A polar sulphur-containing amino acid with the formula HSCH2
)COOH. It is synthesized from the amino acids methionine and serine. Breakdown is to pyruvate and may occur by several routes.
Cysteine is involved in the synthesis of the cofactor biotin. Sulphur-substituted derivatives of cysteine are found in the storage organs of many plants and the sulphide thus stored can be utilized in periods of rapid growth. See also cystine