A competitive inhibitor of succinic dehydrogenase is

Options

A. Malonate
B. Succinate
C. Citrate
D. Fumarate

Answer

**Step-by-Step Solution:**

1. **Understanding Competitive Inhibition:**
- A competitive inhibitor is a substance that competes with the substrate for binding to the active site of an enzyme. This type of inhibition can be reversed by increasing the concentration of the substrate.

2. **Identifying the Enzyme:**
- The enzyme in question is succinic dehydrogenase, which is involved in the citric acid cycle (TCA cycle).

3. **Analyzing the Options:**
- The options given are malonate, succinate, citrate, and fumarate. We need to determine which of these acts as a competitive inhibitor for succinic dehydrogenase.

4. **Evaluating Malonate:**
- Malonate is a structural analog of succinate (the substrate for succinic dehydrogenase). Because of its similar structure, malonate can bind to the active site of succinic dehydrogenase, preventing succinate from binding. Therefore, malonate acts as a competitive inhibitor.

5. **Evaluating Other Options:**
- Succinate is the actual substrate for succinic dehydrogenase, so it cannot be a competitive inhibitor.
- Citrate and fumarate are also intermediates in the citric acid cycle, but they do not compete with succinate for the active site of succinic dehydrogenase.

6. **Conclusion:**
- Based on the analysis, the competitive inhibitor of succinic dehydrogenase is malonate.

**Final Answer:**
- The correct answer is **malonate**.

---