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Query: UNIPROT:P20020 (adenosine triphosphatase)
 3,299 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Tritiated H(3)-digoxin specifically binds to a cardiac (Na(+) + K(+))-activated adenosine triphosphatase. In the presence of adenosine triphosphate and other nucleoside di- and triphosphates, binding is stimulated by sodium ion, the apparent rate constant being similar to that reported for phosphorus-32 incorporation from adenosine triphosphate and for the adenosine triphosphatase activity. In the presence of magnesium, manganese, inorganic phosphate, or other ions, sodium ion inhibits binding. The data support an allosteric type of sodium-potassium ion pump.
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PMID:Tritiated digoxin binding to (Na+ + K+)-activated adenosine triphosphatase: possible allosteric site. 423 May 10

Discrete sites of adenosine triphosphatase (ATPase) activity were demonstrated within the nucleoli of unfixed cultured human fibroblasts (IMR90, VA13, and AG2804 cells) by an adaptation, for electron microscopic cyto-chemistry, of Wachstein and Meisel's lead nitrate method. The majority of nucleoli contained more than one ATPase-positive region, but the total ATPase-positive material appeared to occupy only a minor portion of the nucleolar volume. These regions were roughly spherical with an irregular contour, and at times appeared to be components of perinucleolar chromatin or to be located adjacent to nucleolar interstices. The distribution of these regions within the nucleolus and their segregation by actinomycin D suggested that the ATPase-positive regions correspond to the fibrillar centers, which represent nucleolar organizer regions. The cytochemically demonstrable nucleolar ATPase was strictly dependent on the presence of divalent cations. Optimal reactions was seen at 5 mM Mg2+, but near optimal activity was obtained with lower concentrations of Mg2+ in the presence of Ca2+. Calcium alone and Mn2+ alone produced suboptimal reaction. Studies with different nucleoside phosphates as reaction substrates showed that the enzyme is specific for adenosine derivatives, ATP and dATP being equally good substrates. Guanosine triphosphate, cytidine triphosphate, uridine triphosphate, and d-thymidine triphosphate were ineffective as substrates, as were nucleoside mono- and diphosphates and other phosphate esters tested. It is suggested that the cytochemical ATPase reaction visualized the regions of the nucleolus in which ribosomal DNA of intranucleolar chromatin is undergoing conformational alterations.
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PMID:Visualization of nucleolar substructure in cultured human fibroblasts by magnesium-activated adenosine triphosphatase reaction. 611 91

The activity of divalent cation-stimulated adenosine triphosphatase (ATPase) has been studied in vesicular membranes isolated from ejaculated ram seminal plasma. This nonspecific acidic ATPase can be activated by millimolar concentration of any one of the following cations: Ca2+, Mg2+, Zn2+, or Mn2+ to give high specific activity (approximately 300 mumol/mg/hr), in absence of the other cations. Free Zn2+ inhibits activity of this ATPase. The Km for adenosonine triphosphate (ATP) ranged between 0.17 and 0.24 mM, and for the divalent cation ranged between 0.4 and 0.8 mM. When the ATPase is activated by Ca2+, two Kms for Ca2+ concentration were found: 0.8 and 0.08 mM. It is suggested that the seminal plasma membranes also contain alkaline ATPase, which is more specific for Ca2+.
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PMID:Characterization of Mg2+- and Ca2+-ATPase activity in membrane vesicles from ejaculated ram seminal plasma. 612 63

Quercetin is a naturally occurring flavonoid, chemically related to cromolyn. Quercetin has been shown to inhibit antigen- and mitogen-induced histamine release from rat mast cells and basophils of subjects with hay fever, to increase cyclic adenosine monophosphate (AMP) in Ehrlich ascites tumor cells and to inhibit phosphodiesterase and certain adenosine triphosphatase (ATPase) systems. We have studied the effect of quercetin on mouse T cell responses. When 5 x 10(-6) to 5 x 10(-5) M quercetin is present throughout either allogeneic mixed leukocyte culture (MLC) or cytotoxic T lymphocyte (CTL) assay culture, inhibition of in vitro CTL generation or effector function results, respectively (inhibition is 75-100% at 2 x 10(-5) M and 100% at 5 x 10(-5) M). Quercetin also inhibits concanavalin A-induced DNA synthesis. Addition of Cu2+ strongly blocks the effects of quercetin in all systems tested, in a concentration dependent fashion, while Mg2+ and Ca2+ have little or no effect and Mn2+ and Co2+ have a significant but slight blocking effect on quercetin-mediated inhibition of both CTL generation and function. In kinetic studies, evidence was obtained for the existence of a major quercetin-sensitive step in CTL induction, between 3 and 24 hr of the MLC.
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PMID:Quercetin inhibition of the induction and function of cytotoxic T lymphocytes. 621 17

