ADP glucose pyrophosphorylase from maize endosperm

Abstract

ADP-glucose pyrophosphorylase was isolated from maturing seeds of starchy maize. Several glycolytic intermediates activated the enzyme. 3-Phosphoglycerate and fructose 6-phosphate were the best activators. 3-Phosphoglycerate increased the maximal velocity of the enzyme-catalyzed reaction and increased the affinity of the enzyme toward the substrates ATP, α-glucose 1-phosphate, and ADP-glucose. The hyperbolic 3-phosphoglycerate saturation curve became sigmoid in the presence of inorganic phosphate, an inhibitor. The results suggest that regulation of starch biosynthesis in nonphotosynthetic tissue occurs at the level of ADP-glucose formation.