The Influence of Hexose and Insulin on Glycogen Synthetase in HeLa Cells

Abstract

Abstract 1. d-Glucose or d-galactose in low concentration promptly rendered the glycogen synthetase of growing HeLa cells more dependent on d-glucose 6-phosphate. 2. An essentially inverse relationship obtained between the glucose-6-phosphate-independent fraction of the enzyme and the cellular concentration of glycogen. Some exceptions noted to this general case may have been due to unequal rates of glycogenolysis during the detachment of growing cells. 3. Insulin lowered the glucose 6-phosphate dependence of the enzyme and counteracted the effects observed with hexose. However, the locus of insulin action was distinct from that of hexose or glycogen. Insulin permitted a higher independence of the enzyme at a given glycogen concentration. 4. The control of phosphorylase kinase and of glycogen synthetase by hexose is interpreted as a negative feedback system, which prevents the overaccumulation of glycogen when substrate is abundant and the depletion of limited glycogen reserves when substrate is deficient. The unique suitability of the effectors glucose 6-phosphate and 5'-adenylate is discussed.