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:3.6.1.3 (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

Nucleotides such as ATP, ADP, UTP or the diadenosine polyphosphates and possibly even NAD+ are extracellular signaling substances in the brain and in other tissues. Enzymes located on the cell surface catalyze the hydrolysis of these compounds and thus limit their spatio-temporal activity. As a final hydrolysis product they generate the nucleoside and phosphate. The paper discusses the biochemical properties, cellular localization and functional properties of surface-located enzymes that hydrolyse nucleotides released from nervous tissue. This is preceded by a brief discussion of nucleotide receptors, cellular storage and mechanisms of nucleotide release. In nervous tissue nucleoside 5'-triphosphates are hydrolysed by ecto-ATP-diphosphohydrolase and possibly in addition also by ecto-nucleoside triphosphatase and ecto-nucleoside diphosphatase. The molecular identity of the ATP-diphosphohydrolase has now been revealed. The hydrolysis of nucleoside 5'-monophosphates is catalysed by 5'-nucleotidase whose biochemical properties and molecular structure have been studied in detail. Little is known about the molecular properties of the diadenosine polyphosphatases. Surface located enzymes for the extracellular hydrolysis of NAD+ and also ecto-protein kinases are discussed briefly. The cellular localization of the ecto-nucleotidases is only partly defined. Whereas in adult mammalian brain activity for hydrolysis of ATP and ADP may be associated with nerve cells or glial cells 5'-nucleotidase appears to have a preferential glial allocation in the adult mammal. The extracellular hydrolysis of the nucleotides is of functional importance not only during synaptic transmission where it functions in signal elimination. It plays a crucial role also for the survival and differentiation of neural cells in vitro and presumably during neuronal development in vivo.
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PMID:Biochemistry, localization and functional roles of ecto-nucleotidases in the nervous system. 891 94

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

Ectoenzymic activities capable of hydrolyzing ATP sequentially to adenosine are present on equine epidydimal spermatozoa membranes. Kinetic parameters for ATPase, ADPase and 5'-nucleotidase were obtained by analysis of progress reactions curve when ATP, ADP and AMP were supplied as initial substrates. These values are not different from those found when the substrates were supplied from the preceding reactions. Feed-forward inhibition on 5'-nucleotidase by ATP/ADP was taken into account to fit simulated data to the experimental results. None of the substrates supplied by the preceding reactions showed a preferential delivery to ADPase and/or 5'-nucleotidase. We therefore conclude that the model that fits the equine spermatozoa is that already proposed for pig aortic endothelial cells.
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PMID:Hydrolysis of extracellular adenine nucleotides by equine epidydimal spermatozoa. 929 97


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