Adenosine Diphosphate Glucose Pyrophosphorylase

Abstract

The spinach leaf adenosine diphosphate glucose pyrophosphorylase has been purified about 260-fold. The enzyme was activated by 3-phosphoglycerate and other glycolytic intermediates, and was inhibited by inorganic phosphate and ADP. Phosphate inhibition could be overcome by increasing 3-phosphoglycerate concentrations. ADP inhibition could be only partially overcome by increasing 3-phosphoglycerate concentrations. The 3-phosphoglycerate saturation curve is hyperbolic at neutral pH. At alkaline pH, however, the curve is sigmoidal. Kinetic studies suggest that the activators fructose diphosphate and phosphoenolpyruvate bind to the same sites as 3-phosphoglycerate. These results suggest a mechanism for the regulation of starch synthesis in spinach leaf chloroplasts.