Reactions of Cyanocobalamin and Aquocobalamin with Proteins.

Abstract

[dagger]A short-term dialysis procedure was used to study the binding of cobalamins by proteins Aquocobalamin (vitamin B12b) was much more reactive than cyanocobalamin (vitamin B12), being bound in rather large amounts by several protein preparations of diverse origin. In several instances binding was increased by denatura-tion and decreased in acid media. It was suggested tha this type of binding may occur via cobalichrome formation. A gastric mucosal extract bound large and equal amounts of aquocobalamin and cyanocobalamin, apparently at the same binding site. Excess cyanide had no effect on the cyanocobalamin-gastric extract reaction in neutral media, but exhibited an inhibiting effect at high pH levels. In this reaction the cyano- group of cyanocobalamin was not released, but remained in a photolabile position. It was suggested that the Co atom participated in the reaction and that the position occupied by the substituted benzimidazole moiety was involved.