title: Activation of rat liver and rabbit skeletal muscle glycogen synthases by rat liver cytosolic protein phosphatases.
abstract: To gain more insight into the nature of the substrate specificity of protein phosphatases, four forms of glycogen synthase D were used as substrates for previously characterized protein phosphatases, IA, IB, and II, from rat liver cytosol. The phosphatase activity was measured as the conversion of glycogen synthase D to synthase I. While glycogen synthase isolated from rat liver as the D-form was activated mainly by phosphatase IA, rabbit skeletal muscle glycogen synthase previously phosphorylated in vitro by cyclic AMP-dependent protein kinase or phosphorylase kinase was activated efficiently by phosphatases IA, IB, and II. Glycogen synthase isolated from rabbit skeletal muscle as the D-form, however, was a poor substrate for all three phosphatases. These results suggest that the phosphorylation state as well as the primary structure of synthase D markedly affects the rate of its activation by individual protein phosphatases. A protein phosphatase released from rat liver particulate glycogen, on the other hand, activated all forms of synthase D used here readily and at about the same rate.
authors.affiliation: Biochemistry Laboratory, Tohoku University, Miyagi.
authors.forename: A
authors.initials: A
authors.lastname: Hiraga
authors.forename: S
authors.initials: S
authors.lastname: Tamura
authors.forename: K
authors.initials: K
authors.lastname: Kikuchi
authors.forename: S
authors.initials: S
authors.lastname: Tsuiki
mesh_terms: D000818:Animals; D003600:Cytosol / Q000201:enzymology; D004789:Enzyme Activation; D006006:Glycogen Synthase / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D009132:Muscles / Q000201:enzymology*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D011817:Rabbits; D051381:Rats; D013379:Substrate Specificity
chemical_list: D006006:Glycogen Synthase; D010749:Phosphoprotein Phosphatases