An organic substance bound to an enzyme and essential for its activity is called

Options

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

Answer

To answer the question, "An organic substance bound to an enzyme and essential for its activity is called," we can break down the concepts related to enzymes and their components step by step.

### Step-by-Step Solution:

1. **Understanding Enzymes**: Enzymes are biological catalysts that speed up chemical reactions in living organisms. They are typically proteins.

2. **Apoenzyme**: When an enzyme is inactive, it is referred to as an apoenzyme. This form of the enzyme requires an additional component to become active.

3. **Role of Organic Substances**: Some enzymes require organic molecules to become active. These organic molecules are crucial for the enzyme's functionality.

4. **Coenzymes**: The organic substances that bind to the apoenzyme to activate it are called coenzymes. Coenzymes are often derived from vitamins and are essential for the enzyme's catalytic activity.

5. **Holoenzyme**: When the apoenzyme binds with the coenzyme, the complex formed is called a holoenzyme, which is the active form of the enzyme.

6. **Conclusion**: Therefore, the answer to the question is that an organic substance bound to an enzyme and essential for its activity is called a **coenzyme**.

### Final Answer:
An organic substance bound to an enzyme and essential for its activity is called a **coenzyme**.