Which of the following enzymes is not used in Krebs cycle ?

Options

A. Aconitase
B. Decarboxylase
C. Aldoase
D. Fumarase

Answer

To determine which enzyme is not used in the Krebs cycle, we will analyze each of the given options and their roles in cellular respiration.

### Step-by-Step Solution:

1. **Understanding the Krebs Cycle**:
- The Krebs cycle, also known as the citric acid cycle, is a series of enzymatic reactions that occur in the mitochondria. It plays a crucial role in cellular respiration by producing energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.

2. **Analyzing the Options**:
- **Option A: Echonitase**:
- This enzyme is involved in the isomerization reaction within the Krebs cycle, specifically converting citrate to isocitrate. Therefore, it is used in the Krebs cycle.

- **Option B: Decarboxylase**:
- Decarboxylases are enzymes that facilitate the removal of carboxyl groups. They play a role in the Krebs cycle, particularly in the decarboxylation reactions that occur during the cycle. Hence, this enzyme is also used in the Krebs cycle.

- **Option C: Aldolase**:
- Aldolase is primarily involved in glycolysis, not the Krebs cycle. It catalyzes the cleavage of fructose-1,6-bisphosphate into two three-carbon molecules. Since it is not part of the Krebs cycle, this is the correct answer to the question.

- **Option D: Fumarase**:
- Fumarase catalyzes the conversion of fumarate to malate in the Krebs cycle. Thus, it is also used in the Krebs cycle.

3. **Conclusion**:
- After analyzing all options, the enzyme that is not used in the Krebs cycle is **Aldolase** (Option C).

### Final Answer:
**C. Aldolase**

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