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:3.5.4.4 (adenosine deaminase)
5,136 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Adenine nucleotides displace the binding of the selective adenosine A-1 receptor ligand [3H]cyclopentyladenosine (CPA) to rat brain membranes in a concentration-dependent manner, with the rank order of activity being ATP greater than ADP greater than AMP. Binding was also displaced by GTP, ITP, adenylylimidodiphosphate (AppNHp), 2-methylthioATP, and the beta-gamma-methylene isostere of ATP, but was unaffected by the alpha-beta-methylene isosteres of ADP and ATP, and UTP. At ATP concentrations greater than 100 microM, the inhibitory effects on CPA binding were reversed, until at 2 mM ATP, specific binding of CPA was identical to that seen in controls. Concentrations of ATP greater than 10 mM totally inhibited specific binding. Inclusion of the catabolic enzyme adenosine deaminase in the incubation medium abolished the inhibitory effects of ATP, indicating that these were due to adenosine formation, presumably due to ectonucleotidase activity. The inhibitory effects were also attenuated by the alpha-beta-methylene isostere of ATP, an ectonucleotidase inhibitor. Adenosine deaminase, alpha-beta-methylene ATP (100 microM), and beta-gamma-methylene ATP (100 microM) had no effect on the "stimulatory" phase of binding, although GTP (100 microM) slightly attenuated it. Comparison of the binding of [3H]CPA in the absence and presence of 2 mM ATP by saturation analysis showed that the KD and apparent Bmax values were identical. Examination of the pharmacology of the control and "ATP-dependent" CPA binding sites showed slight changes in binding of adenosine agonists and antagonists. The responses observed with high concentrations of ATP were not observed with GTP, AppNHp, the chelating agents EDTA and EGTA, or inorganic phosphate. The divalent cations Mg2+ and Ca2+ at 10 mM attenuated the stimulatory actions of high (2 mM) concentrations of ATP, whereas EGTA and EDTA (10 mM) enhanced the "stimulatory" actions of ATP. EDTA (10 mM) abolished the inhibitory effects of ATP, indicating a specific dependence on Mg2+ for the inhibitory response. The effects of ATP on [3H]CPA binding were reversible for antagonists but not agonists. The mechanism by which ATP reverses its own inhibitory action on adenosine A-1 radioligand binding is unclear, and from the observed actions of the divalent cations and chelating agents probably does not involve a phosphorylation-dependent process.
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PMID:Effects of purine nucleotides on the binding of [3H]cyclopentyladenosine to adenosine A-1 receptors in rat brain membranes. 308 5

When thymocytes were cultured with adenosine, deoxyadenosine, or deoxyguanosine at 1 mM for 24 h, DNA cleavage at internucleosomal sites with multiples of approximately 180 bp was induced, followed by lactate dehydrogenase release into the medium. In the presence of coformycin, an adenosine deaminase inhibitor, or formycin B, a purine nucleoside phosphorylase inhibitor, DNA cleavage was induced by these nucleosides at concentrations of less than 50 microM. Other purine and pyrimidine ribo- and deoxyribonucleosides did not induce DNA cleavage or LDH release. Because thymocyte nuclei contain a Ca2+,Mg2+-dependent endonuclease, which preferentially cuts DNA in its linker regions, DNA fragmentation induced by the three purine nucleosides was suggested to occur through increased activity of the endonuclease. The DNA cleavage induced by the nucleosides required protein phosphorylation and synthesis, inasmuch as it was inhibited by an inhibitor of protein kinases, H-7, and by an inhibitor of protein synthesis, cycloheximide. The inhibition of DNA cleavage was accompanied by a reduction in lactate dehydrogenase release, suggesting a causal relationship between DNA cleavage and cell death. The DNA cleavage and subsequent cell lysis might be related to the selective thymocyte deletion observed in patients with adenosine deaminase or purine nucleoside phosphorylase deficiency.
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PMID:Adenosine, deoxyadenosine, and deoxyguanosine induce DNA cleavage in mouse thymocytes. 326 57

