S-Methylmethionine

S-Methylmethionine (SMM) is a derivative of methionine with the chemical formula (CH₃)₂SCH₂CH₂CH(NH₃)CO₂. This cation is an intermediate in many biosynthetic pathways owing to the sulfonium functional group. The natural derivative S-methylmethionine is biosynthesized from L-methionine which is first converted to S-adenosylmethionine. The subsequent conversion, involving replacement of the adenosyl group by a methyl group is catalyzed by the enzyme methionine S-methyltransferase. S-methylmethionine is particularly abundant in plants, being more abundant than methionine.