Catalytic activities of the holoenzyme and its single subunits in insect cells. A, Insect cell extracts containing only expressed LS, SS, or both subunits were assayed in the pyrophosphorolysis direction (█) or in the presence of 10 mm 3-PGA (▤), 20 mm Pi (□), or both 10 mm 3-PGA and 20 mm Pi (▨). Enzyme activity from extruded endosperm was assayed immediately after extraction. B and C, Effect of 3-PGA and Pi on catalytic activity of the purified AGPase. Enzyme activity of the purified recombinant AGPase was determined in the ADP-Glc synthesis direction in the presence of 3-PGA at different concentrations (B), or with elevated levels of Pi (C) together with 3-PGA in the assay medium: 0 mm (○), 5 mm (●), and 10 mm (▴). D and E, Effect of 3-PGA and Pi on enzyme activity of SS expressed in insect cells. D, Insect cell extract containing only the expressed SS was assayed in the pyrophosphorolysis direction with various concentrations of 3-PGA. E, Cell extract was assayed in the presence of 10 mm 3-PGA together with various concentration of Pi.