Total synthesis of acetate from CO 2: III. Inhibition by alkylhalides of the synthesis from CO 2, methyltetrahydrofolate, and methyl-B 12 by Clostridium thermoaceticum

Abstract

The synthesis of acetate from CO 2 by cells of Clostridium thermoaceticum fermenting glucose was inhibited by propyl iodide, chloroform, and carbon tetrachloride. Cell-free extracts when fermenting pyruvate synthesized acetate from CO 2, but to a very small extent. However, they converted the methyl groups of N-5-methyltetrahydrofolate and Co-methylcobalamin efficiently to the methyl group of acetate in the presence of pyruvate and ferrous ions. The formation of acetate from either of these methyl donors was inhibited by propyl iodide and carbon tetrachloride. Extracts inhibited by propyl iodide were reactivated by photolysis. With radioactive propyl iodide it was shown that propylated corrinoids were present in the inhibited extract and in whole cells. It is proposed that the inhibitory action of the alkyl halides is by alkylation of a corrinoid enzyme. The transmethylation is thus prevented from methyltetrahydrofolate to the corrinoid enzyme as well as the subsequent carboxylation to yield acetate.