Methionine (Met, M. C5H11NO2S) is a essential nonpolar amino acid, and a lipotropic.
It and cysteine are the only sulfur containing amino acids that are coded for by DNA (Homocysteine is an amino acid and contains sulfur, but is a product of S-adenosylmethionine 1 carbon metabolism and is not coded for by DNA). Methionine is a methyl donor as S-adenosyl methionine (SAM). It is incorporated into the N-terminal position of all proteins in eukaryotes and archaea, though it may be removed by post-translational modification (bacteria incorporate N-formyl methionine instead). Methionine can also occur at other positions in the protein. It plays a role in cysteine, carnitine and taurine synthesis by the transsulfuration pathway , lecithin production, the synthesis of phosphatidylcholine and other phospholipids. Improper conversion of methionine can lead to atherosclerosis. Methionine is a chelating agent.
Methionine is one of only two amino acids encoded by just one codon (AUG) in the standard genetic code (tryptophan, encoded by UGG, is the other).
See also
Formylmethionine