The state of the Na+- and K+-stimulated adenosine triphosphatase ((Na,K)-ATPase) which binds vanadate was investigated by taking advantage of the slow rate of vanadate release (koff = 0.32/h at 25 degrees C and 0.045/h at 4 degrees C). Vanadate release from the enzyme could be accelerated approximately 2-fold by addition of K+ and 50-fold by addition of Na+. The K+ effect saturated hyperbolically with a K1/2 of 0.5 mM, while the Na+ effect had a sigmoidal activation curve and K1/2 of 250 mM. These results indicate that either Na+ or K+ can equilibrate with the vanadate-"trapped" enzyme prior to vanadate release. In the presence of vanadate, a saturable Mn2+ binding site could be detected with a dissociation constant of 120 nM. When 54Mn2+ was added during incubation of the enzyme with vanadate, 1 mol of 54Mn2+ could be trapped/mol of vanadate trapped and the two metals dissociated in parallel. This result indicates a single divalent cation site is involved in stabilizing vanadate (and probably phosphate) binding. Addition of 1 to 4 mM of ATP to the vanadate-trapped enzyme had no affect on the rate of vanadate release. Also, the high affinity ATP site could not be detected in equilibrium-binding studies with the vanadate-trapped enzyme. Since kinetic experiments indicate that vanadate binding is competitive with the low affinity ATP site (Cantley, L. C., Jr., Cantley, L. G., and Josephson, L. (1978) J. Biol. Chem. 253, 7361--7368) and the high affinity ATP site is absent on vanadate-trapped enzyme, it appears unlikely that ATP can occupy either a high or low affinity site on the vanadate-trapped enzyme. We show that nonlinear Lineweaver-Burk plots for ATP hydrolysis can be explained by a single hydrolysis site which exhibits a low affinity for ATP prior to the rate-limiting E2 to E1 conformational change, but a high affinity for ATP following the conformational change.
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PMID:A study of the vanadate-trapped state of the (Na,K)-ATPase. Evidence against interacting nucleotide site models. 625 55

Homogeneous preparations of cytoplasmic membrane isolated from Staphylococcus aureus 6538P exhibited membrane-associated adenosine triphosphatase (ATPase) activity. Membrane ATPase activity was activated by divalent cations (4.0 mM: Mg2+ greater than Mn2+ greater than Co2+ greater than Zn2+), and ATP was hydrolyzed more readily than other nucleoside triphosphates and phosphorylated substrates. The pH optimum for the membrane ATPase was 6.5. The ATPase could not be released from the membrane by differential osmotic treatments, but detergent treatment effectively solubilized active enzyme. The nonionic detergent Triton X-100 (1%) released a protein with ATPase activity, after substrate-dependent staining in polyacrylamide gels, that differed slightly in electrophoretic migration when compared to the active enzyme solubilized with sodium dodecyl sulfate (0.1%). Membrane-associated ATPase activity was inhibited by N,N'-dicyclohexylcarbodiimide (0.001 to 1 mM) and NaF (50% inhibition at 5 mM NaF). Azide and trypsin inhibited activity, whereas ouabain had a slight inhibitory effect. Diethylstilbestrol showed appreciable activation of the membrane ATPase over the range employed (0.001 to 1 mM).
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PMID:Staphylococcus aureus adenosine triphosphatase: inhibitor sensitivity and release from membrane. 645 44

Enzymatic properties of a canine cardiac muscle microsomal fraction were determined to localize in situ a "basic," divalent cation dependent adenosine triphosphatase (ATPase) by ultrastructural cytochemistry. The microsomal fraction had a buoyant density of 1.08--1.13 (20--30% [w/w] sucrose) and hydrolyzed adenosine triphosphate in the presence of Mg2+, Ca2+, Mn2+, or Co2+, but not in that of Sr2+ or Ni2+, under conditions that inhibited interfering (Na+ + K+)-ATPase and sarcoplasmic reticulum Ca2+-ATPase activities. "Basic" ATPase was localized in paraformaldehyde-fixed tissue in a medium containing Mg2+ or a high Ca2+ concentration (4 mM). A free Pb2+ concentration of less than 1 microM was used to capture enzymatically released phosphate anions. Electron-dense lead precipitates were present at the plasmalemma, T-system, and intercalated disc membranes with the exception of the nexus. These studies suggest that "basic" ATPase activity is associated with surface membrane structures of canine cardiac muscle.
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PMID:Cytochemical localization of a "basic" ATPase to canine myocardial surface membrane. 645 53

