Trypsin is an enzyme that cleaves
proteins at specific positions. It cuts at R-X and K-X bonds, unless X is P (see
amino acids for the codes). Many trypsin preparations contain some
chymotrypsin activity. The
pH optimum for trypsin activity is pH 7-9, and it is permanently inactivated at pH > 11. Trypsin retains activity in 0.1%
SDS, 1 M
guanidine[?] HCl, and 30%
ethanol. The
autocatalytic activity[?] of trypsin can be slowed down with 20 mM calcium.
Together with pepsin and chymotrypsin, trypsin is one of the three principal digestive proteinases. It is found in the stomach, where it degrades proteins to polypeptides and amino acids.