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Query: EC:3.6.1.3 (ATPase)
 65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Increasing concentrations of Mg within a range between 0.1-5.0 mmol/l step-by-step activated the Mg-dependent ATPase and ADPase in rat heart sarcolemma. Both Mg-dependent activities were influenced by NaN3 in a similar way. Also, activation of both enzymes by their substrates, ADP and ATP, were affected by NaN3 in a similar mode. It appears that both enzyme activities are secured by the same system which is capable of ADP hydrolysis during ATP insufficiency. In the absence of naN3 the enzyme revealed higher affinity to ATP than to ADP. The activation energy was lower for ATP hydrolysis. The above findings indicate that at non limiting concentrations of Mg2+ the enzyme is favoring ATP.
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PMID:Enzyme kinetics and the activation energy of Mg-ATPase in cardiac sarcolemma: ADP as an alternative substrate. 872 Jun 95

1. The role of ATP, which is co-released with acetylcholine in synaptic contacts of Torpedo electric organ, was investigated by use of suramin. Suramin [8-(3-benzamido-4-methylbenzamido)naphthalene-1,3,5-trisulphoni c acid], a P2 purinoceptor antagonist, potently inhibited in a non-competitive manner the ecto-apyrase activity associated with plasma membrane isolated from cholinergic nerve terminals of Torpedo electric organ. The Ki was 30 microM and 43 microM for Ca(2+)-ADPase and Ca(2+)-ATPase respectively. 2. In Torpedo electric organ, repetitive stimulation decreased the evoked synaptic current by 51%. However, when fragments of electric organ were incubated with suramin the evoked synaptic current declined by only 14%. Fragments incubated with the selective A1 purinoceptor antagonist, DPCPX, showed 5% synaptic depression. 3. The effects of suramin and DPCPX on synaptic depression were not addictive. Synaptic depression may thus be linked to endogenous adenosine formed by dephosphorylation of released ATP by an ecto-apyrase. The final effector in synaptic depression, adenosine, acts via the A1 purinoceptor. 4. ATP hydrolysis is prevented in the presence of suramin. It slightly increased (20%) the mean amplitude of spontaneous miniature endplate currents. The frequency distribution of the amplitude of spontaneous events was shifted to the right, indicating that ATP, when not degraded, may modulate the activation of nicotinic acetylcholine receptors activated by the quantal secretion of acetycholine.
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PMID:Action of suramin upon ecto-apyrase activity and synaptic depression of Torpedo electric organ. 881 48

Apyrase activity has been found in tissue of all investigated plant species. Seedlings soluble fractions accounted for 45-75% of the cell apyrase activity, whereas the apyrases isolated from microsomes accounted for 0.2-7% of the total homogenate activity. The ratio of the rate of ATP hydrolysis to the rate of ADP hydrolysis, Ksh, divides the apyrases into two groups: of Ksh > 1 (enzymes from most of monocot plants and bovine tissues) and of Ksh < 1 (enzymes from dicot plants). Triflupromazine strongly decreased the activity of wheat and bovine apyrases (first group) and does not inhibit the activity of the enzyme from potato (second group). Analysed apyrases reveal a significant antigenic diversity. Antibodies developed against soluble potato apyrase have no affinity to apyrase from microsomes of wheat seedlings. Immunological analysis confirmed that ATPase and ADPase activities of potato apyrase were associated with one protein. Apyrases, including animal ones, are insensitive to ATPases inhibitors and reagents of SH groups, whereas sodium deoxycholate inhibits all of the studied enzymes. NaF decreases activity plant enzymes, whereas erythrosine B and NaN3 only decreases bovine apyrases.
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PMID:Comparative studies on animal and plant apyrases (ATP diphosphohydrolase EC 3.6.1.5) with application of immunological techniques and various ATPase inhibitors. 882 8

