B₁₂-Containing Enzymes

Vitamin B₁₂, or cobalamin, was isolated from liver extracts over 50 years ago as a red crystalline metabolite that cured pernicious anemia in humans. The X-ray crystal structure of the cofactor and various derivatives subsequently showed that it has an elaborate organometallic structure. Cobalamin is widely distributed in nature and biochemical studies have shown that it facilitates enzymatic transformations that involve methyl group transfer and radical-mediated rearrangements. The biosynthesis of cobalamin, the molecular mechanisms of the transformations that are catalyzed by cobalamin-dependent enzymes, and the inherent chemical flexibility in this organometallic cofactor that permits it to participate in these disparate reactions have fascinated chemists and biochemists for decades. This article highlights the chemical transformations that are catalyzed by cobalamin-dependent enzymes.