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

Abstract

In plants that show Crassulacean acid metabolism, phosphoenolpyruvate carboxylase catalyses the key step of CO 2 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 32 P i followed by extraction and immunoprecipitation of phosphoenolpyruvate carboxylase showed that only the night form contained 32 P. This suggests that the activity of the enzyme is controlled by a covalent modification mechanism.