Calcium-dependent regulation of glycogen synthase activity in a muscle glycogen particle |
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Authors: | Ashok K. Srivastava Balwant S. Khatra Thomas R. Soderling |
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Affiliation: | Howard Hughes Medical Institute and Department of Physiology, Vanderbilt University, Nashville, Tennessee 37232 U.S.A. |
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Abstract: | The calcium-dependent inactivation of glycogen synthase in an isolated glycogen-protein complex (glycogen pellet) from rabbit skeletal muscle has been investigated. Addition of 1 mm Ca2+, 10 mm Mg2+, and 1 mm ATP-γ-S to a concentrated suspension of glycogen pellet resulted in a rapid activation of glycogen phosphorylase concomitant with an inactivation of glycogen synthase. These conversion reactions were blocked by ethylene glycol bis(β-aminoethyl ether) N, N′-tetraacetic acid or by pretreatment of the complex with an antiserum to purified phosphorylase kinase. These data suggest that in the glycogen-protein complex, which may be a functional unit of glycogen metabolism in vivo, phosphorylase kinase can catalyze a Ca2+-dependent activation of glycogen phosphorylase synchronized with an inactivation of glycogen synthase. If under similar conditions phosphoprotein phosphatase activity was assayed using exogenous [32P]phosphorylase, there was an apparent inactivation of the phosphatase. Evidence is presented that this apparent inactivation of phosphatase was due to an accumulation of endogenous phosphorylase a which acted as an inhibitor to the exogenous [32P]-phosphorylase. |
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