Direct effect of insulin on the labeling of isolated plasma membranes by [γ32P] ATP

Labeling of isolated plasma membranes from rat adipocytes by γ³²P] ATP was studied and the effect of insulin on this process was determined. Labeling was bi-phasic, increasing to a maximum while the supply of ATP was sufficient, then decreasing as the supply of ATP was depleted by hydrolysis. Insulin added directly to the assay mixture without pre-incubation decreased the level of labeling of plasma membranes at each time of incubation tested, from 30 sec to 10 min. The effect was insulin dose-dependent and was not observed with the inactive insulin derivative, desoctapeptide-insulin.