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  • 1
    ISSN: 1432-072X
    Keywords: Nitrosomonas europaea ; Ammonia uptake ; O2 uptake ; Electrode methods ; Fluorescence emission ; Proton translocation ; Membrane energisation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The uptake of ammonia and O2 by washed cells of Nitrosomonas has been followed simultaneously and continuously using electrode techniques. The stoichiometry of NH 4 + oxidation, O2 uptake and NO 2 - production was 1 : 1.5 : 1.0 and for NH2OH oxidation a ratio of 1 for O2 : NO 2 - . A variety of inhibitors of electron transport and metals as well as uncouplers restricted ammonia uptake more markedly than O2 utilization. There is good evidence for the involvement of copper in the NH 4 + uptake process. A quinacrine fluorescence technique has been used to study the proton extrusion by washed cells on adding NH4Cl and NH2OH respectively as substrates. The uptake of NH 4 + was followed by the extrusion of H+ and this process was depressed by those inhibitors which were also effective in the electrode experiments. A requirement for copper is also established for the translocation of protons into the medium, resulting from the uptake of NH 4 + by cells.
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  • 2
    ISSN: 1432-072X
    Keywords: Ammonia assimilation ; Rhizobium japonicum ; Properties of glutamine synthetase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Glutamine synthetase (EC 6.3.1.2) has been purified from Rhizobium japonicum strains CC705 and CC723 respectively. The purified enzyme, which had a molecular weight of 720,000 (both strains) contained 12 subunits each of 60,000. The enzyme assayed by the γ-glutamyltransferase method had K m values for l-glutamine and hydroxylamine of 7.7 and 1.2 mM respectively. The inhibition of γ-glutamyltransferase by l-glutamate and ammonia was competitive for l-glutamine and non-competitive for hydroxylamine. The transferase activity was markedly (〉65%) inhibited by l-methionine-d-sulfoximine and alanine and to a lesser extent (〈45%) by glycine, arginine, aspartate, asparagine, lysine and serine. Different pairs of amino acids in various combinations resulted in a cumulative inhibition of enzyme activity. The enzyme was also inhibited by the following di- and tri-phosphate nucleotides — IDP, CDP, UDP, ATP, ITP, CTP and UTP. Malate, pyruvate, oxalate, succinate and α-ketoglutarate each at 10 mM depressed enzyme activity.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 6 (1979), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 25 (1984), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract A purified glutamine synthetase was prepared from bacteroids of Rhizobium japonicum from nodules of Glycine max. For the biosynthetic assay the Km values (mM) were l-glutamate 12.9, NH4Cl 8.9 and ATP 14.3. When the enzyme was assayed by the γ-glutamyltransferase reaction the Km values (mM) were l-glutamine 11.1 and hydroxylamine 3.3 compared with 7.7 and 1.2, respectively, for the purified enzyme from Rhizobium japonicum grown in culture. The enzyme prepared from bacteroids of Glycine max was 80% adenylylated.
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  • 5
    ISSN: 1432-2048
    Keywords: Adenylylation (glutamine synthetase) ; Ammonium assimilation ; Bacteroid ; Glutamate dehydrogenase, synthase ; Glutamine synthetase ; Glycine (nitrogen assimilation) ; Rhizobium strains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The growth yields of three strains of Rhizobium japonicum (CB 1809, CC 723, CC 705) in culture solutions containing L-glutamate were about twice those grown with ammonium. The activities of glutamine synthetase (GS; EC 6.3.1.2) and glutamate dehydrogenase (GDH; EC 1.4.1.4) were dependent on the nitrogen source in the medium and also varied with growth. Both NADPH-and NADH-dependent glutamate synthase (GOGAT; EC 1.4.1.13) and NADPH-dependent GDH were found in strains grown with either glutamate or ammonium but NADH-linked GDH was only detected in glutamate-grown cells. Glutamine synthetase was adenylylated in cells grown with NH 4 + (90%) and to lesser extent in those grown with L-glutamate (50%). In root nodules produced by the three strains in Glycine max (L.) Merr., the bulk of GS was located in the nodule cytosol (60–85%). The enzyme was adenylylated in bacteroids (43–75%) and in the nodule tissues (52–68%). The enzyme in cell-free extracts of Rh. japonicum (CC 705) grown in culture solutions containing glutamate and in bacteroids (CC 705) was deadenylylated by snake-venom phosphodiesterase. L-methionine-DL-sulfoximine restricted the incoporation of 15N-labelled (NH4)2SO4 into cells of strains CB 1809 and CC 705, as well as in bacteroids of strain CC 705. It is noteworthy that appreciable activities for GDH were found in the free-living rhizobia grown on glutamate. Thus the presence of an enzyme does not necessarily imply that a particular pathway is operative in assimilating ammonium into cell nitrogen. Based on 15N studies, the GS-GOGAT pathway of rhizobia (strains CB 1809 and CC 705) is important when grown in culture solutions as well as in bacteroids from root nodules of G. max.
