PEP carboxylate enzyme of C4 carries out carboxylation of phosphoenolpyruvate into oxaloacetate..hence the ans is option B

Photosynthetic C4 cycle and the enzyme involved

The photosynthetic C4 cycle, also known as the C4 carbon fixation pathway, is an adaptation found in certain plants that helps them efficiently capture and utilize carbon dioxide (CO2) for photosynthesis. This pathway is particularly important in plants living in hot and dry environments, as it helps minimize water loss and enhance CO2 concentration around the enzyme responsible for initial CO2 fixation. The enzyme that catalyzes the photosynthetic C4 cycle is called PEP carboxylase.

Explanation of the answer

The correct answer to the question is option 'B' - PEP carboxylase. PEP carboxylase is the key enzyme involved in the initial step of the C4 carbon fixation pathway. This enzyme plays a critical role in capturing CO2 and converting it into a four-carbon compound called oxaloacetate (OAA).

Function of PEP carboxylase

PEP carboxylase has a higher affinity for CO2 than Rubisco, which is the main enzyme involved in the Calvin cycle (C3 cycle) of photosynthesis. This higher affinity allows PEP carboxylase to effectively fix CO2 even at low concentrations, which is advantageous in hot and dry environments where CO2 availability may be limited.

Comparison with Rubisco

Unlike Rubisco, PEP carboxylase does not have oxygenase activity, which means it does not participate in the wasteful process of photorespiration. Photorespiration occurs when Rubisco binds to oxygen instead of CO2, leading to the release of CO2 and energy consumption. By using PEP carboxylase in the C4 pathway, plants can minimize photorespiration and enhance their overall efficiency of carbon fixation.

Role of PEP carboxylase in the C4 pathway

In the C4 pathway, PEP carboxylase catalyzes the carboxylation of phosphoenolpyruvate (PEP) using CO2 as a substrate. This reaction results in the formation of OAA, which is subsequently converted into malate or aspartate. These four-carbon compounds are then transported to specialized cells called bundle sheath cells, where they release CO2 for the Calvin cycle, which occurs in the chloroplasts of these cells.

Conclusion

In summary, PEP carboxylase is the enzyme that catalyzes the photosynthetic C4 cycle. This enzyme plays a crucial role in capturing and efficiently utilizing CO2 in plants adapted to hot and dry environments. By utilizing PEP carboxylase in the C4 pathway, plants can enhance their photosynthetic efficiency, minimize water loss, and reduce the impact of photorespiration.