Dependence of hormonal stimulation of adenylate cyclase on the fraction of plasma membrane accessible to the lateral transport of adenylate cyclase complex proteins

: Hormonal activation of the adenylate cyclase complex is associated with lateral mobility of proteins constituting this complex. Modification of interaction of the adenylate cyclase complex proteins due to variations in the "fluid" lipid fraction in cell membranes was studied. The decrease of percentage of "fluid" lipids in rat reticulocyte plasma membranes resulted in a decrease (up to a full stop) of interaction of beta-adrenoreceptors with regulatory N-proteins. The interaction of N-proteins with catalytic proteins was also blocked. On the other hand, an increase in the "fluid" lipid fraction led to a more intensive interaction. The observed phenomena do not result from functional damages of interacting proteins. Analysis of experimental results within the framework of the percolation theory suggests that hormonal activation of the adenylate cyclase complex depends on the "fluid" lipid fraction in the membrane and that the interacting proteins diffuse at distances comparable with the size of the cell membrane. The intrinsic activity of the beta-agonist isoproterenol changes from 1 to 0, depending on the "fluid" lipid fraction. The experimental data also suggest that there are no beta-receptors precoupled with N-proteins in rat reticulocyte membranes in vitro.