Although glycogen synthase is present in a highly inactivated state in hepatocytes from streptozocin-induced diabetic rats, glucagon, vasopressin, and vanadate are still able to further decrease the basal activity of the enzyme. This inactivation was observed with the low-to-high glucose 6-phosphate activity ratio assay. The inactivation of glycogen synthase occurred concomitantly with the activation of glycogen phosphorylase. When hepatocytes from diabetic rats were incubated with [32P]phosphate and then with the agents and when the 32P-labeled glycogen synthase was immunoprecipitated, we observed that the 32P bound to the 88,000-M subunit increased in all cases. All the [32P]phosphate was located in two cyanogen bromide fragments of the enzyme, indicating that the enzyme was phosphorylated at multiple sites. The fragments were precisely those phosphorylated by glycogenolytic hormones in hepatocytes from normal rats. These results demonstrated that hepatic glycogen synthase, although highly inactive, is under potential hormonal control in diabetes and that the enzyme has not reached its maximal level of phosphorylation. Furthermore, they indicated that vanadate behaves as a glycogenolytic agent regarding its effects on glycogen-metabolizing enzymes in hepatocytes from diabetic rats.
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Original Articles|
June 01 1989
Control of Glycogen Synthase and Phosphorylase in Hepatocytes From Diabetic Rats: Effects of Glucagon, Vasopressin, and Vanadate
Joan E Rodríguez-Gil;
Joan E Rodríguez-Gil
Department of Biochemistry, Faculty of Veterinary Medicine, Autonomous University of Barcelona
Barcelona, Spain
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Anna M Gómez-Foix;
Anna M Gómez-Foix
Department of Biochemistry, Faculty of Veterinary Medicine, Autonomous University of Barcelona
Barcelona, Spain
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Joaquín Ariño;
Joaquín Ariño
Department of Biochemistry, Faculty of Veterinary Medicine, Autonomous University of Barcelona
Barcelona, Spain
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Joa J Guinovart;
Joa J Guinovart
Department of Biochemistry, Faculty of Veterinary Medicine, Autonomous University of Barcelona
Barcelona, Spain
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Fátima Bosch
Fátima Bosch
Department of Biochemistry, Faculty of Veterinary Medicine, Autonomous University of Barcelona
Barcelona, Spain
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Address correspondence and reprint requests to Joan J. Guinovart, Departament de Bioquimica, Facultat de Veterinèria, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain.
Diabetes 1989;38(6):793–798
Article history
Received:
September 13 1988
Revision Received:
February 13 1989
Accepted:
February 13 1989
PubMed:
2498142
Citation
Joan E Rodríguez-Gil, Anna M Gómez-Foix, Joaquín Ariño, Joa J Guinovart, Fátima Bosch; Control of Glycogen Synthase and Phosphorylase in Hepatocytes From Diabetic Rats: Effects of Glucagon, Vasopressin, and Vanadate. Diabetes 1 June 1989; 38 (6): 793–798. https://doi.org/10.2337/diab.38.6.793
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