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  • 6
    ISSN: 1432-2048
    Keywords: Bacteroid ; Glycine (bacteroids) ; Denitrification ; Rhizobium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nitrate, nitrite and nitrous oxide were denitrified to N2 gas by washed cells ofRhizobium japonicum CC706 as well as by bacteroids prepared from root nodules ofGlycine max (L.) Merr. (CV. Clark 63). Radiolabelled N2 was produced from either K15NO3 or Na15NO2 by washed cells ofRh. japonicum CC705 grown with either nitrate only (5 mM) or nitrate (5 mM) plus glutamate (10 mM). Nitrogen gas was also produced from N2O. Similar results were obtained with bacteroids ofG. max. The stoichiometry for the utilization of15NO 3 - or15NO 2 - and the produciton of15N2 was 2:1 and for N2O utilization and N2 production it was 1:1. Some of the15N2 gas produced by denitrification of15NO 3 - in bacteroids was recycled via nitrogenase into cell nitrogen.
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  • 7
    ISSN: 1573-4919
    Keywords: cAMP ; prostaglandins ; glomerular basement membrane ; perlecan ; glomerular epithelial cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Perlecan, the basement membrane heparan sulfate proteoglycan (HSPG), has been fully cloned from mouse and human tissues. When a cRNA probe of murine perlecan cDNA was employed in RNase protection assay to test whether rat glomerular epithelial cells (GEC) constitutively express perlecan, several bands of hybridization were seen, suggesting that sequences between rat and murine perlecan may not be identical. Using primers based on published cDNA sequences of murine and human perlecan and polyA+ RNA of rat GEC, we synthesized a 497 by product (RPD-1) by RT PCR. The deduced aminoacid sequence showed an 85% and 88% homology with domain I of murine and human perlecan, respectively. The three putative sites containing the consensus sequence SGD for attachment of heparan sulfate chains were fully conserved in the rat perlecan as was a site (NFT) for attachment of N-linked oligosaccharide. RPD-I detected a 〉 9.5 kb transcript of perlecan in RNA of GEC, similar in size to that present in rat glomeruli. Employing a riboprobe synthesized from RPD-I in RNase protection assay we examined whether dbcAMP regulated perlecan expression in the GEC. At 1, 6, 24 and 48 h of incubation, l mM dbcAMP caused 43%, 32%, 47% and 40% reduction in mRNA abundance of perlecan, respectively. Immunoprecipitation showed a corresponding reduction of 61%, 70% and 65% in the synthesis of 35SO4 labeled basement membrane HSPG by the GEC following 12, 24 and 48 h of incubation with dbcAMP Following incubation for 1 and 24 h prostaglandins, PGE1 and PGE2 (1 uM), known activators of glomerular adenylate cyclase, reduced perlecan mRNA abundance to a similar extent as dbcAMP on northern analysis. Our results show that glomerular basement membrane HSPG synthesized by the GEC belongs to the perlecan family. Decrease of GEC perlecan gene expression and synthesis by cAMP and prostaglandins may be of relevance to proteinuric states characterized by activation of these mediators.
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  • 8
    ISSN: 1573-4919
    Keywords: growth factors ; cytokines ; human ; kidney
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract We have investigated the effect of phorbol 12-myristate 13-acetate (PMA) on platelet-derived growth factor (PDGF) B-chain gene transcription as well as on mRNA stability in cultured human mesangial cells. Addition of actinomycin to cells stimulated with PMA decreases steady state levels of PDGF-B chain mRNA analysed by solution hybridization assay. PDGF-B chain gene transcription was also assayed directly by measuring elongation of transcripts in isolated nuclei followed by hybridization of labeled RNA transcripts to a cDNA encoding for PDGF-B chain. Our data show that PMA induces PDGF-B chain gene transcription by approximately 2-fold. α-Amanitin, an RNA polymerase II inhibitor, blocked transcription by more than 70%. In addition, we determined the effect of PMA on the halflife of PDGF-B chain mRNA directly by pulse chase method. In human mesangial cells, the PDGF-B chain mRNA exhibited halflife of approximately 105 min. In the presence of PMA, the halflife of PDGF-B chain mRNA was reduced to approximately 72 min. These studies indicate that regulation of PDGF-B chain gene by PMA in human mesangial cells involves a coordinate effort at the level of transcription and mRNA stability.
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