Which of the following membrane bound complex in mitochondria is not a proton pump?

Options

A. NADH dehydrogenase
B. Succinate dehydrogenase
C. Cytochrome `bc_1`
D. Cytochrome c oxidase

Answer

To solve the question "Which of the following membrane-bound complexes in mitochondria is not a proton pump?", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks for a membrane-bound complex in mitochondria that is specifically not a proton pump. This means we need to identify which of the given options does not function to pump protons across the mitochondrial membrane.

2. **Identify the Proton Pumps**: In mitochondria, there are several complexes that act as proton pumps. The well-known proton pumps include:
- **Cytochrome bc1 complex** (also known as Complex III)
- **Cytochrome c oxidase** (also known as Complex IV)
- **NADH dehydrogenase** (also known as Complex I)

3. **Identify the Non-Proton Pump**: Among the complexes listed, we need to find the one that does not function as a proton pump. The complex that does not pump protons is:
- **Succinate dehydrogenase** (also known as Complex II)

4. **Conclusion**: Based on the identification, the answer to the question is **Succinate dehydrogenase**, as it does not act as a proton pump.

### Final Answer:
**Succinate dehydrogenase** is the membrane-bound complex in mitochondria that is not a proton pump.

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