Vitamin B₁₂-dependent Methionine Biosynthesis and Its Metabolic Role in Corynebacterium simplex ATCC 6946, a Vitamin B₁₂-producing and Hydrocarbon-utilizable Bacterium

Abstract

A vitamin B₁₂-dependent N⁵-methyltetrahydrofolate-homocysteine methyltransferase was found in cell-free extracts of Corynebacterium simplex ATCC 6946 grown aerobically in a medium containing hydrocarbon as a sole carbon source and the enzyme was partially purified. Absolute requirements for S-adenosylmethionine and an appropriate reducing system were observed for the transmethylation from N⁵-methyltetrahydrofolate. The same preparation catalyzed also the formation of methionine from homocysteine and methyl-B₁₂ under both aerobic and anaerobic conditions. The concentration of cobalt ion in the growth medium had a pronounced effect on the intracellular vitamin B₁₂ level and the activity of the vitamindependent methionine-synthesizing system in the bacterium. The relationship between the methionine synthesis and the methyl branched-chain fatty acid formation was discussed.