Regulation of muscle glycogen synthase phosphorylation and kinetic properties by insulin, exercise, adrenaline and role in insulin resistance

Research output: Contribution to journalArticlepeer-review

Authors

Colleges, School and Institutes

External organisations

  • Natl. Inst. of Occupational Health

Abstract

In mammals, excess carbohydrate is stored as glycogen and glycogen synthase is the enzyme that incorporates glucose units into the glycogen particle. Glycogen synthase activity is regulated by phosphorylation and allosterically activated by glucose 6-phosphate. Phosphorylation of nine serines by different kinases regulates glycogen synthase affinity for glucose 6-phosphate and its substrate UDP-glucose. Glucose 6-phosphate increases both enzyme activity and substrate affinity. Insulin and exercise increase glycogen synthase affinity for glucose 6-phosphate and activity whereas high glycogen content and adrenaline decrease affinity for glucose 6-phosphate and activity. However, insulin, exercise and adrenaline also regulate intracellular concentration of glucose 6-phosphate which will influence in vivo glycogen synthase activity. Importantly, type 2 diabetes is associated with reduced insulin-stimulated glycogen synthase activation. The nine phosphorylation sites theoretically allow 512 combinations of phosphorylation configurations of glycogen synthase with different kinetic properties. However, due to hierarchal phosphorylation, the number of configurations in vivo is most likely much lower. Unfortunately, many studies only report data on glycogen synthase activity measured with high concentration of UDP-glucose which holds back information about changes in substrate affinity. In this paper we discuss the physiological regulation of glycogen synthase phosphorylation and how the phosphorylation pattern regulates glycogen synthase kinetic properties.

Details

Original languageEnglish
Pages (from-to)13-21
Number of pages9
JournalArchives of Physiology and Biochemistry
Volume115
Issue number1
Publication statusPublished - 1 Feb 2009

Keywords

  • Affinity, GSK-3, Muscle contraction, PP-1, Protein phosphatase, Type 2 diabetes, UDP-glucose

ASJC Scopus subject areas