Glycogen synthase (GS) is a key enzyme in the regulation of glycogen synthesis. There are two main isoforms of mammalian GS: the muscle and the liver isoform (1-2). Muscle GS is expressed in several tissues, and liver GS appears to be tissue specific (3). GS is regulated by multi-site phosphorylation and by the binding of allosteric ligands. Phosphorylation leads to inactivation of GS, but activity is restored by the binding of the allosteric activator glucose-6-phosphate, which induces its dephosphorylation and activation (4). |