Affinity of the hepatic insulin receptor is influenced by membrane phospholipids.

The course of '2SI-insulin dissociation from rat liver plasma membranes is biphasic and dependent upon the duration of receptor occupancy.At 15 "C, as the association time is lengthened, the proportion of slow-dissociating insulin increases at the expense of the rapiddissociating component (Donner, D. B., and Corin, R. E. (1980) J. BioL Chem 255,9005-9008).Digestion of membranes with trypsin decreased binding of insulin to its receptor and subsequent retention of slow-dissociating hormone in paralIel suggesting the accumulation of slow-dissociating insulin was receptor mediated.At 23 and 37 "C, the association rate of '261-insulin to membranes did not vary with either the applied insulin concentration or the number of receptors occupied.The accumulation of slow-dissociating hormone at these temperatures therefore reflected a change in the affinity of the insulin receptor.At 4 "C, however, slowdissociating insulin did not accumulate on membranes.Digestion of membranes with phospholipase C ( B u d lus c e n e u s ) enabled slow-dissociating insulin to accumulate at 4 "C.To more completely characterize the influence of membrane lipids on insulin binding, plasma membranes were digested with phospholipase C (Clostridiumperfikingens or B. cereus), phospholipase D, or phospholipase Az, and the subsequent dissociation of insulin was assayed at 23 "C.Phospholipase C from both sources, but not phospholipase D or Az, facilitated the conversion of receptors from the rapid to the slowdissociating state.Exposure of cryptic receptors occurred with a different dose response to phospholipase C digestion than did the affinity change.Phospholipase Az increased insulin binding without altering receptor affinity.Sphingomyelinase augmented the accumulation of slow-dissociating insulin and cryptic site exposure.We conclude that the polar head groups of phosphoglycerides and sphingokipids within the plasma membrane influence the binding properties of the hepatic insulin receptor.The binding of insulin to specific sites on the exterior surface of target cells produces membrane and receptor alterations ultimately changing cellular metabolism (1-3).An observation common to hepatic and adipose tissues is that