Reduced Glutathione as an Effector of Phosphoenolpyruvate Carboxylase of the Crassulacean Acid Metabolism Plant Sedum praealtum D.C.

Reduced glutathione, but not mercaptoethanol or dithiothreitol, inhibits phosphoenolpyruvate carboxylase (PEPC) in desalted leaf extracts from Sedum praealtum D.C. The inhibition is more evident at low pH values (< 7.2) and becomes increasingly smaller at higher pH. In the presence of the inhibitor, the hyperbolic rate curve of night PEPC is transformed to sigmoid and the S(0.5) is increased. When the enzyme is extracted during the day, the rate curve is sigmoid and it is not changed by the inhibitor, though the S(0.5) is further increased. Oxidized glutathione is completely inactive. Levels of reduced glutathione in leaf tissue are distinctly higher in the light. A role of photosynthetically reduced glutathione in the regulation of PEPC in Crassulacean acid metabolism species appears probable.