Question:
What is the enzyme responsible for carboxylation in C4 plants?
What is the enzyme responsible for carboxylation in C4 plants?
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Remember the primary carbon-fixing enzymes:
- C3 Plants: RuBisCO (fixes \( \text{CO}_2 \) to Ribulose-1,5-bisphosphate).
- C4 Plants: PEP Carboxylase (fixes \( \text{CO}_2 \) to Phosphoenolpyruvate).
- C3 Plants: RuBisCO (fixes \( \text{CO}_2 \) to Ribulose-1,5-bisphosphate).
- C4 Plants: PEP Carboxylase (fixes \( \text{CO}_2 \) to Phosphoenolpyruvate).
Updated On: Aug 5, 2026
- Phosphoenol pyruvic acid (PEP) carboxylase
- Phosphophenol pyruvic acid (PEP) carboxylase
- Phospho pyruvic acid (PEP) carboxylase
- Phosphanol pyruvic acid (PEP) carboxylase
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The Correct Option is A
Solution and Explanation
Step 1: Understanding the Concept:
Carboxylation is the biochemical reaction in which a molecule of carbon dioxide (\( \text{CO}_2 \)) is fixed or incorporated into an organic substrate.
In C4 plants, this initial carbon fixation occurs in the mesophyll cells, using a specialized enzyme that has a high affinity for \( \text{CO}_2 \) and does not react with oxygen.
Step 2: Detailed Explanation:
Let us review the carbon fixation pathway in C4 plants:
The C4 Pathway (Hatch-Slack Cycle): In C4 plants, atmospheric carbon dioxide dissolves to form bicarbonate ions (\( \text{HCO}_3^- \)) in the mesophyll cytoplasm.
Primary Carboxylation: The primary acceptor of this carbon is a 3-carbon compound called phosphoenolpyruvate (PEP), or phosphoenol pyruvic acid.
The Enzyme: The reaction is catalyzed by the enzyme phosphoenol pyruvic acid carboxylase (commonly abbreviated as PEP carboxylase or PEPCase).
This enzyme combines PEP and \( \text{HCO}_3^- \) to form a 4-carbon organic acid, oxaloacetic acid (OAA):
\[ \text{PEP} + \text{HCO}_3^- \xrightarrow{\text{PEP Carboxylase}} \text{Oxaloacetate (OAA)} + \text{Pi} \]
Key Advantages: Unlike RuBisCO (the carbon-fixing enzyme in C3 plants), PEP carboxylase has a very high affinity for carbon dioxide and no oxygenase activity.
This prevents photorespiration, allowing C4 plants to photosynthesize efficiently under conditions of high temperature, drought, and low carbon dioxide levels.
Evaluating the options, "Phosphoenol pyruvic acid (PEP) carboxylase" is the correct biochemical name of this enzyme.
Step 3: Final Answer:
The enzyme responsible for primary carboxylation in C4 plants is Phosphoenol pyruvic acid (PEP) carboxylase.
Carboxylation is the biochemical reaction in which a molecule of carbon dioxide (\( \text{CO}_2 \)) is fixed or incorporated into an organic substrate.
In C4 plants, this initial carbon fixation occurs in the mesophyll cells, using a specialized enzyme that has a high affinity for \( \text{CO}_2 \) and does not react with oxygen.
Step 2: Detailed Explanation:
Let us review the carbon fixation pathway in C4 plants:
The C4 Pathway (Hatch-Slack Cycle): In C4 plants, atmospheric carbon dioxide dissolves to form bicarbonate ions (\( \text{HCO}_3^- \)) in the mesophyll cytoplasm.
Primary Carboxylation: The primary acceptor of this carbon is a 3-carbon compound called phosphoenolpyruvate (PEP), or phosphoenol pyruvic acid.
The Enzyme: The reaction is catalyzed by the enzyme phosphoenol pyruvic acid carboxylase (commonly abbreviated as PEP carboxylase or PEPCase).
This enzyme combines PEP and \( \text{HCO}_3^- \) to form a 4-carbon organic acid, oxaloacetic acid (OAA):
\[ \text{PEP} + \text{HCO}_3^- \xrightarrow{\text{PEP Carboxylase}} \text{Oxaloacetate (OAA)} + \text{Pi} \]
Key Advantages: Unlike RuBisCO (the carbon-fixing enzyme in C3 plants), PEP carboxylase has a very high affinity for carbon dioxide and no oxygenase activity.
This prevents photorespiration, allowing C4 plants to photosynthesize efficiently under conditions of high temperature, drought, and low carbon dioxide levels.
Evaluating the options, "Phosphoenol pyruvic acid (PEP) carboxylase" is the correct biochemical name of this enzyme.
Step 3: Final Answer:
The enzyme responsible for primary carboxylation in C4 plants is Phosphoenol pyruvic acid (PEP) carboxylase.
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