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)

In Zajdela hepatoma cells (ZHC) the plasma membrane Ca2+ pump displayed no sensitivity to glucagon (19-29) (mini-glucagon), whereas in hepatocyte this metabolite of glucagon evoked a biphasic regulation of the Ca2+ pump system via a cholera toxin-sensitive G protein. Analysis of G protein subunits in ZHC membranes indicated the presence of cholera toxin-sensitive Gs alpha and G beta gamma proteins, whose functionality was manifested by GTP and NaF stimulation of adenylylcyclase activity, and pertussis toxin-catalyzed ADP-ribosylation of Gi alpha, respectively. However, immunoblotting experiments suggested a lower content in beta gamma subunits in ZHC as compared with hepatocyte plasma membranes. Complementation of ZHC or hepatocyte plasma membranes with purified beta gamma subunits from transducin (T beta gamma) caused inhibition of the basal activity of the Ca2+ pump at 10 and 300 ng/ml, respectively, and revealed (in ZHC) or increased (in hepatocytes) sensitivity of the system to mini-glucagon. After cholera toxin treatment of ZHC, T beta gamma no longer reconstituted the response of the Ca2+ pump to mini-glucagon, suggesting that the mechanism of beta gamma action is dependent on an association with the alpha subunit of a cholera toxin-sensitive G protein. It is concluded that G beta gamma subunits control both the basal activity of the plasma membrane Ca2+ pump and its inhibition by mini-glucagon.
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PMID:Role of G protein beta gamma subunits in the regulation of the plasma membrane Ca2+ pump. 131 Mar 15

Collagen fibres in suspension have been shown to inhibit adenylate cyclase in human platelet preparations. Direct inhibition by collagen fibres was observed when intact platelets were used, although secondary events such as ADP secretion or prostanoid formation were important contributors to the inhibition of adenylate cyclase after treatment of platelets with collagen. The nature of the direct inhibition caused by collagen has been investigated in platelet membrane preparations, with the following results. (1) Collagen fibres inhibit platelet membrane adenylate cyclase in a dose-dependent manner. (2) Inhibition of adenylate cyclase by thrombin, adrenaline or collagen fibres could be abolished in the presence of guanosine 5'-[beta-thio]diphosphate; half-maximal inhibition was obtained at about 100 microM for the inhibitory action of thrombin, and at about 500 microM for that of either adrenaline or collagen. (3) The action of each ligand was blocked to a similar extent by pertussis-toxin treatment of the platelet membranes. Taken together, these results indicate that the action of collagen, like that of thrombin and adrenaline, is G-protein-dependent. (4) inhibition of adenylate cyclase by collagen fibres was additive with that caused by adrenaline, but co-operative with that caused by thrombin, suggesting that inhibitory pathways exists for collagen and adrenaline which are distinct from, but interactive with, that for thrombin. (5) Modification of the collagen fibres by pepsin treatment attenuated the effects of collagen, whereas heat-denaturation of the collagen fibres completely abolished their effects. These data suggest that the effects of collagen are specific, and depend on the detailed structure of the collagen fibres.
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PMID:Inhibition of human platelet adenylate cyclase by collagen fibres. Effect of collagen is additive with that of adrenaline, but interactive with that of thrombin. 131 55

A series of 1H-imidazol-1-yl- and 3-pyridyl-substituted 3,4-dihydroquinolin-2(1H)-ones was designed and synthesized as combined inhibitors of thromboxane (TXA2) synthase and cAMP phosphodiesterase (PDE) in human blood platelets. A number of structures, e.g. 4b, 7a, 7e, 13a, and 21-25, were superior to dazoxiben 26 as inhibitors of TXA2 synthase in in vitro ADP-induced aggregation experiments with human blood platelets. The TXA2 synthase inhibitory activity was confirmed by measurement of the prostanoid metabolites derived from 14C-labeled arachidonic acid. Three compounds (7a, 7e, and 25) demonstrated in vitro inhibition of human platelet cAMP PDE at micromolar concentrations in conjunction with their TXA2 synthase inhibitory activity. Synergistic enhancement of antiaggregatory and antithrombotic actions was expected when simultaneous stimulation of adenylate cyclase (through increased PGI2 production) and inhibition of platelet cAMP PDE were possible from the same compound. Ex vivo and in vivo experiments were conducted in rats and mice, respectively, to evaluate the effects of compounds 7e and 23 on platelet aggregation and thrombotic events within these animals. Compound 7e, which has a comparable level of TXA2 synthase (IC50 1.2 microM) and human platelet cAMP PDE (IC50 6.4 microM) inhibitory activities, was found to be orally bioavailable with a long duration of action and offered effective protection against mortality in a collagen-epinephrine-induced pulmonary thromboembolism model in mice. Significant blood pressure and heart rate effects were observed for several compounds, e.g. 7e, 9e, 13a, 13d, 18, 20, 21, and 23, when dosed orally in conscious spontaneously hypertensive rats.
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PMID:3,4-Dihydroquinolin-2(1H)-ones as combined inhibitors of thromboxane A2 synthase and cAMP phosphodiesterase. 131 63

