Phosphoenolpyruvate carboxylase, which catalyses the nocturnal fixation of CO2 in Crassulacean acid metabolism (CAM) plants, is regulated by reversible phosphorylation. The phosphorylated ‘night’ form of the enzyme is ten-fold less sensitive to inhibition by malate than is the dephosphorylated ‘day’ form. The phosphoenolpyruvate carboxylase of the CAM plant Bryophyllum fedtschenkoi can be dephosphorylated by rabbit muscle protein phosphatase type 2A but not by type 1. B. fedtschenkoi leaves contain protein phosphatase activity that can dephosphorylate phosphoenolpyruvate carboxylase. Inhibitor studies show that this enzyme is a type 2A protein phosphatase.
