the need for large quantities of fresh makeup acceptor materials.

  1. Formation of novel nucleosides from free base and sugar phosphate: aqueous reaction of 2-aminopyrimidine and ribose-5-phosphate.

    PubMed

    Mace, D C

    1983-11-30

    The facile formation of glycosylamines suggests that a base liberated by depurination might react at the free C1 position of the sugar phosphate from which it had been hydrolyzed, effectively repurinating the site. Model experiments testing this hypothesis demonstrate that such a reaction does take place. The primary product of a reaction between 2-aminopyrimidine (a model for guanine) and ribose-5-phosphate is characterized by enzymatic and chemical degradation, and UV spectra. It is shown to be a novel nucleoside with the base attached via its exocyclic amino group to the C1 of the ribose-5-phosphate.

  2. Biodegradation of tert-butylphenyl diphenyl phosphate

    SciTech Connect

    Heitkamp, M.A.; Freeman, J.P.; Cerniglia, C.E.

    1986-02-01

    The biodegradation of tert-butylphenyl diphenyl phosphate (BPDP) was examined in microcosms containing sediment and water from five different ecosystems as part of studies to elucidate the environmental fate of phosphate ester flame retardants. Biodegradation of (/sup 14/C)BPDP was monitored in the environmental microcosms by measuring the evolution of /sup 14/CO/sub 2/. Over 37% of BPDP was mineralized after 8 weeks in microcosms from an ecosystem which had chronic exposure to agricultural chemicals. In contrast, only 1.7% of BPDP was degraded to /sup 14/CO/sub 2/ in samples collected from a noncontaminated site. The exposure concentration of BPDP affected the percentage which was degraded to /sup 14/CO/sub 2/ in microcosms from the two most active ecosystems. Mineralization was highest at a concentration of 0.1 mg of BPDP and was inhibited with 10- and 100-fold higher concentrations of BPDP. The authors observed adaptive increases in both microbial populations and phosphoesterase enzymes in some sediments acclimated to BPDP. Chemical analyses of the residues in the microcosms indicated undegraded BPDP and minor amounts of phenol, tert-butylphenol, diphenyl phosphate, and triphenyl phosphate as biodegradation products. These data suggest that the microbial degradation of BPDP results from at least three catabolic processes and is highest when low concentrations of BPDP are exposed to sediment microorganisms of eutrophic ecosystems which have high phosphotri- and diesterase activities and previous exposure to anthropogenic chemicals.

  3. Biomediated continuous release phosphate fertilizer

    DOEpatents

    Goldstein, A.H.; Rogers, R.D.

    1999-06-15

    A composition is disclosed for providing phosphate fertilizer to the root zone of plants. The composition comprises a microorganism capable of producing and secreting a solubilization agent, a carbon source for providing raw material for the microorganism to convert into the solubilization agent, and rock phosphate ore for providing a source of insoluble phosphate that is solubilized by the solubilization agent and released as soluble phosphate. The composition is provided in a physical form, such as a granule, that retains the microorganism, carbon source, and rock phosphate ore, but permits water and soluble phosphate to diffuse into the soil. A method of using the composition for providing phosphate fertilizer to plants is also disclosed. 13 figs.

  4. Biomediated continuous release phosphate fertilizer

    SciTech Connect

    Goldstein, Alan H.; Rogers, Robert D.

    1999-01-01

    A composition is disclosed for providing phosphate fertilizer to the root zone of plants. The composition comprises a microorganism capable of producing and secreting a solubilization agent, a carbon source for providing raw material for the microorganism to convert into the solubilization agent, and rock phosphate ore for providing a source of insoluble phosphate that is solubilized by the solubilization agent and released as soluble phosphate. The composition is provided in a physical form, such as a granule, that retains the microorganism, carbon source, and rock phosphate ore, but permits water and soluble phosphate to diffuse into the soil. A method of using the composition for providing phosphate fertilizer to plants is also disclosed.

  5. Renal phosphate handling: Physiology

    PubMed Central

    Prasad, Narayan; Bhadauria, Dharmendra

    2013-01-01

    Phosphorus is a common anion. It plays an important role in energy generation. Renal phosphate handling is regulated by three organs parathyroid, kidney and bone through feedback loops. These counter regulatory loops also regulate intestinal absorption and thus maintain serum phosphorus concentration in physiologic range. The parathyroid hormone, vitamin D, Fibrogenic growth factor 23 (FGF23) and klotho coreceptor are the key regulators of phosphorus balance in body. PMID:23961477

  6. Preliminary time-of-flight neutron diffraction studies of Escherichia coli ABC transport receptor phosphate-binding protein at the Protein Crystallography Station.

    PubMed

    Sippel, K H; Bacik, J; Quiocho, F A; Fisher, S Z

    2014-06-01

    Inorganic phosphate is an essential molecule for all known life. Organisms have developed many mechanisms to ensure an adequate supply, even in low-phosphate conditions. In prokaryotes phosphate transport is instigated by the phosphate-binding protein (PBP), the initial receptor for the ATP-binding cassette (ABC) phosphate transporter. In the crystal structure of the PBP-phosphate complex, the phosphate is completely desolvated and sequestered in a deep cleft and is bound by 13 hydrogen bonds: 12 to protein NH and OH donor groups and one to a carboxylate acceptor group. The carboxylate plays a key recognition role by accepting a phosphate hydrogen. PBP phosphate affinity is relatively consistent across a broad pH range, indicating the capacity to bind monobasic (H2PO4-) and dibasic (HPO4(2-)) phosphate; however, the mechanism by which it might accommodate the second hydrogen of monobasic phosphate is unclear. To answer this question, neutron diffraction studies were initiated. Large single crystals with a volume of 8 mm3 were grown and subjected to hydrogen/deuterium exchange. A 2.5 Å resolution data set was collected on the Protein Crystallography Station at the Los Alamos Neutron Science Center. Initial refinement of the neutron data shows significant nuclear density, and refinement is ongoing. This is the first report of a neutron study from this superfamily.

  7. Preliminary time-of-flight neutron diffraction studies of Escherichia coli ABC transport receptor phosphate-binding protein at the Protein Crystallography Station

    PubMed Central

    Sippel, K. H.; Bacik, J.; Quiocho, F. A.; Fisher, S. Z.

    2014-01-01

    Inorganic phosphate is an essential molecule for all known life. Organisms have developed many mechanisms to ensure an adequate supply, even in low-phosphate conditions. In prokaryotes phosphate transport is instigated by the phosphate-binding protein (PBP), the initial receptor for the ATP-binding cassette (ABC) phosphate transporter. In the crystal structure of the PBP–phosphate complex, the phosphate is completely desolvated and sequestered in a deep cleft and is bound by 13 hydrogen bonds: 12 to protein NH and OH donor groups and one to a carboxylate acceptor group. The carboxylate plays a key recognition role by accepting a phosphate hydrogen. PBP phosphate affinity is relatively consistent across a broad pH range, indicating the capacity to bind monobasic (H2PO4 −) and dibasic (HPO4 2−) phosphate; however, the mechanism by which it might accommodate the second hydrogen of monobasic phosphate is unclear. To answer this question, neutron diffraction studies were initiated. Large single crystals with a volume of 8 mm3 were grown and subjected to hydrogen/deuterium exchange. A 2.5 Å resolution data set was collected on the Protein Crystallography Station at the Los Alamos Neutron Science Center. Initial refinement of the neutron data shows significant nuclear density, and refinement is ongoing. This is the first report of a neutron study from this superfamily. PMID:24915101

  8. Anoxic nitrate reduction coupled with iron oxidation and attenuation of dissolved arsenic and phosphate in a sand and gravel aquifer

    USGS Publications Warehouse

    Smith, Richard L.; Kent, Douglas B.; Repert, Deborah A.; Böhlke, J.K.

    2017-01-01

    Nitrate has become an increasingly abundant potential electron acceptor for Fe(II) oxidation in groundwater, but this redox couple has not been well characterized within aquifer settings. To investigate this reaction and some of its implications for redox-sensitive groundwater contaminants, we conducted an in situ field study in a wastewater-contaminated aquifer on Cape Cod. Long-term (15 year) geochemical monitoring within the contaminant plume indicated interacting zones with variable nitrate-, Fe(II)-, phosphate-, As(V)-, and As(III)-containing groundwater. Nitrate and phosphate were derived predominantly from wastewater disposal, whereas Fe(II), As(III), and As(V) were mobilized from the aquifer sediments. Multiple natural gradient, anoxic tracer tests were conducted in which nitrate and bromide were injected into nitrate-free, Fe(II)-containing groundwater. Prior to injection, aqueous Fe(II) concentrations were approximately 175 μM, but sorbed Fe(II) accounted for greater than 90% of the total reactive Fe(II) in the aquifer. Nitrate reduction was stimulated within 1 m of transport for 100 μM and 1000 μM nitrate additions, initially producing stoichiometric quantities of nitrous oxide (>300 μM N). In subsequent injections at the same site, nitrate was reduced even more rapidly and produced less nitrous oxide, especially over longer transport distances. Fe(II) and nitrate concentrations decreased together and were accompanied by Fe(III) oxyhydroxide precipitation and decreases in dissolved phosphate, As(III), and As(V) concentrations. Nitrate N and O isotope fractionation effects during nitrate reduction were approximately equal (ε15N/ε18O = 1.11) and were similar to those reported for laboratory studies of biological nitrate reduction, including denitrification, but unlike some reported effects on nitrate by denitrification in aquifers. All constituents affected by the in situ tracer experiments returned to pre-injection levels after several

  9. Anoxic nitrate reduction coupled with iron oxidation and attenuation of dissolved arsenic and phosphate in a sand and gravel aquifer

    NASA Astrophysics Data System (ADS)

    Smith, Richard L.; Kent, Douglas B.; Repert, Deborah A.; Böhlke, J. K.

    2017-01-01

    Nitrate has become an increasingly abundant potential electron acceptor for Fe(II) oxidation in groundwater, but this redox couple has not been well characterized within aquifer settings. To investigate this reaction and some of its implications for redox-sensitive groundwater contaminants, we conducted an in situ field study in a wastewater-contaminated aquifer on Cape Cod. Long-term (15 year) geochemical monitoring within the contaminant plume indicated interacting zones with variable nitrate-, Fe(II)-, phosphate-, As(V)-, and As(III)-containing groundwater. Nitrate and phosphate were derived predominantly from wastewater disposal, whereas Fe(II), As(III), and As(V) were mobilized from the aquifer sediments. Multiple natural gradient, anoxic tracer tests were conducted in which nitrate and bromide were injected into nitrate-free, Fe(II)-containing groundwater. Prior to injection, aqueous Fe(II) concentrations were approximately 175 μM, but sorbed Fe(II) accounted for greater than 90% of the total reactive Fe(II) in the aquifer. Nitrate reduction was stimulated within 1 m of transport for 100 μM and 1000 μM nitrate additions, initially producing stoichiometric quantities of nitrous oxide (>300 μM N). In subsequent injections at the same site, nitrate was reduced even more rapidly and produced less nitrous oxide, especially over longer transport distances. Fe(II) and nitrate concentrations decreased together and were accompanied by Fe(III) oxyhydroxide precipitation and decreases in dissolved phosphate, As(III), and As(V) concentrations. Nitrate N and O isotope fractionation effects during nitrate reduction were approximately equal (ε15N/ε18O = 1.11) and were similar to those reported for laboratory studies of biological nitrate reduction, including denitrification, but unlike some reported effects on nitrate by denitrification in aquifers. All constituents affected by the in situ tracer experiments returned to pre-injection levels after several weeks

  10. Pigment-acceptor-catalyst triads for photochemical hydrogen evolution.

    PubMed

    Kitamoto, Kyoji; Sakai, Ken

    2014-04-25

    In order to solve the problems of global warming and shortage of fossil fuels, researchers have been endeavoring to achieve artificial photosynthesis: splitting water into H2 and O2 under solar light illumination. Our group has recently invented a unique system that drives photoinduced water reduction through "Z-scheme" photosynthetic pathways. Nevertheless, that system still suffered from a low turnover number (TON) of the photocatalytic cycle (TON=4.1). We have now found and describe herein a new methodology to make significant improvements in the TON, up to around TON=14-27. For the new model systems reported herein, the quantum efficiency of the second photoinduced step in the Z-scheme photosynthesis is dramatically improved by introducing multiviologen tethers to temporarily collect the high-energy electron generated in the first photoinduced step. These are unique examples of "pigment-acceptor-catalyst triads", which demonstrate a new effective type of artificial photosynthesis.

  11. Weak localization and interaction effects in acceptor graphite intercalation compounds

    NASA Astrophysics Data System (ADS)

    Prokopov, O. I.; Ovsiienko, I. V.; Matzui, L. Yu.; Len, T. A.; Naumova, D. D.; Berkutov, I. B.; Mirzoiev, I. G.; Le Normand, F.

    2017-06-01

    The presented work is devoted to investigations of manifestation of quantum effects of weak localization and interaction of charge carriers in electrical conductivity of acceptor graphite intercalation compounds (CICs). As shown by studies intercalation leads to a decrease in the resistivity and to change the resistivity temperature coefficient from negative sign in the source graphite on a positive sign in intercalated graphite. At the low temperature for all GICs specimens the minimum in the temperature dependence of resistivity is observed. In terms of the model of charge carrier's weak localization and interaction for two-dimensional systems temperature dependence of phase relaxation time, localization radius and charge carriers screening constant for all GICs are estimated.

  12. Glycogen synthase can use glucose as an acceptor.

    PubMed

    Salsas, E; Larner, J

    1975-03-10

    Glycogen synthase purified to homogeneity from rabbit skeletal muscle is essentially free of carbohydrate and shows no activity in the absence of added acceptor. It can use glucose as a substrate converting it to a glucose disaccharide in the presence of UDP-glucose as cosubstrate. The reaction is dependent on time, and on UDP-glucose, glucose, and enzyme concentrations. The product of the single step reaction co-chromatographs in two solvent systems with maltose. The glucose disaccharide produced in the reaction with UDP-[14-C]glucose and nonradioactive glucose as well as with nonradioactive UDP-glucoes and [14-C]glucose is labeled asymmetrically. The linkage is characterized as alpha-1,4 and therefore the disaccharide is identified as maltose.

  13. Spectroscopy of donor-pi-acceptor complexes for solar cells

    NASA Astrophysics Data System (ADS)

    Himpsel, F. J.; Zegkinoglou, I.; Johnson, P. S.; Pemmaraju, C. D.; Prendergast, D.; Ragoussi, M.-E.; de la Torre, G.; Pickup, D. F.; Ortega, J. E.

    2014-03-01

    A recent improvement in the design of dye sensitized solar cells has been the combination of light absorbing, electron-donating, and electron-withdrawing groups within the same sensitizer molecule. This dye architecture has contributed to increase the energy conversion efficiency, leading to record efficiency values. Here we investigate a zinc(II)-porphyrin-based complex with triphenylamine donor groups and carboxyl linkers for the attachment to an oxide acceptor. The unoccupied orbitals of these three moieties are probed by element-selective X-ray absorption spectroscopy at the N 1s, C 1s, and Zn 2p edges, complemented by time-dependent density functional theory. The attachment of electron-donating groups to the porphyrin ring significantly delocalizes the highest occupied molecular orbital (HOMO) of the molecule. This leads to a spatial separation between the HOMO and the lowest unoccupied molecular orbital (LUMO), reducing the recombination rate of photoinduced electrons and holes.

  14. Quantum information processing using acceptors in silicon and phonon entanglement

    NASA Astrophysics Data System (ADS)

    Clark, Susan; Reinke, Charles; McGuinness, Hayden; El-Kady, Ihab

    2014-03-01

    Quantum computing with large numbers of qubits remains challenging due to the decoherence and complexity that arise as more qubits are added to a system. Here I propose a new platform for semiconductor quantum computing which may be robust to common sources of decoherence and may not be difficult to fabricate repeatedly. This system consists of a hole bound to an acceptor in silicon which has been implanted in the center of a mechanical cavity (similar to a photonic crystal cavity) and connected to other cavities by a system of waveguides. I will outline a basic entangling gate and calculations showing the promise of this platform as the ideal qubit. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U. S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  15. Biostimulation by Glycerol Phosphate to Precipitate Recalcitrant Uranium(IV) Phosphate.

    PubMed

    Newsome, Laura; Morris, Katherine; Trivedi, Divyesh; Bewsher, Alastair; Lloyd, Jonathan R

    2015-09-15

    Stimulating the microbial reduction of aqueous uranium(VI) to insoluble U(IV) via electron donor addition has been proposed as a strategy to remediate uranium-contaminated groundwater in situ. However, concerns have been raised regarding the longevity of microbially precipitated U(IV) in the subsurface, particularly given that it may become remobilized if the conditions change to become oxidizing. An alternative mechanism is to stimulate the precipitation of poorly soluble uranium phosphates via the addition of an organophosphate and promote the development of reducing conditions. Here, we selected a sediment sample from a U.K. nuclear site and stimulated the microbial community with glycerol phosphate under anaerobic conditions to assess whether uranium phosphate precipitation was a viable bioremediation strategy. Results showed that U(VI) was rapidly removed from solution and precipitated as a reduced crystalline U(IV) phosphate mineral similar to ningyoite. This mineral was considerably more recalcitrant to oxidative remobilization than the products of microbial U(VI) reduction. Bacteria closely related to Pelosinus species may have played a key role in uranium removal in these experiments. This work has implications for the stewardship of uranium-contaminated groundwater, with the formation of U(IV) phosphates potentially offering a more effective strategy for maintaining low concentrations of uranium in groundwater over long time periods.

  16. Recent advances in photoinduced donor/acceptor copolymerization

    NASA Astrophysics Data System (ADS)

    Jönsson, S.; Viswanathan, K.; Hoyle, C. E.; Clark, S. C.; Miller, C.; Morel, F.; Decker, C.

    1999-05-01

    Photoinitiated free radical polymerization of donor (D)/acceptor (A) type monomers has gained considerable interest due to the possibility to efficiently photopolymerize non-acrylate based systems. Furthermore, this photoinduced alternating copolymerization can be accomplished without the presence of a conventional free radical generating photoinitiator. In the past, we have shown that the structural influences in the direct photolysis of N-Alkyl and N-Arylmaleimides as well as their corresponding ground state charge transfer complexes (CTC) with suitable donors have carefully been investigated. For certain combinations of A and D type monomers, a direct photolysis of the ground state complex or the excitation of the acceptor, followed by the formation of an exciplex, has been shown to initiate the copolymerization. Herein, we show that the main route of initiation is based on inter or intra molecular H-abstraction from an excited state maleimide, whereby no exciplex formation takes place. H-abstraction will predominantly take place in systems where easily abstractable hydrogens are present. Our laser flash photolysis investigation, ESR [1] (A. Hiroshi, I. Takasi, T. Nosi, Macromol. Chem. 190 (1989) 2821) and phosphorescence emissions [2,3] (K.S. Chen, T. Foster, J.K.S. Wan, J. Phys. Chem. 84 (1980) 2473; C.J. Seliskar, S.P. McGlynn, J. Chem. Phys. 55 (1971) 4337) studies show that triplet excited states of N-alkyl substituted maleimides (RMI), which are well known strong precursors for direct H-abstractions from aliphatic ethers and secondary alcohols, are formed upon excitation. Rates of copolymerization and degrees of conversion for copolymerization of maleimide/vinyl ether pairs in air and nitrogen have been measured as a function of hydrogen abstractability of the excited triplet state MI as well as the influence of concentration and hydrogen donating effect of the hydrogen donor.

  17. Contrasting performance of donor-acceptor copolymer pairs in ternary blend solar cells and two-acceptor copolymers in binary blend solar cells.

    PubMed

    Khlyabich, Petr P; Rudenko, Andrey E; Burkhart, Beate; Thompson, Barry C

    2015-02-04

    Here two contrasting approaches to polymer-fullerene solar cells are compared. In the first approach, two distinct semi-random donor-acceptor copolymers are blended with phenyl-C61-butyric acid methyl ester (PC61BM) to form ternary blend solar cells. The two poly(3-hexylthiophene)-based polymers contain either the acceptor thienopyrroledione (TPD) or diketopyrrolopyrrole (DPP). In the second approach, semi-random donor-acceptor copolymers containing both TPD and DPP acceptors in the same polymer backbone, termed two-acceptor polymers, are blended with PC61BM to give binary blend solar cells. The two approaches result in bulk heterojunction solar cells that have the same molecular active-layer components but differ in the manner in which these molecular components are mixed, either by physical mixing (ternary blend) or chemical "mixing" in the two-acceptor (binary blend) case. Optical properties and photon-to-electron conversion efficiencies of the binary and ternary blends were found to have similar features and were described as a linear combination of the individual components. At the same time, significant differences were observed in the open-circuit voltage (Voc) behaviors of binary and ternary blend solar cells. While in case of two-acceptor polymers, the Voc was found to be in the range of 0.495-0.552 V, ternary blend solar cells showed behavior inherent to organic alloy formation, displaying an intermediate, composition-dependent and tunable Voc in the range from 0.582 to 0.684 V, significantly exceeding the values achieved in the two-acceptor containing binary blend solar cells. Despite the differences between the physical and chemical mixing approaches, both pathways provided solar cells with similar power conversion efficiencies, highlighting the advantages of both pathways toward highly efficient organic solar cells.

