Which one of the following statements regarding PEPCase is INCORRECT?

Correct option is A

The question asks for the incorrect statement regarding PEPCase (Phosphoenolpyruvate Carboxylase).

1. During the day, C4 PEPCase is inactive whereas CAM PEPCase is active.
• Incorrect. C4 plants and CAM plants regulate PEPCase activity differently. In C4 plants, PEPCase is active during the day to fix CO₂ into Oxaloacetate, whereas in CAM plants, PEPCase is active at night to minimize water loss. Hence, the given statement is incorrect.
2. PEPCase is inactivated by dephosphorylation.
• Correct. PEPCase activity is regulated by phosphorylation. The enzyme is activated by phosphorylation and inactivated by dephosphorylation.
3. PEPCase kinase phosphorylates PEPCase.
• Correct. PEPCase kinase is responsible for phosphorylating PEPCase, activating it in response to certain environmental conditions.
4. The synthesis of PEPCase kinase is modulated by circadian rhythm in CAM leaves.
• Correct. In CAM plants, PEPCase kinase activity follows a circadian rhythm, regulating the phosphorylation state of PEPCase based on the day-night cycle.

Information Booster

1. PEPCase Role: PEPCase is a crucial enzyme in C4 and CAM metabolism that catalyzes the fixation of CO₂ into oxaloacetate.
2. C4 Plants: These plants (e.g., maize, sugarcane) use PEPCase to capture CO₂ during the daytime, storing it as malate for later use in the Calvin cycle.
3. CAM Plants: CAM plants (e.g., cacti, pineapples) fix CO₂ at night using PEPCase to store it as malate, which is then used during the day for photosynthesis.
4. Regulation of PEPCase: The activity of PEPCase is controlled via phosphorylation. Phosphorylation activates it, while dephosphorylation inactivates it.
5. Role of PEPCase Kinase: PEPCase kinase is an enzyme that phosphorylates and activates PEPCase, especially in CAM plants.
6. Circadian Rhythm in CAM Plants: The synthesis of PEPCase kinase in CAM plants is regulated by circadian rhythms, ensuring the enzyme functions optimally according to the day-night cycle

Additional Information

• Option 2 (Correct Statement: PEPCase is inactivated by dephosphorylation)
• PEPCase is activated when phosphorylated by PEPCase kinase and inactivated when dephosphorylated.
• Option 3 (Correct Statement: PEPCase kinase phosphorylates PEPCase)
• PEPCase kinase is an enzyme that adds a phosphate group to PEPCase, increasing its activity.
• Option 4 (Correct Statement: PEPCase kinase synthesis is controlled by circadian rhythm in CAM leaves)
• In CAM plants, the production of PEPCase kinase follows a circadian rhythm, ensuring PEPCase is active at night when CO₂ fixation occurs.