LEVEL OF METHIONINE SYNTHASE ACTIVITY AND INTERCONVERSION OF METHYLCOBALAMIN AND ADENOSYLCOBALAMIN IN A FACULTATIVE METHYLOTROPH, PROTAMINOBACTER RUBER

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Protaminobacter ruber was cultured in a medium containing [57Co]cyanocobalamin with a “two-step cultivation method” and the forms of vitamin B12 compounds in the cells were examined. Methyl cobalamin was detected in the early phases of growth and reached a maximum of about 40% of ail cobalamins extracted from the cells. In the stationary phase of growth, almost all cobalamins consisted of ade nosylcobalamin. Recultivation of the cells of the stationary phase in a fresh medium resulted in the conversion of adenosylcobalamin into methylcobalamin. Interconversion of methylcobalamin and adenosyl cobalamin was presumed from these facts. The formation of adenosylcobalamin from methylcobalamin was de monstrated with a cell-free extract system from P. ruber. The rate of conversion of methylcobalamin into adenosylcobalamin was highest among several cobalamin analogs tested. Propylation of 5-methyltetrahydrofolate: homocysteine methyltransferase with 1-iodopropane did not affect this conversion reaction, which was probably catalyzed by methyltransferase and adenosyltransferase.
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