Chem 135 Fall 2009 PS2 - Chem 135 Fall 2009 Problem Set 2...

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Problem Set 2 Due Friday, Sept 18th, 2009 in class 1. As an alternative to the “catalytic triad” found in chymotrypsin, many proteases use metal ions to effect peptide bond hydrolysis. An example is carboxypeptidase, an enzyme that cleaves the C-terminal amino acid from a polypeptide: a. The active site of this protein was determined to contain a Zn(II) ion bound by two histidine residues and one glutamic acid. Mutation studies have also determined that Glu 72 is required for catalytic function. A sketch of the active site residues is provided below. Using this as a starting point, suggest two different mechanisms for the hydrolysis of a peptide bond that clearly explain the role(s) of the Zn(II) ion. You may add any additional residues that you see fit. For the purposes of this question, you do not have to provide all of the intermediates- -just provide the key reaction steps. Be sure that your mechanism accounts for the three key roles a protease must play in cleaving an amide bond. Active Site: b. Using your knowledge of pK a values for glutamic acid and histidine, what do you think is the optimal pH for carboxypeptidase activity? Briefly explain you r answer. c.
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This note was uploaded on 02/04/2010 for the course CHEM 135 taught by Professor Francis during the Fall '08 term at University of California, Berkeley.

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Chem 135 Fall 2009 PS2 - Chem 135 Fall 2009 Problem Set 2...

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