Appendix 5: S‑Adenosyl-L-Methionine and Analogs
Elmar Weinhold and Saulius Klimasauskas
S‑adenosyl‑l‑methionine (AdoMet, also abbreviated SAM or SAMe, 1) is one of the most versatile biomolecules in nature and one of the most widely used enzyme substrate, second perhaps only to adenosine triphosphate (ATP).1‑3 AdoMet acts as a cofactor in a myriad of enzyme catalyzed reactions and can function as donor for methyl, methylene, aminocarboxypropyl (or aminopropyl after decarboxylation of AdoMet), ribosyl, amino and adenosyl groups. In addition, AdoMet can serve as a radical source in radical reactions. AdoMet is available as different salts from various commercial sources. The radioactive cofactors [methyl‑3H]AdoMet and (methyl‑14C)AdoMet with tritium or 14C incorporated in the methyl group are commercially available and commonly used to assay enzyme activities. After separation of the product from radioactive AdoMet, the radioactivity incorporated into the substrate is measured by scintillation counting.