| CASOther = 59-51-8 (racemic) | PubChem = 876 | SMILES = CSCC[C@H](N)C(O)=O}} | Section2 = | Section3 = }} Methionine (; abbreviated as Met or M)'s an α-amino acid with the chemical formula HO2CCH(NH2)CH2CH2SCH3. This essential amino acid's classified as nonpolar. Function Together with cysteine, methionine's one of two sulfur-containing proteinogenic amino acids. Its derivative S-adenosyl methionine (SAM) serves as a methyl donor. Methionine's an intermediate in the biosynthesis of cyste… (More on Methionine)