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

---

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

In fat cells isolated from the parametrial adipose tissue of rats, the addition of purified adenosine deaminase increased lipolysis and cyclic adenosine 3':5'-monophosphate (cyclic AMP) accumulation. Adenosine deaminase markedly potentiated cyclic AMP accumulation due to norepinephrine. The increase in cyclic AMP due to adenosine deaminase was as rapid as that of theophylline with near maximal effects seen after only a 20-sec incubation. The increases in cyclic AMP due to crystalline adenosine deaminase from intestinal mucosa were seen at concentrations as low as 0.05 mug per ml. Further purification of the crystalline enzyme preparation by Sephadex G-100 chromatography increased both adenosine deaminase activity and cyclic AMP accumulation by fat cells. The effects of adenosine deaminase on fat cell metabolism were reversed by the addition of low concentrations of N6-(phenylisopropyl)adenosine, an analog of adenosine which is not deaminated. The effects of adenosine deaminase on cyclic AMP accumulation were blocked by coformycin which is a potent inhibitor of the enzyme. These findings suggest that deamination of adenosine is responsible for the observed effects of adenosine deaminase preparations. Protein kinase activity of fat cell homogenates was unaffected by adenosine or N6-(phenylisopropyl)adenosine. Norepinephrine-activated adenylate cyclase activity of fat cell ghosts was not inhibited by N6-(phenylisopropyl)adenosine. Adenosine deaminase did not alter basal or norepinephrine-activated adenylate cyclase activity. Cyclic AMP phosphodiesterase activity of fat cell ghosts was also unaffected by adenosine deaminase. Basal and insulin-stimulated glucose oxidation were little affected by adenosine deaminase. However, the addition of adenosine deaminase to fat cells incubated with 1.5 muM norepinephrine abolished the antilipolytic action of insulin and markedly reduced the increase in glucose oxidation due to insulin. These effects were reversed by N6-(phenylisopropyl)adenosine. Phenylisopropyl adenosine did not affect insulin action during a 1-hour incubation. If fat cells were incubated for 2 hours with phenylisopropyl adenosine prior to the addition of insulin for 1 hour there was a marked potentiation of insulin action. The potentiation of insulin action by prior incubation with phenylisopropyl adenosine was not unique as prostaglandin E1, and nicotinic acid had similar effects.
...
PMID:Effects of adenosine deaminase on cyclic adenosine monophosphate accumulation, lipolysis, and glucose metabolism of fat cells. 16 37

Incubation of bovine adrenocortical membranes with corticotropin and 5-guanylylimidodiphosphate produced a state of adenylate cyclase (ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1) with maximal catalytic activity and an increased sensitivity to inhibition by adenosine. Due to metabolism of adenine nucleotides during adenylate cyclase assays a quantitative assessment of the nature of this inhibition was not possible. However, when determined at 0.2--1.0 mM MgATP2-, half-maximal inhibition of the basal and maximally active states of the enzyme was observed at adenosine concentrations of 210--330 and 70--90 micrometer, respectively. The inhibition appeared to be partially competitive, suggesting that the nucleoside may act as an allosteric negative effector which reduces the affinity of the active site for substrate. Adenosine was 5--6 times more potent as an inhibitor of adrenal adenylate cyclase than 2-chloroadenosine. Adenosine deaminase abolished the inhibitory effect of the nucleoside, whilst theophylline had no effect on activity either in the absence or presence of adenosine.
...
PMID:Inhibition of bovine adrenocortical adenylate cyclase activity by adenosine. 71 50

