Question

The enzyme which catalyses the carbon dioxide fixation in $C_4$ cycle is

• A. RuBP carboxylase
• B. PEP carboxylase
• C. Carbonic anhydrase
• D. None of the above

Answer 1

Answer: (B)

PEP carboxylase

RUBISCO is a very large four-subunit enzyme present in the chloroplast stroma and catalyze carboxylation of RuBP followed by immediate splitting of unstable product into 3 phosphoglyceraldehyde. PEP carboxylate enzyme of C4 carries out carboxylation of phosphoenolpyruvate into oxaloacetate. Unlike RUBISCO, it does not have oxidation acitivity and no photorespiration. Correct answer is B.