Which of the following is not a part of enzyme but it activates the enzyme ?

Options

A. K
B. C
C. N
D. Si

Explanation

To answer the question "Which of the following is not a part of enzyme but it activates the enzyme?", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Enzymes**: Enzymes are biological catalysts that speed up chemical reactions in the body. They can sometimes function independently, but often require additional components to be fully active.

2. **Identifying Cofactors**: Cofactors are non-protein molecules that assist enzymes in their function. They can be metal ions or organic molecules. Metal ions such as zinc, manganese, and molybdenum are common cofactors.

3. **Differentiating Holoenzyme and Apoenzyme**: When an enzyme is combined with its cofactor, it is referred to as a holoenzyme. When it lacks the cofactor, it is called an apoenzyme.

4. **Examples of Cofactors**: For instance, the enzyme alcohol dehydrogenase requires zinc as a cofactor to function effectively. Similarly, potassium ions (K+) are essential for the enzyme pyruvate kinase, which is crucial for ATP production.

5. **Analyzing the Options**: The question provides multiple options, and we need to identify which one is a cofactor that activates an enzyme but is not part of the enzyme structure itself.

6. **Selecting the Correct Answer**: Among the options provided, potassium ions (K+) are known to activate the enzyme pyruvate kinase without being part of the enzyme's active site. Therefore, potassium is the correct answer.

### Final Answer:
The correct answer is **potassium ions (K+)**.

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