title: Fasting and diabetes alter adipose tissue glycogen synthase.
abstract: In a previous report (J. Biol. Chem. 254: 4678-4683, 1979), we showed that fasting blunted the ability of insulin to promote glucose incorporation into glycogen in vitro. In addition, we showed that glycogen synthase activity was altered in two ways: the concentration of glucose 6-P causing half-maximal activation increased, and positive cooperativity appeared in the glucose 6-P activation of the enzyme. We now show that streptozotocin-diabetes causes the same changes in glucose incorporation and glycogen synthase activity. We show that these changes in glycogen synthase activity persist during enzyme purification; thus it is likely the changes are a result of a structural alteration of the enzyme. Because glycogenolysis of a glycogen particle from rabbit skeletal muscle also caused the appearance of positive cooperativity, we propose that both phosphorylation and glycogenolysis are involved in the appearance of positive cooperativity.
mesh_terms: D000273:Adipose Tissue / Q000201:enzymology*; D000818:Animals; D003921:Diabetes Mellitus, Experimental / Q000201:enzymology*; D005215:Fasting; D019298:Glucose-6-Phosphate; D005958:Glucosephosphates / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism; D006006:Glycogen Synthase / Q000378:metabolism*; D006019:Glycolysis; D007328:Insulin / Q000494:pharmacology; D007700:Kinetics; D010766:Phosphorylation; D051381:Rats; D013329:Structure-Activity Relationship
chemical_list: D005958:Glucosephosphates; D007328:Insulin; D019298:Glucose-6-Phosphate; D006003:Glycogen; D006006:Glycogen Synthase