Glucose 6-phosphate Plays a Central Role in the Activation of Glycogen Synthase by Glucose in Hepatocytes

The state of activation of glycogen synthase enhanced by glucose, other sugars and gluconeogenic precursors shows a strong positive correlation with the intracellular concentrations of glucose 6-P when ATP concentrations remain constant. The concentrations of glucose 6-P achieved upon incubation of hepatocytes with glucose plus mannoheptulose, an inhibitor of glucokinase and hexokinase, were lower than those found when the incubation was carried out with glucose alone. Under these conditions, in keeping with the decrease in glucose 6-P, the activation of glycogen synthase by glucose was also impaired. On the other hand the inactivation of glycogen phosphorylase was not altered in the presence of mannoheptulose.