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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 norepinephrine in interaction with adrenergic blocking compounds were studied on membrane adenosine triphosphatase (ATPase) activities of human lymphocytes and lymphoblasts. Sodium-potassium ion exchange pump activity was assayed by 86-Rb uptake and ATPase activity of membrane fractions was assayed by ADP and inorganic phosphate generation. The results of these studies indicate that norepinephrine acts by an alpha adrenergic mechanism to enhance membrane sodium-potassium ion exchange pump activity and ATPase activity. The pharmacologic and ionic dissection of the adrenergic sensitivity of ATPase activity indicates that this alpha adrenergic mechanism is related to membrane ATPase activities in addition to that associated with the ion exchange pump. Analysis of fractions obtained by sucrose gradients indicates that the action of norepinephrine is localized in the plasma membrane. Beta adrenergic stimulation was observed to inhibit ATPase activity. The complexity of adrenergic effects on membrane ATPase suggests interactions of hormone modulation of membrane nucleotide cyclases and transport-related ATPase enzymes.
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PMID:Norepinephrine stimulation of lymphocyte ATPase by an alpha adrenergic receptor mechanism. 114 Jan 64

The interaction of a series of bifunctional reagents with skeletal muscle myosin has been studied. In the di-imido ester series dimethylmalonimidate failed to generate any cross-linked species, whereas the adipic and higher analogues gave dimers of myosin heavy chains. Analysis of free amino groups after reaction with these reagents and with the reducible species dimethyldithiobis(propionimidate) showed that no more than two to three cross-links per molecule were introduced. By contrast, the bifunctional reducible acylating agent, dithiobis(succinimidylpropionate), reacted with annihilation of about 10% of the amino groups under mild conditions that precluded the formation of intermolecularly linked species. Digestion of the intramolecularly cross-linked myosin with papain, followed by analysis of the fragments by gel electrophoresis, revealed extensive cross-linking between the globular heads of the myosin molecules. The subfragment 1 dimers regenerated subfragment 1 on reduction, as shown by the electrophoretic mobility and amino acid analysis. The extent of cross-linking, and therefore presumably the average relative orientation or freedom of the two heads, was unaffected by the addition of ADP and calcium ions. The internally cross-linked myosin retains practically its full calcium-activated adenosine triphosphatase activity, but in contrast to native myosin is soluble even at very low ionic strength. Circular dichroism measurements show that the alpha helical conformation is undisturbed in cross-linked myosin, but the sedimentation coefficient is considerably higher than that of the native protein, possibly due to freezing of the heads in a "closed" configuration. The light chaiins are not cross-linked to the heavy chains, except under extreme conditions that leads to intermolecular cross-linking and inactivation. The presence of calcium ions protects dithiobisnitrobenzoate light chains against degradation by papain.
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PMID:Chemical cross-linking of myosin. Disposition of the globular heads. 126 47

Adenosine diphosphatase (ADPase) activity was solubilized with a non-ionic detergent, Tween 20, from human umbilical vessels and purified to homogeneity by diethylaminoethyl-Sepharose CL-6B, adenosine 5'-monophosphate-Sepharose 4B, and concanavalin A-Sepharose chromatography. The apparent molecular mass was 75 kDa. The purified enzyme hydrolyzed pyrophosphate bonds of nucleoside di- and triphosphates in the presence of calcium ion. It was insensitive to the adenosine triphosphatase (ATPase) inhibitors, oligomycin and ouabain, and sensitive to sodium azide. Therefore, we concluded that the ADPase activity in human umbilical vessels does not derive from ADPase degrading only ADP but from ATP diphosphohydrolase (EC 3.6.1.5). The broad substrate specificity and the sensitivity to various inhibitors and calcium ion are common to ATP diphosphohydrolase from bovine aorta. However, there might exist some structural difference around the active site, because the antiserum raised in rabbit against the bovine aorta enzyme scarcely inhibited the human umbilical enzyme.
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PMID:Purification and characterization of adenosine diphosphatase from human umbilical vessels. 142 69

We have studied the effects of hypo- and hyperthyroidism on sarcolemmal (SL) and sarcoplasmic reticular (SR) ion transport processes and mitochondrial energy production in rat heart. The following conclusions were derived. 1) Compared with euthyroid state, hyperthyroidism led to increased SR Ca(2+)-accumulation. In SL, the activities of Ca(2+)-stimulated adenosine triphosphatase (ATPase), ATP-dependent Ca2+ pumping, and Na(+)-Ca2+ exchanger were not affected; but ouabain-sensitive Na(+)-K(+)-ATPase activity was enhanced. 2) Hypothyroidism resulted in depressed activities of Ca2+ pumps both in SL and SR. In SL, the Na(+)-K(+)-ATPase activity was decreased, but Na(+)-Ca2+ exchange was unaltered. 3) Thus slower relaxation of the hypothyroid myocardium may be attributed to depressed functioning of Ca2+ pumps in SR and SL, whereas faster relaxation of the hyperthyroid heart may be based on increased Ca(2+)-pumping activity of SR. 4) Hyperthyroidism and hypothyroidism, respectively, led to enhanced and decreased rates of mitochondrial phosphocreatine synthesis. The thyroid state appears to control the functional coupling between mitochondrial creatine kinase and ATP-ADP translocase: the energy of oxidative phosphorylation was transformed into phosphocreatine more effectively in mitochondria from hypothyroid hearts than in those from hyperthyroid hearts.
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PMID:Thyroid control over membrane processes in rat heart. 165 94

