The enzymes acting as both carboxylase at one time & oxygenase at another time

Options

A. PEP carboxylase
B. RUBISCO
C. Carbonic anhydrase
D. ATP ase

Answer

To solve the question regarding the enzymes that act as both carboxylase and oxygenase, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**:
- We need to identify an enzyme that can function as both a carboxylase and an oxygenase.

2. **Defining Carboxylase and Oxygenase**:
- A **carboxylase** is an enzyme that catalyzes the addition of carbon dioxide (CO2) to a substrate.
- An **oxygenase** is an enzyme that incorporates oxygen (O2) into a substrate.

3. **Evaluating the Options**:
- The options provided are:
- A) PEP carboxylase
- B) Rubisco
- C) Carbonic anhydrase
- D) ATPase

4. **Analyzing Each Option**:
- **PEP Carboxylase**: This enzyme only acts as a carboxylase, fixing CO2 into phosphoenolpyruvate (PEP). It does not function as an oxygenase.
- **Rubisco (Ribulose bisphosphate carboxylase/oxygenase)**: This enzyme can catalyze the carboxylation of ribulose bisphosphate (RuBP) during the Calvin cycle and can also act as an oxygenase under high oxygen concentrations, leading to photorespiration.
- **Carbonic Anhydrase**: This enzyme catalyzes the conversion of carbon dioxide to carbonic acid and does not function as an oxygenase.
- **ATPase**: This enzyme hydrolyzes ATP to ADP and inorganic phosphate and does not have carboxylase or oxygenase activity.

5. **Conclusion**:
- The only enzyme that acts as both a carboxylase and an oxygenase is **Rubisco**. Therefore, the correct answer is **Rubisco**.

### Final Answer:
Rubisco (Ribulose bisphosphate carboxylase/oxygenase) acts as both a carboxylase and an oxygenase.

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