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At least 649 records · Page 36Linked to original sources
PubMed1980

Characterization of a Mg2+-stabilized state of the (Na+ and K+)--stimulated adenosine triphosphatase using a fluorescent reporter group.

A Mg2+-induced change of the (Na+ and K+)-stimulated adenosine triphosphatase (Na+,K+)-ATPase) from Electrophorus electricus was investigated by kinetics and fluorescence techniques. Binding of Mg2+ to a low affinity site(s) caused inhibition of (Na+,K+)-ATPase activity, an effect which was antagonized by both Na+ and ATP. Mg2+ also caused inhibition of K+-dependent dephosphorylation of the enzyme without inhibiting either (Na+)-ATPase activity or Na+-dependent phosphorylation. Mg2+ also induced a 5 to 6% enhancement in the fluorescence intensity of enzyme labeled with the fluorescent sulfhydryl reagent, 2-(4-maleimidylanilino)naphthalene-6-sulfonate. As in the case of Mg2+ inhibition of activity, the affinity for Mg2+ as an inducing agent for this effect was significantly reduced by both Na+ and ATP, suggesting that the same change was being monitored in both cases. The Mg2+ effect was reduced by both Na+ and ATP, suggesting that the same change was being monitored in both cases. The Mg2+ effect was reduced in magnitude by ouabain and prevented by oligomycin, specific inhibitors of the enzyme. In addition, K+ (and cations that substitute for K+ in supporting activity) induced a 3 to 4% enhancement in fluorescence intensity in the presence of Na+, Mg2+, and ATP, although the K+ and Mg2+ effects appeared to be different on the basis of their excitation spectra. The K+ effect was inhibited by ouabain and occurred with a rate greater than the rate of turnover of the enzyme, permitting its involvement in the catalytic cycle.

Animals↗
PubMed1993

In vitro modulation of platelet sodium, potassium adenosine triphosphatase enzyme activity by antiallergy drugs.

Previous studies have documented decreased levels of platelet sodium, potassium adenosine triphosphatase (Na+, K+ ATPase) enzyme activity in allergic subjects. The purpose of this study was to determine the effect of several drugs used to treat allergy and asthma on platelet Na+,K+ ATPase activity. Platelets from five allergic and five nonallergic subjects were incubated at 37 degrees C for 30 minutes with cortisol (1.0 to 3.6 micrograms/ml), theophylline (10 to 40 micrograms/ml), cromolyn (0.5 to 2.0 micrograms/ml), albuterol (3 to 24 ng/ml), chlorpheniramine (2.5 to 20 micrograms/ml), or diluent. The platelets were then rinsed, sonicated, serially centrifuged, and assayed for Na+,K+ ATPase activity nmol/min x micrograms protein by spectrophotometry. Mean activity (+/- 1 SEM) for the diluent incubation was 5.55 +/- 1.27 nmol/min x micrograms protein and 0.91 +/- 0.32 nmol/min x micrograms protein for the nonallergic and allergic subjects, respectively. The enzyme activity of allergic platelets (same units as above) increased after incubation with the following drugs: cortisol, 6.07 +/- 1.75 (p < 0.025) at 1.0 micrograms/ml, 7.55 +/- 1.36 (p < 0.005) at 1.4 micrograms/ml, and 5.95 +/- 0.91 (p < 0.025) at 1.8 micrograms/ml; cromolyn, 5.79 +/- 1.68 (p < 0.050) at 1.0 micrograms/ml; and albuterol, 4.43 +/- 1.61 (p < 0.05) at 12 ng/ml. Theophylline and chlorpheniramine did not have a similar effect on Na+,K+ ATPase activity. These data show that some of the drugs commonly used to treat allergic patients, especially anti-inflammatory agents, can increase the depressed platelet levels of Na+,K+ ATPase activity observed in allergic subjects. Modulation of Na+,K+ ATPase is a possible mechanism of action for these drugs in vivo.

Adult↗
PubMed1994

Effect of chronic lithium chloride on membrane adenosine triphosphatases in certain postural muscles of rats.

