Action of puromycin and actinomycin D on basal and insulin-stimulated glucose and fructose metabolism in isolated fat cells

Abstract

Incubation of collagenase-treated fat cells with 5·10 −4 M puromycin, decreased glucose utilization to about half the control values without affecting the response to insulin. Fructose utilization was only slightly decreased but the response to insulin was diminished. Fructose metabolism was not affected by the presence of glucose in the medium, when glucose uptake was low, but was progressively decreased with rising glucose uptake, irrespective of the presence of insulin. It is suggested that decreased fructose metabolism in the presence of a high glucose uptake is due to competitive inhibition of fructose metabolism at the hexokinase level and that the opposite effects of puromycin on glucose and fructose metabolism in the presence or absence of insulin may be due to the existence of four functionally distinct sites of entry for basal and insulin-stimulated uptake of glucose and fructose. Preincubation with 100 μg of actinomycin D per ml blocked the action of insulin in fat cells but not in whole adipose tissue. Addition of insulin to the cells before actinomycin prevented this effect. It is suggested that actinomycin prevents binding of insulin to cells which have been affected in some way by collagenase. The concentrations of inhibitors required to inhibit protein synthesis were lower than those required for the observed effects on carbohydrate metabolism.