Enzymatic decyanation of cyanocobalamin in rat tissues

Cyanocobalamin is decyanated in vitro to hydroxocobalamin by rat liver and kidney. This appears to be due to an enzyme system which we have called “cyanocobalamindecyanase”. The enzyme is in the soluble fraction of the cells; it requires reduced cozymases and flavins and has an optimum pH of 7.2 under anaerobic conditions. This is consistent with the fact that conversion of cyanocobalamin to hydroxocobalamin and/or its reduced forms (B₁₂r, B₁₂s) involves a reductive process in the earliest stage of the biosynthesis of coenzyme B₁₂.