Oxidative and reductive acetyl CoA/carbon monoxide dehydrogenase pathway inDesulfobacterium autotrophicum

✍ Scribed by Siegfried Länge; Rudolf Scholtz; Georg Fuchs

• Book ID: 104776895
• Publisher: Springer
• Year: 1988
• Tongue: English
• Weight: 795 KB
• Volume: 151
• Category: Article
• ISSN: 0302-8933
• DOI: 10.1007/bf00444673

✦ Synopsis

In Desulfobacterium autotrophicum, a facultatively autotrophic, sulfate reducing eubacterium, CO2-fixing enzymes of the acetyt CoA/CO dehydrogenase pathway but neither key enzymes of the Calvin cycle nor those of the reductive citric acid cycle were detectable. This finding substantiates the proposal that the former pathway is operating in the reductive direction for CO2 fixation into acetyl CoA, and in the oxidative direction for acetyl CoA oxidation to CO2, However, the specific activity of an essential onecarbon metabolizing enzyme of this pathway, formyl-tetrahydrofotate synthetase, was unsufficient (0.01 I~mol -min-i 9 rag-1), and its apparent Kin-value for L-tetrahydrofolate (10 raM) was inadequate. It is shown that the physiological cosubstrate in this bacterium is not tetrahydrofolic acid, but a tetrahydropterin containing 4 tool of L-glutamate per tool of pterin. With this coenzyme the specific formyltetrahydropterin synthetase activity (1.7 ~tmol -rain-t . rag-1) was 170-fold higher and the apparent Km for the tetrahydropterin (0.07 raM) was 140-fold lower, This indicates that it may be essential to reexamine the enzymes of acetyl CoA/CO dehydrogenase pathway in this organism and others with the proper cellular cosubstrate.