Gene/Protein Disease Symptom Drug Enzyme Compound
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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)

The role of O2 free radicals in the reduction of sarcolemmal Na+-K+-ATPase, which occurs during reperfusion of ischemic heart, was examined in isolated guinea pig heart using exogenous scavengers of O2 radicals and an inhibitor of xanthine oxidase. Ischemia and reperfusion reduced Na+-K+-ATPase activity and specific [3H]ouabain binding to the enzyme in ventricular muscle homogenates and also markedly lowered sodium pump activity estimated from ouabain-sensitive 86Rb+ uptake by ventricular muscle slices. These effects of ischemia and reperfusion were prevented to various degrees by O2-radical scavengers, such as superoxide dismutase, catalase, dimethyl-sulfoxide, histidine, or vitamin E or by the xanthine oxidase inhibitor, allopurinol. The degree of protection afforded by these agents paralleled that of reduction in enhanced lipid peroxidation of myocardial tissue as estimated from malondialdehyde production. These results strongly suggest that O2 radicals play a crucial role in the injury to sarcolemmal Na+-K+-ATPase during reperfusion of ischemic heart.
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PMID:O2 free radicals: cause of ischemia-reperfusion injury to cardiac Na+-K+-ATPase. 302 76

We have generated a series of clonally related cell lines which differ in the level of amplified expression of the Na,K-ATPase. These lines, originally derived from the ouabain resistant HeLa variant C+, expressed different numbers of binding sites for the Na,K-ATPase inhibitor ouabain, ranging from 2.9 X 10(6)/cell to 11.8 X 10(6)/cell. Amplification of the genes for both subunits of the enzyme was also seen but was not strictly correlated with level of expression. The influxes of histidine and tetraphenylphosphonium were measured across a series, including HeLa S3 and revertants, expressing from 0.74 X 10(6) to 10.5 X 10(6) ouabain-binding sites per cell. Tetraphenylphosphonium influx rate, presumed to be a function of membrane potential, varied linearly with ouabain binding site number, while histidine influx varied with the log of ouabain binding site number. Our results suggest that membrane potential increases in a simple fashion across our series of amplified lines. However, histidine influx was unaffected by treatments which cause membrane depolarization and a decrease in tetraphenylphosphonium influx rate. We propose that increasing histidine influx rates across our amplified series reflects exchange acceleration of L system transport due to increased intracellular pools of L system reactive amino acids. The Na,K-ATPase is ultimately responsible for most active transport across the plasma membrane. The consistent, graded physiological alterations seen across this series of closely related lines, chosen for graded enzyme expression, demonstrate the value of this novel genetic approach to the study of the energization of membrane transport.
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PMID:Graded amplification of the Na,K-ATPase across a subclonal series: effects on membrane physiology. 302 46

A dog kidney (Na+ + K+)-ATPase preparation also catalyzes K+-independent and K+-activated phosphatase reactions with p-nitrophenyl phosphate as substrate. K+-independent activity increases with declining pH over the range 7.5 to 5.8, whereas the other two activities decrease. The increased K+-independent activity is similar with imidazole, histidine, and several Good buffers, and is thus attributable to free H+, probably by affecting enzyme conformations rather than by changing affinity for Mg2+ or substrate or by H+ occupying specific K+-sites. The decrease in K+-phosphatase and (Na+ + K+)-ATPase activities with pH also occurs similarly with those buffers, and is not due to changes in apparent affinity for substrate or for cation activators. However, the Good buffers Pipes and ADA inhibit the K+-independent phosphatase reaction strongly, the K+-activated reaction moderately, and the (Na+ + K+)-ATPase reaction little; both contain two acidic groups, unlike the other buffers tested. Inhibition of the phosphatase reaction by Pipes is associated with a decreased apparent affinity for K+ and an increased sensitivity to inhibition by Na+ and ADP, consistent with Pipes hindering conformational transitions to the E2 enzyme forms required for phosphatase hydrolytic activity.
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PMID:Buffer, pH, and ionic strength effects on the (Na+ + K+)-ATPase. 303 64

