Chymotrypsin

Chymotrypsin is a digestive, proteolytic enzyme which breaks down proteins in the small intestine. Chymotrypsin is first produced by the pancreas as chymotrypsinogen, which is enzymatically inactive. Then chymotrypsinogen is carried in the pancreatic juice through the pancreatic duct into the duodenum (small intestine). There chymotrypsinogen is activated into chymotrypsin by another enzyme, trypsin, and by molecules of active chymotrypsin.

On cleavage by trypsin into two parts that are still connected via an S-S bond, cleaved chymotrypsinogen molecules can activate each other by removing two small peptides in a trans-proteolysis. The resulting molecule is active chymotrypsin, a three polypeptide molecule interconnected via disulfide bonds.

Chymotrypsin degrades peptides in the small intestine at the carboxyl side of tyrosine, tryptophan, and phenylalanine because these three amino acids contain aromatic rings, which fit into a 'hydrophobic pocket' in the enzyme. Over time, chymotrypsin also hydrolyzes other amide bonds, particularly those with leucine-donated carboxyls.