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)

Previous studies demonstrated that opiate inhibition of adenylate cyclase (AC) in striatal membranes is related to an opiate-stimulated GTPase with a low Km. Dopamine (DA) also dose-dependently activates a high affinity GTPase, with a pattern of stimulation and a receptor selectivity (D1 type) similar to those observed in DA activation of striatal AC. Moreover, the DA- and the opiate-sensitive GTPase activities have different sensitivities to agents that affect the inhibition of AC, such as Na+ and N-ethylmaleimide (NEM), or the stimulation, such as cholera toxin (CTX). Thus, the impairment of opiate-dependent inhibition of AC in the absence of Na+ ions or after NEM pretreatment of the membranes is parallel with preferential impairment of the opiate-dependent GTPase. On the contrary, selective blocking by CTX of the DA-dependent GTPase leads to the enhancement of AC stimulation by DA. These results suggest that DA activation of striatal AC is related to a GTPase that is specifically stimulated by DA and is associated with the Ns protein. A distinct Ni protein seems to be responsible for the opiate effect on AC and GTPase.
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PMID:Opiate and dopamine stimulate different GTPase in striatum: evidence for distinct modulatory mechanisms of adenylate cyclase. 299 84

Previous work has demonstrated that injection of rats with isoproterenol is rapidly (10 min) followed by the development of a homologous form of desensitization of the beta-agonist-coupled adenylate cyclase in lung membranes. Half the receptor pool becomes sequestered in a light membrane fraction while the other half remains in the plasma membranes but becomes functionally uncoupled. In the present work we sought to assess whether "local sequestration" of the functionally intact receptor away from the effector adenylate cyclase in the plasma membrane contributes to the uncoupling of the beta-adrenergic receptor observed in the plasma membranes. We tested the functionality of the desensitized beta-adrenergic receptor in three different ways. We reconstituted the affinity chromatography purified control and "desensitized" receptors with pure Ns from human erythrocytes and assessed the ability to induce GTPase activity in Ns. Both control and desensitized beta-adrenergic receptors stimulate similar levels of GTPase activity in Ns (852 +/- 38 versus 738 +/- 49 fmol of Pi released/30 min (p greater than 0.05, n = 4). To further assess the relative ability of control and desensitized beta-adrenergic receptors to couple to another source of Ns we fused reconstituted beta-adrenergic receptors to Xenopus laevis erythrocytes, which contain Ns and adenylate cyclase but essentially no beta-adrenergic receptors. The functional interactions of control and desensitized beta-adrenergic receptor with the adenylate cyclase system of the acceptor cells was assessed by measuring the beta-agonist-stimulated adenylate cyclase activity and the agonist-induced formation of the high affinity state of the beta-adrenergic receptor (RH). Again both control and desensitized beta-adrenergic receptors appeared to interact with Ns to the same extent. To test if a local sequestration of the beta-adrenergic receptor away from Ns within the plasma membrane might contribute to the uncoupling of the beta-adrenergic receptors during desensitization, plasma membranes from control and desensitized lungs were treated with the fusogen polyethylene glycol to disrupt any compartmentalization of protein components within the plasma membrane. After polyethylene glycol treatment the previously uncoupled beta-adrenergic receptors could be recoupled to Ns as assessed by the formation of RH in agonist competition curves. These data suggest that in marked contrast to the heterologous type of desensitization, homologous desensitization may involve a local sequestration of a functionally intact beta-adrenergic receptor away from the adenylate cyclase effector system.
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PMID:Homologous desensitization of the beta-adrenergic receptor. Functional integrity of the desensitized receptor from mammalian lung. 299 46

