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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 165 (1996), S. 149-163 
    ISSN: 1432-072X
    Schlagwort(e): Methanosarcina ; Methanobacterium ; Hydrogenase ; Heterodisulfide reductase ; CO dehydrogenase ; Methyltransferase ; Formylmethanofuran dehydrogenase ; ATP synthase ; Proton motive force ; Sodium motive force
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Methanogenic archaea are strictly anaerobic organisms that derive their metabolic energy from the conversion of a restricted number of substrates to methane. H2+CO2 and formate are converted to CH4 via the CO2-reducing pathway, while methanol and methylamines are metabolized by the methylotrophic pathway. A limited number of methanogenic organisms utilize acetate by the aceticlastic pathway. Redox reactions involved in these processes are partly catalyzed by membrane-bound enzyme systems that generate or, in the case of endergonic reactions, use electrochemical ion gradients. The H2:heterodisulfide oxidoreductase, the F420H2:heterodisulfide oxidoreductase and the CO:heterodisulfide oxidoreductase, are novel systems that generate a proton motive force by redox-potential-driven H+ translocation. The methyltetrahydromethanopterin:coenzyme M methyltransferase is a unique, reversible sodium ion pump that couples methyl transfer with the transport of Na+ across the cytoplasmic membrane. Formylmethanofuran dehydrogenase is a reversible ion pump that catalyzes formylation and deformylation, of methanofuran. In summary, the pathways are coupled to the generation of an electrochemical sodium ion gradient and an electrochemical proton gradient. Both ion gradients are used directly for ATP synthesis via membrane integral ATP synthases. The function of the above-mentioned systems and their components in the metabolism of methanogens are described in detail.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Archives of microbiology 171 (1999), S. 115-121 
    ISSN: 1432-072X
    Schlagwort(e): Key words Methanogenic archaea ; Methanococcus ; Methanosarcina ; Electron transport ; Hydrogenases ; Coenzyme F420 ; F42OH2 dehydrogenase ; Heterodisulfide reductase
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Washed membranes prepared from H2+CO2- or formate-grown cells of Methanococcus voltae catalyzed the oxidation of coenzyme F420H2 and the reduction of the heterodisulfide (CoB–S–S–CoM) of 2-mercaptoethanesulfonate and 7-mercaptoheptanoylthreonine phosphate, which is the terminal electron acceptor of the methanogenic pathway. The reaction followed a 1:1 stoichiometry according to the equation: F420H2 + COB–S–S–CoM → F420 + CoM–SH + CoB–SH. These findings indicate that the reaction depends on a membrane-bound F420H2-oxidizing enzyme and on the heterodisulfide reductase, which remains partly membrane-bound after cell lysis. To elucidate the nature of the F420H2-oxidizing protein, washed membranes were solubilized with detergent, and the enzyme was purified by sucrose density centrifugation, anion-exchange chromatography, and gel filtration. Several lines of evidence indicate that F420H2 oxidation is catalyzed by a membrane-associated F420-reducing hydrogenase. The purified protein catalyzed the H2-dependent reduction of methyl viologen and F420. The apparent molecular mass and the subunit composition (43, 37, and 27 kDa) are almost identical to those of the F420-reducing hydrogenase that has already been purified from Mc. voltae. Moreover, the N-terminus of the 37-kDa subunit is identical to the amino acid sequence deduced from the fruG gene of the operon encoding the selenium-containing F420-reducing hydrogenase from Mc. voltae. A distinct F420H2 dehydrogenase, which is present in methylotrophic methanogens, was not found in this organism.
