Diurnal changes in the properties of phosphoenolpyruvate carboxylase in Bryophyllum leaves: a possible co valent modification

In plants that show Crassulacean acid metabolism, phosphoenolpyruvate carboxylase catalyses the key step of CO2 fixation at night. We show here that the properties of this enzyme from Bryophyllum fedtschenkoi undergo marked changes between night and day; the night form is much less sensitive to feedback inhibition by malate than is the day form. Incubation of leaves with 32Pi followed by extraction and immunoprecipitation of phosphoenolpyruvate carboxylase showed that only the night form contained 32P. This suggests that the activity of the enzyme is controlled by a covalent modification mechanism.