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

Abstract

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 5 -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.