Trypsinogen is a proenzyme (zymogen) that is activated to form trypsin. It is synthesized in the pancreas and activated by enterokinase once it reaches the lumen of the small intestine. Bovine trypsinogen is a single polypeptide chain of 229 amino acids that is cross linked by six disulfide bridges. Enterokinase cleaves a hexapeptide to from the NH2 terminus of trypsinogen at the Lys6 - Ile7 peptide bond and activates it. Trypsin, thus formed, autocatalytically activates more trypsinogen to trypsin. This native form of trypsin is called β-trypsin, which undergoes autolysis at Lys131 - Ser132 resulting in α-trypsin that is held together by disulfide bridges. Trypsin is a serine protease with His46 and Ser183 at the active site. The pH optimum of trypsin is 7 - 9.
