The enzymes ribulose biphosphate carboxylase-oxygenase and phosphoenol pyruvate carboxylase are activated by

Options

A. `Zn`
B. `Mo`
C. `Mn`
D. `Mg`.

Answer

To answer the question regarding the activation of the enzymes ribulose biphosphate carboxylase-oxygenase (Rubisco) and phosphoenol pyruvate carboxylase (PEP carboxylase), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Enzymes**: The question mentions two specific enzymes: ribulose biphosphate carboxylase-oxygenase (Rubisco) and phosphoenol pyruvate carboxylase (PEP carboxylase). Both of these enzymes play crucial roles in the process of photosynthesis, particularly in the dark reactions.

2. **Understand Their Functions**:
- **Rubisco**: This enzyme is responsible for fixing carbon dioxide in the Calvin cycle of photosynthesis. It can also act as an oxygenase under certain conditions, leading to photorespiration.
- **PEP Carboxylase**: This enzyme is involved in the fixation of carbon dioxide in C4 and CAM plants, helping to efficiently capture CO2.

3. **Activation of Enzymes**: Enzymes often require specific cofactors or activators to function properly. In this case, we need to determine which mineral element activates both Rubisco and PEP carboxylase.

4. **Consider the Options**: The options provided are zinc, molybdenum, manganese, and magnesium. We need to evaluate which of these is known to activate the mentioned enzymes.

5. **Research and Knowledge**: Based on biological knowledge:
- Magnesium is known to be a crucial cofactor for many enzymes, including Rubisco and PEP carboxylase. It plays a significant role in stabilizing the structure of these enzymes and is essential for their catalytic activity.

6. **Conclusion**: Therefore, the correct answer to the question is that both ribulose biphosphate carboxylase-oxygenase and phosphoenol pyruvate carboxylase are activated by **magnesium**.

### Final Answer:
The enzymes ribulose biphosphate carboxylase-oxygenase and phosphoenol pyruvate carboxylase are activated by **magnesium**.

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