The activities of 5'-nucleotidase (5'-ribonucleoside phosphohydrolase, EC 3.1.3.5); adenosine deaminase (adenosine aminohydrolase, EC 3.5.4.4); AMP deaminase (AMP aminohydrolase, EC 3.5.3.6), and ATP-(Mg2+)-ase (ATP phosphohydrolase, EC 3.6.1.3) were assayed in mitochondria of normal and regenerating rat liver 5'-Nucleotidase (5'Nase) and ATP-(Mg2+)-ase activities were compared with similar enzyme activities in the plasma membrane (PM) fraction, obtained from the same biological material. In the regenerating liver, 5'Nase for dTMP diminished its activity by 56% (24 h after partial hepatectomy) and 35 +/- 4% for all substrates in the PM fraction (48 h after operation). In mitochondria, 5'Nase for dTMP manifests sigmoidal substrate activity curve (in contrast with all substrates in the PM fraction and remaining substrates in mitochondria). In vivo 5-azacytidine (a) administered 1 h after partial hepatectomy, prevented changes of 5'Nase activity: (b) administered 24 or 48 h after partial hepatectomy, stabilized low 5'Nase activity (in mitochondria for dTMP, in the PM fraction for all substrates) and decreased ATP-(Mg2+)-ase activity by 51 and 31% in mitochondria and the PM fraction respectively.
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PMID:A distinctive activity of 5'-nucleotidase for dTMP in rat liver mitochondria. 615 75

Adenosine inhibited three Ca2+-dependent potentials recorded intracellularly from post-ganglionic neurones of the rat superior cervical ganglion. A shoulder on the falling phase of the action potential elicited in normal Locke solution, a hyperpolarizing after-potential (h.a.p.) that follows the spike, and a regenerative Ca2+ spike elicited in Locke solution containing TTX and TEA were all reversibly inhibited by adenosine analogues in a dose-dependent fashion. The maximum rate of rise of the Ca2+ spike (dV/dt) was markedly reduced suggesting that the underlying mechanism of adenosine action is inhibition of the Ca2+ conductance mechanism and thus, the voltage-sensitive Ca2+ current. I/V curves in low Ca2+, high Mg2+, TTX, TEA, and Co2+ to block the Ca2+ current show no change in resistance in the presence of 2-chloroadenosine. The actions of adenosine were nearly eliminated in the presence of 1 mM-theophylline, an adenosine receptor antagonist. The order of agonist potency on the inhibition of the h.a.p. was: N-6-[L-phenylisopropyl] adenosine (L-PIA) greater than 2-chloroadenosine greater than adenosine greater than cyclic AMP = 5' AMP. The concentration of L-PIA which produced a half-maximal effect (EC50) was 0.5 microM and that for cyclic AMP was 100 microM. Dipyridamole, an adenosine uptake blocker, potentiated the effects of low concentrations of adenosine and shifted the dose-response curve for adenosine towards that of 2-chloroadenosine (EC50 = 1 microM). These results are consistent with the concept of an external adenosine receptor, but we are unable to assign a receptor subtype. Cyclic AMP mimicked the effects of adenosine, but these effects were eliminated by adenosine deaminase. Our results suggest that the electrogenic effects of bath-applied cyclic AMP may result from the metabolism of cyclic AMP to adenosine by ganglionic tissue. We conclude that adenosine activates a receptor on the neuronal cell surface to inhibit the voltage-dependent Ca2+ current.
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PMID:The ionic basis of adenosine receptor actions on post-ganglionic neurones in the rat. 630 30

A simple, rapid and reliable radiometric assay for the determination of catechol-O-methyltransferase activity is described. The method is based on the conversion of catechol to [3H]guaiacol by catechol-O-methyltransferase in the presence of Mg2+, adenosine deaminase and S-adenosyl L-[methyl-3H]methionine. Incubation and direct extraction of [3H]guaiacol into organic scintillation fluid, as well as counting, are performed in the same standard scintillation vial. The assay is easy to perform and more sensitive than previous analogous procedures. The method has been applied to the assay of catechol-O-methyltransferase activity in discrete brain areas and also peripheral organs of rat and in human erythrocytes.
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PMID:Rapid and sensitive single-step radiochemical assay for catechol-O-methyltransferase. 710 26