  18. Phosphate-Induced Immobilization of Uranium in Hanford Sediments

    SciTech Connect

    Pan, Zezhen; Giammar, Daniel E.; Mehta, Vrajesh; Troyer, Lyndsay D.; Catalano, Jeffrey G.; Wang, Zheming

    2016-12-20

    Phosphate can be added to subsurface environments to immobilize U(VI) contamination. The efficacy of immobilization depends on the site-specific groundwater chemistry and aquifer sediment properties. Batch and column experiments were performed with sediments from the Hanford 300 Area in Washington State and artificial groundwater prepared to emulate the conditions at the site. Batch experiments revealed enhanced U(VI) sorption with increasing phosphate addition. X-ray absorption spectroscopy measurements of samples from the batch experiments found that U(VI) was predominantly adsorbed at conditions relevant to the column experiments and most field sites (low U(VI) loadings, <25 μM), and U(VI) phosphate precipitation occurred only at high initial U(VI) (>25 μM) and phosphate loadings. While batch experiments showed the transition of U(VI) uptake from adsorption to precipitation, the column study was more directly relevant to the subsurface environment because of the high solid:water ratio in the column and the advective flow of water. In column experiments, nearly six times more U(VI) was retained in sediments when phosphate-containing groundwater was introduced to U(VI)-loaded sediments than when the groundwater did not contain phosphate. This enhanced retention persisted for at least one month after cessation of phosphate addition to the influent fluid. Sequential extractions and laser-induced fluorescence spectroscopy of sediments from the columns suggested that the retained U(VI) was primarily in adsorbed forms. These results indicate that in situ remediation of groundwater by phosphate addition provides lasting benefit beyond the treatment period via enhanced U(VI) adsorption to sediments.

  19. Phosphate-Induced Immobilization of Uranium in Hanford Sediments

    SciTech Connect

    Pan, Zezhen; Giammar, Daniel E.; Mehta, Vrajesh; Troyer, Lyndsay D.; Catalano, Jeffrey G.; Wang, Zheming

    2016-12-20

    Phosphate can be added to subsurface environments to immobilize U(VI) contamination. The efficacy of immobilization depends on the site-specific groundwater chemistry and aquifer sediment properties. Batch and column experiments were performed with sediments from the Hanford 300 Area in Washington State and artificial groundwater prepared to emulate the conditions at the site. Batch experiments revealed enhanced U(VI) sorption with increasing phosphate addition. X-ray absorption spectroscopy measurements of samples from the batch experiments found that U(VI) was predominantly adsorbed at conditions relevant to the column experiments and most field sites (low U(VI) loadings, <25 μM), and U(VI) phosphate precipitation occurred only at high initial U(VI) (>25μM) and phosphate loadings. While batch experiments showed the transition of U(VI) uptake from adsorption to precipitation, the column study was more directly relevant to the subsurface environment because of the high solid:water ratio in the column and the advective flow of water. In column experiments, nearly six times more U(VI) was retained in sediments when phosphate-containing groundwater was introduced to U(VI)-loaded sediments than when the groundwater did not contain phosphate. This enhanced retention persisted for at least one month after cessation of phosphate addition to the influent fluid. Sequential extractions and laser-induced fluorescence spectroscopy of sediments from the columns suggested that the retained U(VI) was primarily in adsorbed forms. These results indicate that in situ remediation of groundwater by phosphate addition provides lasting benefit beyond the treatment period via enhanced U(VI) adsorption to sediments.

  20. Electrochemical response of a biofilm community to changes in electron-acceptor redox potential elucidated using microbial fuel cells

    NASA Astrophysics Data System (ADS)

    Arbour, T.; Wrighton, K. C.; Mullin, S. W.; Luef, B.; Gilbert, B.; Banfield, J. F.

    2012-12-01

    Currently, we have limited insight into how mineral properties affect dissimilatory metal-reducing bacteria (DMRB) or the microbial communities that contain them. Advances in our understanding of DMRB metabolism have been achieved using microbial fuel cells (MFCs), which exploit the ability of these organisms to transfer electrons extracellularly. By replacing the mineral electron acceptor with a conductive electrode under potentiostat control, the activity of microorganisms capable of interfacial electron transfer can be quantified by the current flowing through the electrode and related to the thermodynamics of respiration. We seek to understand how communities and their individual members respond to changes in mineralogy, and expect mineral redox potential to be a primary control. The ability to precisely control the redox potential of the electron-accepting anodic electrode is our primary motivation for using MFCs. We inoculated duplicate MFCs containing 10 mM acetate in phosphate buffered media with a slurry of subsurface sediment and groundwater obtained from the Integrated Field-Scale Research Challenge Site at Rifle, CO. Electroactive biofilms were established on graphite anodes poised at a favorable potential (0.0 V vs. SHE) before poising at -0.2 V—a potential representative of natural iron reduction. The current was stable across both anodes over more than 100 days of operation, and the percentage of the electrons in acetate recovered as current ("Coulombic efficiency") was typically 70 to >90%. Current density reached 0.4 A/m2 at -0.2 V, to a max of over 1.0 A/m2 at or above ~0.0 V (based on geometric electrode surface area). Media exchanges and biofilm cyclic voltammetry (CV) experiments indicate that electrode-attached microbial communities were responsible for primary electron transfer. Cryo-electron and confocal fluorescence microscopies of the biofilm reveal numerous morphologies of viable microorganisms that are currently being characterized

  1. Conserved cytoplasmic motifs that distinguish sub-groups of the polyprenol phosphate:N-acetylhexosamine-1-phosphate transferase family.

    PubMed

    Anderson, M S; Eveland, S S; Price, N P

    2000-10-15

    WecA, MraY and WbcO are conserved members of the polyprenol phosphate:N-acetylhexosamine-1-phosphate transferase family involved in the assembly of bacterial cell walls, and catalyze reactions involving a membrane-associated polyprenol phosphate acceptor substrate and a cytoplasmically located UDP-D-amino sugar donor. MraY, WbcO and WecA purportedly utilize different UDP-sugars, although the molecular basis of this specificity is largely unknown. However, domain variations involved in specificity are predicted to occur on the cytoplasmic side of the membrane, adjacent to conserved domains involved in the mechanistic activity, and with access to the cytoplasmically located sugar nucleotides. Conserved C-terminal domains have been identified that satisfy these criteria. Topological analyses indicate that they form the highly basic, fifth cytoplasmic loop between transmembrane regions IX and X. Four diverse loops are apparent, for MraY, WecA, WbcO and RgpG, that uniquely characterize these sub-groups of the transferase family, and a correlation is evident with the known or implied UDP-sugar specificity.

  2. D-Fructose-6-phosphate aldolase-catalyzed one-pot synthesis of iminocyclitols.

    PubMed

    Sugiyama, Masakazu; Hong, Zhangyong; Liang, Pi-Hui; Dean, Stephen M; Whalen, Lisa J; Greenberg, William A; Wong, Chi-Huey

    2007-11-28

    A one-pot chemoenzymatic method for the synthesis of a variety of new iminocyclitols from readily available, non-phosphorylated donor substrates has been developed. The method utilizes the recently discovered fructose-6-phosphate aldolase (FSA), which is functionally distinct from known aldolases in its tolerance of different donor substrates as well as acceptor substrates. Kinetic studies were performed with dihydroxyacetone (DHA), the presumed endogenous substrate for FSA, as well as hydroxy acetone (HA) and 1-hydroxy-2-butanone (HB) as donor substrates, in each case using glyceraldehyde-3-phosphate as acceptor substrate. Remarkably, FSA used the three donor substrates with equal efficiency, with kcat/KMvalues of 33, 75, and 20 M-1 s-1, respectively. This level of donor substrate tolerance is unprecedented for an aldolase. Furthermore, DHA, HA, and HB were accepted as donors in FSA-catalyzed aldol reactions with a variety of azido- and Cbz-amino aldehyde acceptors. The broad substrate tolerance of FSA and the ability to circumvent the need for phosphorylated substrates allowed for one-pot synthesis of a number of known and novel iminocyclitols in good yields, and in a very concise fashion. New iminocyclitols were assayed as inhibitors against a panel of glycosidases. Compounds 15 and 16 were specific alpha-mannosidase inhibitors, and 24 and 26 were potent and selective inhibitors of beta-N-acetylglucosaminidases in the submicromolar range. Facile access to these compounds makes them attractive core structures for further inhibitor optimization.

  3. Method for phosphate-accelerated bioremediation

    DOEpatents

    Looney, Brian B.; Lombard, Kenneth H.; Hazen, Terry C.; Pfiffner, Susan M.; Phelps, Tommy J.; Borthen, James W.

    1996-01-01

    An apparatus and method for supplying a vapor-phase nutrient to contaminated soil for in situ bioremediation. The apparatus includes a housing adapted for containing a quantity of the liquid nutrient, a conduit in fluid communication with the interior of the housing, means for causing a gas to flow through the conduit, and means for contacting the gas with the liquid so that a portion thereof evaporates and mixes with the gas. The mixture of gas and nutrient vapor is delivered to the contaminated site via a system of injection and extraction wells configured to the site. The mixture has a partial pressure of vaporized nutrient that is no greater than the vapor pressure of the liquid. If desired, the nutrient and/or the gas may be heated to increase the vapor pressure and the nutrient concentration of the mixture. Preferably, the nutrient is a volatile, substantially nontoxic and nonflammable organic phosphate that is a liquid at environmental temperatures, such as triethyl phosphate or tributyl phosphate.

  4. Revegetation of serpentine substrates: Response to phosphate application

    NASA Astrophysics Data System (ADS)

    Koide, Roger T.; Mooney, Harold A.

    1987-08-01

    Revegetation was studied on stockpiled serpentine substrate. The native vegetation surrounding the revegetation site is annual grassland. The seed mixture applied to both subsoil and topsoil plots was largely ineffective for revegetation. No growth occurred in the subsoil plots and most of the growth in the topsoil plots was from indigenous seed. Phosphate application (100 kg P ha-1 as NaH2PO4 · H2O) to the topsoil plots resulted in a significant increase in total above-ground productivity. Annual legumes (mostly Lotus subpinnatus Lag.) and, to a lesser degree, Plantago erecta Morris responded to the added phosphate with an increased above-ground productivity. Other annual forbs and annual grasses showed no significant response. The legumes also increased in abundance. Mycorrhizal root colonization for Plantago was not significantly affected by phosphate application, but was lower in this disturbed serpentine site compared to other undisturbed serpentine annual grassland sites nearby.

  5. Evidence for ‘lock and key’ character in an anti-phosphonate hydrolytic antibody catalytic site augmented by non-reaction centre recognition: variation in substrate selectivity between an anti-phosphonate antibody, an anti-phosphate antibody and two hydrolytic enzymes

    PubMed Central

    2004-01-01

    The substrate selectivities of an anti-phosphonate and an anti-phosphate kinetically homogeneous polyclonal catalytic antibody preparation and two hydrolytic enzymes were compared by using hapten-analogous and truncated carbonate and ester substrates each containing a 4-nitrophenolate leaving group. Syntheses of the truncated substrates devoid of recognition features in the non-leaving group parts of the substrates are reported. The relatively high kinetic selectivity of the more active anti-phosphonate antibody preparation is considered to depend on a relatively rigid catalytic site with substantial reaction centre specificity together with other important recognition interactions with the extended non-leaving group part of the substrate. In contrast, the less catalytically active, more flexible anti-phosphate antibody exhibits much lower kinetic selectivity for the substrate reaction centre comparable with that of the hydrolytic enzymes with activity much less dependent on recognition interactions with the non-leaving group part of the substrate. The ways in which haptenic flexibility and IgG architecture might contribute to the differential kinetic selectivities are indicated. PMID:15053743

  6. Multi-scale exciton and electron transfer in multi-level donor-acceptor systems

    NASA Astrophysics Data System (ADS)

    Gurvitz, Shmuel; Nesterov, Alexander I.; Berman, Gennady P.

    2017-09-01

    We study theoretically the noise-assisted quantum exciton (electron) transfer (ET) in bio-complexes consisting of a single-level electron donor and an acceptor which has a complicated internal structure, and is modeled by many electron energy levels. Interactions are included between the donor and the acceptor energy levels and with the protein-solvent noisy environment. Different regions of parameters are considered, which characterize (i) the number of the acceptor levels, (ii) the acceptor ‘band-width’, and (iii) the amplitude of noise and its correlation time. Under some conditions, we derive analytical expressions for the ET rate and efficiency. We obtain equal occupation of all levels at large times, independent of the structure of the acceptor band and the noise parameters, but under the condition of non-degeneracy of the acceptor energy levels. We discuss the multi-scale dynamics of the acceptor population, and the accompanying effect of quantum coherent oscillations. We also demonstrate that for a large number of levels in the acceptor band, the efficiency of ET can be close to 100%, for both downhill and uphill transitions and for sharp and flat redox potentials.

  7. Dichotomous Role of Exciting the Donor or the Acceptor on Charge Generation in Organic Solar Cells.

    PubMed

    Hendriks, Koen H; Wijpkema, Alexandra S G; van Franeker, Jacobus J; Wienk, Martijn M; Janssen, René A J

    2016-08-10

    In organic solar cells, photoexcitation of the donor or acceptor phase can result in different efficiencies for charge generation. We investigate this difference for four different 2-pyridyl diketopyrrolopyrrole (DPP) polymer-fullerene solar cells. By comparing the external quantum efficiency spectra of the polymer solar cells fabricated with either [60]PCBM or [70]PCBM fullerene derivatives as acceptor, the efficiency of charge generation via donor excitation and acceptor excitation can both be quantified. Surprisingly, we find that to make charge transfer efficient, the offset in energy between the HOMO levels of donor and acceptor that govern charge transfer after excitation of the acceptor must be larger by ∼0.3 eV than the offset between the corresponding two LUMO levels when the donor is excited. As a consequence, the driving force required for efficient charge generation is significantly higher for excitation of the acceptor than for excitation of the donor. By comparing charge generation for a total of 16 different DPP polymers, we confirm that the minimal driving force, expressed as the photon energy loss, differs by about 0.3 eV for exciting the donor and exciting the acceptor. Marcus theory may explain the dichotomous role of exciting the donor or the acceptor on charge generation in these solar cells.

  8. Electrogenicity at the secondary quinone acceptor site of cyanobacterial photosystem II.

    PubMed

    Mamedov, M D; Beshta, O E; Samuilov, V D; Semenov AYu

    1994-08-15

    Flash-induced generation of the electric potential difference (delta psi) by a direct electrometrical method was studied in Anacystis nidulans photosystem II-containing proteoliposomes associated with a phospholipid-impregnated collodion film. Besides a rapid phase of delta psi generation corresponding to charge separation between P680 and QA, an additional electrogenic phase with a characteristic time of 0.27 ms at pH 7.0 was observed after the second laser flash. The maximal amplitude of this phase was approx. 4% of that related to the P680+QA- formation. The sensitivity of this phase to DCMU, the flash-number dependence of its amplitude as well as the amplitude and the rate constant pH-dependences, indicate that it is due to the dismutation of QA- and QB- and to subsequent protonation of a doubly reduced plastoquinone QB2-.

  9. Effects of benzotriazole on the magnesium phosphate coating

    NASA Astrophysics Data System (ADS)

    Zuo, Juan; Guo, Fen; Zhu, Junqiu; Chen, Ajiao; Hu, Yanling; Lin, Changjian; Jiang, Chunhai

    2015-12-01

    Magnesium phosphate coatings are extensively used on carbon steel to improve their corrosion resistance. The effect of benzotriazole on the magnesium phosphate coating was investigated. The phosphate coatings were deposited on carbon steel at different bath temperature, room temperature (RM), 60 °C and 80 °C. The change of crystalline phase, morphology, the sludge weight, bath efficiency factor, and corrosion behavior of the coatings after the addition of benzotriazole (BTAH) were investigated by means of Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and potentiodynamic polarization methods. The adsorption of BTAH during the formation of magnesium phosphate coating was also investigated by means of XPS. The effect of BTAH on the formation of magnesium phosphate coating was discussed. The adsorbed BTAH layer could favor the nucleation of phosphate coating by supplying more nuclei centers which leads to the formation of more compact phosphate coating. Meanwhile, the adsorbed atoms can block the active sites and generate a barrier to reduce the transport of corrosive species to the metal surface and hence improve the corrosion behavior of carbon steels.

  10. Mechanism of substrate specificity of phosphatidylinositol phosphate kinases

    PubMed Central

    Muftuoglu, Yagmur; Xue, Yi; Gao, Xiang; Wu, Dianqing; Ha, Ya

    2016-01-01

    The phosphatidylinositol phosphate kinase (PIPK) family of enzymes is primarily responsible for converting singly phosphorylated phosphatidylinositol derivatives to phosphatidylinositol bisphosphates. As such, these kinases are central to many signaling and membrane trafficking processes in the eukaryotic cell. The three types of phosphatidylinositol phosphate kinases are homologous in sequence but differ in catalytic activities and biological functions. Type I and type II kinases generate phosphatidylinositol 4,5-bisphosphate from phosphatidylinositol 4-phosphate and phosphatidylinositol 5-phosphate, respectively, whereas the type III kinase produces phosphatidylinositol 3,5-bisphosphate from phosphatidylinositol 3-phosphate. Based on crystallographic analysis of the zebrafish type I kinase PIP5Kα, we identified a structural motif unique to the kinase family that serves to recognize the monophosphate on the substrate. Our data indicate that the complex pattern of substrate recognition and phosphorylation results from the interplay between the monophosphate binding site and the specificity loop: the specificity loop functions to recognize different orientations of the inositol ring, whereas residues flanking the phosphate binding Arg244 determine whether phosphatidylinositol 3-phosphate is exclusively bound and phosphorylated at the 5-position. This work provides a thorough picture of how PIPKs achieve their exquisite substrate specificity. PMID:27439870

  11. Alkaline phosphatase revisited: hydrolysis of alkyl phosphates.

    PubMed

    O'Brien, Patrick J; Herschlag, Daniel

    2002-03-05

    Escherichia coli alkaline phosphatase (AP) is the prototypical two metal ion catalyst with two divalent zinc ions bound approximately 4 A apart in the active site. Studies spanning half a century have elucidated many structural and mechanistic features of this enzyme, rendering it an attractive model for investigating the potent catalytic power of bimetallic centers. Unfortunately, fundamental mechanistic features have been obscured by limitations with the standard assays. These assays generate concentrations of inorganic phosphate (P(i)) in excess of its inhibition constant (K(i) approximately 1 muM). This tight binding by P(i) has affected the majority of published kinetic constants. Furthermore, binding limits k(cat)/K(m) for reaction of p-nitrophenyl phosphate, the most commonly employed substrate. We describe a sensitive (32)P-based assay for hydrolysis of alkyl phosphates that avoids the complication of product inhibition. We have revisited basic mechanistic features of AP with these alkyl phosphate substrates. The results suggest that the chemical step for phosphorylation of the enzyme limits k(cat)/K(m). The pH-rate profile and additional results suggest that the serine nucleophile is active in its anionic form and has a pK(a) of < or = 5.5 in the free enzyme. An inactivating pK(a) of 8.0 is observed for binding of both substrates and inhibitors, and we suggest that this corresponds to ionization of a zinc-coordinated water molecule. Counter to previous suggestions, inorganic phosphate dianion appears to bind to the highly charged AP active site at least as strongly as the trianion. The dependence of k(cat)/K(m) on the pK(a) of the leaving group follows a Brønsted correlation with a slope of beta(lg) = -0.85 +/- 0.1, differing substantially from the previously reported value of -0.2 obtained from data with a less sensitive assay. This steep leaving group dependence is consistent with a largely dissociative transition state for AP-catalyzed hydrolysis of

  12. Structural Basis for Substrate Specificity in Phosphate Binding (beta/alpha)8-Barrels: D-Allulose 6-Phosphate 3-Epimerase from Escherichia coli K-12

    SciTech Connect

    Chan,K.; Fedorov, A.; Almo, S.; Gerlt, J.

