In the proteolytic enzyme carboxypeptidase, which of the following metal ions acts as a cofactor by forming coordination bonds with side chains at the active site?

Step-by-step solution

Carboxypeptidase is a proteolytic enzyme that requires a metal ion cofactor for its catalytic activity. The active site of carboxypeptidase contains a Zn²⁺ ion, which forms coordination bonds with the side chains of specific amino acid residues (typically two histidine residues and one glutamate residue) and a water molecule. The Zn²⁺ ion plays a crucial role in polarizing the carbonyl oxygen of the peptide bond, making the carbonyl carbon more susceptible to nucleophilic attack during the hydrolysis of the peptide