Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P20020 (adenosine triphosphatase)
 3,299 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of monovalent cations on calcium uptake by fragmented sarcoplasmic reticulum have been clarified. Homogenization of muscle tissue in salt-containing solutions leads to contamination of this subcellular fraction with actomyosin and mitochondrial membranes. When, in addition, inorganic cations are contributed by the microsomal suspension and in association with nucleotide triphosphate substrates there is an apparent inhibition of the calcium transport system by potassium and other cations. However, when purified preparations were obtained after homogenization in sucrose medium followed by centrifugation on a sucrose density gradient in a zonal rotor, calcium uptake and the associated adenosine triphosphatase activity were considerably activated by potassium and other univalent cations. When plotted against the log of the free calcium concentration there was only a slight increase in calcium uptake and ATPase activity in the absence of potassium ions but sigmoid-shaped curves were obtained in 100 mM K+ with half-maximal stimulation occurring at 2 muM Ca2+ for both calcium uptake and ATPase activity. The augmentation in calcium uptake was not due to an ionic strength effect as Tris cation at pH 6.6 was shown to be inactive in this respect. Other monovalent cations were effective in the order K+ greater than Na+ greater than NH4+=Rb+=Cs+ greater than Li+ with half-maximal stimulation in 11 mM K+, 16 mM Na+, 25 mM NH4+, Rb+, and Cs+ and in 50 mM Li+. There was nos synergistic action between K+ AND Na+ ions and both calcium uptak and associated ATPase were insensitive to ouabain. Thallous ions stimulate many K+-requiring enzymes and at one-tenth the concentration were nearly as effective as K+ ions in promoting calcium uptake. The ratio of Ca2+ ions transported to P1 released remained unchanged at 2 after addition of K+ ions indicating an effect on the rate of calcium uptake rather than an increased efficiency of uptake. In support of this it was found that during the stimulation of calcium uptake by Na+ ions there was a reduction in the steady state concentration of phosphorylated intermediate formed from [gamma-32P]ATP. It is considered that there is a physiological requirement for potassium ions in the relaxation process.
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PMID:Caclium uptake and associated adenosine triphosphatase activity in fragmented sarcoplasmic reticulum. Requirement for potassium ions. 1 56

Homogenates of Tritrichomonas foetus exhibited a Mg2+-dependent adenosine triphosphatase (ATPase) activity, with a pH optimum in Tris buffers of 8.2 to 8.3. The activity was not sensitive to oxygen. At high concentrations, quercetin and 4-chloro-7-nitrobenzofurazan inhibited ATPase activity in the cytoplasmic extract by 20 and 70%, respectively, whereas oligomycin, venturicidin, triethyltin, leucinostatin, dibutylchloromethyltin chloride, spegazzinine, efrapeptin, citreoviridin and sodium azide had no effect and N,N'-dicyclohexylcarbodi-imide stimulated the activity somewhat. The activity was localized in a population of small cytoplasmic particles which also contained an acid phosphatase. There was no indication of an association of ATPase with hydrogenosomes. The ATPase activity (or activities) in this aerotolerant anaerobe is different from the ATPases characteristic of mitochondria or of anaerobic bacteria.
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PMID:Adenosine triphosphatase activity of Tritrichomonas foetus. 4 53

Small cultures of human amniotic cells were preincubated for 24 h. Human prolactin was then added to the medium. After a further short period of incubation the tubes were chilled, the medium removed and the cells rinsed with saline. The tubes then received cold Tris-sucrose and were frozen, to disrupt the cells. After thawing, adenosine triphosphatase (ATPase) and p-nitrophenyl phosphatase (PNPase) were measured. Buffer was added containing either ATP or PNP and the tubes were incubated for 30 min. Inorganic phosphate released from ATP and p-nitrophenol was measured spectrophotometrically. Prolactin stimulated both enzyme activities. The ATPase log dose-response curve was linear between approximately 12.5 and 200 mIU/l. It was inhibited by ouabain. Isobutyl-1-methylxanthine inhibited the ATPase but not the alkaline phosphatase activity. One of these human amniotic cell enzymes may provide the basis for a sensitive bioassay for human prolactin.
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PMID:Enzyme activation of human prolactin: a potential basis for a bioassay. 247 90

1. We have isolated a mutant of Escherichia coli K12 (strain AN295) that forms de-repressed amounts of Mg(2+),Ca(2+)-stimulated adenosine triphosphatase. 2. The Mg(2+),Ca(2+)-stimulated triphosphatase activity was separated from membrane preparations from strain AN295 by extraction with 5mm-Tris-HCl buffer containing EDTA and dithiothreitol, resulting in a loss of the ATP-dependent transhydrogenase activity. The non-energy-linked transhydrogenase activity remained in the membrane residue. 3. The solubilized Mg(2+),Ca(2+)-stimulated adenosine triphosphatase activity from strain AN295 was partially purified by repeated gel filtration. The addition of the purified Mg(2+),Ca(2+)-stimulated adenosine triphosphatase to the membrane residue from strain AN295 reactivated the ATP-dependent transhydrogenase activity. 4. Strain AN296, lacking Mg(2+),Ca(2+)-stimulated adenosine triphosphatase activity, was derived by transducing the mutant allele, uncA401, into strain AN295. The ATP-dependent transhydrogenase activity was lost but the non-energy linked transhydrogenase was retained. 5. The ATP-dependent transhydrogenase activity in membrane preparations from strain AN296 (uncA(-)) could not be re-activated by the purified Mg(2+),Ca(2+)-stimulated adenosine triphosphatase from strain AN295. However, after extraction by 5mm-Tris-HCl buffer containing EDTA and dithiothreitol, the ATP-dependent transhydrogenase activity could be re-activated by the addition of the purified Mg(2+),Ca(2+)-stimulated adenosine triphosphatase from strain AN295 to the membrane residue from strain AN296 (uncA(-)).
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PMID:Reconstitution of the energy-linked transhydrogenase activity in membranes from a mutant strain of Escherichia coli K12 lacking magnesium ion- or calcium ion-stimulated adenosine triphosphatase. 426 1

