Glucose-6-phosphate stimulation of human muscle glycogen synthase phosphatase

The influence of glucose-6-phosphate (glucose-6-P) on skeletal muscle glycogen synthase phosphatase was examined in normal glucose-tolerant Southwest American Indians. Phosphatase was stimulated with physiological concentrations of glucose-6-P and inhibited by ATP (5 mmol/L) and glycogen (0.1%). Phosphatase activity was measured before and after insulin infusion using the euglycemic clamp technique. Although glycogen synthase fractional activity increased in all subjects, this increase was not related to a change in phosphatase activity in the absence or presence of glucose-6-P. These results suggest that glycogen synthase phosphatase from human muscle can be regulated by physiological concentrations of glucose-6-P, ATP, and glycogen, and that insulin does not alter glucose-6-P stimulation of the enzyme in normal subjects.