The cafactor of nitrate reductase is

Options

A. Cu
B. Zn
C. Ca
D. Mo

Explanation

To answer the question regarding the cofactor of nitrate reductase, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Function of Nitrate Reductase**:
- Nitrate reductase is an enzyme that catalyzes the reduction of nitrate (NO3-) to nitrite (NO2-). This is an essential step in the nitrogen assimilation process in plants.

2. **Identify the Type of Enzyme**:
- Nitrate reductase is classified as a molybdoflavoprotein. This indicates that it contains both molybdenum and flavin (FAD or FMN) as part of its structure.

3. **Determine the Cofactor**:
- The primary cofactor required for the activity of nitrate reductase is molybdenum. This metal ion plays a crucial role in the enzyme's ability to facilitate the reduction of nitrate.

4. **Coenzymes Involved**:
- In addition to the cofactor, nitrate reductase also requires coenzymes such as NADH or NADPH. These coenzymes are involved in the electron transfer necessary for the reduction process.

5. **Conclusion**:
- Based on the information gathered, we conclude that the cofactor of nitrate reductase is molybdenum.

### Final Answer:
The cofactor of nitrate reductase is **molybdenum**.