Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:4.6.1.1 (adenylate cyclase)
19,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The beta 1-adrenergic receptors of turkey erythrocyte membranes have been identified by binding of the radioactively labeled antagonist (--)-[3H]dihydroalprenolol, solubilized by treatment of the membranes with the detergent digitonin, and purified by affinity chromatography. Binding of (--)-[3H]dihydroalprenolol to the membranes occurred to a single class of non-cooperative binding sites (0.2--0.3 pmol/mg protein) with a equilibrium dissociation constant (Kd) of 8 (+/- 2) nM. These sites were identified as the functional, adenylate-cyclase-linked beta 1-adrenergic receptors on the basis of: firstly, the fast association and dissociation binding kinetics at 30 degrees C; secondly, the stereospecific displacement of bound (--)-[3H]dihydroalprenolol by beta-adrenergic agonists and antagonists; and thirdly, the order of potencies for agonists to displace bound tracer (isoproterenol congruent to protokylol greater than norepinephrine congruent to epinephrine) similar to the one found for adenylate cyclase activation, and typical for beta 1-adrenergic receptors. Treatment of the membranes with the detergent digitonin solubilized 30% of the receptors in an active form. Digitonin solubilized also adenylate cyclase activity with a yield of 20 to 30%, provided the membranes were first treated with an effector known to produce a persistent active state of the enzyme: e.g. sodium fluoride. Binding sites for guanine nucleotides ([3H]p[NH]ppG) were solubilized as well. Their concentration (24 pmol/mg protein) was in large excess over the concentration of solubilized receptors (0.30--0.45 pmol/mg protein). Solubilized receptors were purified 500--2000-fold by affinity chromatography with a 25 to 35% yield, using an alprenolol-agarose affinity matrix. Affinity purified receptors were devoid of measurable adenylate cyclase activity and guanine nucleotide binding sites, thus showing that receptors and adenylate cyclase are distinct membrane constituents, and that guanine nucleotides apparently do not bind directly to the receptor molecules. Membrane-bound, solubilized and purified receptors were sensitive to inactivation by dithiothreitol, but not by N-ethylmaleimide, suggesting that receptors are at least partly constituted of protein molecules, with essential disulfide bonds.
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PMID:Affinity chromatography of the beta-adrenergic receptor from turkey erythrocytes. 22 63

Digitonin-permeabilized adipocytes were used to study the coupling of adenylate cyclase (AC) to lipolysis in exercise-trained rats. Isoproterenol-(IPR) stimulated lipolysis in permeabilized cells was significantly greater in trained than in control rats. Under essentially identical conditions, the dose-response curve for IPR stimulation of AC activity in the absence of 3-isobutyl-1-methylxanthine was similar in trained and control rats. However, the potency of stimulation by IPR as a percentage of the basal level was greater in trained rats. AC activity and lipolysis in the presence of 3-isobutyl-1-methylxanthine were also significantly greater in trained than in control rats. Least-squares analysis by plotting the log AC vs. lipolysis values showed that the regression coefficient was about three-fold greater in trained than in control rats. The concentration of endogenous adenosine 3',5'-cyclic monophosphate (cAMP) needed to produce a half-maximal lipolytic response was 18.58 and 10.81 pmol.min-1.10(6) cells-1 in control and trained rats, respectively. Thus a positive relationship existed between lipolysis and AC activity, with a tighter coupling in trained rats. Lipolysis in response to exogenous cAMP tended to be greater in trained than in control rats, and the difference was statistically significant for 50 microM and 10 mM cAMP. Our finding support the concept that the major mechanism of enhanced lipolysis in trained rats was an increase in the activity of enzymatic step(s) distal to cAMP.
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PMID:Enhanced coupling of adenylate cyclase to lipolysis in permeabilized adipocytes from trained rats. 171 23

Reduced adenylate cyclase (AC) activity of cerebral cortical membrane in the presence of guanine-nucleotide analog [Gpp(NH)p] was observed in 12-month-old rats (aged rats) compared with 2-month-old rats (controls). The EC50 value for Gpp(NH)p activation to AC was slightly but significantly increased in aged rats and the half time for maximal activation of AC by Gpp(NH)p, either with or without isoproterenol was also longer in aged rats. Digitonin-solubilized AC catalytic moiety had a lower activity in the aged rats than in controls. The 125I-pindolol binding to beta-receptor in the cortical membrane from aged rats was decreased. GTP increased the Hill coefficient for isoproterenol displacement binding in controls, but such a change was not noted in aged rats. However, the percent increase of AC activity by 1 microM isoproterenol was greater in aged rats than that in controls. Furthermore, the EC50 value for isoproterenol stimulation of AC in control was lower compared with aged rats. Our results indicate that the decreased AC activity in aged rats may be due to a reduced receptor density, functional changes in GTP-binding protein (G protein) activity, and a reduced catalytic subunit activity. Compensatory changes in the beta receptor-G protein-AC coupling system may also occur during aging.
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PMID:Age-related alteration in the catecholamine-sensitive adenylate cyclase system of the rat cerebral cortex. 256 Aug 83