1-O-Alkyl-2-O-acetyl-sn-glyceryl-3-phosphocholine (platelet activating factor) inhibits human platelet adenylate cyclase via the GTP-dependent mechanism. Inhibition of adenylate cyclase correlates with the stimulation of high affinity hormone-sensitive GTPase. The half-maximal effects of PAF on both enzymes are observed at concentrations about 10(-8) M. Phentolamine, an alpha-adrenergic antagonist, does not abolish the PAF-induced inhibition of adenylate cyclase. The obtained data suggest that PAF receptors are coupled with the GTP-binding inhibitory protein.
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PMID:Stimulation of high-affinity hormone-sensitive GTPase of human platelets by 1-O-alkyl-2-O-acetyl-sn-glyceryl-3-phosphocholine (platelet activating factor). 299 53

Transducin, the guanyl nucleotide-binding protein of the retinal light-activated cGMP phosphodiesterase system, is structurally and functionally similar to the inhibitory and stimulatory guanyl nucleotide-binding proteins, Gi and Gs, of the adenylate cyclase complex. All are heterotrimers composed of alpha, beta, and gamma subunits. Gs and Gi can be activated by NaF with AlCl3 as well as by agonists acting through specific receptors. The effects of NaF and AlCl3 on transducin were investigated in a reconstituted system consisting of the purified subunits of transducin (T alpha, T beta, gamma) and rhodopsin. NaF noncompetitively inhibited the GTPase activity of T alpha in a concentration- and time-dependent manner. Inhibition by NaF was enhanced synergistically by AlCl3 which alone only slightly inhibited GTPase activity. None of the other anions tested reproduced the effect of fluoride. Fluoride inhibited [3H]guanosine 5'-(beta, gamma-imido)triphosphate binding to T alpha and release of bound GDP. The ADP-ribosylation of T alpha by pertussis toxin and binding of T alpha to rhodopsin, both of which are enhanced in the presence of T beta gamma, were inhibited by NaF and AlCl3. These findings are consistent with the hypothesis that fluoride enhances the dissociation of T alpha from T beta gamma, resulting in the inhibition of GTP-GDP exchange, and therefore, GTP hydrolysis.
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PMID:Mechanism of inhibition of transducin GTPase activity by fluoride and aluminum. 299 38

Treatment of beta-adrenergic receptor with dithiothreitol (DTT) or other thiol compounds caused its functional activation in the presence or absence of agonist ligands. Such activation was observed in reconstituted unilamellar phospholipid vesicles that contained beta-adrenergic receptors, purified to greater than or equal to 95% homogeneity from turkey erythrocyte plasma membranes, and the stimulatory GTP-binding protein of the adenylate cyclase system (Gs) purified from rabbit liver. Incubation of the vesicles with 2-10 mM DTT at 0 degrees C for 1 h increased the rate (4-5-fold) and the extent (3-4-fold) of activation of Gs by guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) binding, an effect about equivalent to the addition of beta-adrenergic agonists. Treatment with DTT also markedly potentiated the ability of agonists to stimulate GTP gamma S binding, increasing the initial rate about 10-fold. DTT treatment was as effective as agonist in stimulating GTPase activity, and maximal stimulation was obtained when DTT-treated vesicles were assayed in the presence of agonist. Other thiol compounds produced effects similar to those of DTT but were at least 10-fold less potent. Stimulation of GTP gamma S binding or GTPase activity required active receptor, and treatment of the receptor with DTT prior to reconstitution also increased its efficacy. There was no effect of DTT on Gs alone. Thus, the site of action of DTT appears to be on the beta-adrenergic receptor itself, and the reduction of disulfides and the binding of agonist act synergistically to activate the receptor. DTT treatment made the receptor more labile to thermal denaturation. Inclusion of cholesterol or cholesteryl-hemisuccinate (5-25%) in the vesicles protected the reduced receptor against such denaturation and enhanced its recovery during reconstitution. No effect of cholesterol or cholesteryl-hemisuccinate was observed on the stability of the nonreduced receptor, which was comparable to that observed in native membranes.
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PMID:Functional activation of beta-adrenergic receptors by thiols in the presence or absence of agonists. 299 96

