Which is true?

Options

A. Holoenzyme=Apoenzyme+Endoenzyme
B. Apoenzyme=Holoenzyme+Exoenzyme
C. Coenzyme=Holoenzyme+Apoenzyme
D. Holoenzyme=Coenzyme+Apoenzyme

Answer

To determine which statement is true regarding enzymes, we need to understand the definitions and relationships between different components of enzymes. Here’s a step-by-step breakdown:

### Step 1: Understand the Terminologies
1. **Apoenzyme**: This is the protein part of an enzyme. It is inactive on its own and requires a non-protein component to become active.
2. **Coenzyme**: This is the non-protein part of an enzyme that assists in the enzyme's activity. It can be a vitamin or a derivative of a vitamin.
3. **Holoenzyme**: This is the complete, active form of an enzyme that consists of both the apoenzyme and the coenzyme.
4. **Endoenzyme**: These are enzymes that are produced inside the cell and act within the cell.
5. **Exoenzyme**: These are enzymes that are secreted by the cell and act outside of it.

### Step 2: Analyze the Options
Now, we will analyze the options provided in the question to determine which one is true:

1. **Option A**: Holoenzyme = Apoenzyme + Endoenzyme
- This is incorrect because holoenzyme is defined as the combination of apoenzyme and coenzyme, not endoenzyme.

2. **Option B**: Apoenzyme = Holoenzyme + Exoenzyme
- This is incorrect because apoenzyme is just the protein part of the enzyme, not a combination of holoenzyme and exoenzyme.

3. **Option C**: Coenzyme = Holoenzyme + Apoenzyme
- This is incorrect because coenzyme is the non-protein part of the holoenzyme, not a combination of holoenzyme and apoenzyme.

4. **Option D**: Holoenzyme = Coenzyme + Apoenzyme
- This is correct. Holoenzyme is indeed the complete enzyme formed by the combination of the apoenzyme (protein part) and the coenzyme (non-protein part).

### Conclusion
The correct answer is **Option D**: Holoenzyme is equal to Coenzyme plus Apoenzyme.