Changes in oxidative metabolism were studied in hepatopancreas, muscle, and hemolymph of the edible crab Scylla serrata, exposed to a sublethal concentration (2.5 ppm) of cadmium chloride. A significant decrease in glycogen, total carbohydrates, and pyruvate and an increase in lactate levels in hepatopancreas and muscle were observed. Hemolymph sugar levels were increased in experimental crabs. An increase in phosphorylase suggested increased glycogenolysis during cadmium toxicity. The decrease in lactate dehydrogenase activity and the increase in lactate content indicated reduced mobilization of pyruvate into the citric acid cycle. Krebs cycle enzymes such as succinate dehydrogenase and malate dehydrogenase were found to be decreased, suggesting impairment of mitochondrial oxidative metabolism as a consequence of cadmium toxicity. Glucose-6-phosphate dehydrogenase activity was increased, suggesting enhanced oxidation of glucose by the HMP pathway. Cytochrome-c oxidase and Mg2+ ATPase activity levels decreased, indicating impaired energy synthesis during cadmium stress. Acid and alkaline phosphatase activities increased, suggesting enhanced breakdown of phosphates to release energy in view of impaired ATPase system during cadmium exposure. A significant decrease in protein and free amino acid and an increase in ammonia, urea, and glutamine levels were observed in the tissues during exposure. An increase in protease, alanine aminotransaminase, and aspartate aminotransaminase suggested increased proteolysis and transamination of amino acids. The increase in glutamate dehydrogenase, AMP deaminase, and adenosine deaminase indicated increased ammonia production. The increased arginase and glutamine synthetase suggested the detoxification or mobilization of ammonia toward the production of urea and glutamine. These results suggest that cadmium affects oxidative metabolism and induces hyperammonemia, and crabs switch over their metabolic profiles toward compensatory mechanisms for the survivability in cadmium-polluted habitats.
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PMID:Changes in oxidative metabolism in selected tissues of the crab (Scylla serrata) in response to cadmium toxicity. 753 86

Purified striatal synaptosomes were superfused continuously with L-[3,5-3H]tyrosine to measure simultaneously the synthesis ([3H]water formed during the conversion of [3H]tyrosine into [3H]DOPA) and the release of [3H]dopamine ([3H]DA). Glutamate (10(-3) M) and NMDA (10(-3) M, in the absence of Mg2+) stimulated the release of [3H]DA, but they reduced the efflux of [3H]water. This reduction of [3H]DA synthesis was blocked by 2-amino-5-phosphonovalerate indicating the involvement of NMDA receptors. Although D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionate (AMPA) and kainate stimulated the release of [3H]DA, they did not affect its synthesis. The glutamate-evoked inhibition of [3H]DA synthesis was prevented when synaptosomes were superfused continuously with adenosine deaminase plus quinpirole, a treatment which markedly reduces the phosphorylation of tyrosine hydroxylase by cAMP dependent protein kinase. The opposite effects of glutamate on [3H]DA synthesis and release were mimicked by ionomycin (10(-6) M). It is proposed that both an activation of a cyclic nucleotide phosphodiesterase and a dephosphorylation of tyrosine hydroxylase linked to the influx of calcium through NMDA receptors is responsible for the inhibition of dopamine synthesis by glutamate and that calcineurin could play a critical role in these processes.
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PMID:Opposite presynaptic regulations by glutamate through NMDA receptors of dopamine synthesis and release in rat striatal synaptosomes. 791 26

Adenosine is recognised as an important regulator of myocardial function and coronary vascular tone in the ischaemic myocardium. It is produced by the enzymatic dephosphorylation of 5'-AMP by 5'-nucleotidase and the hydrolysis of SAH by SAH-hydrolase. 5'-Nucleotidase is thought to contribute to adenosine production aside from the accumulation of 5'-AMP in the ischaemic myocardium, while the hydrolysis of SAH plays a major role in adenosine production in the normoxic myocardium. 5'-Nucleotidase activity is reported to increase adenosine production through accumulation of ATP, ADP, H+, Mg2+ and inorganic phosphate during ischaemia. In addition, we have found that alpha 1 adrenergic receptors, activated in ischaemic hearts, increase both 5'-nucleotidase activity and adenosine production. Inactivation of adenosine deaminase and adenosine kinase may also contribute to adenosine production. On the other hand, the major role of endogenous adenosine is to increase coronary blood flow. This adenosine induced coronary vasodilatation is amplified by alpha 2 adrenoceptor stimulation. Adenosine induced vasodilatation is also enhanced by increasing H+ and opening ATP sensitive K+ channels, which occurs in the ischaemic myocardium. However, coronary vasodilatation is not the only effect of adenosine in the ischaemic myocardium. Stimulation of adenosine A2 receptors coupled to Gs proteins attenuates both free radical generation by activated leucocytes and aggregation of platelets. Adenosine A1 receptor activation coupled to G(i) proteins attenuates beta adrenoceptor mediated increases in myocardial contractility, Ca2+ influx into myocytes, and noradrenaline release from the presynaptic nerves. Any or all of these effects may attenuate ischaemic and reperfusion injury.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Role of adenosine and its interaction with alpha adrenoceptor activity in ischaemic and reperfusion injury of the myocardium. 838 27