Forskolin directly stimulates adenylate cyclase activity and acts synergistically with receptor-mediated agonists which stimulate cyclic AMP production. We have previously observed that a 3-hr incubation of C6-2B rat astrocytoma cells with 6 nM cholera toxin in the presence of 1 microM forskolin results in cyclic AMP accumulation 9-fold greater than in the absence of forskolin. Since the action of cholera toxin is mediated by the stimulatory guanine nucleotide-binding regulatory component (GS) of the adenylate cyclase complex, we proposed that the mechanism by which forskolin augments hormone responses involves an enhanced coupling of GS with the adenylate cyclase catalytic component (C). In the present communication, we report the detailed characterization of the synergistic interaction between forskolin and cholera toxin as effectors of cyclic AMP accumulation in intact C6-2B cells. After a 3-hr incubation, maximal cholera toxin-stimulated cyclic AMP accumulation was 990 +/- 34 pmol/mg of protein. In the presence of 1 microM forskolin, the response to cholera toxin increased to 13,137 +/- 1,595 pmol of cyclic AMP/mg of protein. The half-maximally effective cholera toxin concentrations estimated by nonlinear least squares regression analysis determined in the absence or presence of 0.1 mM forskolin were 56.6 and 57.5 pM, respectively. The highly reproducible lag in forskolin-stimulated cyclic AMP accumulation in C6-2B cells was abolished by cholera toxin pretreatment, indicating a possible role for GS-associated GTPase in the mechanism of forskolin action. Cholera toxin treatment markedly augmented forskolin-stimulated cyclic AMP accumulation and shifted the forskolin concentration-response curve to the left approximately 1.5 log units. When C6-2B cells were treated for 1 min with 10 nM cholera toxin, the response to forskolin was significantly potentiated by 10 min. No significant increase in cellular cyclic AMP content in the absence of a forskolin challenge was apparent for up to 45 min. It appears that prior promotion of GS-C coupling by cholera toxin treatment enhances the ability of forskolin to stimulate cyclic AMP accumulation. Whether or not forskolin interacts (i.e., binds) exclusively to C remains to be proven. However, the actions of forskolin to stimulate cyclic AMP formation and potentiate agonist-stimulated cyclic AMP formation are modulated by the activity state of GS, and at least part of the response to forskolin is mediated by GS.
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PMID:Forskolin potentiation of cholera toxin-stimulated cyclic AMP accumulation in intact C6-2B cells. Evidence for enhanced Gs-C coupling. 300 96

The Ha-ras protooncogene product p21, which may be involved in control of cellular growth, is a membrane protein that binds guanine nucleotides and hydrolyzes GTP. p21 GTPase activity is stimulated by lysophosphatidylcholine; a delay in activation was observed unless p21 was incubated with the phospholipid prior to assay. Maximal activation by the phospholipid was observed over a narrow concentration range; the presence in the assay mixture of lysophosphatidylcholine at concentrations above this optimum markedly inhibited p21 GTPase. GTP hydrolysis was also stimulated, but to a lesser degree, by phosphatidylcholine. Phosphatidylinositol and phosphatidylserine did not significantly enhance GTPase activity. The stimulatory effect of phospholipid was mimicked, in part, by nonionic detergents. p21 may be related to other GTPases, the regulatory guanine nucleotide-binding G proteins of the hormone-sensitive adenylate cyclase complex and transducin of the retinal light-activated phosphodiesterase system. The G proteins and transducin are heterotrimers; the alpha subunits possess GTPase activity and the beta gamma subunit complex along with agonist-receptor complex or light-activated rhodopsin enhance GTP hydrolysis. p21 GTPase activity was slightly stimulated by rhodopsin, but, in contrast to the GTPase activity of transducin, stimulation was not light-dependent. GTP hydrolysis was enhanced somewhat by beta gamma subunit complex in the absence, but not in the presence, of rhodopsin. Like the G proteins and transducin, activity of p21 was altered by ADP-ribosylation. Modification of p21 catalyzed by an NAD: arginine ADP-ribosyltransferase purified from turkey erythrocytes decreased both GTPase activity and guanine nucleotide binding activity.
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PMID:Effects of phospholipids and ADP-ribosylation on GTP hydrolysis by Escherichia coli-synthesized Ha-ras-encoded p21. 300 95

