## **Core Concept**
Carboxypeptidase is an enzyme that hydrolyzes peptides and proteins at the carboxy-terminal end. It plays a significant role in protein digestion. This enzyme requires a specific metal ion as a cofactor to function properly.

## **Why the Correct Answer is Right**
The correct answer, **Zinc (Zn)**, is a crucial cofactor for carboxypeptidase. Carboxypeptidase A, a well-known form of this enzyme, is a zinc-containing metalloprotease. The zinc ion is essential for the catalytic activity of carboxypeptidase, facilitating the hydrolysis of peptide bonds.

## **Why Each Wrong Option is Incorrect**
- **Option A: Iron (Fe)** - While iron is a vital mineral for various biological functions, including oxygen transport and enzyme activity, it is not directly associated with carboxypeptidase activity.
- **Option B: Calcium (Ca)** - Calcium ions play critical roles in many physiological processes and can act as cofactors for some enzymes, but they are not specifically required for carboxypeptidase activity.
- **Option D: Potassium (K)** - Potassium is essential for maintaining electrolyte balance and nerve function but is not known to act as a cofactor for carboxypeptidase.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that zinc deficiency can impair enzyme function, including carboxypeptidase, which can affect protein digestion and overall metabolism. Zinc is a cofactor for many enzymes, and its deficiency can lead to various clinical manifestations.

## **Correct Answer:** .