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

p-Nitrophenyl phosphate hydrolysis was studied at neutral pH with tissue preparations of the rat secretory and maturation enamel organs and dental pulp. By introduction of inhibitors to nonspecific alkaline phosphatase activity and stimulants to the K+-stimulated and ouabain-sensitive p-nitrophenyl phosphatase activity, the latter enzyme activity could be demonstrated. This enzyme activity is generally held to be representative of the enzyme sodium- and potassium-stimulated adenosine triphosphatase. The K+-stimulated activity was magnesium dependent and highly sensitive to fluoride. It was inhibited completely by 3 mM fluoride in the incubation medium and about 1 mM produced half the maximum inhibition. The K+-independent enzyme activity was inhibited 50-60% by fluoride in concentrations between 3 and 15 mM. The high fluoride sensitivity of the K+-stimulated activity may perhaps help to explain the vulnerability of dental tissues to fluoride.
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PMID:Demonstration of a K+-stimulated and ouabain-sensitive p-nitrophenyl phosphatase activity in enamel-and dentin-forming tissues in the rat. 2 90

Patulin (4-hydroxy-4H-furo[3,2-c]pyran-2(6H)-one), a carcinogenic lactone produced as a major metabolite by several fungi, inhibited the Mg++-dependent Na+-K+ activated adenosine triphosphatase (ATPase) activity of mouse brain microsomal fractions with an estimated IC50 of 3.0 X 10(-4) M. Inhibition was concentration dependent. Hydrolysis of ATP was linear with both time and enzyme concentration either with or without patulin in reaction mixtures. Altered pH and activity curves for Na+-K+ ATPase demonstrated comparable inhibition by patulin in buffered acidic ranges through an optimum of 7.5, followed by a reduction of toxicity to this system at higher alkaline pH. Kinetic studies of cationic-substrate activation of Na+-K+ ATPase indicated noncompetitive inhibition with respect to ATP (at low affinity nucleotide-directed sites) and Na+ (in the presence of low, noninterfering concentrations of K+). Competitive inhibition with respect to activation of the Na+-k+-stimulated activity and K+-stimulated p-nitrophenyl phosphatase activity of the enzyme system was indicated by altered binding site parameters without change in apparent Vmax in the presence of patulin. Activity was partially restored by washing. Preincubation of patulin with dithiothreitol or glutathione protected the enzyme from inhibition. Results suggest that patulin exerted its effect on Na+-K+ ATPase either directly by interfering with K+ binding or indirectly by inducing a conformational change in the enzyme.
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PMID:Effects of patulin on the kinetics of substrate and cationic ligand activation of adenosine triphosphatase in mouse brain. 2 94

The sodium-potassium activated adenosine triphosphatase (NaKATPase) activity of the rat cornea was investigated histochemically using a Pb2+-precipitation technique in which adenosine triphosphate (ATP) is used as substrate and two methods for potassium-dependent para-nitrophenyl-phosphatase (K-NPPase) activity. With all the three techniques used it was demonstrated that the sodium-potassium-activated adenosine triphosphatase (NaK-ATPase) activity is localized in the cell membranes of the endothelium whereas a much weaker activity was observed in the epithelium. When the Pb2+-technique was used, the epithelial cell membranes showed a weaker reaction in the presence of ouabain. This activity was only Mg2+-dependent and was presumably due to an Mg2+-dependent ATPase. The validity of the histochemical techniques for NaK-ATPase activity is discussed. The results emphasize the importance of the endothelium as the main site of Na+ transport in the cornea. Small amounts of the enzyme are also present in the epithelium, which seems to be rich in Mg2+-ATPase. Provided that careful controls are performed, all the methods give consistent results in the cornea.
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PMID:Transport adenosine triphosphatase activity in the rat cornea. 6 3

