Adaptive Nature of Glycogen Synthetase Activity in Rat Adipose Tissue. Requirement for Insulin and Energy 1

Abstract

Summary

Total glycogen synthetase activity in adipose tissue from fasted meal-fed or nibbling rats increased in activity when the tissue was incubated for 2.5 hr in a buffer containing 5 mM glucose and insulin. Inclusion of puromycin in the incubation medium at a concentration which depressed lysine-U-¹⁴C incorporation into protein by more than 90%, depressed the increase in glycogen synthetase activity by less than 25%. These data indicate that protein synthesis was responsible for no more than a small part of the overall increase in enzyme activity. Glycogen synthetase activity also increased when adipose tissue was incubated with glucose, fructose, or pyruvate without insulin, but the increase was less than when insulin was included in the incubation medium. The greatest increase in enzyme activity occurred in tissue incubated in the presence of both glucose and insulin. The results are consistent with the hypothesis that the increase in glycogen synthetase activity results from the conversion of a form of the enzyme which is inactive under the usual assay conditions to an assayable form.