Extracellular nucleotides interact with specific receptors on the cell surface and are locally metabolized by ecto-nucleotidases. Biochemical characterization of the ATPase and ADPase activities detected in rat heart sarcolemma, under conditions where mitochondrial ATPase and adenylate kinase were blocked, supports our proposal that both activities correspond to a single enzyme, known as ATP-diphosphohydrolase or apyrase. The physiological function of this enzyme could be dephosphorylation of the nucleotides present in the interstitial heart compartment acting together with 5'-nucleotidase. Both hydrolytic activities have similarities in: sarcolemma localization, bivalent metal ion dependence, optimum pH, effect of several amino acid residue modifiers, competitive inhibition of nucleotide analogs, and broad nucleoside di-and triphosphate specificity. The ATPase activity could not be separated from the ADPase either through isoelectrofocusing or electrophoresis under acid conditions.
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PMID:ATP-diphosphophydrolase activity in rat heart tissue. 886 7

Recovery of cell volume in response to osmotic stress is mediated in part by increases in the Cl- permeability of the plasma membrane. These studies evaluate the hypothesis that ATP release and autocrine stimulation of purinergic (P2) receptors couple increases in cell volume to opening of Cl- channels. In HTC rat hepatoma cells, swelling induced by hypotonic exposure increased membrane Cl- current density to 44.8 +/- 7.1 pA/pF at -80 mV. Both the rate of volume recovery and the increase in Cl- permeability were inhibited in the presence of the ATP hydrolase apyrase (3 units/ml) or by exposure to the P2 receptor blockers suramin and Reactive Blue 2 (10-100 microM). Cell swelling also stimulated release of ATP. Hypotonic exposure increased the concentration of ATP in the effluent of perfused cells by 170 +/- 36 nM in the presence of a nucleotidase inhibitor (P < 0.01). In whole-cell recordings with ATP as the charge carrier, cell swelling increased membrane current density approximately 30-fold to 16.5 +/- 10.4 pA/pF. These findings indicate that increases in cell volume lead to efflux of ATP through opening of a conductive pathway consistent with a channel, and that extracellular ATP is required for recovery from swelling. ATP may function as an autocrine factor that couples increases in cell volume to opening of Cl- channels through stimulation of P2 receptors.
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PMID:Autocrine signaling through ATP release represents a novel mechanism for cell volume regulation. 887 55

Ca2+ efflux from frog muscle sarcoplasmic reticulum (SR) vesicles was studied by measuring external free [Ca2+] using Fluo-3 fluorescence. Light SR vesicles were preloaded with Ca2+ in the presence of ATP and inorganic phosphate (Pi). Calcium pump reversal was activated by either depletion of the medium ATP by apyrase in the presence of 20 mM Pi, or resuspending preloaded vesicles in an ATP-free solution containing 1 mM ADP and 20 mM Pi. Cyclopiazonic acid (CPA) and thapsigargin (TG), at concentrations of 2.5 microM, which completely inhibit Ca2+ uptake, both inhibited the pump reversal efflux almost completely. When active Ca2+ uptake was stopped by either ATP-depletion or addition of CPA, a leak efflux of 6-7 nmole/mg/min was recorded. TG (2.5 microM) reduced this leak by over 50%, suggesting that TG, but not CPA, can slow the passage of calcium ions through the Ca(2+)-ATPase passive channel.
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PMID:Ca2+ effluxes from the sarcoplasmic reticulum vesicles of frog muscle: effects of cyclopiazonic acid and thapsigargin. 893 55

We have characterized the ectonucleotidases that catalyse the reaction sequence ATP-->ADP-->AMP-->adenosine on microvascular endothelial cells cultured from the rat heart. Computer simulation and data fitting of progress of reaction curves showed that depletion of substrate at the cell surface dominates the regulation of the rate of hydrolysis of ATP when it is presented to the cells. Preferential delivery of AMP by ADPase to 5'-nucleotidase makes a significant contribution to the regulation of adenosine production from ATP or ADP. By contrast, we found no evidence for the preferential delivery of ADP from ATPase to ADPase. Feed-forward inhibition of AMP hydrolysis by ADP and/or ATP also modulated the rate of adenosine production. The properties of the ectonucleotidases on rat heart microvascular cells are such that adenosine is produced at a steady rate over a wide range of ATP concentrations.
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PMID:Kinetics of extracellular ATP hydrolysis by microvascular endothelial cells from rat heart. 894 25

