Abstract
The effect of cobalamins on the oxidation of thiol form of thiamine was investigated. When 59.4 μmoles of thiamine was incubated with 0.1 μmole of aquocobalamin (OH-B_<12>) in borate buffer (pH 9.4) under aerobic conditions at 37℃ for 2 hours, about 36 μmoles of thiamine was oxidized to thiamine disulfide. The amount of oxygen utilized to oxidize 4 moles of thiamine was found to be 1 mole. The spectrophotometric investigation indicated that reduced cobalamin, B_<12r>, is formed as a catalytic intermediate in the oxidation of thiamine. From these results, it was concluded that the oxidation of thiamine is catalyzed by traces of OH-B_<12>. The catalytic activity of cobalamin analogs decreased in the order of hydroxocobinamide>cyanocobinamide>OH-B_<12>>DBCC, cyanocobalamin The mechanism of the catalytic reaction was discussed.
