In citric acid cycle, the step not using dehydrogenase enzymes is

Options

A. Malic acid to oxaloacetate
B. Succinate to fumarate
C. Oxaloacetate to citric acid
D. Citric acid to `alpha`-ketoglutarate.

Answer

To determine which step in the citric acid cycle does not use dehydrogenase enzymes, we will analyze each of the given options one by one.

### Step-by-Step Solution:

1. **Identify the Reactions in the Citric Acid Cycle:**
- The citric acid cycle (Krebs cycle) consists of several reactions where specific enzymes catalyze the conversion of substrates.

2. **Evaluate Each Option:**
- **Option A: Malic acid to Oxaloacetate**
- This reaction is catalyzed by the enzyme **malate dehydrogenase**. Since it uses a dehydrogenase enzyme, this option is incorrect.

- **Option B: Succinate to Fumarate**
- This reaction is catalyzed by **succinate dehydrogenase**. This also involves a dehydrogenase enzyme, making this option incorrect as well.

- **Option C: Oxaloacetate to Citric Acid**
- The enzyme that catalyzes this reaction is **citrate synthase**. This step does not involve a dehydrogenase enzyme, making this option correct.

- **Option D: Citric Acid to Alpha-Ketoglutarate**
- This reaction is catalyzed by **isocitrate dehydrogenase**. Since it uses a dehydrogenase enzyme, this option is incorrect.

3. **Conclusion:**
- The only step in the citric acid cycle that does not use a dehydrogenase enzyme is **Option C: Oxaloacetate to Citric Acid**.

### Final Answer:
**Option C: Oxaloacetate to Citric Acid** is the step in the citric acid cycle that does not use dehydrogenase enzymes.

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