Glycogen synthase is regulated by multiple phosphorylation/ dephosphorylation events and by allosteric effectors. The liver isoform (GYS2, 81 kDa) is about 70% identical to the muscle isoform (GYS1, 84 kDa) and has several phosphorylation sites near the N- and C-terminus [23]. These sites are phosphorylated in vitro by kinases such as protein kinase A, phosphorylase kinase, protein kinase C, protein kinases CK1 and CK2, glycogen synthase kinase 3 and AMP-activate protein kinase