This family consists of several archaebacterial S-adenosylmethionine synthetase C(AdoMet synthetase or MAT) (EC 2.5.1.6). S-Adenosylmethionine (AdoMet) occupies a central role in the metabolism of all cells. The biological roles of AdoMet include acting as the primary methyl group donor, as a precursor to the polyamines, and as a progenitor of a 5'-deoxyadenosyl radical. S-Adenosylmethionine synthetase catalyses the only known route of AdoMet biosynthesis. The synthetic process occurs in a unique reaction in which the complete triphosphate chain is displaced from ATP and a sulfonium ion formed. MATs from various organisms contain ~400-amino acid polypeptide chains [1].

1: Enzymatic properties of S-adenosylmethionine synthetase from the archaeon Methanococcus jannaschii. Lu ZJ, Markham GD; J Biol Chem 2002;277:16624-16631. PMID:11872742