Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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 branchial osmoregulatory response of gilthead sea bream (Sparus auratus L.) to short-term (2-192 hr) and long-term (2 weeks) exposure to different environmental salinities (5 per thousand, 15 per thousand, 25 per thousand, 38 per thousand and 60 per thousand) was investigated. A "U-shaped" relationship was observed between environmental salinity and gill Na+,K+ -ATPase activity in both long- and short-term exposure to altered salinity, with the increase in activity occurring between 24 and 96 hr after the onset of exposure. Plasma osmolality and plasma ions (sodium, chloride, calcium and potassium) showed a tendency to increase in parallel with salinity. These variables only differed significantly (P<0.05) in fish adapted to 60 per thousand salinity with respect to fish adapted to full-strength sea-water (SW). Plasma glucose remained unchanged whereas plasma lactate was elevated at 5 per thousand and 60 per thousand. Muscle water content (MWC) was significantly lower in fish adapted to 60 per thousand. Chloride cells (CC) were only present on the surface of the gill filaments and absent from the secondary lamellae. CC distribution was not altered by external salinity. However, the number and size of CC were significantly increased at salinity extremes (5 per thousand and 60 per thousand), whereas fish exposed to intermediate salinities (15 per thousand and 25 per thousand) had fewer and smaller cells. Furthermore, the CC of fish exposed to diluted SW became rounder whereas they were more elongated in fish in full-strength and hypersaline SW. This is consistent with previous reports indicating the existence of two CC types in euryhaline fish. At likely environmental salinities, gilthead sea bream show minor changes in plasma variables and the effective regulation of gill Na+,K+ -ATPase. However, at very low salinities both haemodilution and up-regulation of gill Na+,K+ -ATPase predict a poor adaptation most likely related to deficiency or absence of specific components of the CC important for ion xuptake.
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PMID:Branchial osmoregulatory response to salinity in the gilthead sea bream, Sparus auratus. 1594 79

The effect of choline iodide, bromide and chloride on the kinetics of the electrogenic sodium transport by the Na,K-ATPase was investigated in a model system of ATPase-containing membrane fragments adsorbed on the lipid bilayer membrane. The kinetic parameters of Na(+) transport were determined from short circuit currents after fast release of ATP from its caged precursor. The falling phase of the current transients could be fitted by a single exponential with the time constant, tau (2). Its temperature dependence allowed an estimation of the activation energy of the rate-limiting reaction step, the conformation transition E(1)/E(2). Choline iodide and bromide caused a decrease of the activation energy as well as the overall rate of the process expressed as the pre-exponential factor A of the Arrhenius equation. If choline iodide or bromide were present on the cytoplasmic and extracellular sides of the protein, the temperature dependent changes were more pronounced than when present on the cytoplasmic side only. These results can be explained by an effect of the anions on water structure on the extracellular surface of the protein, where a deep access channel connects the ion-binding sites with the solution. Chloride ions also caused a deceleration of the electrogenic transport, however, in contrast to iodide or bromide, they did not affect the activation energy, and were more effective when added on the cytoplasmic side. This effect can be explained by asymmetric screening of the negative surface charges which leads to a transmembrane electric potential that modifies the ion transfer.
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PMID:Effect of chaotropic anions on the sodium transport by the Na,K-ATPase. 1629 45

