Protein portion of an enzyme to which a co-factor binds is known as
(a) Apoenzyme
(b) Isoenzyme
(c) Holoenzyme
(d) Proenzyme

Options

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

Answer

To solve the question, we need to identify the correct term for the protein portion of an enzyme to which a co-factor binds. Let's break it down step by step:

### Step-by-Step Solution:

1. **Understanding Enzyme Structure**: Enzymes are biological catalysts that can be composed of proteins and may require additional non-protein molecules called cofactors to be active.

2. **Identifying Key Terms**:
- **Apoenzyme**: This is the protein portion of an enzyme that is inactive without its cofactor.
- **Isoenzyme**: These are different forms of an enzyme that catalyze the same reaction but may differ in structure and kinetic properties.
- **Holoenzyme**: This is the complete, active form of an enzyme that includes the apoenzyme and its cofactor.
- **Proenzyme**: This refers to an inactive precursor of an enzyme, which requires a biochemical change to become active.

3. **Analyzing the Question**: The question specifically asks for the "protein portion of an enzyme to which a co-factor binds." This indicates we are looking for the term that describes the enzyme's protein part before it combines with the cofactor.

4. **Selecting the Correct Option**:
- Since the apoenzyme is the protein part that requires a cofactor to become active, and the holoenzyme is the complete enzyme (apoenzyme + cofactor), the correct answer must be **(a) Apoenzyme**.

### Conclusion:
The correct answer is **(a) Apoenzyme**.

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