A mechanism has been partially elucidated for the synthesis of acetyl-CoA and acetylphosphate from methyltetrahydrofolate (CH3THF), carbon monoxide (CO), coenzyme A (CoASH), and phosphate by use of enzymes from Clostridium thermoaceticum. The mechanism involves transfer of the methyl group from CH3THF to the cobalt of a corrinoid (vitamin B12) containing enzyme. The CO is converted to a C1 intermediate by a nickel enzyme, CO dehydrogenase. This C1 intermediate together with CoASH, by a mechanism which is as yet unknown, combines with the methyl of the corrinoid to form acetyl-CoA. ATP is required. CO2 and H2 can be substituted for CO as the source of the C1 intermediate. In this case, the CO2 is reduced to the C1 intermediate using electrons generated from the H2 by the enzyme, hydrogenase. These reactions are of particular interest since they may provide a mechanism by which certain bacteria grow with CO or CO2 and H2 as the source of carbon and energy. The objectives of this investigation are: (1) to isolate and purify the enzymes which catalyze this sequence of reactions; (2) to isolate intermediate compounds which occur in the reactions and explore the mechanisms of the reactions; (3) to conduct studies with autotrophic organisms to determine whether or not they utilize this mechanism. Radioactive tracers and 13C-nuclear magnetic resonance will be used in detecting intermediate compounds. Carbon monoxide is a toxic gas which is formed in large quantities by the combustion of fossil fuels and by other processes. Bacteria via CO dehydrogenase remove CO from the atmosphere and assist in maintaining the atmospheric concentration very low. Elucidation of the biochemical reactions by which the metals cobalt, nickel and vitamin B12 function in enzymes in the conversion of CO and CO2 and H2 to acetate will provide basic knowledge of fundamental importance. In the future when oil becomes limiting, the fermentation by acetogenic bacteria using CO and CO2 and H2 may find technical application as a source of acetic acid for synthetic processes.
