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)

It has been hypothesized that secretin may act directly on gastrinoma through the adenylate cyclase system to cause stimulation of gastrin release. We studied gastrinoma cells in vitro to determine whether secretin would stimulate gastrin release directly and whether the gastrinoma cell membrane had a functional secretin receptor adenylate cyclase system. Fresh tumor was prepared in cell suspensions containing 1.5 X 10(6) viable cells and incubated for 2 hours with either 2 mM CaCl2 alone (control) or 2 mM CaCL2 and 0.025 U/ml secretin. The gastrin content of the cells in each incubation chamber and the medium were determined by radioimmunoassay and results were expressed as mean gastrin pg/microgram protein +/- SD. Under basal conditions the cellular gastrin content was 39.9 +/- 6.4 (control) compared with 16.7 +/- 2.1 (secretin). After 2 hours of incubation, cellular gastrin content increased in both groups: 68.5 +/- 11.9 (control) to 68.3 +/- 5.5 (secretin). However, the percent of gastrin released into the medium during incubation decreased by one half in both groups (control 37.3% +/- 4.0% to 22.2% +/- 3.0%; secretin 42.8% +/- 7.0% to 18.9% +/- 1.8%). Adenylate cyclase activity was assessed by measuring cAMP generation in fresh-frozen gastrinoma and cultured gastrinoma cell membranes. Isoproterenol (10(-5) M), PGE1 (10(-4) M), and GppNHp (guanine nucleotide) (10(-5) M) caused fivefold to 25-fold increases in cAMP generation. Secretin did not stimulate adenylate cyclase activity above basal (21.73 +/- 4.07 and 2.29 +/- 1.2 pmol cAMP/mg protein/min) for frozen and cultured gastrinoma, respectively. Secretin failed to stimulate gastrin release and adenylate cyclase in vitro. This suggests that secretin-stimulated gastrin release in vivo may not be due to a direct effect of secretin on the gastrinoma.
 ...
PMID:Failure of secretin to stimulate gastrin release and adenylate cyclase activity in gastrinoma in vitro. 609 76

Long-term exposure of pigeon erythrocytes to isoproterenol causes substantial changes in the regulatory properties of adenylate cyclase. The enzyme sensitivity to isoproterenol (0.2 mM) and GTP (1.0 mM) decreases by 50% after 20 min incubation, while that to guanylyl imidodiphosphate (0.1 mM), a non-hydrolyzeable analogue of GTP, is lowered by 20-25% after 40 min. The decrease of the enzyme sensitivity to the activators is associated with the appearance of a lag period in the effects of isoproterenol and Gpp(NH)p and with an increase of the lag period in the effect of Gpp(NH)p. The observed desensitization is not concomitant with a reduction of the number of beta-adrenoreceptors but leads to the loss of the Gpp(NH)p ability to induce the dissociation of the receptor-bound hormone. Similar effects were observed after simultaneous addition of 0.1 mM cAMP and 1 mM isobutylmethylxanthine to pigeon erythrocytes, although in this case the degree of desensitization was somewhat lower. Desensitization of adenylate cyclase may occur under conditions preventing the formation of cAMP in the cells as a response to the hormone addition (5 mM CaCl2, 10 micrograms/ml of A23187). Under these conditions, the desensitization is characterized by a lag period in the effects of isoproterenol and Gpp(NH)p and a decrease in the number of isoproterenol-binding sites with a high affinity for the agonist. It is assumed that desensitization is a multistep process that requires both isoproterenol and cAMP.
 ...
PMID:[Desensitization of adenylate cyclase of pigeon erythrocytes under the effects of isoproterenol and cAMP]. 609 7