Experiments were conducted to determine whether ultraviolet (UV) radiation exerts its effect through the generation of oxygen intermediates on Langerhans cells (LC). Guinea pigs were exposed to one single dose of UVB (0.9-2.7J/cm2), and biopsy specimens were taken 5 days after the irradiation. The population of LC was evaluated using ATPase-stained epidermal sheets. These exposures reduced the number of LC to 20-25% of the original density. On the other hand, superoxide dismutase (SOD) (0.02-0.2 mg), a scavenger of superoxide anion, which had been injected intradermally just before UV radiation, significantly prevented the depletion of LC, although not completely (37-40% of the original density). The injection immediately after the exposure was still significantly effective, but less so. Other scavengers of oxygen intermediates including catalase, D-mannitol, and L-histidine revealed no detectable effect. A single exposure of UVB at doses of 0.3-0.6 J/cm2 did not deplete the ATPase-positive LC. However, the same dose of UVB reduced the number of LC to 70%, when exposed after the injection of an SOD inactivator, diethyldithiocarbamate, possibly due to inactivation of physiologically existing SOD. These observations indicate that oxygen intermediates such as superoxide anion or its subsequent species are generated by UV radiation exposure and damage the epidermal LC.
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PMID:Oxygen intermediates are involved in ultraviolet radiation-induced damage of Langerhans cells. 303 31

In the absence of K+, the hydrolysis of low-energy phosphoenzyme (E2P) of (Na,K)-ATPase, but not Ca-ATPase of sarcoplasmic reticulum, was inhibited by Na+ or by amine compounds, such as Tris, imidazole, arginine, or lysine, with half-maximum inhibition concentrations of millimolar order at pH 7.4 and 0 degrees C. Histidine was slightly inhibitory. Divalent cations alone were also inhibitors. However, divalent cations, especially Ca2+ or Mn2+, were apparently activators in the presence of another inhibitor, Na+, or an amine compound, probably because the inhibitory action of the divalent cations was less powerful than that of Na+ or amines, which appear to compete for the same binding site on E2P. In most reported experiments on the hydrolysis of the phosphoenzyme, Tris or imidazole (as a buffer component) and Na+ (to obtain a sufficient amount of phosphoenzyme) have been present in the reaction mixture in amounts that are now seen to be inhibitory. Consequently, the reactivity of the phosphoenzyme with water would have been substantially underestimated. Under these inhibitory conditions, however, reactivity with K+ or ADP was little influenced.
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PMID:Inhibition by amine bases or by sodium ions and protection by divalent cations in the hydrolysis of phosphoenzyme of (Na,K)-ATPase. 303 3

The in vitro deproteinized vastus lateralis muscle buffer capacity, carnosine, and histidine levels were examined in 20 men from 4 distinct populations (5 sprinters, 800-m runners; 5 rowers; 5 marathoners; 5 untrained). Needle biopsies were obtained at rest from the vastus lateralis muscle. The buffer capacity was determined in deproteinized homogenates by repeatedly titrating supernatant extracts over the pH range of 7.0-6.0 with 0.01 N HCl. Carnosine and histidine levels were determined on an amino acid AutoAnalyzer. Fast-twitch fiber percentage was determined by staining intensity of myosin adenosinetriphosphatase. High-intensity running performance was assessed on an inclined treadmill run to fatigue (20% incline; 3.5 m X s-1). Significantly (P less than 0.01) elevated buffer capacities, carnosine levels, and high-intensity running performances were demonstrated by the sprinters and rowers, but no significant differences existed between these variables for the marathoners vs. untrained subjects. Low but significant (P less than 0.05) interrelationships were demonstrated between buffer capacity, carnosine levels, and fast-twitch fiber composition. These findings indicate that the sprinters and rowers possess elevated buffering capabilities and carnosine levels compared with marathon runners and untrained subjects.
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PMID:Buffering capacity of deproteinized human vastus lateralis muscle. 396 4

In our experiments the phosphorylation of actin was studied. Similar investigations have been published in the literature, however very long incubation time was applied in these studies and even so a low incorporation of phosphate concentration was found. The present phosphorylation experiments were performed using short incubation periods as usual in our myosin investigations and was characterized by an unexpectedly high phosphate saturation. We suggest that in suitable incubation medium the nucleotide- and phosphate-free actin prepared by using phosphate- and ATP-free solutions takes only 1 minute to become saturated, while in its peptide chain a N-P bond type acid labile phosphate is formed. On maximum saturation 9 M P-arginine, 0.4 M P-histidine and some minor phosphorylated derivatives can be observed. After a longer period of incubation, with a lower incorporation of phosphate (3 mol P) a more stable phosphorylated actin is formed. As a result of preparation and gel filtration a dimer and a monomer form of actin can be obtained. Both of them exhibit the basic properties of actin (polymerization, myosin-ATPase activation) and the phosphate incorporation described in this paper.
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PMID:Composition of amino acid phosphates in phosphorylated G-actin of rabbit skeletal muscle. 403 47

