When examining the TCA cycle, alpha ketoglutarate dehydrogenase complex requires the set of cofactors as which of the following?

Options

A. Citrate synthase
B. Cis-aconitate
C. Pyruvate dehydrogenase
D. Fumarate

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the cofactors required by the alpha-ketoglutarate dehydrogenase complex in the TCA cycle (also known as the Krebs cycle).

2. **Identifying the Role of Alpha-Ketoglutarate Dehydrogenase**: This enzyme catalyzes the conversion of alpha-ketoglutarate into succinyl-CoA, which is a crucial step in the TCA cycle. It involves the removal of hydrogen atoms.

3. **Reviewing the Options**:
- **Option 1: Citrate Synthase**: This enzyme catalyzes the formation of citrate from acetyl-CoA and oxaloacetate. It does not involve the removal of hydrogen, so it is not a cofactor for alpha-ketoglutarate dehydrogenase.
- **Option 2: Cis-Aconitase**: This enzyme catalyzes the conversion of citrate to isocitrate through the intermediate cis-aconitate. Again, this does not involve the removal of hydrogen, making it an incorrect option.
- **Option 3: Pyruvate Dehydrogenase**: This enzyme converts pyruvate into acetyl-CoA by removing hydrogen. Since alpha-ketoglutarate dehydrogenase is similar in function and also requires cofactors for its activity, this is a strong candidate.
- **Option 4: Fumarate**: This compound is involved in the conversion of fumarate to malate in the TCA cycle and does not serve as a cofactor for alpha-ketoglutarate dehydrogenase.

4. **Conclusion**: After analyzing all the options, it is clear that the correct answer is **Option 3: Pyruvate Dehydrogenase**, as it is the only one that acts as a cofactor by facilitating the removal of hydrogen.

### Final Answer:
The correct answer is **Option 3: Pyruvate Dehydrogenase**.

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