In 32PO4-labeled adipocytes, isoproterenol (ISO) or physiologically relevant concentrations of insulin rapidly increased phosphorylation of a particulate 135-kDa protein which has been identified as a cGMP-inhibited "low Km" cAMP phosphodiesterase (CGI-PDE) by several criteria, including selective immunoprecipitation with anti-CGI-PDE IgG (Degerman, E., Smith, C.J., Tornqvist, H., Vasta, V., Belfrage, P., and Manganiello, V.C. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 533-537). The time courses and concentration dependences for phosphorylation of CGI-PDE by ISO and insulin correlated with CGI-PDE activation in the presence of these agents; effects of ISO were somewhat more rapid than those of insulin. Adenosine deaminase, which metabolizes the adenylate cyclase inhibitor adenosine, also rapidly induced phosphorylation and activation of CGI-PDE. Phenylisopropyladenosine (an adenosine deaminase-resistant adenosine analog) prevented or reversed both adenosine deaminase-stimulated phosphorylation and activation of CGI-PDE (IC50 approximately 0.2 nM). Incubation of adipocytes with 0.1 nM insulin in the presence of ISO rapidly produced 30-200% greater activation and phosphorylation of CGI-PDE than the expected added effects of insulin and ISO individually; both effects preceded the insulin-induced decreases in protein kinase A activity and inhibition of lipolysis. These and other results indicate that CGI-PDE can be phosphorylated at distinct sites and activated by cAMP-dependent and insulin-dependent serine kinase(s), that the activation state of CGI-PDE reflects its relative phosphorylation state, and that synergistic phosphorylation/activation of CGI-PDE may be important in the antilipolytic action of insulin.
...
PMID:Hormone-sensitive cyclic GMP-inhibited cyclic AMP phosphodiesterase in rat adipocytes. Regulation of insulin- and cAMP-dependent activation by phosphorylation. 164 89

The histamine-stimulated accumulation of [3H]cAMP (formed by prelabeling with [3H]adenine) was characterized pharmacologically in a vesicular preparation of guinea pig cortex. The H2 antagonist cimetidine maximally blocked 80% of the response, whereas only 45% of the response could be inhibited by H1 antagonists. A combination of H1 and H2 antagonists completely abolished the response. These and other findings show that both H1 and H2 receptors mediate the response, but 25% of the response may require simultaneous activation of both receptors. A role for adenosine as a mediator of the histamine response was investigated. Adenosine deaminase (EC 3.5.4.4., 2.5 units/ml) decreased basal [3H]cAMP levels, abolished the cimetidine-resistant component of the histamine response, and reduced maximal H1 antagonism of the histamine response to 30%. Treatment with a combination of adenosine deaminase and the calcium chelator EGTA (2 mM) appeared to eliminate the H1 component completely. Under these latter conditions only H2 receptors appeared to mediate the histamine response. Thus, both H1 and H2 receptors stimulate [3H]cAMP accumulation in the vesicular preparation, but the H1 response seems to require either concomitant adenosine or H2 receptor stimulation and may be calcium dependent. These findings differ from those found in broken cell membrane preparations, where only H2 receptors appear to be coupled to adenylate cyclase activation.
...
PMID:Histamine receptors coupled to [3H]cAMP accumulation in brain: pharmacological characterization in a vesicular preparation of guinea pig cortex. 282 98

The involvement of adenosine in the coupling of insulin binding to action was investigated in rat adipocytes. Reduction of endogenous adenosine levels by treatment with adenosine deaminase (ADA) had no significant effect on either basal or maximally stimulated glucose transport, but reduced the insulin sensitivity of transport stimulation. Adenosine deaminase treatment also shifted the EC50 of H2O2 stimulation of transport from 0.13 mM to 0.30 mM, and the EC50 for insulin stimulation of protein synthesis from 0.40 +/- 0.06 ng/ml to 1.30 +/- 0.25 ng/ml. Adenosine appears to be acting through the pharmacological Ri adenosine receptor subtype. The mode of action of adenosine does not seem to involve inhibition of adenylate cyclase. Adenosine also influences the kinetics of insulin action. ADA treatment slows the onset of transport stimulation by a maximal insulin concentration (10 ng/ml). Increasing the hormone level to 100 ng/ml overcomes this slowing without increasing transport further. The deactivation of glucose transport following removal of insulin is accelerated by ADA treatment. Thus, adenosine is involved both in maintaining a high efficiency of an early step in the insulin signaling process and in maintaining optimal activity of the insulin-stimulated glucose transport system.
...
PMID:The role of adenosine in insulin action coupling in rat adipocytes. 285 Sep 47

