Chymotrypsin proteolysis mechanism

Acyl enzyme, an intermediate in the catalytic mechanism of serine proteases, such as trypsin and chymotrypsin. After the serine protease has bound a peptide substrate to form the Michaelis complex, Ser (in the case of chymotrypsin) nucleophilically attacks the peptide bond in the rate-determining step, forming a transition-state complex, known as a tetrahedral intermediate. The latter decomposes to the acyl enzyme, an extremely unstable intermediate, that bears the acyl moiety at the hydroxy group of Ser . The acyl enzyme intermediate is deacylated by water during proteolysis, or the attacking nucleophile is an amino component in case of kineticaUy controlled enzymatic peptide synthesis. 

Interestingly, there are many such examples of proteases that exist in nature, such as, trypsin, chymotrypsin, elastase, thrombin, subtilisin, plasmin, pepsin, chymosin, cathepsin D, renin, and HIV-1 protease, etc. To illustrate the direct participation of water in the digestive mechanism we show another example of proteolysis... 

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