Membrane bound (Na,K)-ATPase partially purified from the nauplius larva of the brine shrimp, Artemia salina, was solubilized with the non-ionic detergent C12E8 in the presence of KCl. The addition of KCl was essential for protecting the enzyme against inactivation. With solubilization the enzyme could then be purified to apparent homogeneity. Electron microscopic observation of the purified enzyme revealed a homogeneous population of particles with a diameter of approximately 4 nm. The larger (alpha) subunit of the enzyme formed double bands on sodium dodecyl sulfate-polyacrylamide gels. NH2-terminal sequence analysis of the alpha subunit revealed the possible presence of two isoforms of (Na,K)-ATPase. At the third position a small but distinct amount of lysine was found in addition to glycine, suggesting that the two forms are different from each other at least at the third residue. The NH2-terminal sequence determined is as follows. NH2-Ala-Lys-Gly (Lys)-Lys-Gln-Lys-Lys-Gly-Lys-Asp-Leu-Asn-Glu-Leu-Lys-Lys-Glu-Leu-Asp-Il e-Asp -Phe-His-Lys-Ile-Pro- The sequence is abundant in hydrophilic amino acids, especially lysine, and is quite different from those of vertebrate enzymes reported so far.
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PMID:Solubilization and purification of Artemia salina (Na,K)-activated ATPase and NH2-terminal amino acid sequence of its larger subunit. 609 82

When the bovine mitochondrial F1-ATPase is inactivated with dicyclohexyl[14C]carbodiimide and then gel-filtered, from 2 to 3 g atoms of 14C are incorporated/mol of enzyme. Prior inactivation of the enzyme by the modification of an essential tyrosine residue with 4-chloro-7-nitrobenzofurazan, a reaction that can be reversed by thiols, does not affect the irreversible inactivation of the ATPase by dicyclohexyl[14C]carbodiimide. During the large scale modification of the F1-ATPase by dicyclohexyl[14C]carbodiimide which led to 70% inactivation, 1.9 g atoms of 14C were incorporated/mol of enzyme. Isolation of the alpha, beta, and gamma subunits from this large scale inactivation revealed that the gram atoms of 14C bound per mol of each of the subunits was: alpha, 0.04; beta, 0.56; and gamma, 0.04. The majority of the radioactivity in a cyanogen bromide digest of the 14C-labeled beta subunit was isolated in a fragment that has the following amino acid sequence: Glu-Leu-Ile-Asn-Asn-Val-Ala-Lys-Ala-His-Gly-Gly-Tyr-Ser-Val-Phe-Ala-Gly-Val-Gly -Glu-Arg-Thr-Arg-Glu-Gly-Asn-Asp-Leu-Tyr-Glu*-His-Met; where Glu* represents the N gamma-glutamyl derivative of dicyclohexyl[14C]urea.
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PMID:Inactivation of the bovine mitochondrial F1-ATPase with dicyclohexyl[14C]carbodiimide leads to the modification of a specific glutamic acid residue in the beta subunit. 611 57

The effect of pH and of ATP on the Na : K selectivity of the (Na+ + K+)-ATPase has been tested under equilibrium conditions. The Na+ : K+-induced change in intrinsic tryptophan fluorescence and in fluorescence of eosin maleimide bound to the system has been used as a tool. 1 mol of eosin maleimide per mol of enzyme gives no loss in either ATPase or phosphatase activity and the fluorescence in the presence of Na+ is about 30% higher than in the presence of K+. Choline, protonated Tris, protonated histidine and Mg2+ have an 'Na+' effect on the extrinsic fluorescence, while Rb+, Cs+ and NH4+ have a 'K+' effect. Choline and protonated Tris have an Na+ effect on intrinsic fluorescence. A close correlation between the effect of Na+ compared to K+ on the fluorescence change and on Na+ activation of hydrolysis indicates that the observed changes in fluorescence are due to an effect of Na+ and of K+ on the internal sites of the system. The equilibrium between the two conformations, which are reflected by the difference in fluorescence with Na+ and K+, respectively, is highly influenced by the concentration of protons. At a given Na+ : K+ ratio, an increase in the proton concentration shifts the equilibrium towards the 'K+' fluorescence form while a decrease shifts the equilibrium towards the 'Na+' fluorescence form, i.e., protons increase the apparent affinity for K+ and vice versa, K+ increases pK values of importance for the Na+ : K+ selectivity. Conversely, a decrease in protons increases the apparent affinity for Na+ and vice versa, Na+ decreases the pK. ATP decreases the apparent pK for the protonation-deprotonation, i.e., ATP facilitates the deprotonation which accompanies Na+ binding. The results suggest two effects of ATP for the hydrolysis in the presence of Na+ and K+ : (i) at low ATP concentrations (K0.5 < 10 microM) on the K+-Na+ exchange on the internal sites and (ii) at higher, substrate, concentrations on the activation by K+ on the external sites.
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PMID:Effects of ATP and protons on the Na : K selectivity of the (Na+ + K+)-ATPase studied by ligand effects on intrinsic and extrinsic fluorescence. 615 15


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