Trypsin is a serine protease commonly found in the vertebrate digestive system that hydrolyzes proteins and is secreted in the pancreas as inactive trypsinogen. Its site of cleavage of the peptide chain is located primarily at the carboxyl terminus of lysine or arginine （except when both are immediately followed by proline）. Trypsin consists of two subunits, the alpha subunit （with 2 polypeptide chains forming it） and the beta subunit （with 1 polypeptide chain forming it）. Its hydrolytic activity can be inhibited by a variety of inhibitors, including 1） organophosphorus compounds, such as isopropyl fluorophosphate; 2） natural trypsin inhibitors derived from pancreas, soybeans, green beans, and egg whites; 3） silver ions; and 4） specific protease inhibitors, such as AEBSF, anti-protease, peptidylase, DFP, leucoinhibitory peptidase, PMSF, TLCK, etc.