Response of liver glycogen synthase and phosphorylase to in vivo glucose and glucose analogues.
Glucose causes a rapid increase in the proportion (%) of glycogen synthase in the active (I) form and a rapid decrease in the proportion of phosphorylase in the active (a) form in both fed and fasted rats. The changes in synthase I and phosphorylase a are more rapid in fasted animals. With graded doses of glucose, the maximal decrease in phosphorylase a occurred at a dose that was considerably smaller than that required to maximally stimulate an increase in % synthase I. Thus, in the intact animal a dissociation between the effects of glucose on the synthase and phosphorylase systems was observed. Sorbitol, mannose, galactose, and arabinose all stimulated an increase in synthase I but did not significantly affect the proportion of phosphorylase in the a form. The % synthase I was not significantly affected by a number of other glucose homologues, pentoses, or three-carbon gluconeogenic substrates. The ketoses fructose and mannoheptulose both caused a striking increase in % phosphorylase a and a decrease in % synthase I, i.e., results opposite to those of glucose. The mechanism by which fructose induces these changes is not known, but the mannoheptulose effects may be accounted for by a rise in liver cAMP concentration.
D000818:Animals; D003847:Deoxyglucose / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005215:Fasting; D005690:Galactose / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology*; D006006:Glycogen Synthase / Q000378:metabolism*; D006601:Hexoses / Q000494:pharmacology*; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D008358:Mannose / Q000494:pharmacology; D006005:Phosphorylases / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013012:Sorbitol / Q000494:pharmacology
D006601:Hexoses; D013012:Sorbitol; D003847:Deoxyglucose; D006005:Phosphorylases; D006006:Glycogen Synthase; D005947:Glucose; D008358:Mannose; D005690:Galactose