    2008-01-01

    Enzymes that share the ({beta}/{alpha})8-barrel fold catalyze a diverse range of reactions. Many utilize phosphorylated substrates and share a conserved C-terminal ({beta}/a)2-quarter barrel subdomain that provides a binding motif for the dianionic phosphate group. We recently reported functional and structural studies of d-ribulose 5-phosphate 3-epimerase (RPE) from Streptococcus pyogenes that catalyzes the equilibration of the pentulose 5-phosphates d-ribulose 5-phosphate and d-xylulose 5-phosphate in the pentose phosphate pathway [J. Akana, A. A. Fedorov, E. Fedorov, W. R. P. Novack, P. C. Babbitt, S. C. Almo, and J. A. Gerlt (2006) Biochemistry 45, 2493-2503]. We now report functional and structural studies of d-allulose 6-phosphate 3-epimerase (ALSE) from Escherichia coli K-12 that catalyzes the equilibration of the hexulose 6-phosphates d-allulose 6-phosphate and d-fructose 6-phosphate in a catabolic pathway for d-allose. ALSE and RPE prefer their physiological substrates but are promiscuous for each other's substrate. The active sites (RPE complexed with d-xylitol 5-phosphate and ALSE complexed with d-glucitol 6-phosphate) are superimposable (as expected from their 39% sequence identity), with the exception of the phosphate binding motif. The loop following the eighth {beta}-strand in ALSE is one residue longer than the homologous loop in RPE, so the binding site for the hexulose 6-phosphate substrate/product in ALSE is elongated relative to that for the pentulose 5-phosphate substrate/product in RPE. We constructed three single-residue deletion mutants of the loop in ALSE, ?T196, ?S197 and ?G198, to investigate the structural bases for the differing substrate specificities; for each, the promiscuity is altered so that d-ribulose 5-phosphate is the preferred substrate. The changes in kcat/Km are dominated by changes in kcat, suggesting that substrate discrimination results from differential transition state stabilization. In both ALSE and RPE, the phosphate

  13. Rise-Time of FRET-Acceptor Fluorescence Tracks Protein Folding

    PubMed Central

    Lindhoud, Simon; Westphal, Adrie H.; van Mierlo, Carlo P. M.; Visser, Antonie J. W. G.; Borst, Jan Willem

    2014-01-01

    Uniform labeling of proteins with fluorescent donor and acceptor dyes with an equimolar ratio is paramount for accurate determination of Förster resonance energy transfer (FRET) efficiencies. In practice, however, the labeled protein population contains donor-labeled molecules that have no corresponding acceptor. These FRET-inactive donors contaminate the donor fluorescence signal, which leads to underestimation of FRET efficiencies in conventional fluorescence intensity and lifetime-based FRET experiments. Such contamination is avoided if FRET efficiencies are extracted from the rise time of acceptor fluorescence upon donor excitation. The reciprocal value of the rise time of acceptor fluorescence is equal to the decay rate of the FRET-active donor fluorescence. Here, we have determined rise times of sensitized acceptor fluorescence to study the folding of double-labeled apoflavodoxin molecules and show that this approach tracks the characteristics of apoflavodoxinʼs complex folding pathway. PMID:25535076

  14. Vacancy-Induced Electronic Structure Variation of Acceptors and Correlation with Proton Conduction in Perovskite Oxides.

    PubMed

    Kim, Hye-Sung; Jang, Ahreum; Choi, Si-Young; Jung, WooChul; Chung, Sung-Yoon

    2016-10-17

    In most proton-conducing perovskite oxides, the electrostatic attraction between negatively charged acceptor dopants and protonic defects having a positive charge is known to be a major cause of retardation of proton conduction, a phenomenon that is generally referred to as proton trapping. We experimentally show that proton trapping can be suppressed by clustering of positively charged oxygen vacancies to acceptors in BaZrO3-δ and BaCeO3-δ . In particular, to ensure the vacancy-acceptor association is effective against proton trapping, the valence electron density of acceptors should not significantly vary when the oxygen vacancies cluster, based on the weak hybridization between the valence d or p orbitals of acceptors and the 2p orbitals of oxygen.

  15. Hexa-peri-hexabenzocoronene with Different Acceptor Units for Tuning Optoelectronic Properties.

    PubMed

    Keerthi, Ashok; Hou, Ian Cheng-Yi; Marszalek, Tomasz; Pisula, Wojciech; Baumgarten, Martin; Narita, Akimitsu

    2016-10-06

    Hexa-peri-hexabenzocoronene (HBC)-based donor-acceptor dyads were synthesized with three different acceptor units, through two pathways: 1) "pre-functionalization" of monobromo-substituted hexaphenylbenzene prior to the cyclodehydrogenation; and 2) "post-functionalization" of monobromo-substituted HBC after the cyclodehydrogenation. The HBC-acceptor dyads demonstrated varying degrees of intramolecular charge-transfer interactions, depending on the attached acceptor units, which allowed tuning of their photophysical and optoelectronic properties, including the energy gaps. The two synthetic pathways described here can be complementary and potentially be applied for the synthesis of nanographene-acceptor dyads with larger aromatic cores, including one-dimensionally extended graphene nanoribbons.

  16. The activation energy for Mg acceptor in the Ga-rich InGaN alloys

    NASA Astrophysics Data System (ADS)

    Zhao, Chuan-Zhen; Wei, Tong; Chen, Li-Ying; Wang, Sha-Sha; Wang, Jun

    2017-02-01

    The activation energy for Mg acceptor in InxGa1-xN alloys is investigated. It is found that there are three factors to influence the activation energy for Mg acceptor. One is the stronger dependence of the VBM of InxGa1-xN depending on In content than that of the Mg acceptor energy level. The other is the concentration of Mg acceptors. Another is the extending of the valence band-tail states into the band gap. In addition, a model based on modifying the effective mass model is developed. It is found that the model can describe the activation energy for Mg acceptor in the Ga-rich InxGa1-xN alloys well after considering the influence of the valence band-tail states.

  17. Crystal Structure of Baculovirus RNA Triphosphatase Complexed with Phosphate

    SciTech Connect

    Changela, Anita; Martin, Alexandra; Shuman, Stewart; Mondragon, Alfonso

    2010-03-05

    Baculovirus RNA 5'-triphosphatase (BVP) exemplifies a family of RNA-specific cysteine phosphatases that includes the RNA triphosphatase domains of metazoan and plant mRNA capping enzymes. Here we report the crystal structure of BVP in a phosphate-bound state at 1.5 {angstrom} resolution. BVP adopts the characteristic cysteine-phosphatase {alpha}/{beta} fold and binds two phosphate ions in the active site region, one of which is proposed to mimic the phosphate of the product complex after hydrolysis of the covalent phosphoenzyme intermediate. The crystal structure highlights the role of backbone amides and side chains of the P-loop motif {sup 118}HCTHGXNRT{sup 126} in binding the cleavable phosphate and stabilizing the transition state. Comparison of the BVP structure to the apoenzyme of mammalian RNA triphosphatase reveals a concerted movement of the Arg-125 side chain (to engage the phosphate directly) and closure of an associated surface loop over the phosphate in the active site. The structure highlights a direct catalytic role of Asn-124, which is the signature P-loop residue of the RNA triphosphatase family and a likely determinant of the specificity of BVP for hydrolysis of phosphoanhydride linkages.

  18. Phosphate Barriers for Immobilization of Uranium Plumes

    SciTech Connect

    Burns, Peter C.

    2005-06-01

    Uranium contamination of the subsurface has remained a persistent problem plaguing remedial design at sites across the U.S. that were involved with production, handling, storage, milling, and reprocessing of fissile uranium for both civilian and defense related purposes. Remediation efforts to date have relied upon excavation, pump-and-treat, or passive remediation barriers (PRB?s) to remove or attenuate uranium mobility. Documented cases convincingly demonstrate that excavation and pump-and-treat methods are ineffective for a number of highly contaminated sites. There is growing concern that use of conventional PRB?s, such as zero-valent iron, are a temporary solution to a problem that will persist for thousands of years. Alternatives to the standard treatment methods are therefore warranted. The core objective of our research is to demonstrate that a phosphorous amendment strategy will result in a reduction of dissolved uranium to below the proposed drinking water standard. Our hypothesis is that long-chain polyphosphate compounds forestall precipitation of sparingly soluble uranyl phosphate compounds, which is key to preventing fouling of wells at the point of injection. Our other fundamental objective is to synthesize and correctly characterize the uranyl phosphate phases that form in the geochemical conditions under consideration. This report summarizes work conducted at the University of Notre Dame through November of 2003 under DOE grant DE-FG07-02ER63489, which has been funded since September, 2002. The objectives at Notre Dame are development of synthesis techniques for uranyl phosphate phases, together with detailed structural and chemical characterization of the myriad of uranyl phosphate phases that may form under geochemical conditions under consideration.

  19. Phosphate Barriers for Immobilization of Uranium Plumes

    SciTech Connect

    Burns, Peter C.

    2005-06-01

    Uranium contamination of the subsurface has remained a persistent problem plaguing remedial design at sites across the U.S. that were involved with production, handling, storage, milling, and reprocessing of fissile uranium for both civilian and defense related purposes. Remediation efforts to date have relied upon excavation, pump-and-treat, or passive remediation barriers (PRB's) to remove or attenuate uranium mobility. Documented cases convincingly demonstrate that excavation and pump-and-treat methods are ineffective for a number of highly contaminated sites. There is growing concern that use of conventional PRB?s, such as zero-valent iron, are a temporary solution to a problem that will persist for thousands of years. Alternatives to the standard treatment methods are therefore warranted. The core objective of our research is to demonstrate that a phosphorus amendment strategy will result in a reduction of dissolved uranium to below the proposed drinking water standard. Our hypothesis is that long-chain polyphosphate compounds forestall precipitation of sparingly soluble uranyl phosphate compounds, which is key to preventing fouling of wells at the point of injection. Our other fundamental objective is to synthesize and correctly characterize the uranyl phosphate phases that form in the geochemical conditions under consideration. This report summarizes work conducted at the University of Notre Dame through November of 2003 under DOE grant DE-FG07-02ER63489, which has been funded since September, 2002. The objectives at Notre Dame are development of synthesis techniques for uranyl phosphate phases, together with detailed structural and chemical characterization of the myriad of uranyl phosphate phases that may form under geochemical conditions under consideration.

  20. Potassium acceptor doping of ZnO crystals

    SciTech Connect

    Parmar, Narendra S. Lynn, K. G.; Corolewski, Caleb D.; McCluskey, Matthew D.

    2015-05-15

    ZnO bulk single crystals were doped with potassium by diffusion at 950°C. Positron annihilation spectroscopy confirms the filling of zinc vacancies and a different trapping center for positrons. Secondary ion mass spectroscopy measurements show the diffusion of potassium up to 10 μm with concentration ∼1 × 10{sup 16} cm{sup −3}. IR measurements show a local vibrational mode (LVM) at 3226 cm{sup −1}, at a temperature of 9 K, in a potassium doped sample that was subsequently hydrogenated. The LVM is attributed to an O–H bond-stretching mode adjacent to a potassium acceptor. When deuterium substitutes for hydrogen, a peak is observed at 2378 cm{sup −1}. The O-H peak is much broader than the O-D peak, perhaps due to an unusually low vibrational lifetime. The isotopic frequency ratio is similar to values found in other hydrogen complexes. Potassium doping increases the resistivity up to 3 orders of magnitude at room temperature. The doped sample has a donor level at 0.30 eV.

  1. Effects of hydrogen on acceptor activation in ternary nitride semiconductors

    DOE PAGES

    Fioretti, Angela N.; Stokes, Adam; Young, Matthew R.; ...

    2017-02-09

    Doping control is necessary to unlock the scientific and technological potential of many materials, including ternary II-IV-nitride semiconductors, which are closely related to binary GaN. In particular, ZnSnN2 has been reported to have degenerate doping density, despite bandgap energies that are well suited for solar energy conversion. Here, we show that annealing Zn-rich Zn1+xSn1-xN2 grown with added hydrogen reduces its free electron density by orders of magnitude, down to 4 x 1016 cm-3. This experimental observation can be explained by hydrogen passivation of acceptors in Zn1+xSn1-xN2 during growth, lowering the driving force for unintentional donor formation. Lastly, these results indicatemore » that the doping control principles used in GaN can be translated to ZnSnN2, suggesting that other strategies used in binary III-Vs can be applied to accelerate the technological development of ternary II-IV-N2 materials.« less

  2. Poly(trifluoromethyl)azulenes: structures and acceptor properties

    SciTech Connect

    Clikeman, Tyler T.; Bukovsky, Eric V.; Kuvychko, Igor V.; San, Long K.; Deng, Shihu; Wang, Xue B.; Chen, Yu-Sheng; Strauss, Steven H.; Boltalina, Olga V.

    2014-07-10

    Azulene is a non-alternant, non-benzenoid aromatic hydrocarbon with an intense blue colour, a dipole moment of 1.0 D,1 positive electron affinity, and an “anomalous” emission from the second excited state in violation of Kasha’s rule.2,3 Azulene’s unique properties have potential uses in molecular switches,4,5 molecular diodes,6 organic photovoltaics,7 and charge transfer complexes.8-12 Introduction of electron-withdrawing groups to the azulenic core, such as CN,8,13,14 halogens,15-19 and CF3,20,21 can enhance certain electrical and photophysical properties. In this work, we report six new trifluoromethyl derivatives of azulene (AZUL), three isomers of AZUL(CF3)3 and three isomers of AZUL(CF3)4, and the first X-ray structure of a π-stacked donor-acceptor complex of a trifluoromethyl azulene with donor pyrene.

  3. Analysis of nonlinear optical properties in donor–acceptor materials

    SciTech Connect

    Day, Paul N.; Pachter, Ruth; Nguyen, Kiet A.

    2014-05-14

    Time-dependent density functional theory has been used to calculate nonlinear optical (NLO) properties, including the first and second hyperpolarizabilities as well as the two-photon absorption cross-section, for the donor-acceptor molecules p-nitroaniline and dimethylamino nitrostilbene, and for respective materials attached to a gold dimer. The CAMB3LYP, B3LYP, PBE0, and PBE exchange-correlation functionals all had fair but variable performance when compared to higher-level theory and to experiment. The CAMB3LYP functional had the best performance on these compounds of the functionals tested. However, our comprehensive analysis has shown that quantitative prediction of hyperpolarizabilities is still a challenge, hampered by inadequate functionals, basis sets, and solvation models, requiring further experimental characterization. Attachment of the Au{sub 2}S group to molecules already known for their relatively large NLO properties was found to further enhance the response. While our calculations show a modest enhancement for the first hyperpolarizability, the enhancement of the second hyperpolarizability is predicted to be more than an order of magnitude.

  4. Ultrafast exciton dissociation at donor/acceptor interfaces

    NASA Astrophysics Data System (ADS)

    Grancini, G.; Fazzi, D.; Binda, M.; Maiuri, M.; Petrozza, A.; Criante, L.; Perissinotto, S.; Egelhaaf, H.-J.; Brida, D.; Cerullo, G.; Lanzani, G.

    2013-09-01

    Charge generation at donor/acceptor interface is a highly debated topic in the organic photovoltaics (OPV) community. The primary photoexcited state evolution happens in few femtosecond timescale, thus making very intriguing their full understanding. In particular charge generation is believed to occur in < 200 fs, but no clear picture emerged so far. In this work we reveal for the first time the actual charge generation mechanism following in real time the exciton dissociation mechanism by means of sub-22 fs pump-probe spectroscopy. We study a low-band-gap polymer: fullerene interface as an ideal system for OPV. We demonstrate that excitons dissociation leads, on a timescale of 20-50 fs, to two byproducts: bound interfacial charge transfer states (CTS) and free charges. The branching ratio of their formation depends on the excess photon energy provided. When high energy singlet polymer states are excited, well above the optical band gap, an ultrafast hot electron transfer happens between the polymer singlet state and the interfacial hot CTS* due to the high electronic coupling between them. Hot exciton dissociation prevails then on internal energy dissipation that occurs within few hundreds of fs. By measuring the internal quantum efficiency of a prototypical device a rising trend with energy is observed, thus indicating that hot exciton dissociation effectively leads to a higher fraction of free charges.

  5. Potassium acceptor doping of ZnO crystals

    NASA Astrophysics Data System (ADS)

    Parmar, Narendra S.; Corolewski, Caleb D.; McCluskey, Matthew D.; Lynn, K. G.

    2015-05-01

    ZnO bulk single crystals were doped with potassium by diffusion at 950°C. Positron annihilation spectroscopy confirms the filling of zinc vacancies and a different trapping center for positrons. Secondary ion mass spectroscopy measurements show the diffusion of potassium up to 10 μm with concentration ˜1 × 1016 cm-3. IR measurements show a local vibrational mode (LVM) at 3226 cm-1, at a temperature of 9 K, in a potassium doped sample that was subsequently hydrogenated. The LVM is attributed to an O-H bond-stretching mode adjacent to a potassium acceptor. When deuterium substitutes for hydrogen, a peak is observed at 2378 cm-1. The O-H peak is much broader than the O-D peak, perhaps due to an unusually low vibrational lifetime. The isotopic frequency ratio is similar to values found in other hydrogen complexes. Potassium doping increases the resistivity up to 3 orders of magnitude at room temperature. The doped sample has a donor level at 0.30 eV.

  6. Serum cholesterol acceptor capacity in intrauterine growth restricted fetuses.

    PubMed

    Pecks, Ulrich; Rath, Werner; Bauerschlag, Dirk O; Maass, Nicolai; Orlikowsky, Thorsten; Mohaupt, Markus G; Escher, Geneviève

    2017-02-14

    Intrauterine growth restriction (IUGR) is an independent risk factor for the development of cardiovascular diseases later in life. The mechanisms whereby slowed intrauterine growth confers vascular risk are not clearly established. In general, a disturbed cholesterol efflux has been linked to atherosclerosis. The capacity of serum to accept cholesterol has been repeatedly evaluated in clinical studies by the use of macrophage-based cholesterol efflux assays and, if disturbed, precedes atherosclerotic diseases years before the clinical diagnosis. We now hypothesized that circulating cholesterol acceptors in IUGR sera specifically interfere with cholesterol transport mechanisms leading to diminished cholesterol efflux. RAW264.7 cells were used to determine efflux of [3H]-cholesterol in response to [umbilical cord serum (IUGR), n=20; controls (CTRL), n=20]. Cholesterol efflux was lower in IUGR as compared to controls [controls: mean 7.7% fractional [3H]-cholesterol efflux, standard deviation (SD)=0.98; IUGR: mean 6.3%, SD=0.79; P<0.0001]. Values strongly correlated to HDL (ρ=0.655, P<0.0001) and apoE (ρ=0.510, P=0.0008), and mildly to apoA1 (ρ=0.3926, P=0.0122) concentrations. Reduced cholesterol efflux in IUGR could account for the enhanced risk of developing cardiovascular diseases later in life.

  7. Terahertz Stimulated Emission from Silicon Doped by Hydrogenlike Acceptors

    NASA Astrophysics Data System (ADS)

    Pavlov, S. G.; Deßmann, N.; Shastin, V. N.; Zhukavin, R. Kh.; Redlich, B.; van der Meer, A. F. G.; Mittendorff, M.; Winnerl, S.; Abrosimov, N. V.; Riemann, H.; Hübers, H.-W.

    2014-04-01

    Stimulated emission in the terahertz frequency range has been realized from boron acceptor centers in silicon. Population inversion is achieved at resonant optical excitation on the 1Γ8+ → 1Γ7-, 1Γ6-, 4Γ8- intracenter transitions with a midinfrared free-electron laser. Lasing occurs on two intracenter transitions around 1.75 THz. The upper laser levels are the 1Γ7-, 1Γ6-, and 4Γ8- states, and the lower laser level for both emission lines is the 2Γ8+ state. In contrast to n-type intracenter silicon lasers, boron-doped silicon lasers do not involve the excited states with the longest lifetimes. Instead, the absorption cross section for the pump radiation is the dominating factor. The four-level lasing scheme implies that the deepest even-parity boron state is the 2Γ8+ state and not the 1Γ7+ split-off ground state, as indicated by other experiments. This is confirmed by infrared absorption spectroscopy of Si:B.

  8. Structure of Escherichia coli Ribose-5-Phosphate Isomerase: A Ubiquitous Enzyme of the Pentose Phosphate Pathway and the Calvin Cycle

    PubMed Central

    Zhang, Rong-guang; Andersson, C. Evalena; Savchenko, Alexei; Skarina, Tatiana; Evdokimova, Elena; Beasley, Steven; Arrowsmith, Cheryl H.; Edwards, Aled M.; Joachimiak, Andrzej; Mowbray, Sherry L.

    2009-01-01

    Summary Ribose-5-phosphate isomerase A (RpiA; EC 5.3.1.6) interconverts ribose-5-phosphate and ribulose-5-phosphate. This enzyme plays essential roles in carbohydrate anabolism and catabolism; it is ubiquitous and highly conserved. The structure of RpiA from Escherichia coli was solved by multiwavelength anomalous diffraction (MAD) phasing, and refined to 1.5 Å resolution (R factor 22.4%, Rfree 23.7%). RpiA exhibits an α/β/(α/β)/β/α fold, some portions of which are similar to proteins of the alcohol dehydrogenase family. The two subunits of the dimer in the asymmetric unit have different conformations, representing the opening/closing of a cleft. Active site residues were identified in the cleft using sequence conservation, as well as the structure of a complex with the inhibitor arabinose-5-phosphate at 1.25 Å resolution. A mechanism for acid-base catalysis is proposed. PMID:12517338

  9. Structure of escherichia coli ribose-5-phosphate isomerase : a ubiquitous enzyme of the pentose phosphate pathway and the Calvin cycle.

    SciTech Connect

    Zhang, R.; Andersson, C. E.; Savchenko, A.; Skarina, T.; Evdokimova, E.; Beasley, S.; Arrowsmith, C. H.; Edwards, A.; Joachimiak, A.; Mowbray, S. L.; Biosciences Division; Uppsala Univ.; Univ. Health Network; Univ. of Toronto; Swedish Univ. of Agricultural Sciences

    2003-01-01

    Ribose-5-phosphate isomerase A (RpiA; EC 5.3.1.6) interconverts ribose-5-phosphate and ribulose-5-phosphate. This enzyme plays essential roles in carbohydrate anabolism and catabolism; it is ubiquitous and highly conserved. The structure of RpiA from Escherichia coli was solved by multiwavelength anomalous diffraction (MAD) phasing, and refined to 1.5 Angstroms resolution (R factor 22.4%, R{sub free} 23.7%). RpiA exhibits an {alpha}/{beta}/({alpha}/{beta})/{beta}/{alpha} fold, some portions of which are similar to proteins of the alcohol dehydrogenase family. The two subunits of the dimer in the asymmetric unit have different conformations, representing the opening/closing of a cleft. Active site residues were identified in the cleft using sequence conservation, as well as the structure of a complex with the inhibitor arabinose-5-phosphate at 1.25 A resolution. A mechanism for acid-base catalysis is proposed.