1. A study has been made of the response to injected Gpp(NH)p of the ouabain-insensitive Na efflux in barnacle muscle fibres preexposed to aldosterone. 2. The response to injected Gpp(NH)p is not only greater in size than in unexposed fibres but also sustained. 3. Injection of MgCl2 following peak stimulation causes a partial reversal of the response. 4. Injection of ATPNa2 (and 5'-App(NH)p) leads to a sustained stimulatory response which is not significantly greater than that seen in unexposed fibres. 5. MgCl2 injection causes complete reversal of this response. 6. The response of preexposed fibres to injected CaCl2 in varying concentration and to injected cholera toxin is not significantly different from that seen in unexposed fibres. 7. This is also true of Gpp(NH)p when it is injected after peak stimulation by cholera toxin. 8. Prior application of verapamil (10(-4)M) drastically reduces the response to injected Gpp(NH)p. 9. The residual response is sustained but markedly reduced by injected Mg2+, Fe or Zn. 10. Injection of PKI following Gpp(NH)p reduces the response, provided PKI is also injected before Gpp(NH)p. By contrast, injection of R11 subunits causes a partial reversal if injected only once. 11. Imipramine and trifluoperazine, when applied externally (5 X 10(-5)M), cause almost complete reversal of the response. 12. The suggestion is made that the response to injected Gpp(NH)p is mainly due to activation of Ca2+-channels resulting in activation of the calmodulin/Ca-dependent form of adenylate cyclase and that the primary site of aldosterone action is at the level of the calmodulin form of adenylate cyclase.
 ...
PMID:Increased sensitivity to injected 5'-guanylylimidodiphosphate of the sodium efflux in barnacle muscle fibres preexposed to aldosterone. 613 62

A 16-year old patient had severe end-stage congestive heart failure that was refractory to large doses of beta-agonists. Low serum ionized calcium (Ca2+) levels were corrected by CaCl2 infusions. Myocardial performance correlated directly with serum Ca2+ levels. At the time of transplantation the patient's heart was removed and studied in vitro by both classic and biochemical pharmacologic techniques. Isolated papillary muscles and adenylate cyclase preparations were markedly subsensitive to isoproterenol stimulation, and myocardial membranes were nearly devoid of beta-adrenergic receptors. In contrast, papillary muscles responded normally to calcium, and adenylate cyclase responses to fluoride and histamine were normal. Beta-adrenergic receptor down-regulation may render beta-agonists ineffective, and in such situations the myocardial contractile state may become dependent on extracellular Ca2+.
 ...
PMID:Myocardial performance and extracellular ionized calcium in a severely failing human heart. 613 87

[3H]Octopamine binds to a particulate preparation from heads of Drosophila melanogaster at a level of 0.5 +/- 0.1 pmol/mg protein, with an apparent dissociation constant of 6.0 +/- 0.9 x 10(-9) M at 26 degrees C. The binding is reduced or abolished by heat, trypsin, detergents, sulfhydryl reagents and EDTA. Low concentrations of MgCl2 or CaCl2 increase binding but high ionic strength is inhibitory. Low concentrations of dihydroergotamine, phentolamine, clonidine, chlorimipramine and chlorpromazine, but not of serotonin and propranolol, displace the labeled biogenic amine from its binding sites. The stable GTP analogue, guanosine-5'-(beta-gamma-imido)triphosphate (Gpp(NH)p), at the microM range, decreases the maximal number of the high-affinity [3H]octopamine-binding sites. The properties of the [3H]octopamine-binding sites are compared to the properties of octopamine receptors as revealed by stimulation of adenylate cyclase in insects, including Drosophila.
 ...
PMID:High-affinity [3H]octopamine-binding sites in Drosophila melanogaster: interaction with ligands and relationship to octopamine receptors. 614 69