Stimulation of human platelets with the thromboxane A2 analogue, U46619, after treatment with prostaglandin E1 or forskolin, reduced the inhibition of ADP-evoked Mn2+ influx and the release of Ca2+ from intracellular stores. U46619 decreased the elevated concentration of 3',5'-cyclic AMP in platelets that were pretreated with prostaglandin E1. These results suggest that occupation of prostaglandin H2/thromboxane A2 receptors, like those for other agonists, inhibits adenylate cyclase activity, which can contribute to the promotion of platelet activation.
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PMID:Thromboxane receptor stimulation inhibits adenylate cyclase and reduces cyclic AMP-mediated inhibition of ADP-evoked responses in fura-2-loaded human platelets. 131 24

8-Methoxy-4-[(2-isopropylphenyl)amino]-3-quinolinecarboxylate ethyl ester (AHR-9294) inhibited acid secretion stimulated by histamine, pentagastrin or carbachol in rats, and by histamine or feeding in dogs. AHR-9294 was about half as potent as omeprazole and exhibited a shorter duration of action. Based on its inhibition of acid secretion induced by different secretagogues and its lack of effect on histamine-stimulated adenylate cyclase activity, AHR-9294 does not appear to operate at the histamine receptor or adenylate cyclase. Rather, studies on enriched oxyntic microsomal preparations showed AHR-9294 to be an effective inhibitor of the H+ pump enzyme, H,K-ATPase, suggesting this might be the site of antisecretory activity. Kinetic studies revealed that inhibition of both K(+)-activated ATPase and p-nitrophenylphosphatase by AHR-9294 was purely competitive with K+ and its congeners, indicating that AHR-9294 and its analogs belong to the class of compounds known as "K+)-site" inhibitors. On the other hand, inhibition by AHR-9294 was noncompetitive with both ATP and p-nitrophenylphosphatase on their respective rates of hydrolysis (i.e., both Vmax and the apparent Km were reduced, but Vmax/Km was unchanged). Studies on partial reactions of the H,K-ATPase showed that the rate of ATP/ADP exchange was unaffected by AHR-9294 and the steady-state level of phosphoenzyme was only partially reduced (thus ATP/enzyme interaction was not affected); however, the rate of K(+)-catalyzed dephosphorylation of phosphoenzyme was markedly decreased.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:AHR-9294: a novel inhibitor of H,K-ATPase antagonizes gastric HCl secretion in vivo. 131 65

Five separate guanine nucleotide-binding proteins (G proteins) were immunologically identified in membranes from neuroblastoma x glioma NG108-15 hybrid cells. These alpha subunit proteins were Gi2 alpha, two isoforms of Gi3 alpha, and two isoforms of Go alpha. The G proteins that interacted with delta-opioid receptors in these membranes were identified using cholera toxin (CTX)-induced ADP-ribosylation and antisera selective for various G protein alpha subunits. In the presence of delta-opioid agonists, CTX induced the incorporation of [32P]ADP-ribose into three pertussis toxin substrates. Using antisera generated against peptide sequences from G alpha subunits, these three pertussis toxin substrates were identified as Gi2 alpha, Go2 alpha, and one isoform of Gi3 alpha, which has yet to be identified. This CTX-induced labeling was demonstrated to be mediated via the delta-opioid receptor in these hybrid cells by the observation that delta agonists D-Ala2-D-Leu5-enkephalin (DA-DLE) and D-Pen2-D-Pen5-enkephalin, as well as the nonselective agonists etorphine and bremazocine, were active, but the mu agonist PL017 and the kappa agonist U-50-488H did not show this activity. This incorporation into all three substrates induced by DADLE was dose dependent, with EC50 (95% confidence interval) values ranging from 12 (3-52) to 183 (65-520) nM, which compared with the Kd value of 10 +/- 1.5 nM for this agonist, a dose that produces maximal inhibition of adenylate cyclase activity. Furthermore, pretreatment of the cells with pertussis toxin or treatment of the membranes with the antagonist naloxone blocked the incorporation induced by DADLE. Incorporation of [32P]ADP-ribose into all three substrates decreased 35-83% in membranes in which the receptors had been down-regulated by chronic treatment of the cells with DADLE. Thus, a single opioid receptor type can interact with three separate G proteins.
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PMID:Identification of three separate guanine nucleotide-binding proteins that interact with the delta-opioid receptor in NG108-15 neuroblastoma x glioma hybrid cells. 131

