Which one is not cofactor?

Options

A. Coenzyme
B. Apoenzyme
C. Prosthetic group
D. Metal ions

Answer

To determine which option is not a cofactor, we need to understand the definitions and roles of the given options: coenzyme, apoenzyme, prostatic group, and metal ions.

### Step-by-Step Solution:

1. **Understanding Cofactors**:
- Cofactors are non-protein components that assist enzymes in catalyzing reactions. They can be organic (like coenzymes) or inorganic (like metal ions).

2. **Identifying the Options**:
- **Coenzyme**: This is an organic cofactor that is loosely bound to the enzyme and assists in the enzyme's activity.
- **Apoenzyme**: This is the protein part of an enzyme, which requires a cofactor to be active. It is not a cofactor itself.
- **Prostatic Group**: This is a type of cofactor that is tightly bound to the enzyme and is usually a non-protein component.
- **Metal Ions**: These are inorganic cofactors that can be tightly or loosely bound to enzymes and play a crucial role in enzyme function.

3. **Analyzing Each Option**:
- Coenzyme: This is a type of cofactor.
- Apoenzyme: This is not a cofactor; it is the protein part of the enzyme.
- Prostatic Group: This is a type of cofactor.
- Metal Ions: These are inorganic cofactors.

4. **Conclusion**:
- The option that is **not** a cofactor is **apoenzyme**.

### Final Answer:
**Apoenzyme** is not a cofactor.

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