1. Membrane preparations from both uncA(-) and uncB(-) mutant strains of Escherichia coli K12, in which electron transport is uncoupled from phosphorylation, were fractionated by washing with a low-ionic-strength buffer. The fractionation gave a ;5mm-Tris wash' and a ;membrane residue' from each strain. This technique, applied to membranes from normal cells, separates the Mg(2+),Ca(2+)-stimulated adenosine triphosphatase activity from the membrane-bound electron-transport chain and the non-energy-linked transhydrogenase activity. 2. Reconstitution of both oxidative phosphorylation and the ATP-dependent transhydrogenase activity was obtained by a combination of the ;membrane residue' from strain AN249 (uncA(-)) with the ;5mm-Tris wash' from strain AN283 (uncB(-)). 3. Valinomycin plus NH(4) (+) inhibited oxidative phosphorylation both in membranes from a normal strain of E. coli and in the reconstituted membrane system derived from the mutant strains. 4. The electron-transport-dependent transhydrogenase activity was located in the membrane residue and was de-repressed in both the mutant strains. 5. The spatial and functional relationships between the proteins specified by the uncA and uncB genes and the transhydrogenase protein are discussed.
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PMID:Reconstitution of oxidative phosphorylation and the adenosine triphosphate-dependent transhydrogenase activity by a combination of membrane fractions from unCA- and uncB- mutant strains of Escherichia coli K12. 427 44

The rate coefficient for (22)Na release from previously labeled human erythrocytes was determined in the presence of 0.1-10 mM sodium fluoride (F). The oxidized nicotinamide adenine dinucleotide (NAD(+)) level at the end of 2 hr of incubation in tris(hydroxymethyl)aminomethane (Tris)-Ringer medium was also measured. Both parameters decreased proportionately as F concentration was raised. Both F-induced changes were immediate and were reversed by 10 mM pyruvate. The decrease in NAD(+) concentration following enolase inhibition by F is attributed to a diminished rate of formation in the reaction catalyzed by lactic dehydrogenase (LDH) with undiminished continued utilization in the reaction catalyzed by glyceraldehyde-3-phosphate dehydrogenase (GAPDH). It is postulated that the NAD(+) lowering limited the GAPDH step, resulting in proportionate decreases in the rates of phosphoglycerate kinase (PGK) and Na,K-dependent adenosine triphosphatase (Na,K-ATPase), a reaction sequence thought to link glycolysis with active Na extrusion. Adding pyruvate with F increased NAD(+) production at the LDH step, thus reactivating GAPDH, PGK, and Na,K-ATPase and leading to the observed restoration of (22)Na release. The results suggest, therefore, that F inhibits active Na transport in intact human erythrocytes indirectly through a lowering of NAD(+), although, direct inhibition of the Na,K-ATPase by F may possibly occur simultaneously.
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PMID:The role of oxidized nicotinamide adenine dinucleotide in fluoride inhibition of active sodium transport in human erythrocytes. 434 51

A previous report from this laboratory showed that reserpine pretreatment, in appropriate doses and under restricted conditions, increased the inotropic responsiveness of guinea-pig hearts to calcium. The enhanced responsiveness was characterized by a selective increase in the rate of ventricular relaxation (-dP/dt). We therefore hypothesized that reserpine might alter calcium uptake or (Ca++-Mg++) adenosine triphosphatase (ATPase) activity of guinea-pig ventricular sarcoplasmic reticulum (SR). Pretreatment of guinea pigs with reserpine (2.5 mg/kg/day, 2 days) significantly elevated ATP-dependent, Tris oxalate-facilitated SR Ca++ uptake and increased the calcium-sensitive component of the SR (Ca++) ATPase activity. These changes appeared to be functionally related to a reserpine-induced potentiation of ventricular relaxation rate, as estimated by the relationship between negative and positive left ventricular dP/dt of isolated working guinea-pig hearts. An alternative dose of reserpine (5 mg/kg, -24 hr), which had been demonstrated to produce an equivalent degree of catecholamine depletion, had no effect on either the inotropic responsiveness to calcium or on the SR calcium uptake or ATPase activities. The exact mechanism for these reserpine-induced alterations in calcium homeostasis remains to be elucidated.
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PMID:Effect of reserpine pretreatment on calcium transport and Ca++-Mg++ adenosine triphosphatase activity of guinea-pig cardiac microsomes. 613 19