1) Carboxypeptidase A, a zinc-containing enzyme, hydrolyzes the C- terminal peptide bonds of polypeptides and/or proteins. In the enzyme- substrate complex, the zinc ion is coordinated to three enzyme side chains, the carbonyl oxygen of the scissile peptide bond, and a water molecule. A plausible model for the enzyme's reaction mechanism that is consistent with X-ray and enzymological data is diagrammed below.
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Which of the following statements best describes the role of Glu270 in the catalytic mechanism of Carboxypeptidase A? Choose the single best answer.
a. Glu270 engages in covalent catalysis, forming a covalent linkage to the polypeptide substrate.
b. Glu270 causes strain & distortion of the polypeptide substrate, in much the same way that lysozyme distorts the substrate hexose ring into a half-chair conformation
c. Glu270 initially engages in acid catalysis, via extraction of a proton from the water molecule.
The solution discusses a plausible model for carboxypeptidase A.