The enzymes of Krebs cycle where `NADH+H^(+)` are produced are

Options

A. Isocitrate dehydrogenase, succinate dehydrogenase and malic dehydrogenase
B. Succinate thiokinase, succinate dehydrogenase and aconitase
C. Isocitrate dehydrogenase, `alpha`-ketoglutaric dehydrogenase, malic dehydrogenase
D. Isocitrate dehydrogenase, `alpha`-ketoglutaric dehydrogenase and succinate dehydrogenase

Answer

To answer the question regarding the enzymes of the Krebs cycle where NADH + H⁺ are produced, we will follow these steps:

### Step 1: Understand the Krebs Cycle
The Krebs cycle, also known as the citric acid cycle or TCA cycle, is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.

### Step 2: Identify the Enzymes Involved
In the Krebs cycle, specific enzymes are responsible for the production of NADH + H⁺. The key enzymes that produce NADH + H⁺ are:
1. **Isocitrate Dehydrogenase**
2. **Alpha-Ketoglutarate Dehydrogenase**
3. **Malate Dehydrogenase**

### Step 3: Explain the Function of Each Enzyme
- **Isocitrate Dehydrogenase**: This enzyme catalyzes the conversion of isocitrate to alpha-ketoglutarate, during which NAD⁺ is reduced to NADH + H⁺.

- **Alpha-Ketoglutarate Dehydrogenase**: This enzyme catalyzes the conversion of alpha-ketoglutarate to succinyl-CoA, also reducing NAD⁺ to NADH + H⁺ in the process.

- **Malate Dehydrogenase**: This enzyme converts malate back to oxaloacetate, again reducing NAD⁺ to NADH + H⁺.

### Step 4: Exclude Other Enzymes
- **Succinate Dehydrogenase**: This enzyme is involved in the oxidation of succinate to fumarate but produces FADH₂ instead of NADH + H⁺.

- **Succinyl Thiokinase**: This enzyme is responsible for the conversion of succinyl-CoA to succinate and produces GTP, not NADH + H⁺.

### Step 5: Conclusion
The enzymes of the Krebs cycle that produce NADH + H⁺ are:
1. Isocitrate Dehydrogenase
2. Alpha-Ketoglutarate Dehydrogenase
3. Malate Dehydrogenase

### Final Answer
The enzymes of the Krebs cycle where NADH + H⁺ are produced are:
- Isocitrate Dehydrogenase
- Alpha-Ketoglutarate Dehydrogenase
- Malate Dehydrogenase

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