Chapter 23, Problem 1P

How does the metal ion in carboxypeptidase A increase the enzyme’s catalytic activity

Interpretation Introduction

Interpretation:

The metal ion in carboxypetidase A increases the catalytic activity of the enzyme; this has to be explained.

Explanation of Solution

Carboxypetidase A is a digestive enzyme.  It hydrolyzes the carboxyl terminal peptide bond and it prefers bulky and aliphatic residues.

Proposed mechanism for the catalytic reaction of carboxypetidase is given in figure 1.

Figure 1

The metal ion present in the carboxypeptidase A enzyme is Zinc metal.

This metal ion $\left({\text{Zn}}^{\text{2+}}\right)$ makes the carbonyl $\left(\text{C=O}\right)$ carbon more susceptible to nucleophilic addition, increases the nucleophilicity of water molecule by making it like a hydroxide ion, and the negative charge of the transition state is stabilized by this metal ion.