Form of Vitamin B ₁₂ and Its Role in a Methanol-Utilizing Bacterium Protaminobacter ruber

A methanol-utilizing bacterium, Protaminobacter ruber, produced a large amount of vitamin B(12). The compounds were isolated from the cells and identified as methylcobalamin (methyl-B(12)) and adenosylcobalamin (adenosyl-B(12)) by various tests. The variation in the form of B(12) during cultivation was examined by bioautography with cellulose acetate membrane electrophoresis. Methyl-B(12) and adenosyl-B(12) were the two main B(12) compounds produced in the various phases of bacterial growth. The ratio of the amount of methyl-B(12) to total B(12) compounds was higher during the earlier phases of growth. After the logarithmic phase, adenosyl-B(12) was the predominant form. The existence of N-methyltetrahydrofolate:homocysteine transmethylase and methyl-B(12):homocysteine transmethylase was demonstrated in cell-free extracts of Protaminobacter ruber. Methyl-B(12) in P. ruber seems to function mainly in the B(12)-dependent methionine synthetase system.