title: Functional modification of the guanine nucleotide regulatory protein after desensitization of turkey erythrocytes by catecholamines.
abstract: Densensitization of turkey erythrocytes by exposure to the beta-adrenergic agonist (-)isoproterenol leads to decreased activation of adenylate cyclase by agonist, NaF, and guanyl-5'-yl imido diphosphate, with no reduction in the number of beta-adrenergic receptors. Interactions between the receptor and the guanine nucleotide regulatory protein (N protein) also seem to be impaired. These observations suggest that a component distal to the beta-adrenergic receptor may be a locus of modification. Accordingly we examined the N protein to determine whether it was altered by desensitization. The rate at which (-)isoproterenol stimulated the release of [3H]GDP from the N protein was substantially lower in membranes prepared from desensitized cells, providing further evidence for uncoupling of the receptor and the N protein. The amount of N protein in membranes from control and desensitized cells was compared by labeling the 42,000 Mr component of the N protein with [32P]NAD+ and cholera toxin; no significant difference was found. However, significantly more N protein (p less than .001) was solubilized by cholate extraction of desensitized membranes, suggesting an altered association of the N protein with the membrane after desensitization. The functional activity of the N protein was measured by reconstitution of cholate extracts of turkey erythrocyte membranes into S49 lymphoma cyc- membranes. Reconstitution of (-)isoproterenol stimulation of adenylate cyclase activity was reduced significantly (p less than .05) after desensitization. These observations suggest that desensitization of the turkey erythrocyte by (-)isoproterenol results in functional modifications of the guanine nucleotide regulatory protein, leading to impaired interactions with the beta-adrenergic receptor and reduced activation of adenylate cyclase.
mesh_terms: D000262:Adenylyl Cyclases / Q000097:blood*; D000818:Animals; D002395:Catecholamines / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D019204:GTP-Binding Proteins; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000502:physiology; D011956:Receptors, Cell Surface / Q000502:physiology*; D014422:Turkeys
chemical_list: D002395:Catecholamines; D011943:Receptors, Adrenergic, beta; D011956:Receptors, Cell Surface; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases