CHAPTER 12: The Chemistry of Cobalamins

Cobalamins are water-soluble molecules, indispensable to the biochemistry of human body. The cobalt–carbon bond inserted in the centre of the corrin ring of their molecule offers unique chemical properties to cobalamins. Although cyanocobalamin is the most stable form of cobalamins, usually used for medical purposes, adenosylcobalamin and methylcobalamin are the two active forms of cobalamins in vivo in humans. Heterolytic or homolytic cleavage of the organometallic bond of cobalamins constitutes a main mechanism in the enzymatic reactions to which cobalamins serve as cofactors. Methionine synthase and methylmalonyl CoA mutase are two important enzymes that use cobalamins as cofactors. In this short chapter we discuss the main features of cobalamins’ chemical structure as well as their role as cofactors in the enzymatic function of cobalamin-dependent enzymes.