Insulin receptor interaction in human placental plasma membranes

Abstract

Insulin-receptor interaction in partially purified preparations of human placental plasma membranes from normal mothers at term of pregnancy has been characterized.125I-insulin became rapidly and reversibly bound to plasma membranes, being time and temperature dependent.The binding readily appeared at 1.0 ng/ml insulin concentration which falls within the physiological range of peripheral blood.Low levels of unlabeled insulin inhibited binding; 20 ng/ml insulin produced fifty per cent inhibition.Scatchard plots of data from competitive insulin binding proved to be curvilinear.The insulin greater ability for binding observed in this preparation can be explained by the purification degree achieved at the plasma membranes.125I-insulin was less degraded by partially purified placental plasma membranes than by a microsomal-membrane preparation obtained without differential centrifugation in sucrose linear gradient.All these properties strongly suggest that the insulin-binding sites characterized in the plasma membrane fraction of the placenta represent biologically important receptors to hormone.