Lithium has been extensively used as an antidepressant in the treatment of manic depressive disorders requiring chronic administration. Here, we report a study of the effect of long-term lithium treatment on the activities of membrane adenosine triphosphatases (ATPases) in certain postural muscles of rat. Specifically, Ca(2+)-ATPase, Na+,K(+)-ATPase and Mg(2+)-ATPase activities were measured in the soleus, extensor digitorum longus and plantaris muscles following 6 weeks of treatment with LiCl. Increases were observed in the Na+,K(+)-ATPase activity whereas the Mg(2+)-ATPase activity decreased with prolonged LiCl treatment. The most pronounced effect was a highly significant (P < 0.001) increase in the mitochondrial Ca(2+)-ATPase and Na+,K(+)-ATPase activity to almost 50-100% above the control. The increases in the mitochondrial Ca(2+)-ATPase activity of extensor digitorum longus and plantaris were 70% and 100%, respectively. The corresponding increases in the Na+,K(+)-ATPase activity were 127%, 99% and 87% for soleus, extensor digitorum longus and plantaris, respectively. Irrespective of the differences in the fiber pattern and physiological function, all three muscles responded in a similar way to Li+. The changes in the membrane ATPases reflect a deranged ATP turnover, thus affecting the overall energy state of the animal. Based on these results, we hypothesize that Li+ produces its effects by interfering with cation transport processes. Since Li+ affects the neural excitability of the cell it is suggested that the stimulation of the ATPases may be important in the psychotropic properties of the ion.

Adenosine Triphosphatases↗
PubMed1979

Cardiac atrial myosin adenosine triphosphatase of animals and humans: distinctive enzymatic properties compared with cardiac ventricular myosin.

Cardiac myosin obtained from atria had a higher Ca2+-activated ATPase activity than did cardiac myosin from ventricles in various species of animals and in humans. The increased specific activity of Ca2+-activated adenosine triphosphatase (ATPase) of atrial myosin appeared to correlate with the level of the activity of ventricular myosin ATPase in the animal, since the same order in ATPase activity, as observed in ventricular myosins from various animals, was noted in atrial myosins. The enzymatic properties of atrial myosin also were characterized by no activation by N-ethylmaleimide, low activating energy, and a lower rate of inactivation at alkaline pH compared with the same properties of ventricular myosin. These findings suggest a difference in the myosin molecule at or near the active site, involving some sulfhydryl groups, between the two types of cardiac myosin. The Mg2+-activated ATPase activity, both in the presence and absence of actin (which is thought to be closely related to the basic contraction mechanism), also was enhanced in atrial myosin. Thus, the ATPase activities of atrial and ventricular myosins were different with special reference to the reaction pathway involving calcium and magnesium ions and appear to account for the difference in the velocity of contraction between the atria and the ventricles.

Adenosine Triphosphatases↗
PubMed1976

Rat hepatic sodium plus potassium ion-dependent adenosine triphosphatase after treatment with digoxin and thyroxine.

1. The effect of treating rats with digoxin and thyroxine for 45 days has been studied. 2. Animals fed with digoxin gained significantly more weight than the control animals. 3. Treatment with digoxin, thyroxine or both produced a similar significant increase in the amount of Na+ + K+ -dependent adenosine triphosphatase in liver without an additive effect. 4. It is suggested that digoxin resistance in thyrotoxicosis may be related to this similarity in action.

Adenosine Triphosphatases↗
PubMed1976

Effects of grayanotoxin I on cardiac Na + K + -adenosine triphosphatase activity, transmembrane potential and myocardial contractile force.

The relationship between altered transmembrane sodium movements and myocardial contractility was studied by opposing the action of the sodium pump with grayanotoxin I (GTX), an agent previously shown to increase resting sodium influx. GTX failed to affect Na+,K+-adenosine triphosphatase activity in vitro in concentrations as high as 0.1 mM. In electrically driven left atrial preparations of guinea-pig hearts, 1 mugM GTX produced a slight depolarization and appeared to decrease the upstroke velocity of the action potential, GTX (0.1-1 mugM) also produced a positive inotropic effect which developed over a 20-minute period. At higher concentrations, GTX produced arrhythmias. These effects of GTX were also observed in the presence of 10 mugM propranolol. Positive inotropic and arrhythmic effects of GTX were reversible after washout of the drug. These effects of GTX were also reversed by tetrodotoxin, an agent which has been shown to counteract the effect of GTX on sodium permeability. These data are consistent with a hypothesis that altered transmembrane sodium movement effects myocardial contractility.

Adenosine Triphosphatases↗
PubMedDate not supplied

[Changes in the activity of monoamine oxidase, adenylate cyclase and adenosine triphosphatase in liver cells during the process of hepatocarcinogenesis].

