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:4.6.1.2 (guanylate cyclase)
8,497 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The increase in intracellular cyclic GMP concentrations in response to muscarinic-receptor activation in N1E-115 neuroblastoma cells is dependent on extracellular Ca2+ ion. The calcium ionophore A23187 can also evoke an increase in cyclic GMP in the presence of Ca2+ ion. Most (about 85%) of the guanylate cyclase activity of broken-cell preparations is found in the soluble fraction. The soluble enzyme can utilize MnGTP (Km = 55 micrometer), MgGTP (Km = 310 micrometer) and CaGTP (Km greater than 500 micrometer) as substrates. Free GTP is a strong competitive inhibitor (Ki approximately 20 micrometer). The enzyme possesses an allosteric binding site for free metal ions (Ca2+, Mg2+ and Mn2+). The membrane-bound guanylate cyclase is qualitatively similar to the soluble form, but has lower affinity for the metal-GTP substrates. Entry of Ca2+ into cells may increase cyclic GMP concentration by activating guanylate cyclase through an indirect mechanism.
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PMID:Regulation of synthesis of guanosine 3':5'-cyclic monophosphate in neuroblastoma cells. 3 71

The properties of particulate guanylate cyclase (GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2) from purified rabbit skeletal muscle membrane fragments were studied. Four membrane fractions were prepared by sucrose gradient centrifugation and the fractions characterized by analysis of marker enzymes. Guanylate cyclase activity was highest in the fraction possessing enzymatic properties typical of sarcolemma, while fractions enriched with sarcoplasmic reticulum had lower activities. In the presence of suboptimal Mn2+ concentrations, Mg2+ stimulated particulate guanylate cyclase activity both before and after solubilization in 1% Triton X-100. Guanylate cyclase activity was biphasic in the presence of Ca2+. Increasing the Ca2+ concentration from 10(-8) to 10(-5) M decreased the specific activity. As the Ca2+ concentration was further increased to 5 . 10(-4) M enzyme activity again increased. After solubilization of the membranes in 1% Triton X-100, Ca2+ suppressed enzyme activity. Studies utilizing ionophore X537A indicated that the altered effect of Ca2+ upon the solubilized membranes was independent of asymmetric distribution of Ca2+ and Mg2+.
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PMID:Particulate guanylate cyclase of skeletal muscle: effects of Ca2+ and other divalent cations on enzyme activity. 3 38

A method for the assay of guanylate cyclase is described utilizing alpha-[32P]-GTP as substrate for the enzyme reaction. 100-150 microgram of enzyme protein is incubated in a 15.6 mM Tris-HCl buffer incubation mixture, pH 7.6. The reaction is stopped by the addition of EDTA. The [32P]-cyclic GMP formed is separated by a two-step column chromatography on Dowex 50W-X4 ion-exchange resin and neutral alumina. The recovery for cyclic GMP was about 70%. The blank values ranged from 0.001-0.003% of the added alpha-[32P]-GTP which had been purified by Dowex 50W-X4 column chromatography. This method was employed for the assay of guanylate cyclase activities in different tissues.
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PMID:A sensitive method for the assay of guanylate cyclase activity. 3 7

Paraquat, a herbicide which is known to increase intracellular levels of superoxide anion (O2-), stimulated guanylate cyclase [GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2.] activity. This stimulation by paraquat was seen at concentrations as low as 0.005 mM. The activation of guanylate cyclase by paraquat was not blocked by KCN, an inhibitor of superoxide dismutase [EC 1.15.1.1.], suggesting that the activation process probably does not involve superoxide dismutase which converts superoxide anion to hydrogen peroxide and ultimately to hydroxyl radical. Catalase [EC 1.11.1.6.] did not block the paraquat activation of guanylate cyclase indicating that hydrogen peroxide was probably not involved in the activation process. Butylated hydroxytoluene, a hydroxyl radical scavenger, also had no effect on the paraquat activation of guanylate cyclase activity. Superoxide dismutase inhibited the paraquat activation of guanylate cyclase. Thus, it would appear that superoxide ion itself can activate guanylate cyclase circumventing any requirement for hydroxyl radical formation.
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PMID:Activation of liver guanylate cyclase by paraquat: possible role of superoxide anion. 3 15

