Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:4.6.1.1 (adenylate cyclase)
 19,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The specific beta-adrenergic agonist radioligand (+/-)-[3H]hydroxybenzylisoproterenol ([3H]HBI) was used to investigate alterations in the beta-adrenergic receptors of frog erythrocytes occurring during the process of agonist-induced, receptor-specific desensitization. There was close agreement between the percentage fall in [3H]HBI binding and that in catecholamine-stimulated adenylate cyclase activity following periods of preincubation of up to 7 h with 0.1 mM (-)-isoproterenol. Desensitization was maximal by 5 h, resulting in a 69% reduction in [3H]HBI binding and a 67% reduction in isoproterenol-stimulated adenylate cyclase activity. In contrast, binding of the beta-adrenergic antagonist (-)-[3H]dihydroalprenolol was significantly less affected by desensitization (p is less than 0.05 at 2 1/2, 5, and 7 h), showing a maximum reduction in binding of only 35% in these experiments. The consistent close agreement of reduction in agonist binding with that in hormone-stimulated adenylate cyclase activity, together with the significant difference observed between agonist and antagonist binding, implies that an alteration occurs during desensitization which preferentially interferes with agonist binding, while antagonist binding is less affected. The locus of this agonist-specific alteration may be the receptor binding site or a site involved in receptor-enzyme coupling. Agonist binding studies may now be used to assess more completely the desensitized state of beta-adrenergic receptors in systems in which marked desensitization of beta-adrenergic responses is associated with little or no reduction in antagonist binding.
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PMID:Differences between agonist and antagonist binding following beta-adrenergic receptor desensitization. 2 86

Treatment of frog erythrocytes with N,N' dicyclohexylcarbodiimide (DCCD) leads to a loss of catecholamine stimulated adenylate cyclase activity without any decrease in fluoride or PGE1 stimulated cyclase. However, the concentrations of the reagent which inhibit catecholamine sensitive adenylate cyclase activity are 10 fold lower than those which inhibit specific [3H]dihydroalprenolol ([3H]DHA) beta-adrenergic receptor binding. By contrast binding of the readiolabeled beta-adrenergic agonist [3H]hydroxybenzylisoproterenol ([3H]HBI) is considerably more sensitive than antagonist binding to the effects of DCCD. The data suggest that low concentrations of the reagent may modify the effector portion of the beta-adrenergic receptor leading to functional uncoupling of the beta-receptor adenylate cyclase system. At higher concentrations of the reagent the ligand bidning site of the beta-receptor appears also to be altered.
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PMID:Multiple effects of N, N' dicyclohexyl carbodiimide on the beta-adrenergic receptor--adenylate cyclase system in frog erythrocytes. 20 59

The myometrium of the rat has been found to contain both alpha 1- and beta-adrenergic receptors. To investigate the implication of these adrenergic receptors in uterine reactivity near term delivery, we have measured the number and the affinity of alpha 1-adrenergic antagonist [( 3H]prazosin: [3H]PRAZ)-binding sites and of very high affinity beta 2-adrenergic agonist [( 3H]hydroxybenzylisoproterenol: [3H]HBI)-binding sites in myometrial membranes throughout the last 5 days of pregnancy and at delivery. The number of specific binding sites was constant from Day 18 of pregnancy up to 6 h prior to birth. In the last 6 h of pregnancy, there was a sharp increase in the number of alpha 1-receptors (+70%, p less than 0.05). Simultaneously, the number of beta 2-receptors coupled to the adenylate cyclase system dropped (-75%; p less than 0.001). These results indicate that with the approach of parturition, there is a regulation of uterine reactivity by a modulation of the concentrations of myometrial adrenergic receptors during the last 6 h of gestation.
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PMID:Rat myometrial adrenergic receptors in late pregnancy. 282 23

beta-Adrenergic receptors on membranes prepared from L6 myoblasts, wild-type S49 lymphoma cells, and an adenylate cyclase-deficient variant (cyc-) of S49 lymphoma cells bind the agonist [3H]hydroxybenzylisoproterenol ([3H]HBI) with high affinity. In each case the agonist [3H]HBI is associated with a larger complex than is the antagonist [125I]iodopindolol, and the binding of [3H]HBI can be inhibited by GTP. These observations suggest that there is an agonist-dependent association of the receptor with a guanine nucleotide-binding protein. The goal of the present experiments was to investigate the possibility that an interaction of beta-adrenergic receptors with the inhibitory guanine nucleotide-binding protein of adenylate cyclase was responsible for these observations. Treatment of S49 cells with pertussis toxin decreased the extent of pertussis toxin-catalyzed [32P]ADP-ribosylation of a 41,000-dalton protein, measured in vitro, and decreased the inhibition of adenylate cyclase activity observed in the presence of somatostatin or analogues of GTP. Isoproterenol-stimulated adenylate cyclase activity was potentiated following treatment of wild-type S49 cells and L6 myoblasts with pertussis toxin. Although the ability of receptors on membranes prepared from L6 myoblasts to bind the agonist [3H]HBI was not affected by treatment of cells with pertussis toxin, treatment of cyc- S49 cells with pertussis toxin markedly decreased the ability of receptors to bind [3H]HBI. The observed inhibition of the binding of the agonist [3H]HBI to beta-adrenergic receptors on membranes prepared from cyc- S49 cells after treatment with pertussis toxin could be explained by an interaction between beta-adrenergic receptors and the inhibitory guanine nucleotide-binding protein. Such an interaction may represent a mechanism through which stimulation of the activity of adenylate cyclase by beta-adrenergic receptors can be regulated or through which beta-adrenergic receptors can affect the activity of cyclic AMP-independent cellular processes.
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PMID:Interaction of beta-adrenergic receptors with the inhibitory guanine nucleotide-binding protein of adenylate cyclase in membranes prepared from cyc- S49 lymphoma cells. 284 25