Chloride transport, presumably via a Cl(-)-2H(+) co-transport system, was investigated in Chara corallina. At pH 6.5, the control influx (3.1 picomoles per centimeter(2) per second) was stimulated 4-fold by an 18-hour Cl(-) starvation. The stimulated influx was inhibited to 4.7 picomoles per centimeter(2) per second after a 60-minute pre-exposure to 0.5 millimolar 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene (DIDS). This compares with a nonsignificant inhibition of the control under similar conditions. At 2 millimolar DIDS, both stimulated and control influx were inhibited to values of 1.1 and 2.2 picomoles per centimeter(2) per second, respectively; in all cases, DIDS inhibition was reversible. Over the pH range 4.8 to 8.5, the control and DIDS-inhibited influx showed only slight pH sensitivity; in contrast, the stimulated flux was strongly pH dependent (pH 6.5 optimum). Inasmuch as changes in pH alter membrane potential, N-ethylmaleimide was used to depolarize the membrane; this had no effect on Cl(-) influx. A transient depolarization of the membrane (about 20 millivolts) was observed on restoration of Cl(-) to starved cells. The membrane also depolarized transiently when starved cells were exposed to 0.5 millimolar DIDS, but the depolarization associated with Cl(-) restoration was inhibited by a 40-minute pretreatment with DIDS. Exposure of control cells to DIDS caused only a small hyperpolarization (about 7 millivolts). DIDS may have blocked Cl(-) influx by inhibiting the putative plasmalemma H(+)-translocating ATPase. Histochemical studies on intact cells revealed no observable effect of DIDS on plasmalemma ATPase activity. However, DIDS application after fixation resulted in complete inhibition of ATPase activity.The differential sensitivity of the stimulated and control flux to inhibition by DIDS may reflect an alteration of transport upon stimulation, but could also result from differences in pretreatment. The stimulated cells were pretreated with DIDS in the absence of Cl(-), in contrast to the presence of Cl(-) during pretreatment of controls. The differential effect could result from competition between Cl(-) and DIDS for a common binding site. Our histochemical ATPase results indicate that Cl(-) transport and membrane ATPase are separate systems, and the latter is only inhibited by DIDS from the inside of the cell.
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PMID:Plasmalemma Chloride Transport in Chara corallina: Inhibition by 4,4'-Diisothiocyano-2,2'-Disulfonic Acid Stilbene. 1666 75

The H(+)-ATPase of tonoplast vesicles isolated from red beet (Beta vulgaris L.) storage tissue was studied with respect to the kinetic effects of Cl(-) and NO(3) (-). N-Ethylmaleimide (NEM) was employed as a probe to investigate substrate binding and gross conformational changes of the enzyme. Chloride decreased the K(m) of the enzyme for ATP but caused relatively little alteration of the V(max). Nitrate increased K(m) only. Michaelis-Menten kinetics applied throughout with respect to ATP concentration. Nitrate yielded similar kinetics of inhibition in both the presence and absence of Cl(-). Other monovalent anions that specifically increased the K(m) of the ATPase for ATP were, in order of increasing K(i), SCN(-), ClO(4) (-), and ClO(3) (-). Sulfate, although inhibitory, manifested noncompetitive kinetics with respect to ATP concentration. ADP, like NO(3) (-), was a competitive inhibitor of the ATPase but ADP and NO(3) (-) did not interact cooperatively nor did either interfere with the inhibitory action of the other. It is concluded that NO(3) (-) does not show competitive kinetics because of its stereochemical similarity to the terminal phosphoryl group of ATP. NEM was an irreversible inhibitor of the tonoplast ATPase. Both Mg.ADP and Mg.ATP protected the enzyme from inactivation by NEM but Mg.ADP was the more potent of the two. Chloride and NO(3) (-) exerted little or no effect on the protective actions of Mg.ADP and Mg.ATP suggesting that neither Cl(-) nor NO(3) (-) are involved in substrate binding.
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PMID:Mechanism of Stimulation and Inhibition of Tonoplast H-ATPase of Beta vulgaris by Chloride and Nitrate. 1666 60

Chloride or nitrate decreased a pH gradient (measured as [(14)C]methylamine accumulation) in tonoplast-enriched vesicles. The DeltapH decrease was dependent on the anion concentration. These effects are independent of the anion-sensitive H(+)-ATPase of the tonoplast, since the pH gradient (acid inside) was imposed artificially using a pH jump or a K(+) gradient and nigericin. 4,4'-Diisothiocyano-2,2'-stilbene disulfonic acid partially prevented the decrease in pH gradient induced by Cl(-). Two possible models to account for this anion-dependent decrease of DeltapH are: (a) H(+) loss is accompanied by Cl(-) or NO(3) (-) efflux from the vesicles via H(+)/anion symport systems on the tonoplast and (b) H(+) loss is accompanied by Cl(-) or NO(3) (-) uptake into the vesicles via H(+)/anion antiport systems. Depending on the requirements and conditions of the cell, these two systems would serve to either mobilize Cl(-) and NO(3) (-) stored in the vacuole for use in the cytoplasm or to drive anions into the vacuole. Chloride or nitrate also decreased a pH gradient in fractions containing plasma membrane and Golgi, implying that these membranes may have similar H(+)-coupled anion transport systems.
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PMID:Decrease of pH Gradients in Tonoplast Vesicles by NO(3) and Cl: Evidence for H-Coupled Anion Transport. 1666 77

