In case of `C_4` - plants , which enzyme fixes the `CO_2` released during decarboxylation of malate

Options

A. RuBisCO
B. MDH
C. PEPase
D. None of these

Answer

To answer the question regarding which enzyme fixes the CO₂ released during the decarboxylation of malate in C₄ plants, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding C₄ Photosynthesis**:
- C₄ plants have a specialized mechanism for photosynthesis that allows them to efficiently fix CO₂, especially in conditions of high light intensity and temperature.

2. **Formation of Oxaloacetic Acid**:
- In the mesophyll cells of C₄ plants, CO₂ is initially fixed to phosphoenolpyruvate (PEP) by the enzyme PEP carboxylase (often abbreviated as PEPcase). This reaction produces oxaloacetic acid (OAA), which is a four-carbon compound.

3. **Conversion to Malate**:
- The oxaloacetic acid is then converted into malate (another four-carbon compound) through a series of reactions, which involves the reduction of OAA using NADPH.

4. **Transport to Bundle Sheath Cells**:
- The malate is transported from the mesophyll cells to the bundle sheath cells where it undergoes decarboxylation.

5. **Decarboxylation of Malate**:
- In the bundle sheath cells, malate is decarboxylated to release CO₂ and pyruvate. This reaction is catalyzed by the enzyme malic enzyme.

6. **Fixation of CO₂**:
- The CO₂ released during the decarboxylation of malate is then fixed into the Calvin cycle (C₃ cycle) by the enzyme ribulose bisphosphate carboxylase/oxygenase (commonly known as Rubisco).

7. **Conclusion**:
- Therefore, the enzyme that fixes the CO₂ released during the decarboxylation of malate in C₄ plants is **Rubisco**.

### Final Answer:
The enzyme that fixes the CO₂ released during the decarboxylation of malate in C₄ plants is **Rubisco**.

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