An enzyme not used in Krebs cycle is

Options

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

Answer

To determine which enzyme is not used in the Krebs cycle, we will analyze each of the given options one by one.

### Step-by-Step Solution:

1. **Identify the Enzymes**: The options provided are:
- Aconitase
- Decarboxylase
- Fumarase
- Aldolase

2. **Analyze Aconitase**:
- Aconitase is an enzyme that catalyzes the conversion of citrate to isocitrate in the Krebs cycle.
- Therefore, Aconitase is **used** in the Krebs cycle.

3. **Analyze Decarboxylase**:
- Decarboxylase enzymes are involved in the oxidative decarboxylation processes in the Krebs cycle.
- Thus, Decarboxylase is also **used** in the Krebs cycle.

4. **Analyze Fumarase**:
- Fumarase catalyzes the conversion of fumarate to malate, which is a reaction that occurs in the Krebs cycle.
- Therefore, Fumarase is **used** in the Krebs cycle.

5. **Analyze Aldolase**:
- Aldolase is an enzyme that is involved in glycolysis, specifically in the conversion of fructose 1,6-bisphosphate to dihydroxyacetone phosphate and glyceraldehyde 3-phosphate.
- Aldolase is **not used** in the Krebs cycle.

6. **Conclusion**:
- Based on the analysis, the enzyme that is **not used** in the Krebs cycle is **Aldolase**.

### Final Answer:
The enzyme not used in the Krebs cycle is **Aldolase** (Option 4).