The Role of Cyclic-AMP-Dependent Protein Kinase in the Regulation of Glycogen Metabolism in Mammalian Skeletal Muscle

Abstract

Publisher Summary This chapter discusses the role of cyclic-AMP-dependent protein kinase in the regulation of glycogen metabolism in mammalian skeletal muscle. When assayed at optimal ATP-Mg-concentrations and in the presence of saturating amounts of Ca2+, purified phosphorylase kinase has a very low activity at physiological pH (6.8) relative to the activity at pH 8.2. Phosphorylation of α subunit of phosphorylase kinase controls the rate of dephosphorylation of the β subunit catalyzed by phosphorylase kinase phosphatase. The conversion of phosphorylase kinase a to phosphorylase b correlates with dephosphorylation of the β subunit, and the rate of dephosphorylation of the enzyme in the absence of divalent cations is determined by the extent of phosphorylation of the α subunit. Phosphorylation of the α subunit alters the conformation of phosphorylase kinase in such a way that it facilitates the action of phosphorylase kinase phosphatase on the β subunit. Cyclic-AMP-dependent protein kinase plays two roles: (1) it activates the enzyme through phosphorylation of the β subunit and (2) it determines the time at which dephosphorylation of the β subunit and inactivation of the enzyme can become rapid through phosphorylation of the α subunit.