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Lecture19 - Lecture 19 Background reading Berg et al Pages...

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Lecture 19 11/16/11 Background reading: Berg, et al: Pages 260 - 263 Garrett and Grisham: Pages 458 - 459 Outline: Mechanism of chymotrypsin catalysis Catalytic triad Substrate binding Oxyanion hole Cleavage of peptide bond Deacylation of enzyme Specificity pocket
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Mechanism of chymotrypsin catalysis
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This is the burst phase which produces the colored product.. This acyl-enzyme intermediate complex is then hydrolyzed to release the carboxylic acid component of the substrate and regenerate the free enzyme as shown below. This is the steady-state phase, which takes longer for the enzyme to be released.
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Catalytic triad S 195 is H-bonded to the imidazole ring of H 57. The –NH group of the imidazole ring of H 57 is, in turn, H-bonded to the carboxylate group of D 102. The arrangement of these 3 residues is known as the catalytic triad. The H 57 positions the S 195 to polarize its hydroxyl group so it can be deproton- ated. The D 102 helps orient H 57 and make it a better proton acceptor.
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