  10. Structure of Escherichia coli ribose-5-phosphate isomerase: a ubiquitous enzyme of the pentose phosphate pathway and the Calvin cycle.

    PubMed

    Zhang, Rong guang; Andersson, C Evalena; Savchenko, Alexei; Skarina, Tatiana; Evdokimova, Elena; Beasley, Steven; Arrowsmith, Cheryl H; Edwards, Aled M; Joachimiak, Andrzej; Mowbray, Sherry L

    2003-01-01

    Ribose-5-phosphate isomerase A (RpiA; EC 5.3.1.6) interconverts ribose-5-phosphate and ribulose-5-phosphate. This enzyme plays essential roles in carbohydrate anabolism and catabolism; it is ubiquitous and highly conserved. The structure of RpiA from Escherichia coli was solved by multiwavelength anomalous diffraction (MAD) phasing, and refined to 1.5 A resolution (R factor 22.4%, R(free) 23.7%). RpiA exhibits an alpha/beta/(alpha/beta)/beta/alpha fold, some portions of which are similar to proteins of the alcohol dehydrogenase family. The two subunits of the dimer in the asymmetric unit have different conformations, representing the opening/closing of a cleft. Active site residues were identified in the cleft using sequence conservation, as well as the structure of a complex with the inhibitor arabinose-5-phosphate at 1.25 A resolution. A mechanism for acid-base catalysis is proposed.

  11. Rates of primary electron transfer reactions in the photosystem I reaction center reconstituted with different quinones as the secondary acceptor

    SciTech Connect

    Kumazaki, Shigeichi; Kandori, Hideki; Yoshihara, Keitaro ); Iwaki, Masayo; Itoh, Shigeru ); Ikegamu, Isamu )

    1994-10-27

    Rates of sequential electron transfer reactions from the primary electron donor chlorophyll dimer (P700) to the electron acceptor chlorophyll a-686 (A[sub 0]) and to the secondary acceptor quinone (Q[sub [phi

  12. Phosphate dynamics in an urban sewer: a case study of Nancy, France.

    PubMed

    Houhou, J; Lartiges, B S; Hofmann, A; Frappier, G; Ghanbaja, J; Temgoua, A

    2009-03-01

    The nature of phosphate phases present in suspended matter, biofilm, and sediment of Greater Nancy sewer system was investigated over a period of two years. The phosphate speciation was determined by two approaches: a direct identification of phosphorus mineral phases was conducted by Transmission Electron Microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDXS), whereas a chemical extraction of samples provided an estimate of phosphorus pools defined by the fractionation scheme. Quantitative analysis of 1340 individual particles by TEM-EDXS allowed to draw a picture of phosphate species distributions along the sewer system and over time. Amorphous Ca-phosphates (brushite, whitlockite, octacalcium phosphate, Mg-brushite, hydroxyapatite and carbapatite) were ubiquitous although brushite dominated upstream, and octacalcium phosphate and apatite prevailed downstream and in sediments. Al-Ca-phosphate minerals such as foggite, bearthite, gatumbaite, and crandallite appeared downstream and in biofilms. Ca-phosphate phase assemblages in the different locations of the sewer system were dependent on phase transformations from brushite to hydroxyapatite that were shown to be kinetically driven. The restriction of Al-Ca-phosphates to downstream of the sewer system was most probably related to the lower pHs measured at these sites. The pH dependency was confirmed by stability calculations. Chemical extractions were not reliable. TEM examination of extraction residues revealed the presence of neoformed Al-Ca-phosphate species that invalidated the fractionation scheme. Nonetheless, it confirmed that phosphate phases may undergo significant geochemical changes over a short time scale.

  13. Site-directed deep electronic tunneling through a molecular network

    SciTech Connect

    Caspary, Maytal; Peskin, Uri

    2005-10-15

    Electronic tunneling in a complex molecular network of N(>2) donor/acceptor sites, connected by molecular bridges, is analyzed. The 'deep' tunneling dynamics is formulated using a recursive perturbation expansion, yielding a McConnell-type reduced N-level model Hamiltonian. Applications to models of molecular junctions demonstrate that the donor-bridge contact parameters can be tuned in order to control the tunneling dynamics and particularly to direct the tunneling pathway to either one of the various acceptors.

  14. Trehalose biosynthesis in Thermus thermophilus RQ-1: biochemical properties of the trehalose-6-phosphate synthase and trehalose-6-phosphate phosphatase.

    PubMed

    Silva, Zélia; Alarico, Susana; da Costa, Milton S

    2005-02-01

    The genes for trehalose synthesis in Thermus thermophilus RQ-1, namely otsA [trehalose-phosphate synthase (TPS)], otsB [trehalose-phosphate phosphatase (TPP)], and treS [trehalose synthase (maltose converting) (TreS)] genes are structurally linked. The TPS/TPP pathway plays a role in osmoadaptation, since mutants unable to synthesize trehalose via this pathway were less osmotolerant, in trehalose-deprived medium, than the wild-type strain. The otsA and otsB genes have now been individually cloned and overexpressed in Escherichia coli and the corresponding recombinant enzymes purified. The apparent molecular masses of TPS and TPP were 52 and 26 kDa, respectively. The recombinant TPS utilized UDP-glucose, TDP-glucose, ADP-glucose, or GDP-glucose, in this order as glucosyl donors, and glucose-6-phosphate as the glucosyl acceptor to produce trehalose-6-phosphate (T6P). The recombinant TPP catalyzed the dephosphorylation of T6P to trehalose. This enzyme also dephosphorylated G6P, and this activity was enhanced by NDP-glucose. TPS had an optimal activity at about 98 degrees C and pH near 6.0; TPP had a maximal activity near 70 degrees C and at pH 7.0. The enzymes were extremely thermostable: at 100 degrees C, TPS had a half-life of 31 min, and TPP had a half-life of 40 min. The enzymes did not require the presence of divalent cations for activity; however, the presence of Co2+ and Mg2+ stimulates both TPS and TPP. This is the first report of the characterization of TPS and TPP from a thermophilic organism.

  15. Inositol phosphates in the environment.

    PubMed Central

    Turner, Benjamin L; Papházy, Michael J; Haygarth, Philip M; McKelvie, Ian D

    2002-01-01

    The inositol phosphates are a group of organic phosphorus compounds found widely in the natural environment, but that represent the greatest gap in our understanding of the global phosphorus cycle. They exist as inositols in various states of phosphorylation (bound to between one and six phosphate groups) and isomeric forms (e.g. myo, D-chiro, scyllo, neo), although myo-inositol hexakisphosphate is by far the most prevalent form in nature. In terrestrial environments, inositol phosphates are principally derived from plants and accumulate in soils to become the dominant class of organic phosphorus compounds. Inositol phosphates are also present in large amounts in aquatic environments, where they may contribute to eutrophication. Despite the prevalence of inositol phosphates in the environment, their cycling, mobility and bioavailability are poorly understood. This is largely related to analytical difficulties associated with the extraction, separation and detection of inositol phosphates in environmental samples. This review summarizes the current knowledge of inositol phosphates in the environment and the analytical techniques currently available for their detection in environmental samples. Recent advances in technology, such as the development of suitable chromatographic and capillary electrophoresis separation techniques, should help to elucidate some of the more pertinent questions regarding inositol phosphates in the natural environment. PMID:12028785

  16. New organic donor-acceptor-π-acceptor sensitizers for efficient dye-sensitized solar cells and photocatalytic hydrogen evolution under visible-light irradiation.

    PubMed

    Li, Xing; Cui, Shicong; Wang, Dan; Zhou, Ying; Zhou, Hao; Hu, Yue; Liu, Jin-Gang; Long, Yitao; Wu, Wenjun; Hua, Jianli; Tian, He

    2014-10-01

    Two organic donor-acceptor-π-acceptor (D-A-π-A) sensitizers (AQ and AP), containing quinoxaline/pyrido[3,4-b]pyrazine as the auxiliary acceptor, have been. Through fine-tuning of the auxiliary acceptor, a higher designed and synthesized photoelectric conversion efficiency of 6.02% for the AQ-based dye-sensitized solar cells under standard global AM1.5 solar conditions was achieved. Also, it was found that AQ-Pt/TiO2 photocatalysts displayed a better rate of H2 evolution under visible-light irradiation (420 nm<λ<780 nm) because of the stability of the oxidized states and the lower rates of electron recombination. Importantly, sensitizers AQ and AP-Pt/TiO2 showed strong photocatalytic activity during continuous light soaking for 10 h with methanol as the sacrificial electron donor. Additionally, the processes of their intermolecular electron transfer were further investigated theoretically by using time-dependent DFT. The calculated results indicate that the auxiliary acceptor plays the role of an electron trap and results in broad spectral responses. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Analysis of Shewanella oneidensis Membrane Protein Expression in Response to Electron Acceptor Availability

    SciTech Connect

    Giometti, Carol S.; Khare, Tripti; Verberkmoes, Nathan; O'Loughlin, Ed; Lindberg, Carl; Thompson, Melissa; Hettich, Robert

    2006-04-05

    Shewanella oneidensis MR-1, a gram negative metal-reducing bacterium, can utilize a large number of electron acceptors. In the natural environment, S. oneidensis utilizes insoluble metal oxides as well as soluble terminal electron acceptors. The purpose of this ERSP project is to identify differentially expressed proteins associated with the membranes of S. oneidensis MR-1 cells grown with different electron acceptors, including insoluble metal oxides. We hypothesize that through the use of surface labeling, subcellular fractionation, and a combination of proteome analysis tools, proteins involved in the reduction of different terminal electron acceptors will be elucidated. We are comparing the protein profiles from cells grown with the soluble electron acceptors oxygen and fumarate and with those from cells grown with the insoluble iron oxides goethite, ferrihydrite and lepidocrocite. Comparison of the cell surface proteins isolated from cells grown with oxygen or anaerobically with fumarate revealed an increase in the abundance of over 25 proteins in anaerobic cells, including agglutination protein and flagellin proteins along with the several hypothetical proteins. In addition, the surface protein composition of cells grown with the insoluble iron oxides varies considerably from the protein composition observed with either soluble electron acceptor as well as between the different insoluble acceptors.

  18. Allosteric Regulation of Lactobacillus plantarum Xylulose 5-Phosphate/Fructose 6-Phosphate Phosphoketolase (Xfp)

    PubMed Central

    Glenn, Katie

    2015-01-01

    ABSTRACT Xylulose 5-phosphate/fructose 6-phosphate phosphoketolase (Xfp), which catalyzes the conversion of xylulose 5-phosphate (X5P) or fructose 6-phosphate (F6P) to acetyl phosphate, plays a key role in carbohydrate metabolism in a number of bacteria. Recently, we demonstrated that the fungal Cryptococcus neoformans Xfp2 exhibits both substrate cooperativity for all substrates (X5P, F6P, and Pi) and allosteric regulation in the forms of inhibition by phosphoenolpyruvate (PEP), oxaloacetic acid (OAA), and ATP and activation by AMP (K. Glenn, C. Ingram-Smith, and K. S. Smith. Eukaryot Cell 13:657–663, 2014). Allosteric regulation has not been reported previously for the characterized bacterial Xfps. Here, we report the discovery of substrate cooperativity and allosteric regulation among bacterial Xfps, specifically the Lactobacillus plantarum Xfp. L. plantarum Xfp is an allosteric enzyme inhibited by PEP, OAA, and glyoxylate but unaffected by the presence of ATP or AMP. Glyoxylate is an additional inhibitor to those previously reported for C. neoformans Xfp2. As with C. neoformans Xfp2, PEP and OAA share the same or possess overlapping sites on L. plantarum Xfp. Glyoxylate, which had the lowest half-maximal inhibitory concentration of the three inhibitors, binds at a separate site. This study demonstrates that substrate cooperativity and allosteric regulation may be common properties among bacterial and eukaryotic Xfp enzymes, yet important differences exist between the enzymes in these two domains. IMPORTANCE Xylulose 5-phosphate/fructose 6-phosphate phosphoketolase (Xfp) plays a key role in carbohydrate metabolism in a number of bacteria. Although we recently demonstrated that the fungal Cryptococcus Xfp is subject to substrate cooperativity and allosteric regulation, neither phenomenon has been reported for a bacterial Xfp. Here, we report that the Lactobacillus plantarum Xfp displays substrate cooperativity and is allosterically inhibited by

  19. Synthesis and electrochemical studies of charge-transfer complexes of thiazolidine-2,4-dione with σ and π acceptors

    NASA Astrophysics Data System (ADS)

    Singh, Prashant; Kumar, Pradeep; Katyal, Anju; Kalra, Rashmi; Dass, Sujata K.; Prakash, Satya; Chandra, Ramesh

    2010-03-01

    In the present work, we report the synthesis and characterization of novel charge-transfer complexes of thiazolidine-2,4-dione (TZD) with sigma acceptor (iodine) and pi acceptors (chloranil, dichlorodicyanoquinone, picric acid and duraquinone). We also evaluated their thermal and electrochemical properties and we conclude that these complexes are frequency dependent. Charge-transfer complex between thiazolidine-2,4-dione and iodine give best conductivity. In conclusion, complex with sigma acceptors are more conducting than with pi acceptors.

  20. Templated, layered manganese phosphate

    DOEpatents

    Thoma, Steven G.; Bonhomme, Francois R.

    2004-08-17

    A new crystalline maganese phosphate composition having an empirical formula: O). The compound was determined to crystallize in the trigonal space group P-3c1 with a=8.8706(4) .ANG., c=26.1580(2) .ANG., and V (volume)=1783 .ANG..sup.3. The structure consists of sheets of corner sharing Mn(II)O.sub.4 and PO.sub.4 tetrahedra with layers of (H.sub.3 NCH.sub.2 CH.sub.2).sub.3 N and water molecules in-between. The pronated (H.sub.3 NCH.sub.2 CH.sub.2).sub.3 N molecules provide charge balancing for the inorganic sheets. A network of hydrogen bonds between water molecules and the inorganic sheets holds the structure together.

  1. Light weight phosphate cements

    DOEpatents

    Wagh, Arun S.; Natarajan, Ramkumar,; Kahn, David

    2010-03-09

    A sealant having a specific gravity in the range of from about 0.7 to about 1.6 for heavy oil and/or coal bed methane fields is disclosed. The sealant has a binder including an oxide or hydroxide of Al or of Fe and a phosphoric acid solution. The binder may have MgO or an oxide of Fe and/or an acid phosphate. The binder is present from about 20 to about 50% by weight of the sealant with a lightweight additive present in the range of from about 1 to about 10% by weight of said sealant, a filler, and water sufficient to provide chemically bound water present in the range of from about 9 to about 36% by weight of the sealant when set. A porous ceramic is also disclosed.

  2. 21 CFR 184.1301 - Ferric phosphate.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... GRAS § 184.1301 Ferric phosphate. (a) Ferric phosphate (ferric orthophosphate, iron (III) phosphate, Fe... ferric chloride or ferric citrate. (b) The ingredient meets the specifications of the Food Chemicals...

  3. Biosynthesis of heparin. Availability of glucosaminyl 3-O-sulfation sites

    SciTech Connect

    Kusche, M.; Torri, G.; Casu, B.; Lindahl, U. )

    1990-05-05

    Heparin preparations isolated from pig intestinal mucosa and from bovine lung were fractionated with regard to affinity for antithrombin. The resulting fractions, with high (HA) or low (LA) affinity for the proteinase inhibitor, were analyzed by 13C NMR or by identification of di- and tetrasaccharides obtained through deaminative cleavage with nitrous acid. Structural differences between corresponding HA and LA fractions were essentially restricted to minor constituents, in particular 3-O-sulfated glucosamine units that occurred (1 or 2 residues/chain) in all HA preparations but were scarce or absent in LA heparin. The HA fractions also consistently showed higher contents of nonsulfated iduronic acid and, to a lesser extent, N-acetylated glucosamine units than the LA fractions. The two tetrasaccharide sequences, -IdoA-GlcNAc(6-OSO3)-GlcA-GlcNSO3- and -IdoA-GlcNAc(6-OSO3)-GlcA-GlcNSO3(6-OSO3)- , recently implicated as part of the acceptor site for glucosaminyl 3-O-sulfate groups were identified in mucosal LA heparin; it was calculated that the preparation contained approximately one potential acceptor site/polysaccharide chain. Yet this material did not yield any labeled HA components on incubation with adenosine 3'-phosphate 5'-phospho-(35S)sulfate in the presence of glucosaminyl 3-O-sulfotransferase, solubilized from a mouse mastocytoma microsomal fraction. The failure to incorporate any 3-O-sulfate groups could conceivably be explained by the occurrence of a D-glucuronic rather than L-iduronic acid unit linked at the reducing ends of the above tetrasaccharide sequences. Alternatively, 3-O-sulfation may be restricted by other, as yet unidentified, inhibitory structural elements that are preferentially expressed in polysaccharide sequences selected for the generation of LA heparin.Au

  4. Phosphate nutrition: improving low-phosphate tolerance in crops.

    PubMed

    López-Arredondo, Damar Lizbeth; Leyva-González, Marco Antonio; González-Morales, Sandra Isabel; López-Bucio, José; Herrera-Estrella, Luis

    2014-01-01

    Phosphorus is an essential nutrient that is required for all major developmental processes and reproduction in plants. It is also a major constituent of the fertilizers required to sustain high-yield agriculture. Levels of phosphate--the only form of phosphorus that can be assimilated by plants--are suboptimal in most natural and agricultural ecosystems, and when phosphate is applied as fertilizer in soils, it is rapidly immobilized owing to fixation and microbial activity. Thus, cultivated plants use only approximately 20-30% of the applied phosphate, and the rest is lost, eventually causing water eutrophication. Recent advances in the understanding of mechanisms by which wild and cultivated species adapt to low-phosphate stress and the implementation of alternative bacterial pathways for phosphorus metabolism have started to allow the design of more effective breeding and genetic engineering strategies to produce highly phosphate-efficient crops, optimize fertilizer use, and reach agricultural sustainability with a lower environmental cost. In this review, we outline the current advances in research on the complex network of plant responses to low-phosphorus stress and discuss some strategies used to manipulate genes involved in phosphate uptake, remobilization, and metabolism to develop low-phosphate-tolerant crops, which could help in designing more efficient crops.

  5. Crystallization of calcium phosphate in polyacrylamide hydrogels containing phosphate ions

    NASA Astrophysics Data System (ADS)

    Yokoi, Taishi; Kawashita, Masakazu; Kikuta, Koichi; Ohtsuki, Chikara

    2010-08-01

    Calcium phosphate crystals were formed in polyacrylamide (PAAm) hydrogels containing phosphate ions by diffusion of calcium ions from calcium nitrate (Ca(NO 3) 2) solutions covering the gels. Changes in crystalline phases and crystal morphology of calcium phosphate, and in ion concentrations of the Ca(NO 3) 2 solutions were investigated as a function of reaction time. Single or two coexisting crystalline phases of calcium phosphate, hydroxyapatite (HAp), HAp/dicalcium phosphate dihydrate (DCPD) or octacalcium phosphate (OCP)/DCPD were formed in the gels. HAp crystals are formed near the surface of the gels. The dense HAp layer and HAp/DCPD layer prevented diffusion of calcium ions from the Ca(NO 3) 2 solution, thus formation of calcium phosphate in the gel phase was inhibited. Formation of DCPD was observed to follow the formation of OCP or HAp. The size of the OCP crystals gradually increased with reaction time, while changes in size of HAp crystals were not observed. The reaction time required for DCPD formation depended on the degree of supersaturation with respect to DCPD in the systems. DCPD formed within 1 day under high supersaturation conditions, whereas it formed at 10 days in low supersaturation conditions.

  6. Thioredoxin binding site of phosphoribulokinase overlaps the catalytic site. [R

    SciTech Connect

    Porter, M.A.; Hartman, F.C.

    1986-01-01

    The ATP-regulatory binding site of phosphoribulokinase was studied using bromoacetylethanolamine phosphate (BrAcNHEtOP). BrAcNHEtOP binds to the active-regulatory binding site of the protein. Following trypsin degradation of the labeled protein, fragments were separated by HPLC and sequenced. (DT)

  7. An optimized RAD51 inhibitor that disrupts homologous recombination without requiring Michael acceptor reactivity

    PubMed Central

    Budke, Brian; Kalin, Jay H.; Pawlowski, Michal; Zelivianskaia, Anna S.; Wu, Megan; Kozikowski, Alan P.; Connell, Philip P.

