Carboxypeptidase is a pancreatic digestive enzyme secreted into the small intestine. Carboxypeptidase hydrolyzes the first peptide or amide bond at the carboxyl or C-terminal end of proteins. As a comprehension exercise, let us discuss this enzyme in a few contexts to review some of the basic principles we have been discussing.

One interesting detail is that the catalytic mechanism of carboxypeptidase A provides an example of a coordinated metal ion, in this case zinc, supplying positive charge to a carbonyl oxygen of the substrate to which it is coordinated and increasing the susceptibility of the group to hydrolysis. Did you understand what you just read? Good. That is the important skill we are working on.

Here is some more to read for comprehension: The binding of substrate by carboxypeptidase A is accompanied by a structural change in the active site, corresponding to the induced fit model. Consequences of the structural changes undergone by the enzyme are to surround the substrate with catalytic groups and to exclude water from the active site (the high dielectric constant of water deriving from its high polarity would act to weaken the electric fields surrounding the charge densities in the active site).

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