Phosphorus-31 nuclear magnetic resonance (31P-NMR) analysis was performed on normal (line 412) and dystrophic (line 413) superficial pectoralis muscles excised from chickens between 15 and 116 days after hatching. An apparent alteration in dystrophic muscle energy metabolism was abolished by pretreatment with curare and was attributed to muscle hyperexcitability. Time-dependent 31P-NMR studies demonstrated no apparent difference in the overall tissue adenosine triphosphatase (ATPase) activity of dystrophic as compared to normal muscle. After 55 days of age, a resonance signal attributed to serine ethanolamine phosphodiester (SEPDE) was observed only in dystrophic muscle. Adding the paramagnetic cation Mn2+ to the buffer surrounding the muscle resulted in an approximate 80% decrement in the dystrophic SEPDE signal without apparent alteration of the other phosphatic signals in either the normal or dystrophic muscle. This would argue against any generalized membrane defect in dystrophic chicken muscle and suggest that SEPDE is in a compartment accessible to Mn2+.
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PMID:31P-NMR studies of normal and dystrophic chicken muscle. 654 98

1. Flufenamic and tolfenamic acids have recently been shown to inhibit receptor-mediated calcium influx in human neutrophils. The present work was designed to study the effects of these two nonsteroidal anti-inflammatory drugs on human peripheral blood lymphocyte activation. 2. Peripheral blood mononuclear cells (PBMNCs; containing 90% lymphocytes) were stimulated by mitogen concanavalin A (Con A) or by a combination of an inhibitor of microsomal Ca(2+)-adenosine triphosphatase thapsigargin (TG) and phorbol myristate acetate (PMA). The effects of the two fenamates on cell proliferation were compared with respective changes in calcium metabolism. 3. Flufenamic and tolfenamic acids (10-100 microM) inhibited both Con A and TG + PMA-induced [3H]-thymidine incorporation in a dose-dependent manner. At the same concentration range, the two fenamates inhibited the increase in intracellular free calcium concentration induced by Con A or TG + PMA. This effect was due to inhibition of calcium influx whereas calcium release from intracellular stores remained unaltered. 4. The inhibition of divalent cation influx was confirmed by showing that fenamates inhibited TG + PMA-induced Mn2+ influx. 5. The inhibitory effects of fenamates on PBMNC proliferation and Ca2+ influx were qualitatively similar with those of SK&F 96365, an earlier known inhibitor of receptor-mediated calcium entry. Ketoprofen, a chemically different prostaglandin synthetase inhibitor did not show similar suppressive effects on PBMNCs. 6. The data suggest that flufenamic and tolfenamic acids suppress proliferation of human peripheral blood lymphocytes by a mechanism which involves inhibition of Ca2+ influx and is not related to inhibition of prostanoid synthesis.
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PMID:Inhibition by fenamates of calcium influx and proliferation of human lymphocytes. 889 68

The yeast Ca2+ adenosine triphosphatase Pmr1, located in medial-Golgi, has been implicated in intracellular transport of Ca2+ and Mn2+ ions. We show here that addition of Mn2+ greatly alleviates defects of pmr1 mutants in N-linked and O-linked protein glycosylation. In contrast, accurate sorting of carboxypeptidase Y (CpY) to the vacuole requires a sufficient supply of intralumenal Ca2+. Most remarkably, pmr1 mutants are also unable to degrade CpY*, a misfolded soluble endoplasmic reticulum protein, and display phenotypes similar to mutants defective in the stress response to malfolded endoplasmic reticulum proteins. Growth inhibition of pmr1 mutants on Ca2+-deficient media is overcome by expression of other Ca2+ pumps, including a SERCA-type Ca2+ adenosine triphosphatase from rabbit, or by Vps10, a sorting receptor guiding non-native luminal proteins to the vacuole. Our analysis corroborates the dual function of Pmr1 in Ca2+ and Mn2+ transport and establishes a novel role of this secretory pathway pump in endoplasmic reticulum-associated processes.
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PMID:The medial-Golgi ion pump Pmr1 supplies the yeast secretory pathway with Ca2+ and Mn2+ required for glycosylation, sorting, and endoplasmic reticulum-associated protein degradation. 957 Dec 46


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