    2013-01-01

    Homologous recombination (HR) is an essential process in cells that provides repair of DNA double-strand breaks and lesions that block DNA replication. RAD51 is an evolutionarily conserved protein that is central to HR. Overexpression of RAD51 protein is common in cancer cells and represents a potential therapeutic target in oncology. We previously described a chemical inhibitor of RAD51, called RI-1 (referred to as compound 1 in this report). The chloromaleimide group of this compound is thought to act as a Michael acceptor and react with the thiol group on C319 of RAD51, using a conjugate addition-elimination mechanism. In order to reduce the likelihood of off-target effects and to improve compound stability in biological systems, we developed an analog of compound 1 that lacks maleimide-based reactivity but retains RAD51 inhibitory activity. This compound, 1-(3,4-dichlorophenyl)-3-(4-methoxyphenyl)-4-morpholino-1H-pyrrole-2,5-dione, named RI-2 (referred to as compound 7a in this report), appears to bind reversibly to the same site on the RAD51 protein as does compound 1. Like compound 1, compound 7a specifically inhibits HR repair in human cells. PMID:23231413

  8. Bacterial manganese reduction and growth with manganese oxide as the sole electron acceptor

    NASA Technical Reports Server (NTRS)

    Myers, Charles R.; Nealson, Kenneth H.

    1988-01-01

    Microbes that couple growth to the reduction of manganese could play an important role in the biogeochemistry of certain anaerobic environments. Such a bacterium, Alteromonas putrefaciens MR-1, couples its growth to the reduction of manganese oxides only under anaerobic conditions. The characteristics of this reduction are consistent with a biological, and not an indirect chemical, reduction of manganese, which suggest that this bacterium uses manganic oxide as a terminal electron acceptor. It can also utilize a large number of other compounds as terminal electron acceptors; this versatility could provide a distinct advantage in environments where electron-acceptor concentrations may vary.

  9. Optical spectroscopy of single beryllium acceptors in GaAs/AlGaAs quantum well

    NASA Astrophysics Data System (ADS)

    Petrov, P. V.; Kokurin, I. A.; Klimko, G. V.; Ivanov, S. V.; Ivánov, Yu. L.; Koenraad, P. M.; Silov, A. Yu.; Averkiev, N. S.

    2016-09-01

    We carry out microphotoluminescence measurements of an acceptor-bound exciton (A0X ) recombination in the applied magnetic field with a single impurity resolution. In order to describe the obtained spectra we develop a theoretical model taking into account a quantum well (QW) confinement, an electron-hole and hole-hole exchange interaction. By means of fitting the measured data with the model we are able to study the fine structure of individual acceptors inside the QW. The good agreement between our experiments and the model indicates that we observe single acceptors in a pure two-dimensional environment whose states are unstrained in the QW plain.

  10. Selenium geochemistry in reclaimed phosphate mine soils and its relationship with plant bioavailability

    USDA-ARS?s Scientific Manuscript database

    Background and Aims Selenium contamination and accumulation in vegetation have resulted in Se toxicity in livestock and wildlife in reclaimed phosphate mine soils in Southeastern Idaho. Methods Plant and soil samples were collected from five study sites near phosphate mines. Soil physiochemical pr...

  11. Laboratory comparison of four iron-based filter materials for drainage water phosphate treatment

    USDA-ARS?s Scientific Manuscript database

    Phosphate released with agricultural subsurface drainage water can cause environmental degradation of downstream water bodies. On-site filter treatment with iron-based filter materials could potentially remove phosphate from drainage waters before these waters are discharged into local streams. Th...

  12. Evaluation of several commercially available caitionic polymer flocculants for phosphate sorption in water

    USDA-ARS?s Scientific Manuscript database

    Although inorganic phosphate is an essential plant nutrient, elevated levels in surface waters may lead to adverse effects in the environment. These effects are attributed to runoff from rain or irrigation events that may cause the sorbed phosphate to be transported from the application sites and mo...

  13. Highly Efficient Inverted D:A1:A2 Ternary Blend Organic Photovoltaics Combining a Ladder-type Non-Fullerene Acceptor and a Fullerene Acceptor.

    PubMed

    Chang, Shao-Ling; Cao, Fong-Yi; Huang, Wen-Chia; Huang, Po-Kai; Hsu, Chain-Shu; Cheng, Yen-Ju

    2017-07-26

    A formylated benzodi(cyclopentadithiophene) (BDCPDT) ladder-type structure with forced coplanarity is coupled with two 1,1-dicyanomethylene-3-indanone (IC) moieties via olefination to form a non-fullerene acceptor, BDCPDT-IC. The BDCPDT-IC, as an acceptor (A1) with broad light-absorbing ability and excellent solution processability, is combined with a second PC71BM acceptor (A2) and a medium band gap polymer, PBDB-T, as the donor (D) to form a ternary blend with gradient HOMO/LUMO energy alignments and panchromatic absorption. The device with the inverted architecture using the D:A1:A2 ternary blend has achieved a highest efficiency of 9.79% with a superior Jsc of 16.84 mA cm(-2).

  14. Bioavailability of Fe(III) in Loess Sediments: An Important Source of Electron Acceptors

    SciTech Connect

    Bishop, Michael E.; Jaisi, Deb P.; Dong, Hailiang; Kukkadapu, Ravi K.; Ji, Junfeng

    2010-08-01

    A quantitative study was conducted to understand if Fe (III) in loess sediments is available for microbial respiration by using a common metal reducing bacterium, Shewanella putrefaciens, CN32. The loess samples were collected from three different sites: St. Louis (Peoria), Missouri, USA; Huanxia (HX) and Yanchang (YCH), Shanxi Province of China. Wet chemical analyses indicated that the total Fe concentration for the three samples was 1.69%, 2.76%, and 3.29%, respectively, of which 0.48%, 0.67%, and 1.27% was Fe(III). All unreduced loess sediments contained iron oxides and phyllosilicates (smectite, illite, chlorite, vermiculite), in addition to common minerals such as quartz, feldspar, plagioclase, calcite, and dolomite. Bioreduction experiments were performed at a loess concentration of 20 mg/mL using lactate as the sole electron donor, Fe(III) in loess as the sole electron acceptor in the presence and absence of anthraquinone-2, 6-disulfonate (AQDS) as an electron shuttle. Experiments were performed in non-growth (bicarbonate buffer) and growth (M1) media with a cell concentration of ~2.8 x 107 and 2.1 x 107 cells/mL, respectively. The unreduced and bioreduced solids were analyzed by X-ray diffraction (XRD), Mössbauer spectroscopy, diffuse reflection spectroscopy (DRS), and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) methods. Despite many similarities among the three loess samples, the extent and rate of Fe (III) reduction varied significantly. For example, in presence of AQDS the extent of reduction in the non-growth experiment was 25% in HX, 34% in Peoria, and 38% in YCH. The extent of reduction in the growth experiment was 72% in HX, 94% in Peoria, and 56% in YCH. The extent of bioreduction was lower in absence of AQDS. Overall, AQDS and the M1 growth medium significantly enhanced the rate and extent of bioreduction. Fe(III) in iron oxides and Fe(III)-containing phyllosilicates was bioreduced. Biogenic illite, siderite, and

  15. Influence of competitive electron acceptors during reduction and effective immobilization of technetium by reduced nontronite

    NASA Astrophysics Data System (ADS)

    Jaisi, D. P.; Dong, H.; Heald, S. M.; Fredrickson, J. K.; Plymale, A. E.

    2006-12-01

    The reduction and immobilization of Tc(VII) by Fe(II) in nontronite (NAu-2) was studied in the presence of iron and manganese oxides and nitrate, the coexisting competitive terminal electron acceptors (TEAs) in several DOE subsurface contamination sites, to understand how these TEAs might inhibit Tc(VII) reduction or promote reoxidation of reduced Tc. Manganese oxides (birnessite and manganite) and iron oxides (goethite and hematite) were synthesized and their mineralogical, morphological and surface properties were characterized by XRD, SEM, and BET surface and pore area measurements, respectively. Batch Tc(VII) reduction experiments were performed at different concentrations of Tc and Fe(II) and competing electron acceptors were added at different times. Separate experiments performed with NAu-2 and a TEA only (in the absence of Tc) showed that that the electron transfer from Fe(II) in NAu-2 to manganese oxides was very fast, but the transfer from Fe(II) to nitrate was almost absent. The Tc(VII) reduction was enhanced when iron oxides (goethite and hematite) was added, irrespective of time, however the enhancement was low at later phases of Tc reduction. The addition of manganese oxides during Tc reduction stopped any additional Tc(VII) reduction, but reoxidation of already reduced Tc was not observed at low Tc concentration. In general, the extent of reoxidation of reduced Tc (by manganese oxide) in old samples was slow suggesting that the higher rate of particle aggregation in reduced NAu-2 inhibited the reoxidation of reduced Tc. However, Tc(IV) reoxidation was not observed in the presence of nitrate. The preliminary EXAFS analysis showed that a fraction of reduced Tc occurred as Tc-Fe complex in a ferrihydrite-like solid, in addition to separate TcO2.nH2O particles, which might have promoted additional NAu-2 particle aggregation and thereby incorporation of reduced Tc into NAu-2 aggregates. These results are promising for long-term in-situ immobilization of

  16. Ground-state thermodynamics of bistable redox-active donor-acceptor mechanically interlocked molecules.

    PubMed

    Fahrenbach, Albert C; Bruns, Carson J; Cao, Dennis; Stoddart, J Fraser

    2012-09-18

    Fashioned through billions of years of evolution, biological molecular machines, such as ATP synthase, myosin, and kinesin, use the intricate relative motions of their components to drive some of life's most essential processes. Having control over the motions in molecules is imperative for life to function, and many chemists have designed, synthesized, and investigated artificial molecular systems that also express controllable motions within molecules. Using bistable mechanically interlocked molecules (MIMs), based on donor-acceptor recognition motifs, we have sought to imitate the sophisticated nanoscale machines present in living systems. In this Account, we analyze the thermodynamic characteristics of a series of redox-switchable [2]rotaxanes and [2]catenanes. Control and understanding of the relative intramolecular movements of components in MIMs have been vital in the development of a variety of applications of these compounds ranging from molecular electronic devices to drug delivery systems. These bistable donor-acceptor MIMs undergo redox-activated switching between two isomeric states. Under ambient conditions, the dominant translational isomer, the ground-state coconformation (GSCC), is in equilibrium with the less favored translational isomer, the metastable-state coconformation (MSCC). By manipulating the redox state of the recognition site associated with the GSCC, we can stimulate the relative movements of the components in these bistable MIMs. The thermodynamic parameters of model host-guest complexes provide a good starting point to rationalize the ratio of GSCC to MSCC at equilibrium. The bistable [2]rotaxanes show a strong correlation between the relative free energies of model complexes and the ground-state distribution constants (K(GS)). This relationship does not always hold for bistable [2]catenanes, most likely because of the additional steric and electronic constraints present when the two rings are mechanically interlocked with each other

  17. NuMA is a major acceptor of poly(ADP-ribosyl)ation by tankyrase 1 in mitosis

    PubMed Central

    2005-01-01

    Tankyrase 1 is a PARP [poly(ADP-ribose) polymerase] that localizes to multiple subcellular sites, including telomeres and mitotic centrosomes. Previous studies demonstrated that cells deficient in tankyrase 1 suffered a block in resolution of sister telomeres and arrested in early anaphase [Dynek and Smith (2004) Science 304, 97–100]. This phenotype was dependent on the catalytic PARP activity of tankyrase 1. To identify critical acceptors of PARsylation [poly(ADP-ribosyl)ation] by tankyrase 1 in mitosis, tankyrase 1 immunoprecipitates were analysed for associated PARsylated proteins. We identified NuMA (nuclear mitotic apparatus protein) as a major acceptor of poly(ADP-ribose) from tankyrase 1 in mitosis. We showed by immunofluorescence and immunoprecipitation that association between tankyrase 1 and NuMA increases dramatically at the onset of mitosis, concomitant with PARsylation of NuMA. Knockdown of tankyrase 1 by siRNA (small interfering RNA) eliminates PARsylation of NuMA in mitosis, confirming tankyrase 1 as the PARP responsible for this modification. However, even in the absence of tankyrase 1 and PARsylation, NuMA localizes to spindle poles. By contrast, siRNA knockdown of NuMA results in complete loss of tankyrase 1 from spindle poles. We discuss our result in terms of a model where PARsylation of NuMA by tankyrase 1 in mitosis could play a role in sister telomere separation and/or mitotic progression. PMID:16076287

  18. Central action of dendrotoxin: selective reduction of a transient K conductance in hippocampus and binding to localized acceptors.

    PubMed Central

    Halliwell, J V; Othman, I B; Pelchen-Matthews, A; Dolly, J O

    1986-01-01

    Dendrotoxin, a small single-chain protein from the venom of Dendroaspis angusticeps, is highly toxic following intracerebroventricular injection into rats. Voltage-clamp analysis of CA1 neurons in hippocampal slices, treated with tetrodotoxin, revealed that nanomolar concentrations of dendrotoxin reduce selectively a transient, voltage-dependent K conductance. Epileptiform activity known to be induced by dendrotoxin can be attributed to such an action. Membrane currents not affected directly by the toxin include (i) Ca-activated K conductance; (ii) noninactivating voltage-dependent K conductance; (iii) inactivating and noninactivating Ca conductances; (iv) persistent inward (anomalous) rectifier current. Persistence of the effects of the toxin when Cd was included to suppress spontaneous transmitter release indicates a direct action on the neuronal membrane. Using biologically active, 125I-labeled dendrotoxin, protein acceptor sites of high affinity were detected on cerebrocortical synaptosomal membranes and sections of rat brain. In hippocampus, toxin binding was shown autoradiographically to reside in synapse-rich and white matter regions, with lower levels in cell body layers. This acceptor is implicated in the action of toxin because its affinities for dendrotoxin congeners are proportional to their central neurotoxicities and potencies in reducing the transient, voltage-dependent K conductance. Images PMID:2417246

  19. Central action of dendrotoxin: selective reduction of a transient K conductance in hippocampus and binding to localized acceptors

    SciTech Connect

    Halliwell, J.V.; Othman, I.B.; Pelchen-Matthews, A.; Dolly, J.O.

    1986-01-01

    Dendrotoxin, a small single-chain protein from the venom of Dendroaspis angusticeps, is highly toxic following intracerebroventricular injection into rats. Voltage-clamp analysis of CA/sub 1/ neurons in hippocampal slices, treated with tetrodotoxin, revealed that nanomolar concentrations of dendrotoxin reduce selectively a transient, voltage-dependent K conductance. Epileptiform activity known to be induced by dendrotoxin can be attributed to such an action. Membrane currents not affected directly by the toxin include (i) Ca-activated K conductance; (ii) noninactivating voltage-dependent K conductance; (iii) inactivating the noninactivating Ca conductances; (iv) persistent inward (anomalous) rectifier current. Persistence of the effects of the toxin when Cd was included to suppress spontaneous transmitter release indicates a direct action on the neuronal membrane. Using biologically active, /sup 125/I-labeled dendrotoxin, protein acceptor sites of high affinity were detected on cerebrocortical synapotosomal membranes and sections of rat brain. In hippocampus, toxin binding was shown autoradiographically to reside in synapse-rich and white matter regions, with lower levels in cell body layers. This acceptor is implicated in the action of toxin because its affinities for dendrotoxin congeners are proportional to their central neurotoxicities and potencies in reducing the transient, voltage-dependent K conductance.

  20. Furfural, 5-hydroxymethyl furfural, and acetoin act as external electron acceptors during anaerobic fermentation of xylose in recombinant Saccharomyces cerevisiae.

    PubMed

    Wahlbom, C Fredrik; Hahn-Hägerdal, Bärbel

    2002-04-20

    The electron acceptors acetoin, acetaldehyde, furfural, and 5-hydroxymethylfurfural (HMF) were added to anaerobic batch fermentation of xylose by recombinant, xylose utilising Saccharomyces cerevisiae TMB 3001. The intracellular fluxes during xylose fermentation before and after acetoin addition were calculated with metabolic flux analysis. Acetoin halted xylitol excretion and decreased the flux through the oxidative pentose phosphate pathway. The yield of ethanol increased from 0.62 mol ethanol/mol xylose to 1.35 mol ethanol/mol xylose, and the cell more than doubled its specific ATP production after acetoin addition compared to fermentation of xylose only. This did, however, not result in biomass growth. The xylitol excretion was also decreased by furfural and acetaldehyde but was unchanged by HMF. Thus, furfural present in lignocellulosic hydrolysate can be beneficial for ethanolic fermentation of xylose. Enzymatic analyses showed that the reduction of acetoin and furfural required NADH, whereas the reduction of HMF required NADPH. The enzymatic activity responsible for furfural reduction was considerably higher than for HMF reduction and also in situ furfural conversion was higher than HMF conversion. Copyright 2002 Wiley Periodicals, Inc.

  1. Effect of silver ions on transport and retention of phosphate by Escherichia coli.

    PubMed Central

    Schreurs, W J; Rosenberg, H

    1982-01-01

    Silver ions inhibited phosphate uptake and exchange in Escherichia coli and caused efflux of accumulated phosphate as well as of mannitol, succinate, glutamine, and proline. The effects of Ag+ were reversed by thiols and, to a lesser extent, by bromide. In the presence of N-ethylmaleimide and several uncouplers, Ag+ failed to cause phosphate efflux, but still inhibited exchange of intracellular and extracellular phosphate, indicating an interaction at more than one site. It is unlikely that Ag+ caused metabolite efflux by acting solely as an uncoupler, as an inhibitor of the respiratory chain, or as a thiol reagent. PMID:6749823

  2. DECREASING LEAD BIOAVAILABILITY OF MINE WASTES: TWO PHOSPHATE FIELD STUDIES

    EPA Science Inventory

    Findings from two evaluation studies of phosphate-based in situ treatment of soils for reducing lead (Pb) bioavailability at two lead mining and lead refining Superfund sites will be presented and discussed. These assessments correlated physicochemical data with results obtained...

  3. Preparation and spectroscopic studies on charge-transfer complexes of 2-hydroxypyridine with electron acceptors

    NASA Astrophysics Data System (ADS)

    Gaballa, Akmal S.

    2013-07-01

    The CT-interactions of electron acceptors such as iodine (I2), chloranilic acid (H2CA) and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) with 2-hydroxypyridine (HPyO) have been investigated in the defined solvent. The data indicate the formation of CT-complexes with the general formula [(HPyO)(acceptor)]. The 1:1 stoichiometry of the (HPyO)-acceptors were based on elemental analysis, IR spectra and thermogravimetric analysis of the solid CT-complexes along with the photometric titration measurements for the reactions. The formation constants (KCT) for the CT-complexes are shown to be strongly dependent on the type and structure of the electron acceptors. Factors affecting the CT-processes are discussed.

  4. Preparation and spectroscopic studies on charge-transfer complexes of famciclovir drug with different electron acceptors

    NASA Astrophysics Data System (ADS)

    Gaballa, Akmal S.; Teleb, Said M.; Nour, El-Metwally

    2012-09-01

    The CT-interaction of electron acceptors such as chloranilic acid (H2CA), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and and 7,7',8,8'-tetracyano-p-quinodimethane (TCNQ) with the antiviral drug famciclovir (FCV) have been investigated spectrophotometrically in the defined solvent. The data indicate the formation of CT-complexes with the general formula [(FCV)(acceptor)]. The 1:1 stoichiometry of the (FCV)-acceptors were based on elemental analysis, IR spectra and thermogravimetric analysis of the solid CT-complexes along with the photometric titration measurements for the reactions. The formation constants (KCT) for the CT-complexes are shown to be strongly dependent on the type and structure of the electron acceptor. Factors affecting the CT-processes such as redox potentials and steric hinderance of reactants are discussed.

  5. Disassembly of micelles to impart donor and acceptor gradation to enhance organic solar cell efficiency.

    PubMed

    Arulkashmir, Arulraj; Krishnamoorthy, Kothandam

    2016-02-28

    A transparent, conducting and low surface energy surface was prepared by disassembly of anionic micelles, which altered the orientation of the donor polymer and imparted gradation between the donor and acceptor. This configuration increased the solar cell device efficiency.

  6. Time-resolved spectroscopy of the fluorescence quenching of a donor — acceptor pair by halothane

    NASA Astrophysics Data System (ADS)

    Sharma, A.; Draxler, S.; Lippitsch, M. E.

    1992-04-01

    Donor (anthracene) sensitized acceptor (perylene) fluorescence is quenched more efficiently by halothane than is intrinsic perylene fluorescence. The underlying process of dynamic fluorescence quenching is investigated by time-resolved fluorescence spectroscopy.

  7. Panchromatic donor-acceptor-donor conjugated oligomers for dye-sensitized solar cell applications.

    PubMed

    Stalder, Romain; Xie, Dongping; Islam, Ashraful; Han, Liyuan; Reynolds, John R; Schanze, Kirk S

    2014-06-11

    We report on a sexithienyl and two donor-acceptor-donor oligothiophenes, employing benzothiadiazole and isoindigo as electron-acceptors, each functionalized with a phosphonic acid group for anchoring onto TiO2 substrates as light-harvesting molecules for dye sensitized solar cells (DSSCs). These dyes absorb light to wavelengths as long as 700 nm, as their optical HOMO/LUMO energy gaps are reduced from 2.40 to 1.77 eV with increasing acceptor strength. The oligomers were adsorbed onto mesoporous TiO2 films on fluorine doped tin oxide (FTO)/glass substrates and incorporated into DSSCs, which show AM1.5 power conversion efficiencies (PCEs) ranging between 2.6% and 6.4%. This work demonstrates that the donor-acceptor-donor (D-A-D) molecular structures coupled to phosphonic acid anchoring groups, which have not been used in DSSCs, can lead to high PCEs.

