S-Adenosyl-L-methionine—Donor of Methyl Groups

Abstract

The compound S-adenosyl-L-methionine (AdoMet), shown in Figure 4.1, is the methyl group donor in numerous cellular enzymatic transmethylation reactions, including DNA methylation (Cantoni, 1975). In reality AdoMet is probably second only to ATP in the variety of reactions it serves as a cofactor. When it was first discovered, it appeared to contribute only to the modification of small molecules. However it soon became clear that this is a unique modifying agent, created during evolution to shape the structure of macromolecules as well. Proteins, lipids, polysaccharides, and nucleic acids (RNA and DNA) are all subject to methylation by highly specific enzymes after their primary biosynthesis.