Abstract
The effect of cobalamins on the oxidation of ascorbic acid (AsA) was investigated. When 20 μmol of AsA was incubated with 0.1 μmol of aquocobalamin (OH-B_<12>) in acetate buffer (pH 5) under aerobic conditions at 37℃ for 1 h, about 12 μmol of AsA was oxidized to dehydroascorbic acid. The amount of oxygen consumed to oxidize 1 mol of AsA was found to be 0.67 mol. The spectrophotometric investigation indicated that reduced cobalamin, B_<12r>, is formed as a catalytic intermediate in the oxidation of AsA. From these results, it was concluded that the oxidation of AsA is catalyzed by traces of OH-B_<12>. The catalytic activity of cobalamin analogs decreased in the order of OH-B_<12>, hydroxocobinamide > DBCC > cyanocobalamin, cyanocobinamide. The mechanism of the catalytic reaction was discussed.