The effects of adenosine deaminase and of pertussis toxin on hormonal regulation of lipolysis were investigated in isolated human fat cells. Adenosine deaminase (1.6 micrograms/ml) caused a two-to threefold increase in cyclic AMP, which was associated with an increase in glycerol release averaging 150-200% above basal levels. Clonidine, N6-phenylisopropyladenosine, prostaglandin E2, and insulin caused a dose-dependent inhibition of glycerol release in the presence of adenosine deaminase. Pretreatment of adipocytes with pertussis toxin (5 micrograms/ml) for 180 min resulted in a five- to sevenfold increase in cyclic AMP. Glycerol release was almost maximal and isoproterenol caused either no further increase or only a marginal additional increase of lipolysis after pretreatment with pertussis toxin, whereas cyclic AMP levels were 500 times higher than in controls. The effects of antilipolytic agents known to affect lipolysis by inhibition of adenylate cyclase activity, i.e., clonidine, N6-phenylisopropyladenosine, and prostaglandin E2, were impaired. In contrast, the antilipolytic action of insulin was preserved in adipocytes pretreated with pertussis toxin. As in controls, the peptide hormone had no detectable effect on cyclic AMP after pertussis toxin treatment. The findings support the view that the antilipolytic effect of insulin does not require adenylate cyclase or phosphodiesterase action. In addition, the results demonstrate that, upon relief of endogenous inhibition, human fat cell lipolysis proceeds at considerable (adenosine deaminase) or almost maximal (pertussis toxin) rates. A certain degree of inhibition, therefore, appears to be necessary for human fat cell lipolysis to be susceptible for hormonal activation.
...
PMID:Human fat cell lipolysis is primarily regulated by inhibitory modulators acting through distinct mechanisms. 299 84

Although purine nucleosides have been shown to regulate the secretion of several peptide and steroid hormones, effects on pituitary hormone release have not been reported. We show here that in the clonal GH4C1 pituitary cell line maximal concentrations of adenosine (greater than or equal to 50 microM) inhibited PRL and GH secretion by 40%. Adenosine deaminase abolished the inhibitory effect of adenosine but not that of SRIF or (-)N6(R-2-phenylisopropyl)adenosine (PIA), a nonhydrolyzable adenosine analog. Furthermore, this enzyme increased basal secretion by 50%, and analysis of the incubation medium by HPLC demonstrated that the cells secreted biologically effective concentrations of adenosine. These results indicate that adenosine produced in culture tonically inhibits hormone release. In other target cells, adenosine inhibition is mediated by two types of binding sites: an extracellular Ri-site requiring an intact ribose moiety or an intracellular P-site requiring an intact purine ring. Four lines of evidence indicate that in GH4C1 cells, adenosine acts at an Ri-site. PIA, an Ri-site-specific agonist, was a potent inhibitor of hormone release (ED50 = 30 nM). Theophylline, an Ri-site antagonist, competitively inhibited the action of PIA (Ki = 2.4 microM). 3) 2'5'-Dideoxyadenosine, a P-site-specific agonist, did not inhibit PRL release even at a concentration of 1 mM. 4) Dipyridamole, an adenosine uptake inhibitor, did not reduce adenosine inhibition. In addition to its effect on basal secretion, PIA inhibited stimulation of hormone release by vasoactive intestinal peptide and TRH. PIA also reduced vasoactive intestinal peptide-stimulated cAMP accumulation by 75%, consistent with its action to inhibit adenylate cyclase via Ri receptors in other targets. Since PIA inhibition of PRL release and cAMP accumulation was not additive with the effects of SRIF and carbamyl choline, these inhibitors may act via a common rate-limiting step. Our results demonstrate that adenosine activates an Ri-type of adenosine receptor in GH4C1 cells and that the production of adenosine under normal culture conditions causes autocrine inhibition of secretion.
...
PMID:Adenosine inhibits prolactin and growth hormone secretion in a clonal pituitary cell line. 299 34

