Question

Name the two important enzymes of C₄ pathway, and explain their role in fixing CO₂?

Answer 1

The two important enzymes of C₃ and C₄ pathways are RuBisCO and PEPcase respectively. RuBisCO is the primary CO₂ acceptor in C₃ plants, while PEPcase is the primary CO₂ acceptor in C₄ plants.

Role of RuBisCO: RuBisCO is also called RUBP Carboxylase Oxygenase. As the name indicates; it has both carboxylase and oxygenase actions. This enzyme has more affinity toward carbon dioxide than oxygen. However, some of these enzymes fix oxygen in C₃ plants through a process called photorespiration. Photorespiration is an inefficient process because it does not create any beneficial product for the plants. Moreover, it also reduces carbon fixation in C₃ plants.

Role of PEP case: This is the major carbon dioxide acceptor in C₄ plants. However, RuBisCO is also present in these plants. PEPcase binds with carbon dioxide to produce a 4-carbon compound oxaloacetic acid (OAA). OAA is eventually converted into carbon dioxide. Carbon dioxide eventually enters the Calvin cycle and carbohydrates are generated. It is crucial to memorize that the Calvin Cycle is mutual in both C₃ and C₄ plants.