title: Effect of glucose phosphorylation on the activation by insulin of skeletal muscle glycogen synthase.
abstract: The effect of insulin injection on skeletal muscle glycogen synthase activation was studied in anesthetized, normal, fed rats. Insulin stimulated the conversion of glycogen synthase to the active I form, increased the concentration of glucose 6-phosphate, and activated glycogen synthase phosphatase. A close correlation between glucose 6-phosphate concentrations, per cent glycogen synthase in the active I form, and phosphatase activity was found. When boiled extracts of muscle from control and insulin-injected animals were added to glycogen pellets containing phosphatase 1G, the difference in phosphatase activity between muscle extracts from insulin-injected and control rats was restored, indicating that the phosphatase was activated by heat-stable factors. Deproteinized muscle extracts from control and insulin-injected rats, at concentrations equivalent to those present in muscle, were tested for the activation of glycogen synthase by purified protein phosphatases 1 and 2A. The activation with the insulin extracts was four-fold larger than with the control extracts. When the extracts from insulin-injected rats were treated with glucose 6-phosphatase, the difference in activation with the control rat extracts was canceled. It would appear that, as in other insulin sensitive tissues, in skeletal muscle the increase in glucose 6-phosphate subsequent to the activation of glucose transport by insulin contributes to the activation of glycogen synthase.
authors.affiliation: Department of Pharmacology, Medical School, University of Virginia, Charlottesville 22908, USA.
authors.forename: C
authors.initials: C
authors.lastname: Villar-Palasi
mesh_terms: D000818:Animals; D004789:Enzyme Activation / Q000187:drug effects; D005958:Glucosephosphates / Q000378:metabolism*; D006006:Glycogen Synthase / Q000378:metabolism*; D006007:Glycogen-Synthase-D Phosphatase / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D009132:Muscles / Q000201:enzymology*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
chemical_list: D005958:Glucosephosphates; D007328:Insulin; D006006:Glycogen Synthase; D006007:Glycogen-Synthase-D Phosphatase