  8. Computational design of donor-bridge-acceptor systems exhibiting pronounced quantum interference effects.

    PubMed

    Gorczak, Natalie; Renaud, Nicolas; Galan, Elena; Eelkema, Rienk; Siebbeles, Laurens D A; Grozema, Ferdinand C

    2016-03-07

    Quantum interference is a well-known phenomenon that dictates charge transport properties of single molecule junctions. However, reports on quantum interference in donor-bridge-acceptor molecules are scarce. This might be due to the difficulties in meeting the conditions for the presence of quantum interference in a donor-bridge-acceptor system. The electronic coupling between the donor, bridge, and acceptor moieties must be weak in order to ensure localised initial and final states for charge transfer. Yet, it must be strong enough to allow all bridge orbitals to mediate charge transfer. We present the computational route to the design of a donor-bridge-acceptor molecule that features the right balance between these contradicting requirements and exhibits pronounced interference effects.

  9. Interface-induced heavy-hole/light-hole splitting of acceptors in silicon

    SciTech Connect

    Mol, J. A.; Salfi, J.; Simmons, M. Y.; Rogge, S.; Rahman, R.; Hsueh, Y.; Klimeck, G.; Miwa, J. A.

    2015-05-18

    The energy spectrum of spin-orbit coupled states of individual sub-surface boron acceptor dopants in silicon have been investigated using scanning tunneling spectroscopy at cryogenic temperatures. The spatially resolved tunnel spectra show two resonances, which we ascribe to the heavy- and light-hole Kramers doublets. This type of broken degeneracy has recently been argued to be advantageous for the lifetime of acceptor-based qubits [R. Ruskov and C. Tahan, Phys. Rev. B 88, 064308 (2013)]. The depth dependent energy splitting between the heavy- and light-hole Kramers doublets is consistent with tight binding calculations, and is in excess of 1 meV for all acceptors within the experimentally accessible depth range (<2 nm from the surface). These results will aid the development of tunable acceptor-based qubits in silicon with long coherence times and the possibility for electrical manipulation.

  10. Reversal-bounded multipushdown machines. [Turing acceptors for context free languages

    NASA Technical Reports Server (NTRS)

    Baker, B. S.; Book, R. V.

    1974-01-01

    Several representations of the recursively enumerable (r.e.) sets are presented. The first states that every r.e. set is the homomorphic image of the intersection of two linear context-free languages. The second states that every r.e. set is accepted by an on-line Turing acceptor with two pushdown stores such that in every computation, each pushdown store can make at most one reversal (that is, one change from 'pushing' to 'popping'). It is shown that this automata theoretic representation cannot be strengthened by restricting the acceptors to be deterministic multitape, nondeterministic one-tape, or nondeterministic multicounter acceptors. This provides evidence that reversal bounds are not a natural measure of computational complexity for multitape Turing acceptors.

  11. Characterization of a phosphate binding domain on the alpha-subunit of chloroplast ATP synthase using the photoaffinity phosphate analogue 4-azido-2-nitrophenyl phosphate.

    PubMed

    Groth, G; Mills, D A; Christiansen, E; Richter, M L; Huchzermeyer, B

    2000-11-14

    The photoaffinity phosphate analogue 4-azido-2 nitrophenyl phosphate (ANPP) was shown previously (Pougeois, R., Lauquin, G. J.-M., and Vignais, P. V. (1983) Biochemistry 22, 1241-1245) to bind covalently and specifically to a single catalytic site on one of the three beta-subunits of the isolated chloroplast coupling factor 1 (CF(1)). Modification by ANPP strongly inhibited ATP hydrolysis activity. In this study, we examined labeling of membrane-bound CF(1) by ANPP by exposing thylakoid membranes to increasing concentrations of the reagent. ANPP exhibited saturable binding to two sites on CF(1), one on the beta-subunit and one on the alpha-subunit. Labeling by ANPP resulted in the complete inhibition of both ATP synthesis and ATP hydrolysis by the membrane-bound enzyme. Labeling of both sites by ANPP was reduced by more than 80% in the presence of P(i) (> or = 10 mM) and ATP (> or = 0.5 mM). ADP was less effective in competing with ANPP for binding, giving a maximum of approximately 35% inhibition at concentrations > or = 2 mM. ANPP-labeled tryptic peptides of the alpha-subunit were isolated and sequenced. The majority of the probe was contained in three peptides corresponding to residues Gln(173) to Arg(216), Gly(217) to Arg(253), and His(256) to Arg(272) of the alpha-subunit. In the mitochondrial F(1) (Abrahams, J. P., Leslie, A. G. W., Lutter, R., and Walker, J. E. (1994) Nature 370, 621-628), all three analogous peptides are located within the nucleotide binding pocket and within close proximity to the gamma-phosphate binding site. The data indicate, however, that the azidophenyl group of bound ANPP is oriented at approximately 180 degrees in the opposite direction to the adenine binding site with reference to the phosphate binding site on the alpha-subunit. The study has confirmed that ANPP is a bona fide phosphate analogue and suggests that it specifically targets the gamma-phosphate binding site within the nucleotide binding pockets on the alpha- and beta

  12. Phosphorylation sites in human erythrocyte band 3 protein.

    PubMed

    Yannoukakos, D; Vasseur, C; Piau, J P; Wajcman, H; Bursaux, E

    1991-01-30

    The human red cell anion-exchanger, band 3 protein, is one of the main phosphorylated proteins of the erythrocyte membrane. Previous studies from this laboratory have shown that ATP-depletion of the red blood cell decreased the anion-exchange rate, suggesting that band 3 protein phosphorylation could be involved in the regulation of anion transport function (Bursaux et al. (1984) Biochim. Biophys. Acta 777, 253-260). Phosphorylation occurs mainly on the cytoplasmic domain of the protein and the major site of phosphorylation was assigned to tyrosine-8 (Dekowski et al. (1983) J. Biol. Chem. 258, 2750-2753). This site being very far from the integral, anion-exchanger domain, the aim of the present study was to determine whether phosphorylation sites exist in the integral domain. The phosphorylation reaction was carried out on isolated membranes in the presence of [gamma-32P]ATP and phosphorylated band 3 protein was then isolated. Both the cytoplasmic and the membrane spanning domains were purified. The predominant phosphorylation sites were found on the cytoplasmic domain. RP-HPLC analyses of the tryptic peptides of whole band 3 protein, and of the isolated cytoplasmic and membrane-spanning domains allowed for the precise localization of the phosphorylated residues. 80% of the label was found in the N-terminal tryptic peptide (T-1), (residues 1-56). In this region, all the residues susceptible to phosphorylation were labeled but in varying proportion. Under our conditions, the most active membrane kinase was a tyrosine kinase, activated preferentially by Mn2+ but also by Mg2+. Tyrosine-8 was the main phosphate acceptor residue (50-70%) of the protein, tyrosine-21 and tyrosine-46 residues were also phosphorylated but to a much lesser extent. The main targets of membrane casein kinase, preferentially activated by Mg2+, were serine-29, serine-50, and threonine(s)-39, -42, -44, -48, -49, -54 residue(s) located in the T-1 peptide. A tyrosine phosphatase activity was

  13. Ternary Organic Solar Cells Based on Two Compatible Nonfullerene Acceptors with Power Conversion Efficiency >10.

    PubMed

    Liu, Tao; Guo, Yuan; Yi, Yuanping; Huo, Lijun; Xue, Xiaonan; Sun, Xiaobo; Fu, Huiting; Xiong, Wentao; Meng, Dong; Wang, Zhaohui; Liu, Feng; Russell, Thomas P; Sun, Yanming

    2016-12-01

    Two different nonfullerene acceptors and one copolymer are used to fabricate ternary organic solar cells (OSCs). The two acceptors show unique interactions that reduce crystallinity and form a homogeneous mixed phase in the blend film, leading to a high efficiency of ≈10.3%, the highest performance reported for nonfullerene ternary blends. This work provides a new approach to fabricate high-performance OSCs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. An Electron Acceptor with Porphyrin and Perylene Bisimides for Efficient Non-Fullerene Solar Cells.

    PubMed

    Zhang, Andong; Li, Cheng; Yang, Fan; Zhang, Jianqi; Wang, Zhaohui; Wei, Zhixiang; Li, Weiwei

    2017-03-01

    A star-shaped electron acceptor based on porphyrin as a core and perylene bisimide as end groups was constructed for application in non-fullerene organic solar cells. The new conjugated molecule exhibits aligned energy levels, good electron mobility, and complementary absorption with a donor polymer. These advantages facilitate a high power conversion efficiency of 7.4 % in non-fullerene solar cells, which represents the highest photovoltaic performance based on porphyrin derivatives as the acceptor.

  15. ABAB Phthalocyanines: Scaffolds for Building Unprecedented Donor-π-Acceptor Chromophores.

    PubMed

    Fazio, Ettore; Jaramillo-García, Javier; Medel, María; Urbani, Maxence; Grätzel, Michael; Nazeerudin, Mohammad K; de la Torre, Gema; Torres, Tomas

    2017-02-01

    Unique donor-π-acceptor phthalocyanines have been synthesized through the asymmetric functionalization of an ABAB phthalocyanine, crosswise functionalized with two iodine atoms through Pd-catalyzed cross-coupling reactions with adequate electron-donor and electron-acceptor moieties. These push-pull molecules have been optically and electrochemically characterized, and their ability to perform as chromophores for dye-sensitized solar cells has been tested.

  16. ABAB Phthalocyanines: Scaffolds for Building Unprecedented Donor–π–Acceptor Chromophores

    PubMed Central

    Fazio, Ettore; Jaramillo‐García, Javier; Medel, María; Urbani, Maxence; Grätzel, Michael

    2016-01-01

    Abstract Unique donor–π–acceptor phthalocyanines have been synthesized through the asymmetric functionalization of an ABAB phthalocyanine, crosswise functionalized with two iodine atoms through Pd‐catalyzed cross‐coupling reactions with adequate electron‐donor and electron‐acceptor moieties. These push–pull molecules have been optically and electrochemically characterized, and their ability to perform as chromophores for dye‐sensitized solar cells has been tested. PMID:28168157

  17. Electron Donor-Acceptor Quenching and Photoinduced Electron Transfer for Coumarin Dyes.

    DTIC Science & Technology

    1983-10-31

    Mechanism of cousarin photodegradation . Ithe behavior of eoiuma dyes is water ad In aqueous detergent media,. and the effsects of medism aud, additives on...D-i36 345 ELECTRON DONOR-ACCEPTOR UENCHING AND PHOTOINDUCED i/i Ai ELECTRON TRANSFER FOR COUMARIN DYES (U) BOSTON UNIY MR DEPT OF CHEMISTRY G JONES...TYPE OF REPORT & PEIOD COVERED Electron Donor-acceptor Quenching and Photo- Technical, 1/1/82-10/31/82 induced Electron Transfer for Coumarin Dyes S

  18. Experiments probing the viability of donor-acceptor norbornenes for (5 + 2)-annulation.

    PubMed

    Walker, Morgan M; Goodman, C Guy; Johnson, Jeffrey S

    2014-10-03

    This Note details experiments that probe the mechanism by which donor-acceptor norbornene systems epimerize. A number of mechanistic studies indicate that epimerization in these systems occurs via a Lewis acid catalyzed retro-Diels-Alder/Diels-Alder sequence, rather than bond rotation in an intimate ion pair. These results suggest that, under the reaction conditions examined, the ring strain present in norbornene is inadequate to induce zwitterion formation analogous to that observed with donor-acceptor cyclopropanes.

  19. Process for gasification using a synthetic CO/sub 2/ acceptor

    SciTech Connect

    Curran, G.P.; Lancet, M.S.

    1980-11-04

    A gasification process is disclosed using a synthetic CO/sub 2/ acceptor consisting essentially of at least one compound selected from the group consisting of calcium oxide and calcium carbonate supported in a refractory carrier matrix, the carrier having the general formula Ca/sub 5/(SiO/sub 4/)/sub 2/CO/sub 3/. A method for producing the synthetic CO/sub 2/ acceptor is also disclosed.

  20. Discovery of coumarin derivatives as fluorescence acceptors for intrinsic fluorescence resonance energy transfer of proteins.

    PubMed

    Kim, Ju Hwan; Sumranjit, Jitapa; Kang, Hyo Jin; Chung, Sang J

    2014-01-01

    Coumarin analogues were synthezised and evaluated as acceptors for the intrinsic fluorescence resonance energy transfer (iFRET) of tryptophan residues in target proteins. The fluorescence properties such as quantum yields, iFRET efficiencies, and Förster distances of the prepared coumarin analogs were determined in a model system, by their conjugation to biotin, utilizing streptavidin (SAV) as the iFRET donor. The coumarin derivatives reported here represent the most efficient iFRET acceptors for tryptophan, known to date.

  1. Process for gasification using a synthetic CO.sub.2 acceptor

    DOEpatents

    Lancet, Michael S.; Curran, George P.

    1980-01-01

    A gasification process is disclosed using a synthetic CO.sub.2 acceptor consisting essentially of at least one compound selected from the group consisting of calcium oxide and calcium carbonate supported in a refractory carrier matrix, the carrier having the general formula Ca.sub.5 (SiO.sub.4).sub.2 CO.sub.3. A method for producing the synthetic CO.sub.2 acceptor is also disclosed.

  2. A water setting tetracalcium phosphate-dicalcium phosphate dihydrate cement.

    PubMed

    Burguera, E F; Guitián, F; Chow, L C

    2004-11-01

    The development of a calcium phosphate cement, comprising tetracalcium phosphate (TTCP) and dicalcium phosphate dihydrate (DCPD), that hardens in 14 min with water as the liquid or 6 min with a 0.25 mol/L sodium phosphate solution as the liquid, without using hydroxyapatite (HA) seeds as setting accelerator, is reported. It was postulated that reduction in porosity would increase cement strength. Thus, the effects of applied pressure during the initial stages of the cement setting reaction on cement strength and porosity were studied. The cement powder comprised an equimolar mixture of TTCP and DCPD (median particle sizes 17 and 1.7 microm, respectively). Compressive strengths (CS) of samples prepared with distilled water were 47.6 +/- 2.4 MPa, 50.7 +/- 4.2 MPa, and 52.9 +/- 4.7 MPa at applied pressures of 5 MPa, 15 MPa, and 25 MPa, respectively. When phosphate solution was used, the CS values obtained were 41.5 +/- 2.3 MPa, 37.9 +/- 1.7 MPa, and 38.1 +/- 2.3 MPa at the same pressure levels. Statistical analysis of the results showed that pressure produced an improvement in CS when water was used as liquid but not when the phosphate solution was used. Compared to previously reported TTCP-DCPD cements, the greater CS values and shorter setting times together with a simplified formulation should make the present TTCP-DCPD cement a useful material as a bone substitute for clinical applications.

  3. A comparative study of calcium phosphate formation on bioceramics in vitro and in vivo.

    PubMed

    Xin, Renlong; Leng, Yang; Chen, Jiyong; Zhang, Qiyi

    2005-11-01

    Formation of calcium phosphate (Ca-P) on various bioceramic surfaces in simulated body fluid (SBF) and in rabbit muscle sites was investigated. The bioceramics were sintered porous solids, including bioglass, glass-ceramics, hydroxyapatite, alpha-tricalcium phosphate and beta-tricalcium phosphate. The ability of inducing Ca-P formation was compared among the bioceramics. The Ca-P crystal structures were identified using single-crystal diffraction patterns in transmission electron microscopy. The examination results show that ability of inducing Ca-P formation in SBF was similar among bioceramics, but considerably varied among bioceramics in vivo. Sintered beta-tricalcium phosphate exhibited a poor ability of inducing Ca-P formation both in vitro and in vivo. Octacalcium phosphate (OCP) formed on the surfaces of bioglass, A-W, hydroxyapatite and alpha-tricalcium phosphate in vitro and in vivo. Apatite formation in physiological environments cannot be confirmed as a common feature of bioceramics.

  4. Localization of a renal sodium-phosphate cotransporter gene to human chromosome 5q35

    SciTech Connect

    Kos, C.H.; Tenenhouse, H.S. ); Tihy, F.; Lemieux, N. ); Econs, M.J. ); Murer, H. )

    1994-01-01

    Several Mendelian disorders of renal phosphate reabsorption, associated with hypophosphatemia and bone disease, have been described. These include X-linked hypophosphatemia (XLH), hereditary hypophosphatemic rickets with hypercalciuria, hypophosphatemic bone disease, and autosomal dominant and autosomal recessive hypophosphatemic rickets. The underlying mechanisms for renal phosphate wasting in these disorders remain unknown. The proximal tubule is the major site of renal phosphate reabsorption. Thus, mutations in genes that participate in the transepithelial transport of phosphate in this segment of the nephron may be responsible for these disorders. Recently, a cDNA encoding a renal proximal tubular, brush-border membrane Na[sup +]-phosphate cotransporter (NaP[sub i]-3) was cloned from human kidney cortex. As a first step in establishing whether mutations in the NaP[sub i]-3 gene are the cause of inherited disorders in phosphate homeostasis, the authors sought to determine its chromosomal localization. 9 refs., 1 fig.

  5. Final Report: Dominant Mechanisms of Uranium-Phosphate Reactions in Subsurface Sediments

    SciTech Connect

    Catalano, Jeffrey G.; Giammar, Daniel E.; Wang, Zheming

    2016-03-08

    Phosphate addition is an in situ remediation approach that may enhance the sequestration of uranium without requiring sustained reducing conditions. However, the geochemical factors that determine the dominant immobilization mechanisms upon phosphate addition are insufficiently understood to design efficient remediation strategies or accurately predict U(VI) transport. The overall objective of our project is to determine the dominant mechanisms of U(VI)-phosphate reactions in subsurface environments. Our research approach seeks to determine the U(VI)-phosphate solid that form in the presence of different groundwater cations, characterize the effects of phosphate on U(VI) adsorption and precipitation on smectite and iron oxide minerals, examples of two major reactive mineral phases in contaminated sediments, and investigate how phosphate affects U(VI) speciation and fate during water flow through sediments from contaminated sites. The research activities conducted for this project have generated a series of major findings. U(VI) phosphate solids from the autunite mineral family are the sole phases to form during precipitation, with uranyl orthophosphate not occurring despite its predicted greater stability. Calcium phosphates may take up substantial quantities of U(VI) through three different removal processes (adsorption, coprecipitation, and precipitation) but the dominance of each process varies with the pathway of reaction. Phosphate co-adsorbs with U(VI) onto smectite mineral surfaces, forming a mixed uranium-phosphate surface complex over a wide range of conditions. However, this molecular-scale association of uranium and phosphate has not effect on the overall extent of uptake. In contrast, phosphate enhanced U(VI) adsorption to iron oxide minerals at acidic pH conditions but suppresses such adsorption at neutral and alkaline pH, despite forming mixed uranium-phosphate surface complexes during adsorption. Nucleation barriers exist that inhibit U(VI) phosphate

  6. Piperaquine phosphate: reproduction studies.

    PubMed

    Longo, Monica; Pace, Silvia; Messina, Monica; Ferraris, Laura; Brughera, Marco; Ubben, David; Mazuè, Guy

    2012-12-01

    In embryofetal studies in rat and rabbit Piperaquine phosphate (PQP) was not teratogenic at the maximal tolerated dose, even in presence of fetal exposure. In peri- post-natal study in rat, PQP did not interfere with the course of delivery at the dose of 5 mg/kg/day (treatment Gestation Day(GD)6-Lactation Day(LD)21) as well as up to the dose of 20 mg/kg/day (treatment GD6-17 and LD1-21). PQP at the dose of 80 mg/kg, induced prolonged gestation, dystocic delivery and increase perinatal mortality both with interruption of treatment (GD6 to GD17 and LD1-21) and with continuous dosing (GD19-LD21). PQP did not interfere with lactation and pup growth and development, in presence of clear exposure during suckling period, irrespective of the dose and treatment schedules. It was not possible to identify the mechanism leading to the delivery delay. In a comparative study using other antimalarials, only Mefloquine gave similar findings to PQP. Copyright © 2012 Elsevier Inc. All rights reserved.

  7. Effect of phosphate on U(VI) sorption to montmorillonite: Ternary complexation and precipitation barriers

    NASA Astrophysics Data System (ADS)

    Troyer, Lyndsay D.; Maillot, Fabien; Wang, Zheming; Wang, Zimeng; Mehta, Vrajesh S.; Giammar, Daniel E.; Catalano, Jeffrey G.

    2016-02-01

    reveals that ternary complexation may occur without a macroscopic signature, which is attributed to phosphate not appreciably binding to smectite in the absence of U(VI), with U(VI) surface complexes serving as the sole reactive surface sites for phosphate. This study shows that phosphate does not enhance U(VI) adsorption to smectite clay minerals, unlike oxide phases, and that a barrier to homogeneous nucleation of U(VI) phosphates was not affected by the presence of the smectite surface.

  8. Effect of Phosphate on U(VI) Sorption to Montmorillonite: Ternary Complexation and Precipitation Barriers

    SciTech Connect

    Troyer, Lyndsay D.; Maillot, Fabien; Wang, Zheming; Wang, Zimeng; Mehta, Vrajesh; Giammar, Daniel; Catalano, Jeffrey G.