    Materialart: Digitale Medien
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  • 3
    ISSN: 1432-072X
    Schlagwort(e): Archaebacteria ; methanogenesis ; energy conservation ; membranes ; F420-dependent hydrogenase ; Methanosarcina
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The distribution of the F420-reactive and F420-nonreactive hydrogenases from the methylotrophic Methanosarcina strain Gö1 indicated a membrane association of the F420-nonreactive enzyme. The membrane-bound F420-nonreactive hydrogenase was purified 42-fold to electrophoretic homogeneity with a yield of 26.7%. The enzyme had a specific activity of 359 μmol H2 oxidized · min-1 · mg protein-1. The purification procedure involved dispersion of the membrane fraction with the detergent Chaps followed by anion exchange, hydrophobic and hydroxylapatite chromatography. The aerobically prepared enzyme had to be reactivated anaerobically. Maximal activity was observed at 80°C. The molecular mass as determined by native gel electrophoresis and gel filtration was 77000 and 79000, respectively. SDS gel electrophoresis revealed two polypeptides with molecular masses of 60000 and 40000 indicating a 1:1 stoichiometry. The purified enzyme contained 13.3 mol S2-, 15.1 mol Fe and 0.8 mol Ni/mol enzyme. Flavins were not detected. The amino acid sequence of the N-termini of the subunits showed a higher degree of homology to cubacterial uptake-hydrogenases than to F420-dependent hydrogenases from other methanogenic bacteria. The physiological function of the F420-nonreactive hydrogenase from Methanosarcina strain Gö1 is discussed.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Theoretical and applied genetics 56 (1980), S. 71-79 
    ISSN: 1432-2242
    Schlagwort(e): Gene-ecology ; Fasciated mutants ; Penetrance ; Flowering behaviour ; Seed production
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Six mutants and nine recombinants of Pisum sativum were grown along with the mother variety at Kurukshetra, North India. The findings obtained were compared with those obtained for the same material grown at Bonn, Germany. The following observations were made. Stem length and degree of branching are influenced differentially in the various genotypes tested in India as a consequence of a specific reaction of the genes to the climatic conditions. A gene for weak stem fasciation and gene efr for earliness in a specific gene combination are unable to express their action in North India whereas they are fully active in Germany. Furthermore, in Kurukshetra early flowering of some recombinants does not result in early ripening because their seeds require about double the time for full ripening than those of the mother variety. At Kurukshetra, recombinant R 674A proved to be highly heat susceptible. All the plants died in early stages of ontogenetic development. Four other genotypes died due to heat before completing seed ripening. One mutant and three recombinants were found to be more tolerant to powdery mildew attack than the mother variety and Indian local lines. The seed production of eight genotypes in relation to that of the initial line was essentially better in North India than in Germany. They are obviously better adapted to the semi-arid conditions. Some of them appear to be useful for pea breeding in India. In contrast, a fasciated mutant, high yielding in Germany, is not able to express this potentiality at Kurukshetra. At Udaipur (Rajasthan, Western India), this mutant is unable to flower. Another four genotypes, tested at both Indian locations, exhibited an essentially poorer seed production at Udaipur than at Kurukshetra due to some ecological factors. The findings indicate a specific response of some of the genotypes tested to the specific ecological conditions of the three locations, their response differing from that of the mother variety demonstrating thereby a different adaptational optimum.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Theoretical and applied genetics 70 (1985), S. 207-212 
    ISSN: 1432-2242
    Schlagwort(e): Pisum mutants and recombinants ; Phytotron experiments ; Gene-ecology ; Temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The flowering behaviour of 17 Pisum mutants and 20 recombinants was studied under three different temperatures using long-day phytotron conditions. A constant low temperature of 12.5 ° C led to a strong delay in flowering in all the genotypes tested but distinct relative differences could be found between them. Relative differences were also present with regard to speed of ontogenetic development under a permanent high temperature of 25.5 °C or under an alternating change between low and high temperature. Under the low temperature, recombinants R 20D and R 20E, carrying gene efr for earliness, entered the flowering period more than 4 weeks later than the donor of efr, demonstrating thereby a negative influence of one of the other mutant genes on efr. The high temperature of 25 °C influenced the flowering behaviour of 4 fasciated genotypes negatively — in contrast to the other strains studied. The plants of recombinant R 405 produced only tiny flower buds under these conditions. None of the plants of recombinant R 142F flowered under either the constant low or high temperature — they need the change of low and higher temperature for normal flower formation. The experiments show that most of the genotypes tested react specifically to the three temperature conditions offered to them.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Theoretical and applied genetics 75 (1988), S. 344-349 
    ISSN: 1432-2242
    Schlagwort(e): Pisum mutants and recombinants ; Phytotron experiments ; Gene-ecology ; Photoperiod ; Suppressor genes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The flowering behavior of 59 Pisum mutants and 228 recombinants was studied in the phytotron in four different photoperiods (continuous light, long-day 18/6 h, short-day 12/12 h, extreme short-day 6/18 h). There was no or little difference in the response of the genotypes to long-day and permanent light, whereas great differences were observed between long- and short-day 12/12 h and between the two short-day trials. About half the genotypes tested were unable to survive or to flower in extreme short-day. Some recombinants, however, had an almost normal development under these unfavorable conditions. Gene fis controls the photoperiodic reaction of the plants: they are unable to flower in short-day. Gene fds negatively influences gene efr for earliness: it causes a strong delay of flowering of efr recombinants in long-day and suppresses the formation of functionable flowers in short-day. Most of the genotypes tested showed a specific reaction to the four photoperiods different from that of the mother variety and the other genotypes. The practical aim of our phytotron experiments is the preselection of Pisum genotypes which might be suited for cultivation in countries with short-day climate.
    Materialart: Digitale Medien
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