Adenosine triphosphate (ATP) hydrolysis catalyzed by the plasma membrane (Na+,K+)ATPase isolated from several sources was inhibited by Mg+, provided that K+ and ATP were also present. Phosphorylation of the adenosine triphosphatase (ATPase) by ATP and by inorganic phosphate was also inhibited, as was p-nitrophenyl phosphatase activity. (Ethylenedinitrilo)tetraacetic acid (EDTA) and catecholamines protected from and reversed the inhibition of ATP hydrolysis by Mg2+, K+ and ATP. EDTA was protected by chelation of Mg2+ but catecholamines acted by some other mechanism. The specificities of various nucleotides as inhibitors (in conjunction with Mg2+ and K+) and as substrates for the (Na+, K+) ATPase were strikingly different. ATP, ADP, beta,gamma-CH2-ATP and alpha,beta-CH2-ADP were active as inhibitors, whereas inosine, cytidine, uridine, and guanosine triphosphates (ITP, CTP, UTP, and GTP) and adenosine monophosphate (AMP) were not. On the other hand, ATP and CTP were substrates and beta,gamma-NH-ATP was a competitive inhibitor of ATP hydrolysis, but not an inhibitor in conjunction with Mg2+ and K+. The Ca2+-ATPase from sarcoplasmic reticulum and F1, the Mg2+-ATPase from the inner mitochondrial membrane, were also inhibited by Mg2+. Catecholamines reversed inhibition of the Ca2+-ATPase, but not that of F1.
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PMID:Reversible inhibition of (Na+, K+) ATPase by Mg2+, adenosine triphosphate, and K+. 13 42

1. Treatment of hamster heart cells in primary culture with 5-bromo-2'-deoxyuridine resulted in the greatly increased activity of a particulate Ca2+- or Mg2+-dependent ATPase (adenosine triphosphatase). 2. 5-Bromo-2'-deoxyuridine exerted these effects only when it was incorporated into cellular DNA, and then in a concentration-dependent manner. 3. Serially replated cells contained less of the activity (expressed as a function of total cell protein) than did the primary cultures, but the stimulation caused by 5-bromo-2'-deoxyuridine addition was much greater. 4. The affected enzyme was apparently localized in the plasma membrane of the cells with its active centre exposed to the outer environment [ecto-(ATPase) dependent on Ca2+ or Mg2+].5. The activity was unaffected by treatment with p-chloromercuriphenylsulphonate, ouabain andverapamil. 6. Ecto (5'-nucleotidase) activity was not increased by 5-bromo-2'-deoxyuridine treatment of cells, and ecto-(p-nitrophenyl phosphatase) activity was only slightly enhanced.
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PMID:5-bromo-2'-deoxyuridine-stimulated calcium ion- or magnesium ion-dependent ecto-(adenosine triphosphatase) activity of cultured hamster cardiac cells. 14 81

The reaction of 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole [NBD-Cl] with purified eel electrophax Na+ and K+ stimulated adenosine triphosphatase [(Na-K)ATPase] has been monitored by changes in the (Na-K)ATPase activity, the K+ stimulated p-nitrophenyl phosphatase [PNPase] activity, and the protein ultraviolet absorption spectrum. The NBD-Cl reacts with two tyrosine residues per mol of enzyme (approximately 6-7 nmol/mg of protein), as judged by changes in protein absorption spectra and incorporation of [14C]NBD-Cl. The modified tyrosine groups are located on the Mr = 95 000 polypeptide chain and react at different rates. Only one tyrosine modification is necessary for complete inhibition of (Na-K)ATPase activity, although both must be modified for complete inhibition of PNPase activity. Reversal of these modifications by 2-mercaptoethanol restores 65% of both activities. Na+ increases the rate of tyrosine modification, K+ decreases the rate, and ATP affords the more reactive tyrosine group complete protection. NBD-Cl modification of approximately 6-7 nmol of tyrosine groups/mg of protein results in a large decrease in ATP affinity as judged by equilibrium binding. These results are compared with similar results obtained from NBD-Cl modification of the coupling factors of oxidative phosphorylation and photophosphorylation. A model is presented suggesting an asymmetric arrangement of two 95 000 polypeptide chains with a single tyrosine residue at the ATP site.
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PMID:Reaction of (Na-K)ATPase with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole: evidence for an essential tyrosine at the active site. 14 73