The mechanisms of action of lithium and antidepressants were investigated with reference to effects of these drugs on monoaminergic receptors and receptor-coupled adenylate cyclase systems in rat brain. Oral administration of lithium carbonate for 21 days decreased significantly the density of beta-adrenergic receptors in rat cerebral cortex, which is the same change as reported as the result of long-term treatment with many antidepressants. With regard to 5-hydroxytryptamine (5-HT) receptor subtypes, lithium treatment reduced the maximum number of 5-HT1A receptors in rat hippocampus but not in cerebral cortex, whereas repetitive injections with imipramine or desipramine did not. beta-Adrenoceptor-coupled adenylate cyclase activity was subsensitized by long-term lithium treatment in consistency with above-mentioned down-regulation of beta-adrenergic receptors. Stimulation of adenylate cyclase activity by non-hydrolyzable GTP analogue, guanyl-5'-ylimidodiphosphate (Gpp(NH)p), was, however, unaltered in lithium-treated rats as compared with controls. On the other hand, 5-HT1A-mediated inhibition of forskolin-stimulated adenylate cyclase in rat hippocampal membranes was not altered by chronic treatment with lithium or antidepressants. Gpp(NH)p-induced inhibition of forskolin-stimulated adenylate cyclase activity was not influenced by lithium treatment, either. [3H]Forskolin binding to rat cerebral cortex, which is assumed to be associated with the activated complex of catalytic subunit of adenylate cyclase and stimulatory guanine nucleotide-binding regulatory proteins (Gs), was not changed by administration of lithium or antidepressants under any condition studied. Pertussis toxin (islet-activating protein, IAP) sensitive G proteins (Gi/Go) as determined by using IAP-catalyzed [32P]ADP-ribosylation was not altered by lithium- or antidepressant-treatment, either. The implication of these results is discussed with a view of clarifying the mechanisms of action of these thymoleptic drugs.
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PMID:[Effects of lithium and antidepressants on monoaminergic receptors and receptor-coupled adenylate cyclase system in rat brain]. 131 19

In vivo microdialysis of cyclic AMP from prefrontal cortex complemented by ex vivo measures was used to investigate the possibility that lithium produces functional changes in G proteins that could account for its effects on adenylate cyclase activity. Four weeks of lithium administration (serum lithium concentration of 0.85 +/- 0.05 mM; n = 11) significantly increased the basal cyclic AMP content in dialysate from prefrontal cortex of anesthetized rats. Forskolin infused through the probe increased dialysate cyclic AMP, but the magnitude of this increase was unaffected by chronic lithium administration. Inactivation of the inhibitory guanine nucleotide binding protein Gi with pertussis toxin increased dialysate cyclic AMP in control rats, as did stimulation with cholera toxin (which activates the stimulatory guanine nucleotide binding protein Gs). The effect of pertussis toxin was abolished following chronic lithium, whereas the increase in cyclic AMP after cholera toxin was enhanced. In vitro pertussis toxin-catalyzed ADP ribosylation of alpha i (and alpha o) was increased by 20% in prefrontal cortex from lithium-treated rats, but the alpha i and alpha s contents (as determined by immunoblot) as well as the cholera toxin-catalyzed ADP ribosylation of alpha s were unchanged. Taken together, these results suggest that chronic lithium administration may interfere with the dissociation of Gi into its active components and thereby remove a tonic inhibitory influence on adenylate cyclase, with resultant enhanced basal and cholera toxin-stimulated adenylate cyclase activity.
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PMID:In vivo evidence that lithium inactivates Gi modulation of adenylate cyclase in brain. 131 65