Guanylate cyclase activity (GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2.), measured in purified rat liver plasma membranes, was markedly increased by treatment with various purified proteases. The effect was maximal with trypsin, alpha-chymotrypsin, papain, and thermolysin (6- to 8-fold increase with 5 to 20 microgram of protease/ml) and lower with subtilisin and elastase (3- to 4-fold increase). The activation was due to an increase in the maximal velocity of the cyclizing reaction. No modification was observed either in the apparent affinity for the substrate MnGTP or in the cooperative behavior of the enzyme kinetics which displayed Hill coefficients of 1.6 for both basal and activated states. The Triton X-100-dispersed guanylate cyclase remained sensitive to papain, which suggests that the action of proteases was not restricted to an indirect action upon the membranous environment of the guanylate cyclase. In contrast, the cytosolic soluble guanylate cyclase, assayed in the presence or absence of sodium azide, was absolutely insensitive to papain. Thus, proteolysis represents a previously undescribed mechanism for activating membranous guanylate cyclase systems, which might be of importance in the physiological regulation of this enzyme.
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PMID:Activation of rat liver guanylate cyclase by proteolysis. 3 29

The 105 000 X g gupernatant fractions from homogenates of various rat tissues catalyzed the formation of both cyclic GMP and cyclic AMP from GTP and ATP, respectively. Generally cyclic AMP formation with crude or purified preparations of soluble guanylate cyclase was only observed when enzyme activity was increased with sodium azide, sodium nitroprusside, N-methyl-N'-nitro-N-nitrosoguanidine, sodium nitrite, nitric oxide gas, hydroxyl radical and sodium arachidonate. Sodium fluoride did not alter the formation of either cyclic nucleotide. After chromatography of supernatant preparations on Sephadex G-200 columns or polyacrylamide gel electrophoresis, the formation of cyclic AMP and cyclic GMP was catalyzed by similar fractions. These studies indicate that the properties of guanylate cyclase are altered with activation. Since the synthesis of cyclic AMP and cyclic GMP reported in this study appears to be catalyzed by the same protein, one of the properties of activated guanylate cyclase is its ability to catalyze the formation of cyclic AMP from ATP. The properties of this newly described pathway for cyclic AMP formation are quite different from those previously described for adenylate cyclase preparations. The physiological significance of this pathway for cyclic AMP formation is not known. However, these studies suggest that the effects of some agents and processes to increase cyclic AMP accumulation in tissue could result from the activation of either adenylate cyclase or guanylate cyclase.
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PMID:Synthesis of adenosine 3',5'-monophosphate by guanylate cyclase, a new pathway for its formation. 3 26

Both testosterone and cyclic GMP stimulate DNA synthesis. Because cyclic GMP and testosterone seem to have similar actions, the objective of this investigation was to determine if testosterone and its precursors might have part of their mechanism of action through stimulation of guanylate cyclase [GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2], the enzyme that catalyzes the formation of cyclic GMP from GTP. The precursors--namely, progesterone, pregnenolone, 17 alpha-progesterone, 17 alpha-hydroxypregnenolone, androstenedione, and dehydroepiandrosterone--caused a 2- to 3 1/2-fold enhancement of guanylate cyclase activity in rat liver, kidney, skeletal muscle, and ventral prostate at a concentration of 1 microM. These precursors are generated from cholesterol, which had no effect itself on guanylate cyclase activity. Testosterone, 19-nortestosterone, 17-methyltestosterone, and 5 alpha-dihydrotestosterone enhanced guanylate cyclase activity 2- to 5-fold in the same tissues at 1 microM. Etiocholanolone, androsterone, and epiandrosterone, metabolites of testosterone metabolism, enhanced guanylate cyclase activity 1 1/2- to 2-fold at this same concentration. Dose-response relationships revealed that testosterone and its precursors and metabolites had their maximal effect at 1 microM but still had some effect at 0.001 microM. The data in this investigation suggest that the guanylate cyclase-cyclic GMP system plays a role in the mechanism of action of testosterone and its precursors.
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PMID:Testosterone and its precursors and metabolites enhance guanylate cyclase activity. 4 Feb 26