The purpose of this study was to characterize the beta-adrenoceptor subtypes in pregnant rat myometrial membrane fractions and to determine the concentration of beta 2-adrenoceptors in uterus during late pregnancy. Two methods are compared. A non-subtype-selective antagonist radioligand [3H]dihydroalprenolol ([3H]DHA) was used to label all of the beta-adrenoceptors. [3H]DHA bound to both beta 1- and beta 2-adrenoceptors with indistinguishable affinity (KD = 1.31 nM, Bmax = 174 fmol/mg protein). Computer modelling of competition curves of unlabeled selective antagonists or agonists was then required in order to determine reliably beta 1- and beta 2-adrenoceptor affinities and proportions: the beta 1-adrenoceptors represent 35.5% and the beta 2-adrenoceptors 64.5% of the entire beta-adrenoceptor population in rat gravid myometrium at term. The second approach utilized the radioligand [3H]hydroxybenzylisoproterenol ([3H]HBI) which is a very high-affinity beta-adrenoceptor agonist. The characteristics of the [3H]HBI binding sites are essentially those expected of beta 2-adrenoceptors, but the [3H]HBI binding sites represent only 34% of [3H]DHA binding sites and may represent the fraction of beta 2-adrenoceptors that mediate adenylate cyclase stimulation and uterine relaxation. Between 21 d 09 h and 22 d 09 h of gestation, the number of beta 2-adrenoceptors was constant (mean = 225.6 +/- 20.2 fmol/mg protein). At term, the number of [3H]HBI binding sites dropped (-75%) during the last 7 h of pregnancy, suggesting a reduced ability to elicit relaxation through beta-adrenoceptor activation in parturient myometrium of rat.
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PMID:Characterization of beta-adrenoceptors in myometrium of preparturient rats. 285 25

The radiolabeled agonist [3H]hydroxybenzylisoproterenol ([3H]HBI) and antagonist [125I]iodopindolol ([125I]IPIN) were used to investigate the properties of beta-adrenergic receptors on membranes prepared from L6 myoblasts and S49 lymphoma cells. The high affinity binding of (-)-[3H]HBI to membranes prepared from L6 myoblasts was stereoselectively inhibited by the active isomers of isoproterenol and propranolol. The density of receptors determined with (-)-[3H]HBI was less than that determined with [125I]IPIN. The binding of (-)-[3H]HBI was inhibited by guanine nucleotides, suggesting an agonist-mediated association of the receptor with a guanine nucleotide-binding protein, presumably the stimulatory guanine nucleotide-binding protein (Ns) of adenylate cyclase. Results obtained in studies with membranes prepared from wild-type S49 lymphoma cells and the adenylate cyclase-deficient variant (cyc-) were similar to those obtained in experiments carried out with membranes prepared from L6 myoblasts. Thus, the high affinity binding of (-)-[3H]HBI to membranes prepared from wild-type and cyc- S49 lymphoma cells was stereoselectively inhibited by the active isomers of isoproterenol and propranolol, and was inhibited by GTP. Moreover, the density of sites determined with (-)-[3H]HBI was less than that determined with [125I]IPIN. These results suggest either that cyc- cells contain a partially functional Ns, or alternatively, that the inhibitory guanine nucleotide-binding protein (Ni) is capable of interacting with beta-adrenergic receptors.
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PMID:Properties of beta-adrenergic receptors of cultured mammalian cells. Interaction of receptors with a guanine nucleotide-binding protein in membranes prepared from L6 myoblasts and from wild-type and cyc- S49 lymphoma cells. 299 14

Beta-adrenergic receptors on membranes prepared from rat lung, wild-type S49 lymphoma cells, and the adenylate cyclase-deficient variant of S49 lymphoma cells (cyc-) bind the agonist [3H]hydroxybenzylisoproterenol ([3H]HBI) with high affinity and this binding of [3H]HBI can be inhibited by GTP. Membranes prepared from these tissues were incubated with the agonist [3H]HBI or the antagonist [125I]iodopindolol ([125I]IPIN), labeled receptors were solubilized with digitonin, and the apparent molecular sizes of the ligand-bound receptor complexes were determined by high-performance size-exclusion chromatography. Results with all three tissues demonstrated that receptors labeled with [125I]IPIN were retained by the size-exclusion columns longer than receptors labeled with [3H]HBI. Thus, the apparent molecular size of soluble beta-adrenergic receptors from rat lung, wild-type S49 cells, and cyc- S49 cells was larger when receptors were occupied with an agonist rather than an antagonist. The results suggest that receptors, including those on cyc- S49 cells, interact with a membrane protein, presumably a guanine nucleotide-binding protein. Since cyc- S49 cells do not contain a functional stimulatory guanine nucleotide-binding protein, but do contain a functional inhibitory guanine nucleotide-binding protein, an interaction between beta-adrenergic receptors and the inhibitory guanine nucleotide-binding protein may be responsible for the apparent increase in the molecular size of the receptor after occupation of the receptor with an agonist.
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PMID:Interactions of beta-adrenergic receptors with a membrane protein other than the stimulatory guanine nucleotide-binding protein. 303 20