When coenzyme is combined with apoenzyme, it is called

Options

A. Cofactor
B. Holoenzyme
C. Substrate enzyme complex
D. Vitamin A

Explanation

To solve the question "When coenzyme is combined with apoenzyme, it is called," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Terms**:
- **Apoenzyme**: This is the protein part of an enzyme, which is inactive on its own.
- **Coenzyme**: This is a non-protein molecule that assists enzymes in catalyzing reactions. It often acts as a carrier for chemical groups or electrons.

2. **Combining Apoenzyme and Coenzyme**:
- When a coenzyme binds to an apoenzyme, it activates the enzyme. This combination is crucial for the enzyme's functionality.

3. **Identifying the Resulting Complex**:
- The combination of an apoenzyme and a coenzyme forms a complete, active enzyme. This active enzyme is referred to as a **holoenzyme**.

4. **Reviewing the Options**:
- The options given are:
- A) Cofactor
- B) Holoenzyme
- C) Substrate-enzyme complex
- D) Vitamin A
- From our understanding, the correct term for the combination of an apoenzyme and a coenzyme is **holoenzyme**.

5. **Conclusion**:
- Therefore, the answer to the question is **B) Holoenzyme**.