A phosphohydrolase with a preferential activity for GTP has been isolated and partially purified from E. coli extracts. The enzyme purification has been achieved through precipitation by ammonium sulfate and chromatography on DEAE-cellulose, DEAE-Sephadex, Ultragel and a second DEAE-cellulose column. The phosphohydrolase activity is poly (C) dependent. The chromatographic analysis on PEI-cellulose has shown that the main product of GTP hydrolysis is GDP. The possibility that the enzyme partially purified in this work has an important role in the control of GTP availability as substrate for guanylate cyclase into the cells has been discussed.
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PMID:[Guanylate cyclase in E. coli. III. Purification and possible physiological role of GTPase]. 4 Jun 73

The purpose of this study was to elucidate the mechanisms by which arachidonic acid activates guanylate cyclase from guinea pig lung. Guanylate cyclase activities in both homogenate and soluble fractions of lung were examined. Guanylate cyclase activity was determined by measuring formtion of [32-P] cyclic GMP from alpha-[32-P] GTP in the presence of Mn2+, a phosphodiesterase inhibitor and a suitable GTP regenerating system. Arachidonic acid, and to a slight extent dihomo-gamma-linolenic acid, activated guanylate cyclase in homogenate but not soluble fractions. Similarly, phospholipase A2 activated homogenate but not soluble guanylate cyclase. Methyl arachidonate, linolenic, linoleic and oleic acids did not activate guanylate cyclase in either fraction. High concentrations of indomethacin, meclofenamate and aspirin inhibited activation of homogenate guanylate cyclase by arachidonic acid and phospholipase A2, without altering basal enzyme activity. These data suggested that a product of cyclooxygenase activity, present in the microsomal fraction, may have accounted for the capacity of arachidonic acid to activate homogenate guanylate cyclase. This view was supported by the findings that addition of the microsomal fraction to be soluble fraction enabled arachidonic acid to activate soluble guanylate cyclase, an effect which was reduced with cycloooxygenase inhibitors. Lipoxygenase activated guanylate cyclase in homogenate and soluble fractions. Arachidonic acid potentiated the activation of soluble guanylate cyclase by lipoxygenase, and this effect was inhibited with nordihydroguairetic acid, 1-phenyl-3-pyrazolidone and hydroquinone, but not with high concentrations of indomethacin, meclofenamate or aspirin. These data suggest that arachidonic acid activates guinea pig lung guanylate cyclase indirectly, via two independent mechanisms, one involving the microsomal fraction and the other involving lipoxygenase.
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PMID:Arachidonic acid activation of guinea pig lung guanylate cyclase by two independent mechanisms. 4 57

The channel-forming antibiotic alamethicin activated rat lung particulate guanylate cyclase (GTP pyrophosphate-lyase (cyclizing) EC 4.6.1.2), and the activated enzyme was further stimulated by sodium nitroprusside when a thiol such as 2-mercaptoethanol was present. Similar effects were seen with the antibiotic gramicidin S and with melittin, a polypeptide purified from bee venom. All of these agents are amphiphilic polypeptides. Nitroprusside was not able to stimulate both particulate and soluble enzyme treated with the nonionic amphiphile, Lubrol PX, suggesting that the membrane-active polypeptides had a different mechanism of action. These polypeptides are known to alter the membrane matrix by binding to phospholipid, and we suggest that this alteration allowed greater access of substrate and of nitroprusside to the enzyme. Lubrol PX, however, may interact preferentially with the enzyme, and thus block nitroprusside activation. The most potent of these agents was melittin, which stimulated nitroprusside activation at a concentration which had little effect by itself (7 microns), and at which others have demonstrated lytic effects on cells.
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PMID:Effect of alamethicin, gramicidin S and melittin upon the particulate guanylate cyclase from rat lung. 9 May 24


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