Methionine Adenosyltransferase I Alpha (MAT1a)

MAT1a catalyzes a two-step reaction that involves the transfer of the adenosyl moiety of ATP to methionine to form S-adenosylmethionine and tripolyphosphate, which is subsequently cleaved to PPi and Pi. S-adenosylmethionine is the source of methyl groups for most biological methylations. The encoded protein is found as a homotetramer (MAT I) or a homodimer (MAT III) whereas a third form, MAT II (gamma), is encoded by the MAT2A gene. Mutations in this gene are associated with methionine adenosyltransferase deficiency.

The peptide maps of the 2 forms were possibly identical, although they showed different specific activities at physiologic concentrations of methionine. The findings suggested that the 2 isoforms are encoded by the same gene.