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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)

1. Calcium binding to (Na+ + K+)-ATPase (ATP phosphohydrolase, EC 3.6.1.3) preparations from beef and pig heart preparations of varying degrees of purity was measured. 2. Binding was inhibited by Mg2+, Na+ and K+. Inhibition by Na+ and K+ appeared to be due to an ionic strength effect. 3. Four classes of binding sites were identified with Kd values for calcium of about 0.03, 1, 15 and 200 micrometer. 4. Cyclic AMP-dependent phosphorylation of the enzyme by protein kinase (ATP: protamine O-phosphotransferase, EC 2.7.1.70) had no effect on (Na+ + K+)-ATPase activity. 5. Phosphorylation also had no effect on either Kd or Bmax for calcium binding at any of the four sites whether measured in the presence of absence of NaCl or KCl. 6. It is concluded that previous reports of an effect of phosphorylation on calcium binding to a (Na+ + K+)-ATPase preparation may have been due to the presence of membrane material not directly associated with (Na+ + K+)-ATPase.
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PMID:Cyclic AMP-dependent protein kinase phosphorylation of cardiac (Na+ + K+)-ATPases. Effect on calcium binding. 1 66

Study of pH-dependence of Ca-ATPase activity of heavy meromyosin (HMM) at low and high ionic strength showed essential differences in the modifying effect of two sulfhydryl reagents, p-CMB and silver. Silver ions in conditions studied independently on pH and KCl concentration produce an inhibition of ATP hydrolysis by myosin and HMM, the shape of the pH-dependence curve remaining similar to that of the native enzyme up to 40% of blocking free sulfhydryl groups. At the same degree of binding of sulfhydryl groups with p-CMB at 0,5 M KCl the pH-dependence curve due to activation at neutral pH changes it's shape and becomes similar to that for dissociation of two ionizable groups (at neutral and alkaline regions). In contrast to this, a low or zero concentrations of KCl no activation was observed for the enzyme with 40-50% of SH-Groups modified by p-CMB and Ca-ATPase in this case seemed to be independent of pH. The data obtained suggest that SH-Groups are not included into the active site of myosin, and the activating effect observed for some sulfhydryl reagents, is due to conformational changes and it can be the result of the penetrance of the organic part of the reagent molecule into hydrophobic region of the protein.
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PMID:[pH-dependence characteristics of Ca-ATPase activity of heavy meromyosin with modified SH-groups]. 1 1

The in vitro optimum pH of renal (Na+, K+)-ATPase, assumed to be 7.8, depends on the type of ATP used. The accepted value is obtained with 'grade II' ATP but with purer ATP ('Sigma grade') it lies close to the intracellular pH in rat medulla and cortex (pH 7.0, 7.2). Values were identical in rats subjected to dietary potassium depletion for 2-4 weeks. The optimal Mg2+ concentration was also influenced by the type of ATP but Mg ATPase activity was unaffected. Both types of ATP were hydrolysed by trichloracetic acid. Where the purer ATP is used the assay conditions need to be modified accordingly.
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PMID:The optimum pH of renal adenosine triphosphatase and its variation with the type of ATP. 1 37

Myosin from rabbit stomach was highly purified by ammonium sulfate fractionation in the presence of ATP and MgCl2, ultracentrifugation and Sepharose 4B chromatography. The myosin composed of one heavy and two light chains as determined by SDS-gel electrophoresis. The molecular weights of the light chains were the same as those of gizzard myosin, about 20,000 and 17,000, respectively. The pH-activity curve and the KCl concentration dependency of Ca-ATPase of the stomach myosin were similar to those of other smooth muscle myosins. The stomach myosin was more resistant to pepsin digestion than skeletal myosin. Other proteolytic enzymes, trypsin, chymotrypsin, papain, and nagarse, digested the myosin in the same way as skeletal myosin.
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PMID:Purification and some properties of rabbit stomach myosin. 1 37

Ciliary 30S dynein of Tetrahymena was investigated with regard to modification of the ATPase activity with N-ethylmaleimide (NEM) in the presence of ATP. The elevation of enzyme activity due to the modification was largely repressed by addition of ATP at a concentration of 1 mM or more during preincubation of 20 h at 0 degrees C. The repression was highly specific for ATP, though ADP and AMPPNP showed slight repressive effects. After complete hydrolysis of ATP added to the preincubation mixture, however, elevation of 30S dynein ATPase activity occurred. It is suggested that the repression by ATP of NEM-induced elevation of 30S dynein ATPase activity is simply due to a protecting effect of ATP on certain SH group(s) (probably SH1-type group(s)) around the active center of 30S dynein. When 30S dynein was maximally activated by modification with NEM, ATP or ADP did not significantly promote the inactivation of the modified enzyme upon further treatment with NEM, indicating that 30S dynein lacks the characteristics of SH2-type groups. On the other hand, ATP also showed a protective effect against inhibition of native 30S dynein by high concentrations of NEM. High concentrations of ADP and AMPPNP were inhibitory to 30S dynein ATPase activity but inorganic phosphate did not inhibit 14S or 30S dynein ATPase activities at all.
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PMID:Effects of adenosine triphosphate on N-ethylmaleimide-induced modification of 30S dynein from Tetrahymena cilia. 1 51

