Explanation
The correct answer is D: Zn++.
Zinc ion (Zn++) is the cofactor essential for the catalytic activity of carboxypeptidase enzyme. Carboxypeptidase is an enzyme that cleaves the terminal peptide bond from the carboxy end of a peptide chain, resulting in the release of a single amino acid. This enzyme requires Zn++ ion as a cofactor to catalyze the hydrolysis reaction. The Zn++ ion binds to the enzyme and plays a critical role in stabilizing the transition state of the reaction, lowering the activation energy and increasing the rate of the reaction.
