Chymotrypsin is a serine protease active in food breakdown in the mammalian digestive system. It is synthesized in the pancreas as a zymogen before being activated by trypsin. There are three known isozymes in humans: chymotrypsinogen B1 (CTRB1), chymotrypsinogen B2 (CTRB2), and chymotrypsin-C/caldecrin (CTRC). All three have preferential cleavage sites after tyrosine, phenylalanine, tryptophan and leucine residues. Chymotrypsin-C has additional cleavage sites after methionine, asparagine, and glutamine.