Activity of specific mitochondrial enzymes was studied in rat liver during 2-acetylamine fluorene or diethylnitrosamine-induced hepatocancerogenesis. The results of enzymatic activities studied correlated with morphological changes in cancerogenesis. Alterations in activity of monoamine oxidase, adenylate cyclase and adenosine triphosphatase depended on the step of cancerogenesis. Activity of adenylate cyclase in cell membranes decreased gradually during the impairment. Change in activity of the enzymes, observed at the step of enhanced liver cell proliferation, proceeded at further steps of cancerogenesis. The data obtained suggest that alterations in activity of mitochondrial enzymes are related to modified metabolism observed in the impaired cells.

2-Acetylaminofluorene↗
PubMed1976

Properties of Escherichia coli mutants with alterations in Mg2+-adenosine triphosphatase.

A mutant Escherichia coli, selected for resistance to the antibiotic neomycin, was unable to utilize nonfermentable carbon sources for growth. Two strains were selected from this mutant on the basis of their ability to grow utilizing succinate as a carbon source. All three strains had approximately equal amounts of the Mg2+-adenosine triphosphatase (ATPase) (EC 3.6.1.3) protein, but the activity of the enzyme differed in each strain. The Mg2+-ATPase from each of the three strains lost activity upon solubilization and appeared to undergo rapid dissociation once solubilized. This dissociation is similar to that described for the wild type after cold exposure.

Adenosine Triphosphatases↗
PubMed1990

Scopadulcic acid B, a new tetracyclic diterpenoid from Scoparia dulcis L. Its structure, H+, K(+)-adenosine triphosphatase inhibitory activity and pharmacokinetic behaviour in rats.

The structure of scopadulcic acid B (2, SDB), a major ingredient of the Paraguayan herb "Typychá kuratũ" (Scoparia dulcis L.), was elucidated mainly by comparison of its spectral data with that of scopadulcic acid A (1). SDB inhibited both the K(+)-dependent adenosine triphosphatase (ATPase) activity of a hog gastric proton pump (H+, K(+)-ATPase) with a value of 20-30 microM for IC50 and proton transport into gastric vesicles. Pharmacokinetic studies of SDB in rats indicated that plasma SDB concentrations after i.v. injection of the sodium salt of SDB (SDB-Na) were described reasonably well by a two-compartment open model with Michaelis-Menten elimination kinetics. Plasma concentrations after oral administration of SDB-Na or SDB showed a much slower decline than what was expected following the i. v. study. It was suggested that the sustained plasma level of SDB after oral administration of SDB-Na or SDB was accounted for by relatively slow but efficient gastro-intestinal absorption in rats.

Adenosine Triphosphatases↗
PubMed1977

Different effects of inhibitors on two mutants of Escherichia coli K12 affected in the Fo portion of the adenosine triphosphatase complex.

The effects of the inhibitors dicyclohexyl-carbodiimide (DCCD), bathophenanthroline and tertiary octylcatechol, on some enzyme activities in membranes from strains of Escherichia coli carrying mutations in the uncB or uncC genes have been studied. Membranes prepared from uncC mutants retain a normal DCCD-sensitive Mg2+-stimulated adenosine triphosphatase (Mg-ATPase) activity whereas in uncB mutants this enzyme activity is insensitive to DCCD. The membrane-bound Mg-ATPase activity from the uncC mutant strain, as compared with that from the normal strain, is only partially sensitive to the inhibitors bathophenanthroline or tertiary-octylcatechol. Both of these inhibitors stimulate the membrane-bound Mg-ATPase from uncB mutant strains. A DCCD-insensitive Mg-ATPase activity is found in the cytoplasmic fraction following cell disruption of either the uncB or the uncC mutants. The lipophilic chelators bathophenanthroline and tertiary-octylcatechol stimulate the activity of the 'soluble' Mg-ATPase in the uncB mutant but partially inhibit the activity in the uncC mutant. The NADH oxidase activities in membranes from both mutant and normal strains are strongly inhibited by tertiary-octylcatechol and bathophenanthroline but not by DCCD.

Adenosine Triphosphatases↗
PubMed1978

Characteristics of lead ion-stimulated phosphorylation of Electrophorus electricus electroplax (Na+ + K+)-adenosine triphosphatase and inhibition of ATP-ADP exchange.

