Autotrophic growth: the methyl binding site of CO dehydrogenase in the synthesis of acetyl-CoA

A pathway in which CO or CO/sub 2/ and H/sub 2/ is used as a source of energy and carbon to synthesize acetyl-CoA is used for autotrophic growth of acetogenes, methanogens and some sulfate-reducing bacteria. All enzymes involved in this pathway have been purified from C. thermoaceticum. Five of them: CO dehydrogenase (CODH), corrinoid protein, methyltransferase, CODH disulfide reductase (SSRd) and ferredoxin catalyzed synthesis of acetyl-CoA from methyltetrahydrofolate, CO and CoA. CODH is a central enzyme catalyzing the condensation of CH/sub 3/, CO and CoA and per se it catalyzes a reversible exchange of CO with acetyl-CoA. Thus, CODH must have binding sites for CH/sub 3/, CO and CoA. They have succeeded in methylating ..beta.. subunits of CODH using /sup 14/CH/sub 3/I or /sup 14/CH-corrinoid protein, a native donor of the CH/sub 3/ group in synthesis of acetyl-CoA. With resulting (/sup 14/CH/sub 3/)CODH, only SSRd is required for synthesis of (/sup 14/C)acetyl-CoA from CO and CoA. The kinetic studies show that CH/sub 3/I is a competitive inhibitor for exchange reaction between CO and acetyl-CoA. Acetaldehyde and acetyl-CoA but not acetic acid and CoA protected CODH against methylation by CH/sub 3/I. Methyl group bound to CODH is very slowly removed bymore » CO and CoA and acetyl-CoA accelerated this process. These data confirm that CH/sub 3/ group from CH/sub 3/I and CH/sub 3/-corrinoid protein is bound to the methyl binding site of CODH.« less