[32] Liver calmodulin-dependent glycogen synthase kinase

This chapter discusses liver calmodulin-dependent glycogen synthase kinase. Calmodulin-dependent glycogen synthase kinase, which catalyzes the transfer of the γ-phosphate of ATP to serine seven residues from the amino terminus of glycogen synthase, has been isolated from liver. This kinase is completely dependent on the presence of calmodulin and calcium for activity and completely inhibited by trifluoperazine. Calmodulin-dependent glycogen synthase kinase is active toward both skeletal muscle glycogen synthase and liver glycogen synthase but does not phosphorylate skeletal muscle phosphorylase, liver phosphorylase, skeletal muscle or cardiac myosin light chain, liver pyruvate kinase, casein, or histone IIA. It catalyzes the rapid incorporation of synthase subunit resulting in partial inactivation of glycogen synthase. Glycogen synthase α has been purified from rabbit skeletal muscle. The major steps used in purifying liver calmodulin-dependent glycogen synthase kinase are outlined in the chapter. This procedure is used to reproducibly purify the enzyme from rabbit and rat liver.