Studies on the Reduction of Dehydroascorbic Acid by Glutathione in the Presence of Aquahydroxocobinamide.

This study reports that aquahydroxocobinamide [(H2O)(HO–)Cbi(III)], a nucleotide‐free analogue of cobalamin (vitamin B12; Cbl), is capable of catalyzing the reduction of the two‐electron oxidized form of vitamin C, dehydroascorbic acid (DHA), to ascorbic acid by glutathione (GSH), whereas catalytic quantities of aquacobalamin do not accelerate the reaction. This observation is explained by different reactions taking place with the CoIII‐species of these complexes and GSH: Cbl(III) forms a stable complex with GSH, but Cbi(III) is relatively rapidly reduced to Cbi(II). The reaction of Cbi(II) with DHA in the presence of GSH includes the coordination of GSH onto CoII, the reaction of GS––Cbi(II) with DHA produces GS––Cbi(III) and the ascorbyl radical, which rapidly disproportionates to a mixture of ascorbic and dehydroascorbic acids, and further regeneration of Cbi(II). [ABSTRACT FROM AUTHOR]