It has been demonstrated using a membrane preparation of human platelets that stable analogs of PGH2, U46619 and U44069, control the activity of adenylate cyclase and a high-affinity hormone-sensitive GTPase. At 10(-8)-10(-6) M, the analogs inhibit the basal activity of adenylate cyclase by 20-25%. With a further rise in U46619 and U44069 concentrations up to 10(-5)-10(-4) M, the inhibition is abolished and adenylate cyclase activity is stimulated in a dose-dependent fashion. In the presence of PGE1, only inhibitory action of U46619 was observed at all the concentrations tested. The inhibitory action of the analogs on adenylate cyclase correlates with the activation of the high-affinity hormone-sensitive GTPase. It is concluded that U46619 and U44069 inhibit human platelet adenylate cyclase via specific receptors coupled to the GTP-binding inhibitory protein.
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PMID:Interaction of stable prostaglandin endoperoxide analogs U46619 and U44069 with human platelet membranes: coupling of receptors with high-affinity GTPase and adenylate cyclase. 300 58

Inhibition of receptor-coupled adenylate cyclase by hormones is proposed to be associated with GTP hydrolysis. Since adenosine inhibits cerebral-cortical adenylate cyclase via A1 adenosine receptors, the present study attempts to verify this mechanism for A1-selective adenosine derivatives. In guinea-pig cortical membranes N6-(phenylisopropyl)adenosine (PIA) increased the Vmax. of the low-Km GTPase, with an EC50 (concentration causing 50% of maximal stimulation) of about 0.1 microM, and the stimulatory effect was competitively antagonized by 5 microM-8-phenyltheophylline. The rank order of potency of the stereoisomers of PIA and of 5-(N-ethylcarboxamido)adenosine (NECA) to stimulate GTPase correlated with their ability to inhibit adenylate cyclase activity (R-PIA greater than NECA greater than S-PIA). Competition binding studies with (-)-N6- ([125I]iodo-4-hydroxyphenylisopropyl)adenosine suggest that adenylyl imidodiphosphate (p[NH]ppA), an essential component of the GTPase assay system, is a more potent A1-receptor agonist than ATP, with an IC50 (concentration giving half-maximal displacement of radioligand binding) of 7.9 microM. On the basis of the p[NH]ppA concentration used in the GTPase assay (1.25 mM), enzyme stimulation by adenosine seems to be highly underestimated. Nevertheless, adenosine-induced GTP hydrolysis reflects an increased turnover of guanine nucleotides at the Ni regulatory site and appears to be a crucial step in the sequence of events processing the inhibitory signal to adenylate cyclase.
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PMID:Adenosine-receptor-mediated stimulation of low-Km GTPase in guinea-pig cerebral cortex. 300 7

A protein factor which inhibited adenylate cyclase was purified to apparent homogeneity from rat brain and identified as the beta gamma-subunits of the GTP-binding regulatory proteins of adenylate cyclase. (i) The beta gamma-subunits (protein factor) inhibited the partially purified catalytic unit of adenylate cyclase in the presence of an activator, forskolin or the stimulative regulatory protein (Ns), to 60 and 40% of the control, respectively; inhibition of the catalytic unit in the presence of forskolin required no guanine nucleotides. (ii) The subunits enhanced the GTPase activity of the purified alpha-subunit of the inhibitory regulatory protein (Ni alpha) 3.8-fold. (iii) The subunits stimulated ADP-ribosylation of Ni alpha catalyzed by islet-activating protein (pertussis toxin). ADP-ribosylation had no effect on the GTPase activity of Ni alpha in the presence of the beta gamma-subunits. The results suggest that direct inhibition of the catalytic unit by the beta gamma-subunits liberated from Ni is essential for the receptor-mediated inhibition of adenylate cyclase.
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PMID:Inhibition of catalytic unit of adenylate cyclase and activation of GTPase of Ni protein by beta gamma-subunits of GTP-binding proteins. 301 80


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