    2016-02-15

    reveals that ternary complexation may occur without a macroscopic signature, which is attributed to phosphate not appreciably binding to smectite in the absence of U(VI), with U(VI) surface complexes serving as the sole reactive surface sites for phosphate. This study shows that phosphate does not enhance U(VI) adsorption to smectite clay minerals, unlike oxide phases, and that a barrier to homogeneous nucleation of U(VI) phosphates was not affected by the presence of the smectite surface

  9. Beyond Fullerenes: Designing Alternative Molecular Electron Acceptors for Solution-Processable Bulk Heterojunction Organic Photovoltaics.

    PubMed

    Sauvé, Geneviève; Fernando, Roshan

    2015-09-17

    Organic photovoltaics (OPVs) are promising candidates for providing a low cost, widespread energy source by converting sunlight into electricity. Solution-processable active layers have predominantly consisted of a conjugated polymer donor blended with a fullerene derivative as the acceptor. Although fullerene derivatives have been the acceptor of choice, they have drawbacks such as weak visible light absorption and poor energy tuning that limit overall efficiencies. This has recently fueled new research to explore alternative acceptors that would overcome those limitations. During this exploration, one question arises: what are the important design principles for developing nonfullerene acceptors? It is generally accepted that acceptors should have high electron affinity, electron mobility, and absorption coefficient in the visible and near-IR region of the spectra. In this Perspective, we argue that alternative molecular acceptors, when blended with a conjugated polymer donor, should also have large nonplanar structures to promote nanoscale phase separation, charge separation and charge transport in blend films. Additionally, new material design should address the low dielectric constant of organic semiconductors that have so far limited their widespread application.

  10. Enhanced natural attenuation of BTEX in the nitrate-reducing environment by different electron acceptors.

    PubMed

    Zhao, Yongsheng; Qu, Dan; Hou, Zhimin; Zhou, Rui

    2015-01-01

    Enhancing natural attenuation of benzene, toluene, ethylbenzene, and xylene (BTEX) in groundwater is a potential remediation technology. This study focused on selecting appropriate electron acceptors to promote BTEX degradation in a nitrate-reducing environment. Nitrate-reducing soil was obtained from simulated BTEX-contaminated column. Enhancing experiments were conducted in the microcosm with nitrate-reducing material and simulated BTEX-polluted groundwater to investigate the promoting feasibility of adding dissolved oxygen (DO), nitrate, chelated Fe(III), and sulphate as electron acceptors. The concentrations of BTEX, electron acceptors, and their reducing products were measured. The order of promoting BTEX degradation with four electron acceptors was nitrate>sulphate>chelated Fe(III)>DO, and the first-order decay coefficients were 0.0432, 0.0333, 0.0240, and 0.0155, respectively. Nitrate, sulphate, and chelated Fe(III) enhanced attenuation. Nitrate was the most effective electron acceptor under nitrate-reducing conditions. Selecting proper electron acceptor is significant in promoting BTEX degradation according to the biogeochemical characteristics of local underground environment.

  11. Molecular helices as electron acceptors in high-performance bulk heterojunction solar cells

    PubMed Central

    Zhong, Yu; Trinh, M. Tuan; Chen, Rongsheng; Purdum, Geoffrey E.; Khlyabich, Petr P.; Sezen, Melda; Oh, Seokjoon; Zhu, Haiming; Fowler, Brandon; Zhang, Boyuan; Wang, Wei; Nam, Chang-Yong; Sfeir, Matthew Y.; Black, Charles T.; Steigerwald, Michael L.; Loo, Yueh-Lin; Ng, Fay; Zhu, X.-Y.; Nuckolls, Colin

    2015-01-01

    Despite numerous organic semiconducting materials synthesized for organic photovoltaics in the past decade, fullerenes are widely used as electron acceptors in highly efficient bulk-heterojunction solar cells. None of the non-fullerene bulk heterojunction solar cells have achieved efficiencies as high as fullerene-based solar cells. Design principles for fullerene-free acceptors remain unclear in the field. Here we report examples of helical molecular semiconductors as electron acceptors that are on par with fullerene derivatives in efficient solar cells. We achieved an 8.3% power conversion efficiency in a solar cell, which is a record high for non-fullerene bulk heterojunctions. Femtosecond transient absorption spectroscopy revealed both electron and hole transfer processes at the donor−acceptor interfaces. Atomic force microscopy reveals a mesh-like network of acceptors with pores that are tens of nanometres in diameter for efficient exciton separation and charge transport. This study describes a new motif for designing highly efficient acceptors for organic solar cells. PMID:26382113

  12. Molecular helices as electron acceptors in high-performance bulk heterojunction solar cells

    DOE PAGES

    Yu M. Zhong; Nam, Chang -Yong; Trinh, M. Tuan; ...

    2015-09-18

    Despite numerous organic semiconducting materials synthesized for organic photovoltaics in the past decade, fullerenes are widely used as electron acceptors in highly efficient bulk-heterojunction solar cells. None of the non-fullerene bulk heterojunction solar cells have achieved efficiencies as high as fullerene-based solar cells. Design principles for fullerene-free acceptors remain unclear in the field. Here we report examples of helical molecular semiconductors as electron acceptors that are on par with fullerene derivatives in efficient solar cells. We achieved an 8.3% power conversion efficiency in a solar cell, which is a record high for non-fullerene bulk heterojunctions. Femtosecond transient absorption spectroscopy revealedmore » both electron and hole transfer processes at the donor–acceptor interfaces. Atomic force microscopy reveals a mesh-like network of acceptors with pores that are tens of nanometres in diameter for efficient exciton separation and charge transport. As a result, this study describes a new motif for designing highly efficient acceptors for organic solar cells.« less

  13. Molecular helices as electron acceptors in high-performance bulk heterojunction solar cells.

    PubMed

    Zhong, Yu; Trinh, M Tuan; Chen, Rongsheng; Purdum, Geoffrey E; Khlyabich, Petr P; Sezen, Melda; Oh, Seokjoon; Zhu, Haiming; Fowler, Brandon; Zhang, Boyuan; Wang, Wei; Nam, Chang-Yong; Sfeir, Matthew Y; Black, Charles T; Steigerwald, Michael L; Loo, Yueh-Lin; Ng, Fay; Zhu, X-Y; Nuckolls, Colin

    2015-09-18

    Despite numerous organic semiconducting materials synthesized for organic photovoltaics in the past decade, fullerenes are widely used as electron acceptors in highly efficient bulk-heterojunction solar cells. None of the non-fullerene bulk heterojunction solar cells have achieved efficiencies as high as fullerene-based solar cells. Design principles for fullerene-free acceptors remain unclear in the field. Here we report examples of helical molecular semiconductors as electron acceptors that are on par with fullerene derivatives in efficient solar cells. We achieved an 8.3% power conversion efficiency in a solar cell, which is a record high for non-fullerene bulk heterojunctions. Femtosecond transient absorption spectroscopy revealed both electron and hole transfer processes at the donor-acceptor interfaces. Atomic force microscopy reveals a mesh-like network of acceptors with pores that are tens of nanometres in diameter for efficient exciton separation and charge transport. This study describes a new motif for designing highly efficient acceptors for organic solar cells.

  14. Alternansucrase acceptor reactions with D-tagatose and L-glucose.

    PubMed

    Côté, Gregory L; Dunlap, Christopher A; Appell, Michael; Momany, Frank A

    2005-02-07

    Alternansucrase (EC 2.4.1.140) is a d-glucansucrase that synthesizes an alternating alpha-(1-->3), (1-->6)-linked d-glucan from sucrose. It also synthesizes oligosaccharides via d-glucopyranosyl transfer to various acceptor sugars. Two of the more efficient monosaccharide acceptors are D-tagatose and L-glucose. In the presence of d-tagatose, alternansucrase produced the disaccharide alpha-d-glucopyranosyl-(1-->1)-beta-D-tagatopyranose via glucosyl transfer. This disaccharide is analogous to trehalulose. We were unable to isolate a disaccharide product from L-glucose, but the trisaccharide alpha-D-glucopyranosyl-(1-->6)-alpha-d-glucopyranosyl-(1-->4)-l-glucose was isolated and identified. This is analogous to panose, one of the structural units of pullulan, in which the reducing-end D-glucose residue has been replaced by its L-enantiomer. The putative L-glucose disaccharide product, produced by glucoamylase hydrolysis of the trisaccharide, was found to be an acceptor for alternansucrase. The disaccharide, alpha-D-glucopyranosyl-(1-->4)-L-glucose, was a better acceptor than maltose, previously the best known acceptor for alternansucrase. A structure comparison of alpha-D-glucopyranosyl-(1-->4)-L-glucose and maltose was performed through computer modeling to identify common features, which may be important in acceptor affinity by alternansucrase.

  15. Molecular helices as electron acceptors in high-performance bulk heterojunction solar cells

    NASA Astrophysics Data System (ADS)

    Zhong, Yu; Trinh, M. Tuan; Chen, Rongsheng; Purdum, Geoffrey E.; Khlyabich, Petr P.; Sezen, Melda; Oh, Seokjoon; Zhu, Haiming; Fowler, Brandon; Zhang, Boyuan; Wang, Wei; Nam, Chang-Yong; Sfeir, Matthew Y.; Black, Charles T.; Steigerwald, Michael L.; Loo, Yueh-Lin; Ng, Fay; Zhu, X.-Y.; Nuckolls, Colin

    2015-09-01

    Despite numerous organic semiconducting materials synthesized for organic photovoltaics in the past decade, fullerenes are widely used as electron acceptors in highly efficient bulk-heterojunction solar cells. None of the non-fullerene bulk heterojunction solar cells have achieved efficiencies as high as fullerene-based solar cells. Design principles for fullerene-free acceptors remain unclear in the field. Here we report examples of helical molecular semiconductors as electron acceptors that are on par with fullerene derivatives in efficient solar cells. We achieved an 8.3% power conversion efficiency in a solar cell, which is a record high for non-fullerene bulk heterojunctions. Femtosecond transient absorption spectroscopy revealed both electron and hole transfer processes at the donor-acceptor interfaces. Atomic force microscopy reveals a mesh-like network of acceptors with pores that are tens of nanometres in diameter for efficient exciton separation and charge transport. This study describes a new motif for designing highly efficient acceptors for organic solar cells.

  16. The Effect of Acceptor and Donor Doping on Oxygen Vacancy Concentrations in Lead Zirconate Titanate (PZT)

    PubMed Central

    Slouka, Christoph; Kainz, Theresa; Navickas, Edvinas; Walch, Gregor; Hutter, Herbert; Reichmann, Klaus; Fleig, Jürgen

    2016-01-01

    The different properties of acceptor-doped (hard) and donor-doped (soft) lead zirconate titanate (PZT) ceramics are often attributed to different amounts of oxygen vacancies introduced by the dopant. Acceptor doping is believed to cause high oxygen vacancy concentrations, while donors are expected to strongly suppress their amount. In this study, La3+ donor-doped, Fe3+ acceptor-doped and La3+/Fe3+-co-doped PZT samples were investigated by oxygen tracer exchange and electrochemical impedance spectroscopy in order to analyse the effect of doping on oxygen vacancy concentrations. Relative changes in the tracer diffusion coefficients for different doping and quantitative relations between defect concentrations allowed estimates of oxygen vacancy concentrations. Donor doping does not completely suppress the formation of oxygen vacancies; rather, it concentrates them in the grain boundary region. Acceptor doping enhances the amount of oxygen vacancies but estimates suggest that bulk concentrations are still in the ppm range, even for 1% acceptor doping. Trapped holes might thus considerably contribute to the charge balancing of the acceptor dopants. This could also be of relevance in understanding the properties of hard and soft PZT. PMID:28774067

  17. A new classification of the amino acid side chains based on doublet acceptor energy levels.

    PubMed Central

    Sneddon, S F; Morgan, R S; Brooks, C L

    1988-01-01

    We describe a new classification of the amino acid side chains based on the potential energy level at which each will accept an extra (doublet) electron. The doublet acceptor energy level, and the doublet acceptor orbital were calculated using semiempirical INDO/2-UHF molecular orbital theory. The results of these calculations show that the side chains fall into four groups. We have termed these groups repulsive, insulating, semiconducting, and attractive in accordance with where each lies on the relative energy scale. We use this classification to examine the role of residues between the donor and acceptor in modulating the rate and mechanism of electron transfer in proteins. With the calculated acceptor levels, we construct a potential barrier for those residues between the donor and acceptor. It is the area beneath this barrier that determines the decay of electronic coupling between donor and acceptor, and thus the transfer rate. We have used this schematic approach to characterize the four electron transfer pathways in myoglobin recently studied by Mayo et al. (Mayo, S.L., W.R. Ellis, R.J. Crutchley, and H.B. Gray. 1986. Science [Wash. DC]. 233:948-952). PMID:3342271

  18. Molecular helices as electron acceptors in high-performance bulk heterojunction solar cells

    SciTech Connect

    Yu M. Zhong; Nam, Chang -Yong; Trinh, M. Tuan; Chen, Rongsheng; Purdum, Geoffrey E.; Khlyabich, Petr P.; Sezen, Melda; Oh, Seokjoon; Zhu, Haiming; Fowler, Brandon; Zhang, Boyuan; Wang, Wei; Sfeir, Matthew Y.; Black, Charles T.; Steigerwald, Michael L.; Loo, Yueh -Lin; Ng, Fay; Zhu, X. -Y.; Nuckolls, Colin

    2015-09-18

    Despite numerous organic semiconducting materials synthesized for organic photovoltaics in the past decade, fullerenes are widely used as electron acceptors in highly efficient bulk-heterojunction solar cells. None of the non-fullerene bulk heterojunction solar cells have achieved efficiencies as high as fullerene-based solar cells. Design principles for fullerene-free acceptors remain unclear in the field. Here we report examples of helical molecular semiconductors as electron acceptors that are on par with fullerene derivatives in efficient solar cells. We achieved an 8.3% power conversion efficiency in a solar cell, which is a record high for non-fullerene bulk heterojunctions. Femtosecond transient absorption spectroscopy revealed both electron and hole transfer processes at the donor–acceptor interfaces. Atomic force microscopy reveals a mesh-like network of acceptors with pores that are tens of nanometres in diameter for efficient exciton separation and charge transport. As a result, this study describes a new motif for designing highly efficient acceptors for organic solar cells.

  19. Density and energy level of a deep-level Mg acceptor in 4H-SiC

    NASA Astrophysics Data System (ADS)

    Matsuura, Hideharu; Morine, Tatsuya; Nagamachi, Shinji

    2015-01-01

    Reliably determining the densities and energy levels of deep-level dominant acceptors in heavily doped wide-band-gap semiconductors has been a topic of recent discussion. In these discussions, the focus is on both Hall scattering factors for holes and distribution functions for acceptors. Mg acceptor levels in 4H-SiC seem to be deep, and so here the electrical properties of Mg-implanted 4H-SiC layers are studied by measuring Hall effects. The obtained Hall scattering factors are not reliable because they drop to less than 0.5 at high measurement temperatures. Moreover, the Fermi-Dirac distribution function is unsuitable for examining Mg acceptors because the obtained acceptor density is much higher than the concentration of implanted Mg atoms. However, by using a distribution function that includes the influence of the excited states of a deep-level acceptor, the density and energy level of Mg acceptors can be reliably determined.

  20. Recent advances in phosphate biosensors.

    PubMed

    Upadhyay, Lata Sheo Bachan; Verma, Nishant

    2015-07-01

    A number of biosensors have been developed for phosphate analysis particularly, concerning its negative impact within the environmental and biological systems. Enzymatic biosensors comprising either a single or multiple enzymatic system have been extensively used for the direct and indirect analysis of phosphate ions. Furthermore, some non-enzymatic biosensors, such as affinity-based biosensors, provide an alternative analytical approach with a higher selectivity. This article reviews the recent advances in the field of biosensor developed for phosphate estimation in clinical and environmental samples, concerning the techniques involved, and the sensitivity toward phosphate ions. The biosensors have been classified and discussed on the basis of the number of enzymes used to develop the analytical system, and a comparative analysis has been performed.

  1. A broadly applicable NHC-Cu-catalyzed approach for efficient, site-, and enantioselective coupling of readily accessible (pinacolato)alkenylboron compounds to allylic phosphates and applications to natural product synthesis.

    PubMed

    Gao, Fang; Carr, James L; Hoveyda, Amir H

    2014-02-05

    A set of protocols for catalytic enantioselective allylic substitution (EAS) reactions that allow for additions of alkenyl units to readily accessible allylic electrophiles is disclosed. Transformations afford 1,4-dienes that contain a tertiary carbon stereogenic site and are promoted by 1.0-5.0 mol % of a copper complex of an N-heterocyclic carbene (NHC). Aryl- as well as alkyl-substituted electrophiles bearing a di- or trisubstituted alkene may be employed. Reactions can involve a variety of robust alkenyl-(pinacolatoboron) [alkenyl-B(pin)] compounds that can be either purchased or prepared by various efficient, site-, and/or stereoselective catalytic reactions, such as cross-metathesis or proto-boryl additions to terminal alkynes. Vinyl-, E-, or Z-disubstituted alkenyl-, 1,1-disubstituted alkenyl-, acyclic, or heterocyclic trisubstituted alkenyl groups may be added in up to >98% yield, >98:2 SN2':SN2, and 99:1 enantiomeric ratio (er). NHC-Cu-catalyzed EAS with alkenyl-B(pin) reagents containing a conjugated carboxylic ester or aldehyde group proceed to provide the desired 1,4-diene products in good yield and with high enantioselectivity despite the presence of a sensitive stereogenic tertiary carbon center that could be considered prone to epimerization. In most instances, the alternative approach of utilizing an alkenylmetal reagent (e.g., an Al-based species) represents an incompatible option. The utility of the approach is illustrated through applications to enantioselective synthesis of natural products such as santolina alcohol, semburin, nyasol, heliespirone A, and heliannuol E.

  2. In situ formation of an oxygen-evolving catalyst in neutral water containing phosphate and Co2+.

    PubMed

    Kanan, Matthew W; Nocera, Daniel G

    2008-08-22

    The utilization of solar energy on a large scale requires its storage. In natural photosynthesis, energy from sunlight is used to rearrange the bonds of water to oxygen and hydrogen equivalents. The realization of artificial systems that perform "water splitting" requires catalysts that produce oxygen from water without the need for excessive driving potentials. Here we report such a catalyst that forms upon the oxidative polarization of an inert indium tin oxide electrode in phosphate-buffered water containing cobalt (II) ions. A variety of analytical techniques indicates the presence of phosphate in an approximate 1:2 ratio with cobalt in this material. The pH dependence of the catalytic activity also implicates the hydrogen phosphate ion as the proton acceptor in the oxygen-producing reaction. This catalyst not only forms in situ from earth-abundant materials but also operates in neutral water under ambient conditions.