The effects of the alkaline phosphatase inhibitors levamisole and R 8231 on p-nitro-phenylphosphatase, inorganic pyrophosphatase and adenosine triphosphatase (ATPase) activities in dentingenically active odontoblasts were studied. The p-nitrophenylphosphatase and inorganic pyrophosphatase activities were inhibited, while 40% of the ATP-splitting enzyme activity remained under the assay condition used. This finding, togeather with earlier studies, indicates that at least two different phosphatase are active at alkaline pH in hard tissue-forming cells; on nonspecific alkaline phosphatase and one specific ATPase. The ATPase activity is uninfluenced by ouabain and ruthenium red and is activated by Ca-2+ ions.
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PMID:Inhibition studies of alkaline phosphatase in hard tissue-forming cells. 16 33

Pieces of rat and human gastric mucosa were fixed in glutaraldehyde and paraformaldehyde and were processed by the methods of Wachstein-Meisel and of Ernst for the cytochemical demonstration of adenosine triphosphatase (ATPase) and p-nitrophenylphosphatase (NPPase) respectively. Electron microscopic examination of reacted sections revealed the ATPase reaction to be localized to the plasmalemma and to mitochondrial cristae and the NPPase reaction to the plasmalemma. The tubulovesicles were unreactive. By thus demonstrating a cytochemical difference between the plasmalemma and tubulovesicle membrane, this study suggests that the tubulovesicles do not represent an extension of or reserve of mature plasmalemma. If the tubulovesicles represent a reserve of membrane that can be rapidly utilized to expand the plasmalemma, then these studies suggest that additional membrane constituents are added, activated, or unmasked in the process.
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PMID:Demonstration of a cytochemical difference between the tubulovesicles and plasmalemma of gastric parietal cells by ATPase and NPPase reactions. 17 59

A microsomal fraction rich in Na+, K+-ATPase (sodium-plus-potassium ion-dependent adenosine triphosphatase) and the corresponding K+-dependent p-nitrophenyl phosphatase from the rectal salt gland of the spiny dogfish was solubilized by treatment with deoxycholate at high ionic strength. On gel filtration through Sepharose 6B, the ATPase apoenzyme could be separated, in apparently soluble form, from the tissue-fraction phospholipids and was almost free of enzymic activity (2% of the p-nitrophenyl phosphatase activity and 0.2% of the ATPase activity being recovered). On mixing the apoenzyme with an activator consisting of cooked ox brain, a large proportion of the original enzymic activity was obtained. Specific activities of the re-activated enzyme were somewhat higher than in the material before gel filtration: values of 1300-1450 mumol and 250-290 mumol/h per mg of protein were obtained for the hydrolysis of ATP and of p-nitrophenyl phosphate respectively. The activity was inhibitible by ouabain.
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PMID:The reversible delipidation of a solubilized sodium-plus-potassium ion-dependent adenosine triphosphatase from the salt gland of the spiny dogfish. 17 57

Potassium-stimulated p-nitrophenylphosphatase (K+-pNPPase) activity was investigated in rat somatosensory cortex where 64-88% of enzymatic activity survived 5-10 min of fixation with 3% formaldehyde in 0.1 M cacodylate buffer, pH 7.4. Potassium-stimulated activity was inhibited by 1-10 mM ouabain. Levamisole (1.7 mM) inhibited brain alkaline phosphatase activity, facilitating the detection of K+-pNPPase activity. Strontium (10-20 mM) inhibited enzymatic activity by 38-75%. In parallel histochemical studies reaction product was found in strata, with cortical layers 2, 3, 4 and the outer portion of 5 containing the heaviest deposits. Highly reactive, vertically oriented, large diameter fibers were seen as groups between the outer portion of layer 5 and the pail surface. These fibers apparently arborize in the superficial layers. Smaller fibers were also positive and were oriented in various planes. The highest density of smaller, positive fibers occurred in layers 2 through 5. All positive fibers appeared to be axons or dendrites. Reaction product was not heavily concentrated in neuron perikarya or in glial elements. Sections did not contain reaction product when incubated in media lacking K+ or containing ouabain. The convergence of data from parallel histochemical and biochemical approaches supports the conclusion that the reactivity localized in the cerebral cortex represented the site of K+-pNPPase, a known component of the Na+,K+-adenosine triphosphatase complex. Neuronal processes demonstrated the highest enzymatic activity and may be most important in the active transport of Na+ and K+ in somatosensory cortex.
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PMID:Histochemical localization of potassium-stimulated P-nitrophenylphosphatase activity in the somatosensory cortex of the rat. 18 89


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