chymotrypsin

Chymotrypsin is a digestive serine protease produced by the pancreas in many animals. It catalyzes the hydrolysis of peptide bonds on the carboxyl side of bulky hydrophobic amino acids, with a preference for phenylalanine, tyrosine, and tryptophan in the P1 position.

Chymotrypsin belongs to the chymotrypsin family of serine proteases. The catalytic mechanism uses a catalytic triad consisting of Ser195, His57, and Asp102. The Ser195 acts as a nucleophile to form an acyl-enzyme intermediate, which is then hydrolyzed by water to regenerate the enzyme. The S1 specificity pocket accommodates bulky hydrophobic side chains, giving its selectivity.

Chymotrypsin is synthesized in the pancreas as the inactive zymogen chymotrypsinogen and is activated by proteolytic cleavage by trypsin to yield the active enzyme. The mature enzyme is typically composed of two polypeptide chains linked by disulfide bonds and has a molecular mass around 25 kDa, consisting of about 245 amino acids.

Its activity is optimal near neutral pH (about 7.5–8.0) and is inhibited by classic serine protease inhibitors such as phenylmethylsulfonyl fluoride (PMSF) and diisopropyl fluorophosphate (DFP). It is used in laboratory settings to digest proteins for peptide mapping, sequencing, and structural studies and is commonly employed alongside other proteases like trypsin due to its distinct specificity. It cleaves after bulky hydrophobic residues but not after proline in most cases.