Adenosine receptors in human platelet membranes have been characterized by radioligand binding and measurement of adenylate cyclase activity. Binding of 5'-N-ethylcarboxamido[3H]adenosine ([3H] NECA ) was rapid, reversible and dependent on protein concentration, pH and temperature. Due to a rapid rate of dissociation (t 1/2 approximately 20 s) binding was highest at 0 degree C. Adenosine deaminase and GTP alone did not influence [3H] NECA binding, whereas several divalent cations decreased binding. Saturation experiments revealed two different binding sites for [3H] NECA , with KD values of 0.16 and 2.9 mumol/l and Bmax values of 8.4 and 33.4 pmol/mg of protein. In competition experiments NECA was the most potent adenosine agonist (IC50 0.5 mumol/l), followed by 2-chloroadenosine (IC50 6.3 mumol/l) and adenosine (IC50 12 mumol/l). A similar rank order of potencies was observed for the stimulatory effect of adenosine analogues on platelet adenylate cyclase. NECA stimulated adenylate cyclase activity with an EC50 value of 0.5 mumol/l and was approximately 4-fold more potent than (-)N6-phenylisopropyladenosine [(-)PIA]. However, (-)PIA and N6-cyclohexyladenosine did not significantly affect [3H] NECA binding, an observation not consistent with the stimulatory effect on adenylate cyclase. The adenosine antagonists 3-isobutyl-1-methylxanthine, theophylline and caffeine showed IC50 values between 98 and 5,600 mumol/l. [3H]PIA bound to platelet membranes with very low affinity and was not displaced by NECA . The [3H] NECA binding to human platelet membranes satisfies essential criteria for Ra adenosine receptors and, with some limitations, should be of value for the characterization of adenosine receptors in Ra subtype selective cells.
...
PMID:Ra adenosine receptors in human platelets. Characterization by 5'-N-ethylcarboxamido[3H]adenosine binding in relation to adenylate cyclase activity. 632 33

This report demonstrates that platelets possess P2 purinoceptors with unique properties that distinguish them from the ADP (P2T) receptor. Extracellular ATP, and its poorly hydrolyzable analogues, inhibit collagen- and U46619 (a thromboxane mimetic)-induced platelet aggregations. Adenosine deaminase was without effect on ATP action while reversing the inhibitory effect of adenosine. A unique aspect of the P2 receptor is the sensitivity to UTP and CTP and insensitivity to GTP. The rank order of inhibition by beta gamma-methylene ATP, alpha beta-methylene ATP > ATP indicates that a P2x-like receptor is present on the platelet membrane. This conclusion is further supported by the nearly complete desensitization to ATP by pre-exposure of platelets to alpha beta-methylene-ATP. However, unlike previously described P2x purinoceptors, the inhibition of platelet aggregation by extracellular ATP appears to result, at least in part, from the ATP-induced increase of intracellular cyclic AMP levels apparently coupled through a Gs protein. The combined addition of iloprost (0.14 to 1.39 nM) and ATP (18 microM) or ATP (20-40 microM) and the phosphodiesterase inhibitor theophylline (0.5 to 1 mM) synergistically inhibited platelet aggregation implying a common interactive site with adenylate cyclase. This is further substantiated by the ability of the adenylate cyclase inhibitor, 2',5'-dideoxyadenosine, to abrogate the inhibitory effects of ATP. The protein kinase A (PKA) inhibitor H1004 blocks ATP inhibition of platelet aggregation while the protein kinase C inhibitor H7 did not. This implies that the generation of cyclic AMP, with the subsequent activation of PKA and phosphorylation of selected proteins is required, in part, for the action of ATP.
...
PMID:Occupancy of P2 purinoceptors with unique properties modulates the function of human platelets. 768 12

Previous work has suggested that adenosine may be involved in ethanol-induced heterologous desensitization of adenylate cyclase in NG108-15 cells. It was proposed that chronic ethanol causes adenosine to accumulate extracellularly, activating adenosine A2 receptors and so leading to a reduction in Gs alpha mRNA and Gs alpha protein (Nagy et al., 1989). In this study we further investigated the effect of chronic ethanol on G-protein expression in NG108-15 cells. Pretreatment of NG108-15 cells with ethanol (200 mM, 48h) reduced membrane levels of Gs alpha and Gi alpha but increased Go alpha expression. The effects of ethanol on alpha-subunit expression were not reversed by adenosine deaminase and could not be mimicked by the adenosine agonist 5'- (n-ethyl)-carboxamidoadenosine (NECA). Chronic ethanol pretreatment did not appear to reduce the levels of Gs alpha or Gi alpha 2 mRNA. This same ethanol pretreatment reduced cell proliferation and increased differentiation without altering cell viability. Adenosine deaminase did not reverse any of these effects. These results indicate that ethanol differentially regulates G-protein alpha-subunit expression and induces morphological alterations in these cells independently of extracellular adenosine.
...
PMID:Involvement of adenosine in ethanol-induced changes in G-protein expression in NG108-15 cells? 774 34


1 2 Next >>

---