A complex enzyme system functional in Krebs cycle is

Options

A. Citrate sysnthetase
B. Isocitrate dehydrogenase.
C. Oxalosuccinate decarboxylase
D. `alpha`-ketoglutarate dehydrogenase.

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for a complex enzyme system that is functional in the Krebs cycle. The Krebs cycle, also known as the citric acid cycle, is a series of chemical reactions used by all aerobic organisms to generate energy.

2. **Identifying Key Enzymes**: In the Krebs cycle, there are several key enzymes that facilitate various reactions. We need to identify which of these is considered a complex enzyme system.

3. **Analyzing the Options**: The options provided in the question likely include various enzymes involved in the Krebs cycle. Among these, we need to determine which one is a complex enzyme system.

4. **Identifying Alpha-Ketoglutarate Dehydrogenase**: The enzyme alpha-ketoglutarate dehydrogenase is known to be a major enzyme in the Krebs cycle. It catalyzes the fifth step of the cycle, where alpha-ketoglutarate is converted into succinyl CoA.

5. **Understanding the Reaction**: In this reaction, alpha-ketoglutarate (a 5-carbon molecule) reacts with coenzyme A (CoA) to produce succinyl CoA (a 4-carbon molecule), releasing carbon dioxide (CO2) and generating NADH from NAD+ in the process.

6. **Conclusion**: Based on the analysis, the correct answer to the question is that the complex enzyme system functional in the Krebs cycle is **alpha-ketoglutarate dehydrogenase**.

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