Acetate synthesis from carbon monoxide by Clostridium thermoaceticum. Purification of the corrinoid protein.

A corrinoid protein has been purified from Clostridium thermoaceticum which is required for the synthesis of acetyl-CoA from carbon monoxide and methyltetrahydrofolate. The purified protein is an alpha beta dimer with subunit molecular weights of 34,000 and 55,000, respectively, and contains 0.69 mol of corrinoid/mol of dimer. The corrinoid protein is methylated in the presence of methyltransferase and methyltetrahydrofolate; methylation is on the cobalt of the corrinoid moiety of the protein. When 14C-methylated protein is incubated with Fraction F3, ATP, CoASH, and CO, [14C]acetyl-CoA is formed. Methylation of cobalamin (B12) is catalyzed by the methyltransferase but methylcobalamin does not substitute for the methylated corrinoid protein as the source of methyl in the formation of acetyl-CoA.