title: The beta-adrenergic receptor in the human neutrophil plasma membrane: receptor-cyclase uncoupling is associated with amplified GTP activation.
abstract: We compared the properties of the adenylate cyclase system in plasma membranes derived from gas cavitation and sonication of human neutrophils. In membranes prepared from cavitated cells, cyclase was stimulated by fluoride ion and Gpp(NH)p. Stimulation by isoproterenol (and PGE1) was absent, although the beta-receptor was present as judged by 125I-HYP binding. Two unusual characteristics of this cyclase system are a) substantial activation of cyclase by GTP in the absence of hormone, and b) reduction in the regulation of the beta-receptor by GTP. By contrast, vesicles isolated from sonicated cells displayed normal GTP-dependent activation by isoproterenol (as well as PGE1) and GTP regulation of the beta-receptor, while hormone-independent stimulation by GTP was negligible. Cholera toxin-catalyzed ADP ribosylation revealed a prominent band at 42K in both membranes, and a minor band at 35K, although the degree of labeling of this protein was lower in the "cavitated" vesicles. Our results suggest that the mode of cell lysis and membrane preparation influence receptor-cyclase interactions and that receptor-cyclase uncoupling is associated with amplified GTP activation and altered receptor regulation by GTP.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology / Q000378:metabolism; D004789:Enzyme Activation; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006801:Humans; D009504:Neutrophils / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D014475:Uncoupling Agents / Q000378:metabolism
chemical_list: D011943:Receptors, Adrenergic, beta; D014475:Uncoupling Agents; D006160:Guanosine Triphosphate; D000262:Adenylyl Cyclases