Chymotrypsins are digestive enzymes that can perform proteolysis by cleaving peptides at the carboxyl side of tyrosine, tryptophan, leucine and phenylalanine, although over time they can also hydrolyze other amide bonds, especially those with leucine-donated carboxyls. Chymotrypsins cleave peptide bonds by attacking the non-reactive carbonyl group with a powerful nucleophile, which momentarily becomes covalently bonded to the substrate to form an intermediate. Chymotrypsin B (CTRB1) and Chymotrypsin B2 (CTRB2) are synthesized in the pancreas by protein biosynthesis as precursors that are enzymatically inactive, but become active as three polypeptide molecules that are interconnected by disulfide bonds.