  3. Quantitative assay and subcellular distribution of enzymes acting on dolichyl phosphate in rat liver

    PubMed Central

    Ravoet, A; Amar-Costesec, A; Godelaine, D; Beaufay, H

    1981-01-01

    To establish on a quantitative basis the subcellular distribution of the enzymes that glycosylate dolichyl phosphate in rat liver, preliminary kinetic studies on the transfer of mannose, glucose, and N-acetylglucosamine-1-phosphate from the respective (14)C- labeled nucleotide sugars to exogenous dolichyl phosphate were conducted in liver microsomes. Mannosyltransferase, glucosyltransferase, and, to a lesser extent, N- acetylglucosamine-phosphotransferase were found to be very unstable at 37 degrees C in the presence of Triton X-100, which was nevertheless required to disperse the membranes and the lipid acceptor in the aqueous reaction medium. The enzymes became fairly stable in the range of 10-17 degrees C and the reactions then proceeded at a constant velocity for at least 15 min. Conditions under which the reaction products are formed in amount proportional to that of microsomes added are described. For N- acetylglucosaminephosphotransferase it was necessary to supplement the incubation medium with microsomal lipids. Subsequently, liver homogenates were fractionated by differential centrifugation, and the microsome fraction, which contained the bulk of the enzymes glycosylating dolichyl phosphate, was analyzed by isopycnic centrifugation in a sucrose gradient without any previous treatment, or after addition of digitonin. The centrifugation behavior of these enzymes was compared to that of a number of reference enzymes for the endoplasmic reticulum, the golgi complex, the plasma membranes, and mitochondria. It was very simily to that of enzymes of the endoplasmic reticulum, especially glucose-6-phosphatase. Subcellular preparations enriched in golgi complex elements, plasma membranes, outer membranes of mitochondira, or mitoplasts showed for the transferases acting on dolichyl phosphate relative activities similar to that of glucose- 6-phosphatase. It is concluded that glycosylations of dolichyl phosphate into mannose, glucose, and N-acetylglucosamine-1

  4. Toxicological review of inorganic phosphates.

    PubMed

    Weiner, M L; Salminen, W F; Larson, P R; Barter, R A; Kranetz, J L; Simon, G S

    2001-08-01

    Inorganic phosphate salts are widely used as food ingredients and in a variety of commercial applications. The United States Food and Drug Administration (FDA) considers inorganic phosphates "Generally Recognized As Safe" (GRAS) (FDA, 1973a, 1979) [FDA: Food and Drug Administration 1973a. GRAS (Generally Recognized as Safe) food ingredients-phosphates. NTIS PB-221-224, FDA, Food and Drug Administration, 1979. Phosphates; Proposed Affirmation of and Deletion From GRAS Status as Direct and Human Food Ingredients. Federal Register 44 (244). 74845-74857, 18 December (1979)] and the European Union (EU) allows inorganic phosphates to be added directly to food (EU Directive 95/2/EC as amended by 98/72/EC). In this review, data on the acute, subchronic and chronic toxicity, genotoxicity, teratogenicity and reproductive toxicity from the published literature and from unpublished studies by the manufacturers are reviewed. Based on the toxicity data and similar chemistry, the inorganic phosphates can be separated into four major classes, consisting of monovalent salts, divalent salts, ammonium salts and aluminum salts. The proposed classification scheme supports the use of toxicity data from one compound to assess the toxicity of another compound in the same class. However, in the case of eye and skin irritation, the proposed classification scheme cannot be used because a wide range of responses exists within each class. Therefore, the eye and skin hazards associated with an individual inorganic phosphate should be assessed on a chemical-by-chemical basis. A large amount of toxicity data exists for all four classes of inorganic phosphates. The large and comprehensive database allows an accurate assessment of the toxicity of each class of inorganic phosphate. Overall, all four classes of inorganic phosphates exhibit low oral, inhalation and dermal toxicities. Based on these data, humans are unlikely to experience adverse effects when the daily phosphorus consumption remains

  5. Selection of a new whole cell biocatalyst for the synthesis of 2-deoxyribose 5-phosphate.

    PubMed

    Valino, Ana L; Palazzolo, Martín A; Iribarren, Adolfo M; Lewkowicz, Elizabeth

    2012-01-01

    2-deoxyribose 5-phosphate (DR5P) is a key intermediate in the biocatalyzed preparation of deoxyribonucleosides. Therefore, DR5P production by means of simpler, cleaner, and economic pathways becomes highly interesting. One strategy involves the use of bacterial whole cells containing DR5P aldolase as biocatalyst for the aldol addition between acetaldehyde and D: -glyceraldehyde 3-phosphate or glycolytic intermediates that in situ generate the acceptor substrate. In this work, diverse microorganisms capable of synthesizing DR5P were selected by screening several bacteria genera. In particular, Erwinia carotovora ATCC 33260 was identified as a new biocatalyst that afforded 14.1-mM DR5P starting from a cheap raw material like glucose.

  6. 21 CFR 137.175 - Phosphated flour.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 2 2014-04-01 2014-04-01 false Phosphated flour. 137.175 Section 137.175 Food and... CONSUMPTION CEREAL FLOURS AND RELATED PRODUCTS Requirements for Specific Standardized Cereal Flours and Related Products § 137.175 Phosphated flour. Phosphated flour, phosphated white flour, and...

  7. 21 CFR 137.175 - Phosphated flour.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 2 2013-04-01 2013-04-01 false Phosphated flour. 137.175 Section 137.175 Food and... CONSUMPTION CEREAL FLOURS AND RELATED PRODUCTS Requirements for Specific Standardized Cereal Flours and Related Products § 137.175 Phosphated flour. Phosphated flour, phosphated white flour, and...

  8. 21 CFR 137.175 - Phosphated flour.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 2 2012-04-01 2012-04-01 false Phosphated flour. 137.175 Section 137.175 Food and... CONSUMPTION CEREAL FLOURS AND RELATED PRODUCTS Requirements for Specific Standardized Cereal Flours and Related Products § 137.175 Phosphated flour. Phosphated flour, phosphated white flour, and...

  9. Last step in the conversion of trehalose to glycogen: a mycobacterial enzyme that transfers maltose from maltose 1-phosphate to glycogen.

    PubMed

    Elbein, Alan D; Pastuszak, Irena; Tackett, Alan J; Wilson, Tyler; Pan, Yuan T

    2010-03-26

    We show that Mycobacterium smegmatis has an enzyme catalyzing transfer of maltose from [(14)C]maltose 1-phosphate to glycogen. This enzyme was purified 90-fold from crude extracts and characterized. Maltose transfer required addition of an acceptor. Liver, oyster, or mycobacterial glycogens were the best acceptors, whereas amylopectin had good activity, but amylose was a poor acceptor. Maltosaccharides inhibited the transfer of maltose from [(14)C]maltose-1-P to glycogen because they were also acceptors of maltose, and they caused production of larger sized radioactive maltosaccharides. When maltotetraose was the acceptor, over 90% of the (14)C-labeled product was maltohexaose, and no radioactivity was in maltopentaose, demonstrating that maltose was transferred intact. Stoichiometry showed that 0.89 micromol of inorganic phosphate was produced for each micromole of maltose transferred to glycogen, and 56% of the added maltose-1-P was transferred to glycogen. This enzyme has been named alpha1,4-glucan:maltose-1-P maltosyltransferase (GMPMT). Transfer of maltose to glycogen was inhibited by micromolar amounts of inorganic phosphate or arsenate but was only slightly inhibited by millimolar concentrations of glucose-1-P, glucose-6-P, or inorganic pyrophosphate. GMPMT was compared with glycogen phosphorylase (GP). GMPMT catalyzed transfer of [(14)C]maltose-1-P, but not [(14)C]glucose-1-P, to glycogen, whereas GP transferred radioactivity from glucose-1-P but not maltose-1-P. GMPMT and GP were both inhibited by 1,4-dideoxy-1,4-imino-d-arabinitol, but only GP was inhibited by isofagomine. Because mycobacteria that contain trehalose synthase accumulate large amounts of glycogen when grown in high concentrations of trehalose, we propose that trehalose synthase, maltokinase, and GMPMT represent a new pathway of glycogen synthesis using trehalose as the source of glucose.

  10. Impact of donor-acceptor geometry and metal chelation on photophysical properties and applications of triarylboranes.

    PubMed

    Hudson, Zachary M; Wang, Suning

    2009-10-20

    Three-coordinate organoboron compounds have recently found a wide range of applications in materials chemistry as nonlinear optical materials, chemical sensors, and emitters for organic light-emitting diodes (OLEDs). These compounds are excellent electron acceptors due to the empty p(pi) orbital on the boron center. When accompanied by electron donors such as amines, these molecules possess large electronic dipoles, which promote donor-acceptor charge-transfer upon excitation with light. Because of this, donor-acceptor triarylboranes are often highly luminescent both in the solid state and in solution. In this Account, we describe our research to develop donor-acceptor triarylboranes as efficient blue emitters for OLEDs. Through the use of hole-transporting donor groups such as 1-napthylphenylamines, we have prepared multifunctional triarylboranes that can act as the emissive, electron transport, or hole transport layers in OLEDs. We have also examined donor-acceptor compounds based on 2,2'-dipyridylamine or 7-azaindolyl donors, several of which have fluorescent quantum efficiencies approaching 100%. We are also investigating the chemistry of metal-containing triarylboranes. Our studies show that the electron-deficient boryl group can greatly facilitate metal-to-ligand charge-transfer transitions and phosphorescence. In addition, electronegative linker groups such as 2,2'-bipyridine can act in synergy with metal chelation to greatly improve the electron-accepting ability and Lewis acidity of triarylboranes. Donor-acceptor triarylboranes developed in our laboratory can also serve as a series of "switch-on" sensors for fluoride ions. When the donor and acceptor are linked by rigid naphthyl or nonrigid silane linkers, donor-acceptor conjugation is disrupted and charge transfer occurs primarily through space. The binding of fluoride ions to the boron center disrupts this charge transfer, activating alternative pi --> pi* transitions in the molecule and changing the

  11. Conduction electrons in acceptor-doped GaAs/GaAlAs heterostructures: a review

    NASA Astrophysics Data System (ADS)

    Zawadzki, Wlodek; Raymond, Andre; Kubisa, Maciej

    2016-05-01

    We review magneto-optical and magneto-transport effects in GaAs/GaAlAs heterostructures doped in GaAlAs barriers with donors, providing two-dimensional (2D) electron gas (2DEG) in GaAs quantum wells (QWS), and additionally doped with smaller amounts of acceptors (mostly Be atoms) in the vicinity of 2DEG. One may also deal with residual acceptors (mostly C atoms). The behavior of such systems in the presence of a magnetic field differs appreciably from those doped in the vicinity of 2DEG with donors. Three subjects related to the acceptor-doped heterostructures are considered. First is the problem of bound states of conduction electrons confined to the vicinity of negatively charged acceptors by the joint effect of a QW and an external magnetic field parallel to the growth direction. A variational theory of such states is presented, demonstrating that an electron turning around a repulsive center has discrete energies above the corresponding Landau levels. Experimental evidence for the discrete electron energies comes from the work on interband photo-magneto-luminescence, intraband cyclotron resonance and quantum magneto-transport (the Quantum Hall and Shubnikov-de Haas effects). An electron rain-down effect at weak electric fields and a boil-off effect at strong electric fields are introduced. It is demonstrated, both theoretically and experimentally, that a negatively charged acceptor can localize more than one electron. The second subject describes experiment and theory of asymmetric quantized Hall and Shubnikov-de Haas plateaus in acceptor-doped GaAs/GaAlAs heterostructures. It is shown that the main features of the plateau asymmetry can be attributed to asymmetric density of Landau states in the presence of acceptors. However, at high magnetic fields, the rain-down effect is also at work. The third subject deals with the so-called disorder modes (DMs) in the cyclotron resonance of conduction electrons. The DMs originate from random distributions of negatively

  12. Sorption of phosphate onto calcite; results from batch experiments and surface complexation modeling

    NASA Astrophysics Data System (ADS)

    Ugilt Sø, Helle; Postma, Dieke; Jakobsen, Rasmus; Larsen, Flemming

    2011-05-01

    The adsorption of phosphate onto calcite was studied in a series of batch experiments. To avoid the precipitation of phosphate-containing minerals the experiments were conducted using a short reaction time (3 h) and low concentrations of phosphate (⩽50 μM). Sorption of phosphate on calcite was studied in 11 different calcite-equilibrated solutions that varied in pH, P, ionic strength and activity of Ca 2+, CO32- and HCO3-. Our results show strong sorption of phosphate onto calcite. The kinetics of phosphate sorption onto calcite are fast; adsorption is complete within 2-3 h while desorption is complete in less than 0.5 h. The reversibility of the sorption process indicates that phosphate is not incorporated into the calcite crystal lattice under our experimental conditions. Precipitation of phosphate-containing phases does not seem to take place in systems with ⩽50 μM total phosphate, in spite of a high degree of super-saturation with respect to hydroxyapatite (SI HAP ⩽ 7.83). The amount of phosphate adsorbed varied with the solution composition, in particular, adsorption increases as the CO32- activity decreases (at constant pH) and as pH increases (at constant CO32- activity). The primary effect of ionic strength on phosphate sorption onto calcite is its influence on the activity of the different aqueous phosphate species. The experimental results were modeled satisfactorily using the constant capacitance model with >CaPO 4Ca 0 and either >CaHPO 4Ca + or > CaHPO4- as the adsorbed surface species. Generally the model captures the variation in phosphate adsorption onto calcite as a function of solution composition, though it was necessary to include two types of sorption sites (strong and weak) in the model to reproduce the convex shape of the sorption isotherms.

  13. Antibiotic selectivity for prokaryotic vs. eukaryotic decoding sites.

    PubMed

    Xie, Yun; Dix, Andrew V; Tor, Yitzhak

    2010-08-14

    A FRET assembly reports antibiotic affinities to two different RNA targets. A binder was labeled with a fluorophore that acts both as an acceptor for the emissive nucleoside on the bacterial A-site and a donor fluorophore for the terminally-labeled human A-site. Unlabeled drugs were used to dissociate the labeled antibiotic.

  14. Multi-spectral characterization & effect of metal ions on the binding of bovine serum albumin upon interaction with a lincosamide antibiotic drug, clindamycin phosphate.

    PubMed

    Meti, Manjunath D; Byadagi, Kirthi S; Nandibewoor, Sharanappa T; Chimatadar, Shivamurti A

    2014-09-05

    The interaction of clindamycin phosphate (CP) with bovine serum albumin (BSA) is studied by using fluorescence spectra, UV-visible absorption, synchronous fluorescence spectra (SFS), CD, 3D fluorescence spectra and lifetime measurements under simulated physiological conditions. CP effectively quenched intrinsic fluorescence of BSA. The binding constants KA values are 2.540×10(5), 4.960×10(5), 7.207×10(5) L mol(-1), the number of binding sites n and corresponding thermodynamic parameters ΔG(o), ΔH(o) and ΔS(o) between CP and BSA were calculated at different temperatures. The interaction between CP and BSA occurs through dynamic quenching and the effect of CP on the conformation of BSA was also analyzed using SFS. The average binding distance r between the donor (BSA) and acceptor (CP) was determined based on Förster's theory. The results of fluorescence spectra, UV-vis absorption spectra and SFS show that the secondary structure of the protein has been changed in the presence of CP.

  15. Umpolung of Michael acceptors catalyzed by N-heterocyclic carbenes.

    PubMed

    Fischer, Christian; Smith, Sean W; Powell, David A; Fu, Gregory C

    2006-02-08

    N-Heterocyclic carbenes can catalyze beta-alkylations of a range of alpha,beta-unsaturated esters, amides, and nitriles that bear pendant leaving groups to form a variety of ring sizes. In this process, the nucleophilic catalyst transiently transforms the normally electrophilic beta carbon into a nucleophilic site through an unanticipated addition-tautomerization sequence.

  16. Metabolic response of Geobacter sulfurreducens towards electron donor/acceptor variation.

    PubMed

    Yang, Tae Hoon; Coppi, Maddalena V; Lovley, Derek R; Sun, Jun

    2010-11-22

    Geobacter sulfurreducens is capable of coupling the complete oxidation of organic compounds to iron reduction. The metabolic response of G. sulfurreducens towards variations in electron donors (acetate, hydrogen) and acceptors (Fe(III), fumarate) was investigated via (13)C-based metabolic flux analysis. We examined the (13)C-labeling patterns of proteinogenic amino acids obtained from G. sulfurreducens cultured with (13)C-acetate. Using (13)C-based metabolic flux analysis, we observed that donor and acceptor variations gave rise to differences in gluconeogenetic initiation, tricarboxylic acid cycle activity, and amino acid biosynthesis pathways. Culturing G. sulfurreducens cells with Fe(III) as the electron acceptor and acetate as the electron donor resulted in pyruvate as the primary carbon source for gluconeogenesis. When fumarate was provided as the electron acceptor and acetate as the electron donor, the flux analysis suggested that fumarate served as both an electron acceptor and, in conjunction with acetate, a carbon source. Growth on fumarate and acetate resulted in the initiation of gluconeogenesis by phosphoenolpyruvate carboxykinase and a slightly elevated flux through the oxidative tricarboxylic acid cycle as compared to growth with Fe(III) as the electron acceptor. In addition, the direction of net flux between acetyl-CoA and pyruvate was reversed during growth on fumarate relative to Fe(III), while growth in the presence of Fe(III) and acetate which provided hydrogen as an electron donor, resulted in decreased flux through the tricarboxylic acid cycle. We gained detailed insight into the metabolism of G. sulfurreducens cells under various electron donor/acceptor conditions using (13)C-based metabolic flux analysis. Our results can be used for the development of G. sulfurreducens as a chassis for a variety of applications including bioremediation and renewable biofuel production.

  17. Metabolic response of Geobacter sulfurreducens towards electron donor/acceptor variation

    PubMed Central

    2010-01-01

    Background Geobacter sulfurreducens is capable of coupling the complete oxidation of organic compounds to iron reduction. The metabolic response of G. sulfurreducens towards variations in electron donors (acetate, hydrogen) and acceptors (Fe(III), fumarate) was investigated via 13C-based metabolic flux analysis. We examined the 13C-labeling patterns of proteinogenic amino acids obtained from G. sulfurreducens cultured with 13C-acetate. Results Using 13C-based metabolic flux analysis, we observed that donor and acceptor variations gave rise to differences in gluconeogenetic initiation, tricarboxylic acid cycle activity, and amino acid biosynthesis pathways. Culturing G. sulfurreducens cells with Fe(III) as the electron acceptor and acetate as the electron donor resulted in pyruvate as the primary carbon source for gluconeogenesis. When fumarate was provided as the electron acceptor and acetate as the electron donor, the flux analysis suggested that fumarate served as both an electron acceptor and, in conjunction with acetate, a carbon source. Growth on fumarate and acetate resulted in the initiation of gluconeogenesis by phosphoenolpyruvate carboxykinase and a slightly elevated flux through the oxidative tricarboxylic acid cycle as compared to growth with Fe(III) as the electron acceptor. In addition, the direction of net flux between acetyl-CoA and pyruvate was reversed during growth on fumarate relative to Fe(III), while growth in the presence of Fe(III) and acetate which provided hydrogen as an electron donor, resulted in decreased flux through the tricarboxylic acid cycle. Conclusions We gained detailed insight into the metabolism of G. sulfurreducens cells under various electron donor/acceptor conditions using 13C-based metabolic flux analysis. Our results can be used for the development of G. sulfurreducens as a chassis for a variety of applications including bioremediation and renewable biofuel production. PMID:21092215

  18. Natural alkaloid Luotonin A and its affixed acceptor molecules: Serum albumin binding studies.

    PubMed

    Kesavan, Mookkandi Palsamy; Kumar, Gujuluva Gangatharan Vinoth; Anitha, Kandasamy; Ravi, Lokesh; Raja, Jeyaraj Dhaveethu; Rajagopal, Gurusamy; Rajesh, Jegathalaprathaban

    2017-08-01

    Effective interaction of natural alkaloid Luotonin A (L) and its affixed acceptor molecules 1 and 2 with donor molecule as Bovine serum albumin (BSA) at various pH (4.0, 7.4 and 10.0) medium have been demonstrated using various conventional spectroscopic techniques. These analyses provide some valuable features on the interaction between BSA and acceptor molecules (L, 1 and 2). From the absorption and fluorescence spectral titration studies, the formation of ground-state complexes between the acceptor molecules (L, 1 and 2) and the BSA have been confirmed. The results of the afore titrations analysis reveal that, the strong binding of receptor 1 with BSA (Kapp 5.68×10(4)M(-1); KSV 1.86×10(6)Lmol(-1); Ka 6.42×10(5)Lmol(-1); Kass 8.09×10(6)M(-1); ΔG -33.35kJ/mol) at physiological pH medium (7.4) than other receptor molecules 2 and L. The Förster resonance energy transfer (FRET) efficiency between the tryptophan (Trp) residues of BSA and acceptor molecules L, 1 and 2 during the interaction, are 28.85, 85.24 and 53.25 % respectively. The superior binding efficacy of acceptor 1 at physiological pH condition has been further confirmed by FT-IR and Raman spectral analysis methods. Moreover, theoretical docking studies of acceptors L, 1 and 2 towards HSA have been demonstrated to differentiate their binding behaviours. It reveals that, acceptor 1 has the strongest binding ability with HSA through two hydrogen bonding and the Atomic contact energy (ACE) value of -483.96kcal/mol. Copyright © 2017 Elsevier B.V. All rights reserved.

  19. Inorganic Phosphate and Sulfate Transport in S. cerevisiae.

    PubMed

    Samyn, D R; Persson, B L

    2016-01-01

    Inorganic ions such as phosphate and sulfate are essential macronutrients required for a broad spectrum of cellular functions and their regulation. In a constantly fluctuating environment microorganisms have for their survival developed specific nutrient sensing and transport systems ensuring that the cellular nutrient needs are met. This chapter focuses on the S. cerevisiae plasma membrane localized transporters, of which some are strongly induced under conditions of nutrient scarcity and facilitate the active uptake of inorganic phosphate and sulfate. Recent advances in studying the properties of the high-affinity phosphate and sulfate transporters by means of site-directed mutagenesis have provided further insight into the molecular mechanisms contributing to substrate selectivity and transporter functionality of this important class of membrane transporters.

  20. Bioreduction of U(VI) in the presence of phosphate

    NASA Astrophysics Data System (ADS)

    Boyanov, M. I.; Mishra, B.; Latta, D. E.; Rui, X.; Kwon, M.-J.; Fletcher, K. E.; Loeffler, F. E.; O'Loughlin, E. J.; Kemner, K. M.

    2012-04-01

    Phosphate/phosphoryl moieties are ubiquitous in biological and environmental systems and can potentially affect the speciation of uranium during natural attenuation or stimulated bioremediation processes. The reactivity between U(VI) and phosphate has been studied extensively, but the significant influence of phosphate groups on the formation of reduced U(IV) species has only recently been recognized. We will compare and contrast the bioreduction of dissolved and solid-phase U(VI) by Gram-positive and Gram-negative metal-reducing bacteria (Shewanella, Anaeromyxobacter, Geobacter, and Desulfitobacterium) in the presence and absence of phosphate, from the perspective of solid-phase U speciation as determined by U L-edge x-ray absorption spectroscopy (XANES and EXAFS). In all cases examined, the presence of phosphate at concentrations of P/U > 1 led to the formation of reduced, inner-sphere complexed U(IV)-phosphate species that prevented the lowest-solubility U(IV) mineral uran