The level of adenosine 3',5'-monophosphate (cyclic AMP) in the eggs of the sea urchin, Anthocidaris crassispina, was found to change periodically after fertilization. The minimum and maximum levels of cyclic AMP were 1.0 X 10(-7)M and 1.5 X 10(-6)M, respectively. The activity of adenylate cyclase in a 105 000 X g precipitate reached a plateau at 20 min after fertilization and stayed constant for at least 2 h. It was also found that 1.0 mM CaCl2 increased the activity of adenylate cyclase in the same precipitate from unfertilized eggs. In contrast, phosphodiesterase activity changed periodically and correlated with cyclic AMP levels in the eggs. Up to a concentration of 1.5 X 10(-6)M cyclic AMP, phosphodiesterase activity was low, but it became activated when the level of cyclic AMP rose beyond this level. These results indicate that the change in the intracellular level of cyclic AMP is regulated mainly by the change in phosphodiesterase activity.
 ...
PMID:The periodic change in adenosine 3',5'-monophosphate concentration in sea-urchin eggs. 628 94

Vitamin D-deficient rats subjected to thyroparathyroidectomy (TPTX) were used to evaluate in vivo the biological properties of native bovine parathyroid hormone (bPTH) and chemically synthesized fragments and analogues of the hormone on several parameters of hormone action: calcium and phosphorus fluxes, generation of cyclic adenosine 3',5'-monophosphate (cAMP), and the metabolism of 25-hydroxyvitamin D3 [25(OH)D3]. Vitamin D-deficient rats, after TPTX or sham operation, were intravenously infused with a nutrient containing 7.5 mM CaCl2 for 30 h. During the last 7 h, PTH or one of its analogues was infused intravenously at rates between 0.04 and 20 nmol/h. One hour after the start of the peptide infusion, tritiated 25(OH)D3 was injected. Urine was collected hourly for phosphate and cAMP determinations and, at the end of the experiment, blood was obtained to determine the relative accumulation of tritiated 1,25-dihydroxyvitamin D3 ([3H]1,25(OH)2D3). Infusion of bPTH-(1--84), bPTH-(1--34), human (h)PTH-(1--34), or [Nle8, Nle18, Tyr34]bPTH-(1--34) amide was accompanied by a comparable dose-dependent decrease in plasma phosphate and a dose-dependent increase in plasma calcium and [3H]-1,25(OH)2D3, and urinary excretion of phosphate and cAMP. An evaluation of [Nle8, Nle18, Tyr34]bPTH-(3--34) amide, a potent inhibitor of PTH action in vitro in the renal adenylate cyclase assay, revealed that the analogue possessed weak agonist properties in vivo. The analogue increased excretion of both cAMP and phosphate in the urine, decreased plasma phosphate levels, and increased the accumulation of [3H]-1,25(OH)2D3 in the plasma. This multiparameter model system should aid in the elucidation of the in vivo biological effects of PTH and its analogues.
 ...
PMID:A multiresponse parathyroid hormone assay: an inhibitor has agonist properties in vivo. 630 2

[12-3H]Forskolin (27 Ci/mmol) has been used to study binding sites in rat brain tissue by using both centrifugation and filtration assays. The binding isotherm measured in the presence of 5 mM MgCl2 by using the centrifugation assay is described best by a two-site model: Kd1 = 15 nM, Bmax1 (maximal binding) = 270 fmol/mg of protein; Kd2 = 1.1 microM; Bmax2 = 4.2 pmol/mg of protein. Only the high-affinity binding sites are detected when the binding is determined by using a filtration assay; Kd = 26 nM, Bmax = 400 fmol/mg of protein. Analogs of forskolin that do not activate adenylate cyclase (EC 4.6.1.1) do not compete effectively for [3H]forskolin binding sites. Analogs of forskolin that are less potent than forskolin in activating adenylate cyclase are also less potent in competing for forskolin binding sites. The presence of 5 mM MgCl2 or MnCl2 was found to enhance binding. In the presence of 1 mM EDTA the amount of high-affinity binding is reduced to 110 fmol/mg of protein with no change in Kd. There is no effect of CaCl2 (20 mM) or NaCl (100 mM) on the binding. No high-affinity binding can be detected in membranes from ram sperm, which contains an adenylate cyclase that is not activated by forskolin. It is proposed that the high-affinity binding sites for forskolin are associated with the activated complex of catalytic subunit and stimulatory guanine nucleotide binding protein.
 ...
PMID:Binding of [3H]forskolin to rat brain membranes. 643 43

