Thermolabile protein part of enzyme is
(a) Apoenzyme
(b) Proenzyme
(c) Holoenzyme
(d) Isoenzyme

Options

A. Apoenzyme
B. Proenzyme
C. Holoenzyme
D. Isoenzyme.

Answer

To solve the question regarding the thermolabile protein part of an enzyme, we can break down the information as follows:

### Step-by-Step Solution:

1. **Understanding Enzymes**: Enzymes are biological catalysts that speed up chemical reactions in the body. They are typically composed of two main components: a protein part and a non-protein part.

2. **Identifying the Protein Part**: The protein part of an enzyme is referred to as the **apoenzyme**. This is the portion that is sensitive to temperature changes and can denature at high temperatures.

3. **Role of Cofactors**: For the apoenzyme to be active, it often requires a non-protein component known as a cofactor. When the apoenzyme combines with its cofactor, it forms a complete, active enzyme known as a **holoenzyme**.

4. **Thermolabile Nature**: The term "thermolabile" refers to the sensitivity of a protein to heat. In this context, the apoenzyme is thermolabile because it can denature (lose its functional shape) when exposed to high temperatures.

5. **Evaluating Other Options**:
- **Proenzyme**: This refers to an inactive form of an enzyme that requires activation. It is not the thermolabile part.
- **Holoenzyme**: This is the complete enzyme (apoenzyme + cofactor) and not just the protein part.
- **Isoenzyme**: These are different forms of an enzyme that catalyze the same reaction but may have different properties. This is also not the thermolabile part.

6. **Conclusion**: Based on the definitions and roles of each component, the correct answer to the question is (a) **Apoenzyme**.

### Final Answer:
The thermolabile protein part of the enzyme is (a) Apoenzyme.