The enzyme S-adenosylmethionine synthetase, or MAT, catalyzes the formation of S- adenosylmethionine (AdoMet or SAMe) from methionine and ATP. AdoMet is the principal biological source of synthesized methyl, and is found in all cells but most prominently in the liver. In mammalian tissues, there are three distinct AdoMet synthases - the alpha, beta, and gamma isoforms. While the alpha and beta variants are uniquely expressed solely in the adult liver, gamma is more widely distributed in the extrahepatic tissues.