The aurovertin-F1 complex was used to monitor fluorescence changes of the mitochondrial adenosine triphosphatase during multi- and uni-site ATP hydrolysis. It is known that the fluorescence intensity of the complex is partially quenched by addition of ATP or Mg2+ and enhanced by ADP (Chang, T., and Penefsky, H. S. (1973) J. Biol. Chem. 248, 2746-2754). In the present study low concentrations of ATP (0.03 mM) induced a marked fluorescence quenching which was followed by a fast fluorescence recovery. This recovery could be prevented by EDTA or an ATP regenerating system. The rate of ATP hydrolysis by the aurovertin-F1 complex and the reversal of the ATP-induced fluorescence quenching were determined in these various conditions. ITP hydrolysis also resulted in fluorescence quenching that was followed by a recovery of fluorescence intensity. Under conditions for single site catalysis, fluorescence quenching was observed upon the addition of ATP. This strongly indicates that fluorescence changes in the aurovertin-F1 complex are due to the binding and hydrolysis of ATP at a catalytic site. Therefore the resulting ADP molecule bound at this catalytic site possibly induces the fluorescence recovery observed.
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PMID:Aurovertin fluorescence changes of the mitochondrial F1-ATPase during multi- and uni-site ATP hydrolysis. 252 56

Polyphosphate kinase (ATP:polyphosphate phosphotransferase; EC 2.7.4.1), partially purified from Escherichia coli, has been immobilized on glutaraldehyde-activated aminoethyl cellulose with a 10% retention of enzymatic activity. The immobilized enzyme can carry out the synthesis of ATP from ADP, using long-chain inorganic polyphosphate as a phosphoryl donor. Chromatographic analyses of the product mixture produced from ADP and [32P]polyphosphate demonstrated that 98% of the 32P was incorporated into ATP, indicating that the immobilized polyphosphate kinase is substantially free from contaminating polyphosphate phosphohydrolase (EC 3.6.1.11), adenosine triphosphatase (EC 3.6.1.4), and adenylate kinase (EC 2.7.4.3). Immobilized polyphosphate kinase loses no activity when stored in an aqueous suspension for 2 months at 5 degrees C or for 1-2 weeks at 25 degrees C. It may be stored indefinitely as a lyophilized powder at -10 degrees C. Michaelis constants for ADP and polyphosphate were determined to be 160 and 120 microM, respectively, for the immobilized enzyme. A small-batch reactor was found to produce ATP linearly with time up to 65% conversion of polyphosphate into ATP and to attain greater than 85% conversion to ATP at equilibrium. The ease of purification and immobilization of E. coli polyphosphate kinase, its storage stability, the purity and yield of its ATP product, and the low values of the Michaelis constants for its substrates make it a highly promising enzyme for ATP regeneration.
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PMID:Immobilized polyphosphate kinase: preparation, properties, and potential for use in adenosine 5'-triphosphate regeneration. 283 45

We have examined intermediate Pi-water oxygen exchange during [gamma-18O]ATP hydrolysis by the F1 adenosine triphosphatase from Escherichia coli K-12. Water oxygen incorporation into each Pi released was increased as ATP concentration was lowered as observed previously for the same reaction catalyzed by the enzyme from eukaryotic sources. Heterogeneous distributions of 18O in product Pi were produced by coexisting epsilon subunit-replete and epsilon subunit-depleted enzyme molecules. The epsilon-replete enzyme showed a much higher probability for oxygen exchange. These data imply that the epsilon subunit inhibits net ATP hydrolysis by imposing conformational constraints which reduce the cooperative conformational interactions that promote ADP and Pi release. Four enzyme variants altered in alpha or beta subunit structure with reduced net hydrolytic activity showed sharply increased oxygen exchange during ATP hydrolysis. Heterogeneity was apparent in the 18O distribution of the product Pi, however. That behavior could reflect hindered conformational interactions and/or increased affinity of the alpha 3 beta 3 gamma delta complex for the epsilon subunit. In contrast, enzyme from mutant uncA401 showed very little oxygen exchange accompanying hydrolysis of 20 microM ATP. This is the only enzyme so far reported with this unusual property. Its rate limitation appears to be in the hydrolytic rather than the product release step of the catalytic sequence.
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PMID:Catalytic properties of the F1-adenosine triphosphatase from Escherichia coli K-12 and its genetic variants as revealed by 18O exchanges. 288 Aug 43

