Apoenzyme is

Options

A. Always a protein
B. Often a metal
C. Always an inorganic compound
D. Often a vitamin

Answer

**Step-by-Step Solution:**

1. **Understanding Enzymes**: Enzymes are biological catalysts that speed up chemical reactions in living organisms. They are crucial for various metabolic processes.

2. **Components of Enzymes**: Enzymes are made up of two main parts:
- **Apoenzyme**: This is the protein portion of the enzyme.
- **Cofactor**: This is the non-protein portion that can be either organic or inorganic.

3. **Role of Cofactors**: Cofactors are essential for the catalytic activity of the enzyme. They assist in the enzyme's function and can be classified into three types:
- **Prosthetic groups**: Tightly bound to the enzyme.
- **Coenzymes**: Organic molecules, often derived from vitamins.
- **Metal ions**: Inorganic ions that assist in enzyme activity.

4. **Identifying Apoenzyme**: The question specifically asks about the apoenzyme. Based on the definitions:
- The apoenzyme is specifically the protein part of the enzyme.
- It does not include any cofactors, which are separate entities.

5. **Evaluating the Options**: The options provided in the question may include:
- A protein
- A metal
- An inorganic compound
- A vitamin
- Based on the definitions and roles, the only correct option that describes an apoenzyme is "a protein".

6. **Conclusion**: Therefore, the correct answer to the question "Apoenzyme is" is that it is a protein.

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