Methionine (abbreviated as Met or M)is an a-amino acid. It is an essential amino acid,meaning it cannot be made by the body.
Methionine is an intermediate in the biosynthesis of cysteine, carnitine, taurine, lecithin, phosphatidylcholine, and other phospholipids. Improper conversion of methionine can lead to heart disease (see homocysteine).
Selhub, J. (1999). "Homocysteine metabolism.". Annual Review of Nutrition 19: 217–246. doi:10.1146/annurev.nutr.19.1.217. PMID 10448523.