one of the natural L-amino acids, obtainable as a white crystalline nitrogenous substance by the action of dilute sulphuric acid on silk gelatin. It is found in many proteins, and, having a free primary hydroxyl group on the side chain, is involved in the catalytic action at the active site of some enzymes, such as proteases. The IUPAC abbreviation for serine in protein sequences is Ser. Chemically it is 2-amino-3-hydroxy-propanoic acid (C3H7NO3), HO.CH2.CH(NH2).COOH.  [1913 Webster]