Chymotrypsin Specificity explain

Chymotrypsin Specificity explain

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Chymotrypsin Specificity：Chymotrypsin is activated through cleavage of the bond between arginine and isoleucine (R15 and I16) by trypsin, causing structural modifications and formation of the substrate binding site (Sears 2010). Chymotrypsin differs from trypsin in that trypsin cleaves peptides at arginine and lysine residues, while chymotrypsin prefers large hydrophobic residues (Hedstrom et al. 1992). Chymotrypsin preferentially catalyzes the hydrolysis of peptide bonds involving L-isomers of tyrosine, phenylalanine, and tryptophan. It also readily acts upon amides and esters of susceptible amino acids. Chymotrypsin’s specificity for large hydrophobic residues can be explained by a hydrophobic S1 binding pocked formed by residues 189 through 195, 214 through 220, and 225 through 228 (Cohen et al. 1981).

Although the structure of trypsin and chymotrypsin’s S1 site show only one difference (at position 189), site-directed mutagenesis of trypsin and chymotrypsin have failed to interchange specificities, suggesting the mechanism by which trypsin and chymotrypsin achieve substrate specific catalysis is not fully understood