ABSTRACT
Glycogen degradation and glycogen synthesis are controlled both by allosteric regulation and by hormonal control. Glycogen synthase is also regulated by covalent modification and allosteric interactions. The enzyme exists as an active glycogen synthase a and a normally inactive glycogen synthase b. Glycogen metabolism is tightly controlled by hormones. When blood glucose levels fall, glucagon is secreted by the cells of the pancreas and acts on the liver to stimulate glycogen breakdown to glucose which is then released into the bloodstream to boost blood glucose levels again. To prevent the operation of a futile cycle, it is essential that glycogen synthesis is switched off during epinephrine or glucagon stimulation of glycogen breakdown. Insulin is released into the bloodstream by the ß cells of the pancreas when blood glucose levels are high after feeding, and stimulates glycogen synthesis to store excess glucose as glycogen.
