Phosphorylation of the glycogen‐binding subunit of protein phosphatase‐1G by cyclic‐AMP‐dependent protein kinase promotes translocation of the phosphatase from glycogen to cytosol in rabbit skeletal muscle

Abstract

The glycogen‐bound form of protein phosphatase‐1 (termed protein phosphatase‐1_G) is composed of the catalytic (C) subunit complexed to a glycogen‐binding (G) subunit that anchors the enzyme to glycogen [Strålfors et al. (1985) Eur. J. Biochem. 149, 295–303]. Incubation of purified protein phosphatase‐1_G with cyclic‐AMP‐dependent protein kinase and MgATP, which leads to stoichiometric phosphorylation of the G‐subunit [Caudwell et al. (1986) FEBS Lett. 194, 85–90], was found to promote the release of the phosphatase from glycogen; similar observations were made using glycogen‐protein particle preparations. An intravenous injection of adrenaline decreased protein phosphatase‐1 activity associated with the glycogen‐protein particles by 50% with a corresponding increase in the amount present in the cytosol. By contrast, adrenaline did not affect the distribution of glycogen synthase or glycogen phosphorylase which remained entirely bound to glycogen in these experiments. The specific release of protein phosphatase‐1 from glycogen may facilitate its inactivation by inhibitor‐1 in the cytosol, thereby preventing dephosphorylation of the glycogen metabolising enzymes. Translocation of protein phosphatase‐1 may represent a novel mechanism for the activation of glycogenolysis and inhibition of glycogen synthesis by adrenaline.