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Regulation of glycogen synthetase. Specificity and stoichiometry of phosphorylation of the skeletal muscle enzyme by cyclic 3':5'-AMP-dependent protein kinase


, : Regulation of glycogen synthetase. Specificity and stoichiometry of phosphorylation of the skeletal muscle enzyme by cyclic 3':5'-AMP-dependent protein kinase. Journal of Biological Chemistry 250(14): 5407-5412

Complete conversion of skeletal muscle glycogen synthetase from the I form to the D form requires incorporation of 2 mol of phosphate per enzyme subunit (90,000 g). Incubation of sythetase I with low concentrations of adenosine 3':5'-monophosphate(cAMP)-dependent protein kinase (10 units/ml) and ATP (0.1 to 0.3 mM) plus magnesium acetate (10 mM) results in incorporation within 1/2 hour of 1 mol of phosphate persubunit concomitant with a decrease in the synthetase activity ratio (minus glucose-6-P/plus glucose-6-P) from 0.85 to 0.25. Further incubation for 6 hours does not greatly increase the phosphate content of the synthetase or promote conversion to the D form. This level of phosphorylation is not increased by raising the concentration of protein kinase to 150 units/ml and is not influenced by the presence of glucose-6-P, UDP-glucose, or glycogen. However, at protein kinase concentrations of 10,000 to 30,000 units/ml a second mol of phosphate is incorporated per subunit, and the sythetase activity ratio decreases to 0.05 or less. In addition to the 2 mol of phosphate persubunit which are required for formation of sythetase D, further phosphorylation can be observed which is not associated with changes in synthetase activity. This phosphorylation occurs at a slow rate, is increased by raising the ATP concentration to 2 to 4mM, and is not blocked by the heat-stable protein inhibitor of cAMP-dependent protein kinase. These data indicate that skeletal muscle glycogen synthetase contains multiple phosphorylation sites only two of which are involved in the synthetase I to D conversion.

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Accession: 041210793

PMID: 167014

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Related references

Soderling, T.R., 1975: Regulation of glycogen synthetase specificity and stoichiometry of phosphorylation of the skeletal muscle enzyme by cyclic amp dependent protein kinase. Journal of Biological Chemistry 250(14): 5407-5412

Sivaramakrishnan, S.; High, C.W.; Walsh, D.A., 1982: Regulation of cardiac glycogen synthase ec 2.4.1.11 by phosphorylation catalysis of inactivation by cyclic amp dependent and cyclic amp independent protein kinases and comparison with the phosphorylation of the skeletal muscle enzyme. Glycogen synthase was purified from bovine heart to near homogeneity by a procedure including zonal sucrose gradient ultracentrifugation. The purified enzyme had a subunit MW of 88,000 .+-. 2000, an I/D [active form/less active phosphorylated form...

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Soderling T.R., 1975: Specificity and stoichiometry of phosphorylation of muscle glycogen synthetase by protein kinases. Federation Proceedings 34(3): 514

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Nimmo, H.G.; Proud, C.G.; Cohen, P., 1976: The phosphorylation of rabbit skeletal muscle glycogen synthase ec 2.4.1.11 by glycogen synthase kinase 2 and cyclic amp dependent protein kinase ec 2.7.1.37. Purified glycogen synthase [EC 2.4.1.11] is contaminated with traces of 2 protein kinases that can phosphorylate the enzyme. One is protein kinase [EC 2.7.1.37] dependent on cyclic[c]AMP and the 2nd is an activity termed glycogen synthase kinase-2...