In the present study we investigated the ability of the arachidonic acid metabolites, prostaglandin H2 and thromboxane A2, to release Ca2+ from isolated platelet vesicles. The vesicles were prepared through modification of previously described procedures. 45Ca uptake and release were determined by Millipore filtration and isotope counting of the filter paper. Incubation of the vesicles (25 degrees C) with 50 microM CaCl2 (plus 45Ca) resulted in the accumulation of 13 nmol Ca2+ per mg of protein under steady-state conditions. Addition of arachidonic acid (25 microM) resulted in a 42% release of the accumulated Ca2+ and the production of 150 ng thromboxane B2/mg protein. Pretreatment of the vesicles with indomethacin (4 microM) completely inhibited arachidonic acid-induced Ca2+ release and reduced thromboxane B2 synthesis by 82%. Pretreatment of the vesicles with the specific thromboxane A2/prostaglandin H2 antagonist, 13-azaprostanoic acid (20 microM), also resulted in complete inhibition of Ca2+ release but no inhibition of thromboxane B2 production. Addition of prostaglandin H2 (0.3 microM) to the platelet vesicles produced a significant release of Ca2+ only in the presence of the adenylate cyclase inhibitor, 2',5'-dideoxyadenosine (100 microM). This Ca2+ release was totally blocked by 13-azaprostanoic acid (20 microM). The thromboxane synthetase inhibitor 9,11-azoprosta-5,13-dienoic acid (azo analog I, 3.6 microM), in the presence of 2',5'-dideoxyadenosine, only slightly inhibited Ca2+ release in response to added prostaglandin H2, even though thromboxane B2 production was blocked by 95%.
 ...
PMID:The thromboxane antagonist, 13-azaprostanoic acid, inhibits arachidonic acid-induced Ca2+ release from isolated platelet membrane vesicles. 683 Aug 32

The adenylate cyclase (CyaA) secreted by Bordetella pertussis is a toxin that is able to enter eukaryotic cells and cause a dramatic increase in cAMP level. In addition, the toxin also exhibits an intrinsic hemolytic activity that is independent from the ATP cycling catalytic activity of the toxin. Both the cytotoxic and hemolytic activities are calcium-dependent. In this work, we have analyzed the calcium interacting properties of CyaA. We have shown that CyaA exposed to CaCl2 could retain membrane binding capability and hemolytic activity when it was further assayed in the presence of an excess of EGTA. Determination of the calcium content of CyaA exposed first to calcium and subsequently to EGTA indicated that some (3-5) calcium ions remained bound to the protein, suggesting the existence of Ca2+ binding sites of high affinity. Binding of Ca2+ to these sites might be necessary for both the membrane binding capability and the hemolytic activity of the toxin. In addition, CyaA possesses a large number (about 45) of low affinity (KD = 0.5-0.8 mM) Ca2+ binding sites that are located in the C terminus of the toxin, between amino acids 1007 and 1706. This region mainly consists of about 45 repeated sequences of the type GGXGXDXLX (where X represents any amino acid) that are characteristic of the RTX (Repeat in ToXin) bacterial protein family. Our data suggest that each one can bind one calcium ion. Circular dichroism spectroscopy analysis showed that calcium binding to the low affinity sites induces a large conformational change of CyaA, as revealed by an important increase in the content of alpha-helical structures. This conformational change might be directly involved in the Ca(2+)-dependent translocation of the catalytic domain of CyaA through the plasma membrane of target cells.
 ...
PMID:Interaction of calcium with Bordetella pertussis adenylate cyclase toxin. Characterization of multiple calcium-binding sites and calcium-induced conformational changes. 759 50


<< Previous 1 2 3 4 Next >>