Aluminum chloride (AlCl3), a neurotoxic compound, inhibited ATP diphosphohydrolase activity of synaptosomes obtained from cerebral cortex of adult rats. The metal ion significantly inhibited ATPase and ADPase activities of the enzyme at all concentrations tested in vitro (0.01, 0.05, 0.5, 5, and 10 mM) in the presence of 1.5 mM calcium. When tested in the absence of Ca2+, and with increasing amounts of Al3+, enzyme activity remained below basal levels, suggesting that the trivalent cation Al3+ is not a substitute for the divalent cation Ca2+ in ATP-Ca2+ and ADP-Ca2+ complexes. The Al3+ inhibition was competitive with respect to Ca2+. The enzyme inhibition was reversed by the addition of deferoxamine (DFO). NaF significantly inhibited ATP diphosphohydrolase activity, and this inhibition was reversed by the addition of Ca2+ to the medium. Such inhibition was not potentiated by AlF4, which is an inhibitor of cation-transport ATPases.
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PMID:Effects of aluminum chloride on the kinetics of rat cortex synaptosomal ATP diphosphohydrolase (EC 3.6.1.5). 896 92

ATP-diphosphohydrolase (apyrase. EC 3.6.1.5) has both ATPase and ADPase activity that are stimulated by bivalent metals, with Ca2+ being the most effective. The possible physiological function of this enzyme, associated with placental and renal microvilli, is related to the extracellular metabolism of nucleotides. A comparison of the biochemical properties of human placenta and rat kidney apyrase is presented, showing similarities in Mr. bivalent metal stimulation, nucleotide nonspecificity, insensitivity towards specific ATPase inhibitors, and lack of essential sulfhydryl and aliphatic hydroxyl groups. We describe the treatment of membrane preparations from both tissues with different detergents and the isoelectric focusing of the solubilized proteins to partially purify apyrase. An ectoenzyme localization is assigned both in microvillus membranes and in the vasculature on the basis of organ perfusion experiments with nucleotides in the presence of antibodies. Placental and kidney microvillus membranes inhibited ADP-induced platelet aggregation, in agreement with an extracellular role. Initial studies on enzyme regulation suggested the existence of at least two types of modulatory proteins: an activating protein in the cytosol of both tissues, and an inhibitory protein associated with placental microsomes. Possible hormonal regulation was investigated in kidneys using in vivo estradiol treatment, but only slight changes in total apyrase activity were observed.
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PMID:Comparison of the biochemical properties, regulation and function of ATP-diphosphohydrolase from human placenta and rat kidney. 903 8

The in vitro effects of membrane lipid peroxidation on ATPase-ADPase activities in synaptic plasma membranes from rat forebrain were investigated. Treatment of synaptic plasma membranes with an oxidant generating system (H(2)0(2)/Fe(2+)/ascorbate) resulted in lipid peroxidation and inhibition of the enzyme activity. Besides, trolox as a water soluble vitamin E analogue totally prevented lipid peroxidation and the inhibition of enzyme activity. These results demonstrate the susceptibility of ATPase-ADPase activities of synaptic plasma membranes to free radicals and suggest that the protective effect against lipid peroxidation by trolox prevents the inhibition of enzyme activity. Thus, inhibition of ATPase-ADPase activities of synaptic plasma membranes in cerebral oxidative stress probably is related to lipid peroxidation in the brain.
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PMID:Sensitivity of ATPase-ADPase activities from synaptic plasma membranes of rat forebrain to lipid peroxidation in vitro and the protective effect of vitamin E. 913 34


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