In the search for gastric ATPases that might be related to the mechanism of HCl secretion, an interesting and rather unique K+-stimulated ATPase has been discovered. This enzyme is isolated from oxyntic cells and has been associated with the apical plasma membrane and/or tubulovesicular system. Membrane vesicles containing the K+-stimulated ATPase transport H+ into the vesicular lumen under the appropriate conditions of ATP, Mg2+, and KCl. This process can be measured by pH electrode, binding of certain metachromatic dyes to "energized" sites, or accumulation ratios of substances with appropriate pK values. Vesicular interior can be acidified to pH 3.5 or below. At the present time, it is difficult to distinguish between an electrogenic H+ pump and an electroneutral H+/K+ exchange mechanism. A hypothetical scheme for the gastric H+ secretory mechanism is proposed which fits much of the data from studies on the K+-ATPase, vesicular transport, and intact gastric mucosa.
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PMID:Gastric adenosine triphosphatases: a review of their possible role in HCl secretion. 2 Mar 86

Cytochemical localization of ATPase activities in cilia and basal bodies of Tetrahymena pyriformis revealed a number of possible sites of ATPases. In basal bodies, reaction product was localized on the periphery of basal body microtubules, in the core of the B-microtubules, on the dense basal body core, and on the basal plate; some reaction product was associated with the postciliary and basal microtubules. In the cilium, reaction product was associated with the ciliary membrane, the basal granule, the periphery of the outer doublet microtubules, in the core of the B-microtubules, and on the arms and either the central microtubules or the radial spoke heads. Reaction product deposition required ATP and either Ca2+ or Mg2+ or ADP and Mg2+. When incubated in the presence of ATP and Na+, reaction product was only found at the base of the cilium in the region of the ciliary necklace. Implications of the various sites of activity are discussed with respect to possible mechanisms of ciliary motility.
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PMID:Fine structural localization of phosphatases in cilia and basal bodies of Tetrahymena pyriformis. 2 Jun 78

The ATPase (EC 3.6.1.3) activity of 30 S dynein from Tetrahymena cilia was remarkably stimulated by porcine brain tubulin at pH 10. The activity increased with increasing concentration of tubulin until the molar ratio of tubulin dimer to 30 S dynein reached approx. 10. The optimum of the ATPase activity of 30 S dynein in the presence of tubulin was 1-2 mM for MgCl2 and 2 mM for CaCl2. Increasing ionic strength gradually inhibited the stimulation effects of tubulin. Activation energies of 30 S dynein in the presence and absence of tubulin were almost the same. At the temperatures beyond 25 degrees C stimulation effects of tubulin disappeared. ATP was a specific substrate even in the presence of tubulin. In kinetic investigations parallel reciprocal plots were observed in a constant ratio of divalent cations to ATP of 2, indicating that tubulin was less tightly bound to 30 S dynein in the presence of ATP than the absence. The similar results were obtained at pH 8.2. 14 S dynein and the 12 S fragment which have poor ability to recombine with outer fibers were also activated with brain tubulin.
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PMID:Interactions of Tetrahymena dynein with microtubule protein. Tubulin-induced stimulation of dynein ATPase activity. 2 Sep 50

A deviation from optimal conditions of the Na, K-ATPase reaction results in a drastic change in the plot: enzyme activity versus Na/K ratio. Acidification of the medium and a decrease in Mg2+ concentration and temperature results in two peaks on the curve at Na/K ratio of about 1 and at Na/K ratio greater than 4. The enhancement of pH of the medium and increase in Mg2+ concentration decreases the first peak and increases the second one. A comparison of these curves for hydrolysis of ATP, UTP and p-nitrophenylphosphate and temperature dependence of the hydrolysis of the substrates suggest that the anomalies observed may be accounted for the Na+ effect on the K-sites or K+ effect on the Na-sites under conditions when cation-binding sites are heterogeneous.
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PMID:[Regulation of Na, K-ATPase activity by monovalent cations]. 2 Sep 94

Facilitated diffusion of [14C]lactose into inverted membrane vesicles of Escherichia coli was measured using HgCl2 as a stopping reagent and polylysine to flocculate the vesicles for filtration. Equilibration of lactose between the internal and external volumes required expression of the y gene of the lac operon and was inhibited by thiodigalactoside or by prior incubation with N-ethylmaleimde or HgCl2. The initial rate of uptake was saturable, with a Kt of 0.95 mM. Counterflow of [14C]lactose was demonstrated in either direction. ATP hydrolysis or respiration drove the efflux of internal lactose. The effect of ATP required addition of F1 coupling factor (ATPase) from E. coli when lactose transport was studied in F1-deficient inverted vesicles. Accumulation of lactose against a concentration gradient was achieved by forming an artificial electrochemical proton gradient consisting of a membrane potential negative inside or a pH gradient basic inside. Addition of ATP inhibited this proton driven uptake showing that it occurred in inverted vesicles. It was concluded that the lactose-proton co-transport protein (M protein) is qualitatively symmetrical with respect to the facilitated diffusion of lactose and the coupling of proton and lactose transport.
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PMID:Studies of the beta-galactoside transporter in inverted membrane vesicles of Escherichia coli. I. Symmetrical facilitated diffusion and proton gradient-coupled transport. 2 Nov 83


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