Human fibroblast lysosomes, purified on Percoll density gradients, contain an adenosine deaminase (ADA) activity that accounts for approximately 10% of the total ADA activity in GM0010A human fibroblasts. In assays of lysosomal ADA, the conversion of [3H]adenosine into [3H]inosine was proportional to incubation time and the amount of lysosomal material added to reaction mixtures. Maximal activity was observed between pH 7 and 8, and lysosomal ADA displayed a Km of 37 microM for adenosine at 25 degrees C and pH 5.5. Lysosomal ADA was completely inhibited by 2.5 mM Cu2+ or Hg2+ salts, but not by other bivalent cations (Ba2+, Cd2+, Ca2+, Fe2+, Mg2+, Mn2+ and Zn2+). Coformycin (2.5 mM), deoxycoformycin (0.02 mM), 2'-deoxyadenosine (2.5 mM), 6-methylaminopurine riboside (2.5 mM), 2'-3'-isopropylidene-adenosine (2.5 mM) and erythro-9-(2-hydroxy-3-nonyl)adenine (0.2 mM) inhibited lysosomal ADA by > 97%. In contrast, 2.5 mM S-adenosyl-L-homocysteine and cytosine were poor inhibitors. Nearly all lysosomal ADA activity is eluted as a high-molecular-mass protein (> 200 kDa) just after the void volume on a Sephacryl S-200 column, and is very heat-stable, retaining 70% of its activity after incubation at 65 degrees C for 80 min. We speculate that compartmentalization of ADA within lysosomes would allow deamination of adenosine to occur without competition by adenosine kinase, which could assist in maintaining cellular energy requirements under conditions of nutritional deprivation.
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PMID:Demonstration of adenosine deaminase activity in human fibroblast lysosomes. 845 34

For murine adenosine deaminase, we have determined that a single zinc or cobalt cofactor bound in a high affinity site is required for catalytic function while metal ions bound at an additional site(s) inhibit the enzyme. A catalytically inactive apoenzyme of murine adenosine deaminase was produced by dialysis in the presence of specific zinc chelators in an acidic buffer. This represents the first production of the apoenzyme and demonstrates a rigorous method for removing the occult cofactor. Restoration to the holoenzyme is achieved with stoichiometric amounts of either Zn2+ or Co2+ yielding at least 95% of initial activity. Far UV CD and fluorescence spectra are the same for both the apo- and holoenzyme, providing evidence that removal of the cofactor does not alter secondary or tertiary structure. The substrate binding site remains functional as determined by similar quenching measured by tryptophan fluorescence of apo- or holoenzyme upon mixing with the transition state analog, deoxycoformycin. Excess levels of adenosine or N6- methyladenosine incubated with the apoenzyme prior to the addition of metal prevent restoration, suggesting that the cofactor adds through the substrate binding cleft. The cations Ca2+, Cd2+, Cr2+, Cu+, Cu2+, Mn2+, Fe2+, Fe3+, Pb2+, or Mg2+ did not restore adenosine deaminase activity to the apoenzyme. Mn2+, Cu2+, and Zn2+ were found to be competitive inhibitors of the holoenzyme with respect to substrate and Cd2+ and Co2+ were noncompetitive inhibitors. Weak inhibition (Ki > or = 1000 microM) was noted for Ca2+, Fe2+, and Fe3+.
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PMID:The role of divalent cations in structure and function of murine adenosine deaminase. 914 74


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