Subunit alpha (Mr 89,000) from vacuolar membrane H+-translocating adenosine triphosphatase of the yeast Saccharomyces cerevisiae was found to bind 8-azido[alpha-32P]adenosine triphosphate. Labeling by this photosensitive ATP derivative was saturable with an apparent dissociation constant of 10(-6) to 10(-5) M and decreased in the presence of ATP and ADP. The enzyme was inactivated by 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl), with about 1 microM causing half-maximal inactivation in the neutral pH range. This inactivation was prevented by the presence of ATP, ADP, or adenosyl-5'-yl imidodiphosphate (AMP-PNP). The original activity was restored by treating the inactivated enzyme with 2-mercaptoethanol. Kinetic and chemical studies of the inactivation showed that the activity was lost on chemical modification of a single tyrosine residue per molecule of the enzyme. When the enzyme was inactivated with [14C]NBD-Cl, subunit alpha was specifically labeled, and this labeling was completely prevented by the presence of ATP, GTP, ADP, or AMP-PNP. From these results, it was concluded that subunit alpha of yeast vacuolar H+-ATPase has a catalytic site that contains a single, essential tyrosine residue. The kinetics of single site hydrolysis of [gamma-32P]ATP (Grubmeyer, C., Cross, R. L., and Penefsky, H. S. (1982) J. Biol. Chem. 257, 12092-12100) indicated the formation of an enzyme-ATP complex and subsequent hydrolysis of bound ATP to ADP and Pi at the NBD-Cl-sensitive catalytic site. NBD-Cl inactivated the single site hydrolysis and inhibited the formation of an enzyme-ATP complex. Dicyclohexylcarbodiimide did not affect the single site hydrolysis, but inhibited the enzyme activity under steady-state conditions.
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PMID:Characterization and function of catalytic subunit alpha of H+-translocating adenosine triphosphatase from vacuolar membranes of Saccharomyces cerevisiae. A study with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole. 289 98

Thermoacidophilic archaebacteria have gained much interest because of their phylogenetic distance to eubacteria and eukaryotes and also because of their unique living conditions. Investigation of the energy-converting system therefore offers a key for understanding the evolutionary position and environmental adaptation of these unusual bacteria. A plasma-membrane-associated adenosine triphosphatase with specific activities of 0.3-0.6 mumol min-1 (mg protein)-1 has been detected in the thermoacidophilic archaebacterium Sulfolobus acidocaldarius (DSM 639). The enzyme exhibits two optima at pH 5.5 and 8.0, sulfite activation leads to only one optimum at pH 6.25. In the presence of the divalent cations Mg2+ or Mn2+ it hydrolyzes ATP with highest reactivity and also other purine and pyrimidine nucleotides, but not ADP and pyrophosphate. A specific stimulation by monovalent cations is not observed. The ATPase activity is not inhibited by N,N'-dicyclohexylcarbodiimide, azide or vanadate, but it is by the vascular ATPase inhibitor nitrate with an [I]50 of 8 mM. Linear Arrhenius plots up to 75 degrees C reflect pronounced adaptation to the hot environment of the archaebacterium. The solubilized ATPase as localized by activity staining in non-denaturating gels and further analyzed by sodium dodecyl sulfate electrophoresis is composed of two major polypeptides of 65 and 51 kDa reminiscent of the alpha and beta subunits of eubacterial and eukaryotic F0F1-ATPases. The ATPase is suggested as a probable candidate for a reversibly acting ATP synthase responsible for oxidative phosphorylation found in Sulfolobus acidocaldarius.
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PMID:A plasma-membrane associated ATPase from the thermoacidophilic archaebacterium Sulfolobus acidocaldarius. 295 1

Hydrolysis of adenosine 5'-triphosphate (ATP) and p-nitrophenyl phosphate by the hydrogen ion-transporting potassium-stimulated adenosine triphosphatase (H,K-ATPase) was investigated. Hydrolysis of ATP was studied at pH 7.4 in vesicles treated with the ionophore nigericin. The kinetic analysis showed negative cooperativity with one high affinity (Km1 = 3 microM) and one low affinity (Km2 = 208 microM) site for ATP. The rate of hydrolysis decreased at 2000 microM ATP indicating a third site for ATP. When the pH was decreased to 6.5 the experimental results followed Michaelis-Menten enzyme kinetics with one low affinity site (Km = 116 microM). Higher concentrations than 750 microM ATP were inhibitory. Proton transport was measured as accumulation of acridine orange in vesicles equilibrated with 150 mM KCl. The transport at various concentrations of ATP in the pH interval from 6.0 to 8.0 correlated well with the Hill equation with a Hill coefficient between 1.5-1.9. The concentration of ATP resulting in half-maximal transport rate (S0.5) increased from 5 microM at pH 6.0 to 420 microM at pH 8.0. At acidic pH the rate of proton transport decreased at 1000 microM ATP. The K+-stimulated p-nitrophenylphosphatase (pNPPase) activity resulted in a Hill coefficient close to 2 indicating cooperative binding of substrate. The pNPPase was noncompetitively inhibited by ATP and ADP; half-maximal inhibition was obtained at 2 and 100 microM, respectively. Phospholipase C-treated vesicles lost 80% of the pNPPase activity, but the Hill coefficient did not change. These kinetic results are used for a further development of the reaction scheme of the H,K-ATPase.
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PMID:Kinetics of the acid pump in the stomach. Proton transport and hydrolysis of ATP and p-nitrophenyl phosphate by the gastric H,K-ATPase. 298 93


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