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  • Citric acid cycle  (2)
  • Methanobacterium thermoautotrophicum  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Carbon isotope fractionation by Methanobacterium thermoautotrophicum (1979)
    Springer
    Archives of microbiology 120 (1979), S. 135-139 
    Details
    ISSN: 1432-072X
    Keywords: Carbon isotope discrimination ; Autotrophic CO2 fixation ; Methane formation ; Methanobacterium thermoautotrophicum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The fractionation of carbon isotopes by Methanobacterium thermoautotrophicum was studied during growth of the bacterium on H2 plus CO2 as sole carbon and energy sources. A 80% H2/20% CO2 gas mixture was continuously bubbled through the culture. At high gassing rates, in the absence of a “closed system effect”, cells and methane were found to be depleted in 13C relative to CO2 in the gas mixture by 2.4% and 3.4%, respectively. At low gassing rates, when more than 90% of the CO2 was converted to methane, the cells were enriched in 13C by 1.3% and methane was depleted in 13C by 0.5%; residual CO2 was enriched in 13C by 3.4%. The magnitude of isotope fractionation suggests that CO2 rather than bicarbonate is the active species of CO2 mainly utilized in both CO2 assimilation and CO2 reduction to methane. The apparent positive 13C-discrimination in cell carbon synthesis, which was observed at low gassing rates, indicates that most of the CO2 assimilated into cell material is not incorporated via reactions involved in CO2 reduction to methane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00409099
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  • 2
    Electronic Resource
    Electronic Resource
    Enzymes of gluconeogenesis in the autotroph Methanobacterium thermoautotrophicum (1983)
    Springer
    Archives of microbiology 136 (1983), S. 160-162 
    Details
    ISSN: 1432-072X
    Keywords: Methanobacterium thermoautotrophicum ; Aldolase ; Fructose 1,6-bisphosphatase ; Autotrophic ; Methanogen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In Methanobacterium thermoautotrophicum fructose 1,6-bisphosphate aldolase and fructose 1,6-bisphosphate phosphatase were studied, which could not be detected in previous investigations. Aldolase appeared to be a class I enzyme. Enzyme activity was only detectable in direction of aldol condensation in presence of Mg2+ and under anaerobic conditions. It was stimulated by dithioerythritol. The regulatory properties of the hexose bisphosphate phosphatase differed in many ways from those of the enzyme from other organisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00404793
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  • 3
    Electronic Resource
    Electronic Resource
    Acetate oxidation to CO2 via a citric acid cycle involving an ATP-citrate lyase: a mechanism for the synthesis of ATP via substrate level phosphorylation in Desulfobacter postgatei growing on acetate and sulfate (1987)
    Springer
    Archives of microbiology 148 (1987), S. 202-207 
    Details
    ISSN: 1432-072X
    Keywords: ATP-citrate lyase ; Citric acid cycle ; Acetate oxidation ; ATP synthesis via substrate level phosphorylation ; Sulfate-reducing bacteria ; Desulfobacter postgatei
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Desulfobacter postgatei is an acetate-oxidizing, sulfate-reducing bacterium that metabolizes acetate via the citric acid cycle. The organism has been reported to contain a si-citrate synthase (EC 4.1.3.7) which is activated by AMP and inorganic phosphate. It is show now, that the enzyme mediating citrate formation is an ATP-citrate lyase (EC 4.1.3.8) rather than a citrate synthase. Cell extracts (160,000xg supernatant) catalyzed the conversion of oxaloacetate (apparent K m=0.2 mM), acetyl-CoA (app. K m=0.1 mM), ADP (app. K m=0.06 mM) and phosphate (app. K m=0.7 mM) to citrate, CoA and ATP with a specific activity of 0.3 μmol·min-1·mg-1 protein. Per mol citrate formed 1 mol of ATP was generated. Cleavage of citrate (app. K m=0.05 mM; V max=1.2 μmol · min-1 · mg-1 protein) was dependent on ATP (app. K m=0.4 mM) and CoA (app. K m=0.05 mM) and yielded oxaloacetate, acetyl-CoA, ADP, and phosphate as products in a stoichiometry of citrate:CoA:oxaloacetate:ADP=1:1:1:1. The use of an ATP-citrate lyase in the citric acid cycle enables D. postgatei to couple the oxidation of acetate to 2 CO2 with the net synthesis of ATP via substrate level phosphorylation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00414812
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  • 4
    Electronic Resource
    Electronic Resource
    Carbon assimilation pathways in sulfate-reducing bacteria II. Enzymes of a reductive citric acid cycle in the autotrophic Desulfobacter hydrogenophilus (1987)
    Springer
    Archives of microbiology 148 (1987), S. 218-225 
    Details
    ISSN: 1432-072X
    Keywords: Desulfobacter hydrogenophilus ; Sulfate-reducing bacteria ; Autotrophy ; Citric acid cycle ; ATP-citrate lyase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The strict anaerobe Desulfobacter hydrogenophilus is able to grow autotrophically with CO2, H2, and sulfate as sole carbon and energy sources. The generation time at 30°C under autotrophic conditions in a pure mineral medium was 15 h, the growth yield was 8 g cell dry mass per mol sulfate reduced to H2S. Enzymes of the autotrophic CO2 assimilation pathway were investigated. Key enzymes of the Calvin cycle and of the acetyl CoA pathway could not be found. All enzymes of a reductive citric acid cycle were present at specific activities sufficient to account for the observed growth rate. Notably, an ATP-citrate lyase (1.3 μmol · min-1 · mg cell protein-1) was present both in autotrophically and in heterotrophically grown cells, which was rapidly inactivated in the absence of ATP. The data indicate that in D. hydrogenophilus a reductive citric acid cycle is operating in autotrophic CO2 fixation. Since other autotrophic sulfate reducers possess an acetyl CoA pathway for CO2 fixation, two different autotrophic pathways occur in the same physiological group.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00414815
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    Paper (German National Licenses)
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