Pb2+-stimulated phosphorylation of Electrophorus electricus electroplax (Na+ + K+)-adenosine triphosphatase is prevented by stoichiometric quantities of 2,3-dimercaptopropanol. The chelator in the same low concentrations does not block Na+-dependent phosphorylation. Both Pb2+-and Na+-dependent phosphorylation reactions show the same dependence on MgCl2. Phosphorylation in the presence of both Na+ and Pb2+ is cumulative suggesting that Pb2+ and Na+ bind at separate, independent sites. The enthalpy change due to binding of Pb2+ is about -1.76 kcal/mol. 32P-phosphopeptides obtained from pronase or pepsin digests of Pb2+-and Na+-dependent phosphoproteins are electrophoretically identical. Pb2+ does not stimulate but does inhibit ATP-ADP exchange activity under the conditions in which this activity is stimulated by Na+. Since the phosphorylation sites are identical, it is concluded that the differences in reactivity of the Na+- and Pb2+-phosphoenzymes are due to different conformational changes produced by binding of Na+ and Pb2+. The Pb2+-sensitive conformation is critical for Na+ specificity of phosphorylation, reversibility of phosphorylation, and for phosphatase activity but not for acceptor site phosphorylation by ATP. These findings have implications for enzyme reaction models.

Adenosine Diphosphate↗
PubMed1977

The value of enzyme histochemical techniques in the classification of fibre types of human skeletal muscle. 2. The histochemical demonstration of myosin adenosine triphosphatase in skeletal muscles from adult patients with or with no diseases of the neuromuscular system. A comparison between results obtained by calcium salt and lead salt techniques.

In the present investigation the results of a lead salt technique and two calcium salt techniques for the deomonstration of the activity of myosin adenosine triphosphatase in sections of both normal and pathological human skeletal muscle specimens are compared. It was seen that the histochemical results obtained by the different techniques are similar, especially with regard to the identification of fibre-types. It can be clearly stated, that the alkaline phosphatase activity present in muscle fibers of diseased skeletal msucles revealed only a very slight activity with the substrate ATP, so the alkaline phosphatase activity in general did not disturb the reliability of the different myosin ATPase techniques. Moreover it was found that the presence of the mitochondrial Ca2+ -ion activated ATPase with a high pH-optimum in muscle fibers did not give rise to faulty results. From studies with dinitrophenol it can be concluded that this substance activates the myosin ATPase present in type I fibres especially.

Adenosine Triphosphatases↗
PubMed1978

Increased sodium plus potassium adenosine triphosphatase activity in erythrocyte membranes in Huntington's disease.

Dopa-decarboxylase, acetylcholinesterase, sodium plus potassium stimulated adenosine triphosphatase (Na+ + K+-ATPase), and membrane-bound protein kinase were compared in the erythrocytes of patients with Huntington's disease and normal controls. All these enzymes also exist in the basal ganglia. The Na+ +K+-ATPase level was elevated (p less than 0.05) in Huntington's disease, while no significant changes were observed in the other enzymes. This finding is consistent with the concept that Huntington's disease is associated with a general membrane abnormality.

Acetylcholinesterase↗
PubMed1987

Electron microscopic cytochemical localization of a basolateral calcium adenosine triphosphatase in vitamin D replete chick enterocytes.

A cytochemical technique for the electron microscopic localization of calcium adenosine triphosphatase (Ca-ATPase) was utilized to localize this enzyme in the enterocytes of rachitic and vitamin D-replete chicks. In animals treated with cholecalciferol (CC, vitamin D3), an electron-dense reaction product was located along the basolateral membranes of the absorptive cells within 72 hr after injection. Similarly, a reaction product was identified in association with the basolateral membranes within 24 hr after injection of 1,25-dihydroxycholecalciferol, the active metabolite of vitamin D. A microvillar reaction product was not seen in either of these two groups. Electron-dense reaction products were also seen in association with mitochondria and scattered throughout the cytoplasm of these enterocytes. The Ca-ATPase reaction product was dependent upon the presence of medium calcium and substrate (ATP), was inhibited by vanadate, and was heat labile. In the rachitic animals, a reaction product indicative of Ca-ATPase activity was not seen in association with either the basolateral membranes or the mitochondria. These data appear to indicate that an energy-requiring calcium-activated membrane pump plays a role in the flux of calcium across the enterocytes of the small intestine.

