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Bovine γ-chymotrypsin A (residues 1-13 in pink, 16-146 in cyan, 149-245 in gold) complex with inhibitor (PDB code 7gch)



The hydrolysis occurs in two steps. First, the peptide bond with the C-terminal part of the substrate is replaced by an ester bond to the active site serine. Second, the covalent intermediate is hydrolyzed by water, releasing the N-terminal part of the substrate as carboxylic acid. Both steps occur via a tetrahedral intermediate containing an oxyanion that is stabilized by hydrogen bond donors lining the so-called oxyanion hole. Throughout the reaction, active site residue histidine 57 acts as base or acid to deprotonate nucleophiles or protonate leaving groups, respectively. The following 5-minute video shows the mechanism step by step.

Mechanism of chymotrypsin (image source)

3D Structures of Chymotrypsin

Chymotrypsin 3D structures


  1. Appel W. Chymotrypsin: molecular and catalytic properties. Clin Biochem. 1986 Dec;19(6):317-22. PMID:3555886

Further reading

You can learn more about chymotrypsin structure, function and regulation in this publicly available chapter of the Biochemistry textbook by Berg, Tymoczka and Stryer.

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Michal Harel, Karsten Theis, Alice Harmon, Alexander Berchansky

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