Topographic separation of adenylate cyclase and hormone receptors in the plasma membrane of toad erythrocyte ghosts

Abstract

Brief sonication of whole erythrocyte plasma membranes (ghosts) from toads [Bufo marinus] at 4.degree. does not inactive adenylate cyclase [ATP pyrophosphate-lyase (cyclizing); EC 4.6.1.1] or destroy the receptor binding properties of hydroxybenzylpindolol or insulin. The hormonal (but not the fluoride-induced) stimulation of this enzyme is, however, lost. Fractionation of the small, resealed membrane fragments (vesicles) on discountinuous sucrose gradients results in the separation of vesicle populations differing grossly in size and protein composition. In addition, the distribution of the .beta.-adrenergic receptor, an insulin binding site, and adenylate cyclase among these vesicle fractions differs. The pattern of distribution of these functional structures can be altered differentially by manipulations of the ghosts before sonication. For example brief preincubation with isoproterenol leads to a change in the relative distribution of .beta.-receptor (but not adenylate cyclase) among the various vesicle fractions; this effect is not obtained with .beta.-receptor antagonists, which block the isoproterenol effect. Exposure of the ghosts to different temperatures, changes in the divalent cation composition of the medium, or the addition of ATP also leads to changes in the distribution of surface markers of the subsequently formed vesicles. The results indicate gross asymmetries in the distribution of protein components within the plane of the membrane and raise inportant questions regarding the manner whereby functionally related and coupled components, such as hormone receptors and adenylate cyclase, interact.