The present study investigated whether reduced adenylate cyclase activity and an increase in inhibitory guanine nucleotide binding proteins (Gi alpha), which have been observed in the failing human heart, already occur in myocardial hypertrophy before the stage of heart failure. In membranes of hypertrophic hearts from rats with different forms of experimentally induced hypertension without heart failure (one-kidney, one clip rats, deoxycorticosterone-treated rats, and rats with reduced renal mass), basal as well as isoprenaline-, 5'-guanylylimidodiphosphate-, and forskolin-stimulated adenylate cyclase activity was reduced. The activity of the catalyst was depressed in deoxycorticosterone but unchanged in one-kidney, one clip and reduced renal mass compared with controls. The number of beta-adrenergic receptors was similar in all groups. Radioimmunological quantification of Gi alpha proteins revealed an increase by 73% in one-kidney, one clip, 67% in reduced renal mass, but only 20% in deoxycorticosterone compared with sham-operated, age-matched control rats. The increase of Gi alpha was accompanied by smaller changes of pertussis toxin-induced [32P]ADP-ribosylation of a 40-kd membrane protein. It is concluded that Gi alpha contributes to the reduced adenylate cyclase activity in cardiac hypertrophy in one-kidney, one clip and reduced renal mass and to a smaller extent in deoxycorticosterone. It is suggested that an enhanced expression of Gi alpha could occur not only in severe heart failure but also in cardiac hypertrophy and could, therefore, contribute to myocardial depression and progression of disease in heart failure. In addition, Gi alpha might represent an important regulatory mechanism for cardiac adenylate cyclase activity and thus, might play an important role in various cardiac diseases.
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PMID:Desensitization of adenylate cyclase and increase of Gi alpha in cardiac hypertrophy due to acquired hypertension. 131 58

Guanyl nucleotide binding-proteins, or G-proteins, are ubiquitous molecules that are involved in cellular signal transduction mechanisms. Because a role has been established for cAMP in meiosis and G-proteins participate in cAMP-generating systems by stimulating or inhibiting adenylate cyclase, the present study was conducted to examine the possible involvement of G-proteins in the resumption of meiotic maturation. Cumulus cell-free mouse oocytes (denuded oocytes) were maintained in meiotic arrest in a transient and dose-dependent manner when microinjected with the nonhydrolyzable GTP analog, GTP gamma S. This effect was specific for GTP gamma S, because GppNHp, GTP, and ATP gamma S were without effect. Three compounds, known to interact with G-proteins, were tested for their ability to modulate meiotic maturation: pertussis toxin, cholera toxin, and aluminum fluoride (AlF4-). Pertussis toxin had little effect on maturation in either cumulus cell-enclosed oocytes or denuded oocytes when meiotic arrest was maintained with dibutyryl cAMP (dbcAMP) or hypoxanthine. Cholera toxin stimulated germinal vesicle breakdown (GVB) in cumulus cell-enclosed oocytes during long-term culture, but its action was inhibitory in denuded oocytes. AlF4- stimulated GVB in both cumulus cell-enclosed oocytes and denuded oocytes when meiotic arrest was maintained with hypoxanthine but was much less effective in dbcAMP-arrested oocytes. In addition, AlF4- abrogated the inhibitory action of cholera toxin in denuded oocytes and also that of follicle-stimulating hormone (FSH) in cumulus cell-enclosed oocytes. Cholera toxin or FSH alone each stimulated the synthesis of cAMP in oocyte-cumulus cell complexes, whereas pertussis toxin or AlF4- alone were without effect. Both cholera toxin and AlF4- augmented the stimulatory action of FSH on cAMP. These data suggest the involvement of guanyl nucleotides and G-proteins in the regulation of GVB, although different G-proteins and mediators may be involved at the oocyte and cumulus cell levels. Cholera toxin most likely acts by ADP ribosylation of the alpha subunit of Gs and increased generation of cAMP, whereas AlF4- appears to act by antagonizing a cAMP-dependent step.
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PMID:Modulation of meiotic arrest in mouse oocytes by guanyl nucleotides and modifiers of G-proteins. 132 Jun 58


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