Intestinal brush border guanylate cyclase was previously reported to be activated by the Escherichia coli enterotoxin (STa). This system was reexamined in order to develop a hypothesis for the mechanism of activation. The extent of activation was previously underestimated, since by using sodium azide to inhibit competing reactions and ethylene glycol bis(beta-aminoethyl ether) N,N-tetraacetic acid to chelate Ca2+, which is inhibitory, maximal activations of 30- to 50-fold were obtained. Ca2+ inhibition was only partially relieved by the calmodulin inhibitor calmidazolium. Inhibitors of the O2-dependent activation of soluble guanylate cyclase had no effect on STa activation; hence, it was concluded that STa activation did not involve arachidonate release and oxidation. STa was able to further increase activity already elevated by the nonionic detergent Lubrol PX. The membrane-active agent filipin, which was previously reported to inhibit both basal and agonist-stimulated adenylate cyclase, did not inhibit STa activation of guanylate cyclase. Digitonin, another cholesterol binder, inhibited STa activation at low concentrations, which disappeared at higher concentrations. Both of these agents stimulated basal activity. Dimethyl sulfoxide produced a concentration-dependent inhibition of STa activation, while increasing basal activity 7-fold. Ethanol inhibited both basal and STa-stimulated activity, with the former being more affected. Benzyl alcohol, like ethanol, a "fluidizer" of cell membranes, also inhibited both basal and activated enzymes. We concluded that STa directly activates this guanylate cyclase and, because of the differential effects of inhibitors on basal and STa-stimulated activity, propose a receptor-mediated mechanism.
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PMID:Characterization of intestinal brush border guanylate cyclase activation by Escherichia coli heat-stable enterotoxin. 286 96

Digitonin-permeabilized monolayers of C6-2B rat astrocytoma cells exhibit adenylate cyclase activity in the presence of exogenously added ATP. The adenylate cyclase retains the qualitative and quantitative characteristics of hormone stimulated cyclic AMP accumulation in whole cells including GTP dependency and 100 fold stimulation by isoproterenol. Forskolin increased enzymatic activity in the absence of added GTP, however forskolin efficacy and potency was enhanced by GTP. Low non-efficacious concentrations of forskolin, without added GTP, supported isoproterenol-stimulated cyclase activity. The GTP-stimulated isoproterenol response was potentiated by forskolin. Forskolin support of isoproterenol stimulated cyclase in the absence of GTP raises the possibility that forskolin can act independently of GTP in coupling receptors to cyclase catalytic units and/or that forskolin could increase the efficacy and potency of GTP in the coupling reaction. Permeabilization of C6-2B and other cultured cells yields a preparation of adenylate cyclase which retains the enzyme in a state which closely approximates its activity in the native membrane--a system which could prove useful in studies of the regulation of adenylate cyclase in vivo.
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PMID:Maintenance of whole cell isoproterenol and forskolin responsiveness in adenylate cyclase of permeabilized cells. 373 26

Rat erythrocyte plasma membranes have been extracted exhaustively with digitonin at low temperature, and the residual, detergent-extracted membrane cytoskeletal material is compared to that prepared with Triton X-100 with respect to protein, glycoprotein, phospholipid, and cholesterol content. Digitonin, a weaker detergent than Triton X-100, solubilizes only 26% of the phospholipids and none of the cholesterol. SDS-polyacrylamide gel electrophoresis reveals that differences between the proteins extracted by the two detergents are primarily quantitative. In terms of functional preservation, digitonin retains in the cytoskeleton 28% of the beta-adrenergic receptor binding activity (with the balance accounted for in the supernatant), greater than 90% of the adenylate cyclase and greater than 90% of the 45,000 mol wt polypeptide cholera toxin substrate. The cytoskeletal-associated beat-adrenergic receptor retains binding properties for antagonist and agonist which are identical to those of the native membrane receptor. The digitonin-extracted cytoskeleton containing the beta-adrenergic receptor may provide a useful vehicle for the reconstitution of a hormone-sensitive adenylate cyclase.
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PMID:Properties of rat erythrocyte membrane cytoskeletal structures produced by digitonin extraction: digitonin-insoluble beta-adrenergic receptor, adenylate cyclase, and cholera toxin substrate. 627 53

The binding function of purified receptors can be assessed with radioligands, but the interaction of receptors with their biochemical effectors has not been amenable to direct study. Toward this end, procedures have been developed for directly demonstrating functionality of purified beta-adrenergic receptor preparations. Digitonin-solubilized beta-adrenergic receptors from frog erythrocytes or rat lung were purified approximately equal to 100- to 5,000-fold by affinity chromatography and inserted into a mixture of frog erythrocyte lipids and dimyristoyl phosphatidylcholine in the presence of octyl glucoside. Reconstitution of beta-adrenergic receptor binding was typically 25-50% and could also be effected with soybean phosphatidylcholine in the presence of octyl glucoside. The reconstituted beta-adrenergic receptors were then fused with Xenopus laevis erythrocytes, which contain prostaglandin E1-sensitive adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] but few beta-adrenergic receptors and little or no catecholamine-sensitive adenylate cyclase. Fusion of reconstituted receptor with Xenopus laevis erythrocytes establishes a substantial (2- to 10-fold) stimulation of the hybrid adenylate cyclase by the beta-agonist isoproterenol. The extent of stimulation depends on the amount of reconstituted beta-adrenergic receptor added, is blocked by propranolol, and is eliminated by boiling the beta-adrenergic receptor prior to reconstitution. The successful coupling of a purified receptor to a heterologous adenylate cyclase opens the way to the study of receptor structure---function relationships.
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PMID:Reconstitution of beta-adrenergic receptors in lipid vesicles: affinity chromatography-purified receptors confer catecholamine responsiveness on a heterologous adenylate cyclase system. 630 59

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