Change in Properties of Phosphoenolpyruvate Carboxylase From the Crassulacean Acid Metabolism Plant Mesembryanthemum crystallinum After Isolation

Abstract

Phosphoenolpyruvate carboxylase (EC 4.1.1.31) in desalted extracts from the inducible crassulacean acid metabolism plant M. crystallinum exists in a highly malate-sensitive state when isolated from plants in the light, and after isolation rapidly changes into a less sensitive state typical of the dark period. Loss of sensitivity to malate inhibition after isolation is largely prevented when the enzyme is extracted and stored at acid pH and in the presence of malate. This demonstrates that, in addition to its effect as a strong inhibitor of enzyme catalysis during the light, malate may also maintain the highly malate-sensitive state of phosphoenolpyruvate carboxylase during the light, particularly in combination with a lowered cytoplasmic pH. These experiments also establish conditions necessary for the study of the molecular basis for the change in properties of phosphoenolpyruvate carboxylase.