How does insulin activate glycogen synthase?

A major physiological role of insulin is formation of glycogen from glucose in a number of tissues. Glycogen formation is controlled by the activity of a glycogen synthase. This enzyme is active in the dephosphorylated state and inactive in the phosphorylated state. Insulin mediates its action by an inhibition of the phosphorylated state of this enzyme. In both muscle and liver, insulin acts to regulate glycogen synthase via PT-3-kinase mediated activation of protein phosphatase 1, a phosphatase that dephosphorylates (and activates) glycogen synthase. Insulin trigger activation of glycogen synthase b by blocking the activity of GSK 3 (Glycogen Synthetase kinases 3) and activating a phosphoprotein phosphatase (PP1 in muscle). The GSK-3 phosphorylates glycogen synthase and making it inactive whereas PP1 dephosphorylates glycogen synthase b making it active.