Animals↗
PubMed1984

Cytochemical localization of ouabain-sensitive, K+ -dependent p-nitrophenylphosphatase and Ca++-stimulated adenosine triphosphatase activities in human parotid and submandibular glands.

K+ -dependent p-nitrophenylphosphatase (pNPPase) and Ca++ -stimulated adenosine triphosphatase (ATPase) activities were studied in human parotid and submandibular glands using cytochemical methods at the ultrastructural level. In both glands, only the striated-duct epithelium showed K+ -pNPPase reaction product, thereby indicating the localization of Na+, K+ -ATPase. The precipitate was concentrated on the deep invaginations of the basolateral plasma membranes, in close association with their cytoplasmic surface. Ca++ -ATPase activity was also found on the basolateral plasma membranes, but two striking differences from the K+ -pNPPase distribution were observed: firstly, Ca++ -ATPase appeared in both acinar and ductal cells, and secondly, it was localized on the outer side of the plasma membranes.

4-Nitrophenylphosphatase↗
PubMed1985

Localization of Mg++-dependent adenosine triphosphatase and alkaline phosphatase activities in the postimplantation mouse embryos in day 5 and 6.

Mg++-dependent adenosine triphosphatase (Mg-ATPase) and alkaline phosphatase (ALPase) activities were histo- and cytochemically investigated in postimplantation mouse embryos from day 5 to day 6. In day 5 postimplantation embryos, Mg-ATPase activity was detected in the embryonic ectoderm and weakly in the visceral endoderm. Weak ALPase activity was found in the embryonic ectoderm and visceral endoderm. Parietal endoderm, both in day 5 and in day 6 embryos, had very weak or no Mg-ATPase and ALPase activities. Mg-ATPase activity in day 6 embryos was found with the same localization as that in day 5 embryos. No ALPase activity was observed in their embryonic ectoderm. Extraembryonic ectodermal cell mass had the strongest Mg-ATPase activity in these stage embryos. These results suggest that the localization of both enzyme activities in postimplantation mouse embryos is closely related to the morphogenesis. As regards the proamniotic cavity formation, the fact that Mg-ATPase activity was still observed in the embryonic ectoderm in these stages suggests the involvement of active transport system on the production of nascent proamniotic cavity fluid.

Alkaline Phosphatase↗
PubMed1985

Dependence of adenosine triphosphatase activity of rabbit psoas muscle fibres and myofibrils on substrate concentration.

The rate of hydrolysis of adenosine triphosphate (ATP) by chemically skinned rabbit muscle fibres was measured as a function of Mg ATP concentration in the range 5 microM to 5 mM. Pyruvate kinase and lactate dehydrogenase were used to link adenosine diphosphate formation to oxidation of nicotinamide adenine dinucleotide which was followed by the change in absorption at 340 nm. The ATPase rate of a fully activated fibre (pCa = 4.5) increased monotonically with Mg ATP concentration in a manner that could be readily fitted by a hyperbola. At 15 degrees C, pH 7 and an ionic strength of 0.2 M the rate at saturating Mg ATP (Vm) was 1.78 +/- 0.2 s-1 per myosin head (mean +/- S.D.; n = 6) and the Mg ATP concentration needed for half the maximal rate (Km) was 16.6 +/- 2 microM. The ATPase of fibres that had been stabilized by cross-linking with 1-ethyl-3-(3-dimethyl-aminopropyl)carbodiimide (EDC) was also investigated. Cross-linking did not significantly affect the Vm or Km and these fibres proved useful for investigating the adequacy of the pyruvate kinase activity for regenerating hydrolysed ATP. Myofibrils were cross-linked with EDC or glutaraldehyde to prevent shortening. Their ATPase properties were investigated: the values of Vm were 0.85 +/- 0.18 (mean +/- S.D.; n = 14) and 0.82 +/- 0.05 s-1 (n = 6) and of Km were 18.0 +/- 2.8 and 12.4 +/- 2.4 microM respectively. The values of Vm and Km for EDC cross-linked myofibrils were fairly insensitive to ionic strength, the Km decreasing 40% and the Vm increasing 50% for a change from 0.2 to 0.3 M. This slight dependence on ionic strength is considered in relation to the ionic strength dependence of the elementary rate constants of the actomyosin subfragment-1 ATPase cycle.

Adenosine Triphosphatases↗