<P> Chymotrypsin ( EC 3.4. 21.1 , chymotrypsins A and B , alpha - chymar ophth , avazyme , chymar , chymotest , enzeon , quimar , quimotrase , alpha - chymar , alpha - chymotrypsin A , alpha - chymotrypsin ) is a digestive enzyme component of pancreatic juice acting in the duodenum where it performs proteolysis , the breakdown of proteins and polypeptides . Chymotrypsin preferentially cleaves peptide amide bonds where the side - chain of the amino acid N - terminal to the scissile amide bond ( the P position ) is a large hydrophobic amino acid ( tyrosine , tryptophan , and phenylalanine ) . These amino acids contain an aromatic ring in their sidechain that fits into a ' hydrophobic pocket ' ( the S position ) of the enzyme . It is activated in the presence of trypsin . The hydrophobic and shape complementarity between the peptide substrate P sidechain and the enzyme S binding cavity accounts for the substrate specificity of this enzyme . Chymotrypsin also hydrolyzes other amide bonds in peptides at slower rates , particularly those containing leucine and methionine at the P position . </P>
where does cleavage of the peptide bond by chymotrypsin occur
where the side - chain of the amino acid N - terminal to the scissile amide bond ( the P position ) is a large hydrophobic amino acid ( tyrosine , tryptophan , and phenylalanine )