An anion-sensitive H(+)-translocating ATPase was identified in membrane vesicles isolated from mature green tomato (Lycopersicon esculentum) fruit. The H(+)-ATPase was associated with a low density membrane population having a peak density of 1.11 grams per cubic centimeter, and its activity was inhibited by NO(3) (-), N,N'-dicyclohexylcarbodiimide and diethylstilbestrol but not by vanadate, azide, molybdate, or oligomycin. This H(+)-ATPase has an unusual pH dependence indicating both a slightly acidic and a near neutral peak of activity. Chloride was found to be a potent stimulator of ATPase activity. The K(m) for the H(+)-ATPase was approximately 0.8 millimolar ATP. The characteristics of this H(+)-ATPase are very similar to those described for a number of plant cell tonoplast H(+)-ATPases suggesting that the activity identified in tomato fruit membranes is tonoplast-associated. This report demonstrates the feasibility of isolating tonoplast vesicles from acidic fruit tissues for studies of transport activities associated with fruit development and maturation.
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PMID:Transport Properties of the Tomato Fruit Tonoplast : I. Identification and Characterization of an Anion-Sensitive H-ATPase. 1666 35

The electrical response of nitrate-grown maize (Zea mays L.) roots to 0.1 millimolar nitrate was comprised of two sequential parts: a rapid and transient depolarization of the membrane potential, followed by a slower, net hyperpolarization to a value more negative than the original resting potential. The magnitude of the response was smaller in roots of seedlings grown in the absence of nitrate, but, within 3 hours of initial exposure to 0.1 millimolar nitrate, increased to that of nitrate-grown roots. Chloride elicited a separate electrical response with a pattern similar to that of the nitrate response. However, the results presented in this study strongly indicate that the electrical response to nitrate reflects the activity of a nitrate-inducible membrane transport system for nitrate which is distinct from that for chloride. Inhibitors of the plasmalemma H(+)-ATPase (vanadate, diethylstilbestrol) completely inhibited both parts of the electrical response to nitrate, as did alkaline external pH. The magnitude of the initial nitrate-dependent, membrane potential depolarization was independent of nitrate concentration, but the subsequent nitrate-dependent hyperpolarization showed saturable dependence with an apparent K(m) of 0.05 millimolar. These results support a model for nitrate uptake in maize roots which includes a depolarizing NO(3) (-)/H(+) symport. The model proposes that the nitrate-dependent membrane potential hyperpolarization is due to the plasma membrane proton pump, which is secondarily stimulated by the operation of the NO(3) (-)/H(+) symport.
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PMID:Evidence for cotransport of nitrate and protons in maize roots : I. Effects of nitrate on the membrane potential. 1666 48

To determine whether the detergent-solubilized and purified vacuolar H(+)-ATPase from plants was active in H(+) transport, we reconstituted the purified vacuolar ATPase from oat roots (Avena sativa var Lang). Triton-solubilized ATPase activity was purified by gel filtration and ion exchange chromatography. Incorporation of the vacuolar ATPase into liposomes formed from Escherichia coli phospholipids was accomplished by removing Triton X-100 with SM-2 Bio-beads. ATP hydrolysis activity of the reconstituted ATPase was stimulated twofold by gramicidin, suggesting that the enzyme was incorporated into sealed proteoliposomes. Acidification of K(+)-loaded proteoliposomes, monitored by the quenching of acridine orange fluorescence, was stimulated by valinomycin. Because the presence of K(+) and valinomycin dissipates a transmembrane electrical potential, the results indicate that ATP-dependent H(+) pumping was electrogenic. Both H(+) pumping and ATP hydrolysis activity of reconstituted preparations were completely inhibited by <50 nanomolar bafilomycin A(1), a specific vacuolar type ATPase inhibitor. The reconstituted H(+) pump was also inhibited by N,N'-dicyclohexylcarbodiimide or NO(3) (-) but not by azide or vanadate. Chloride stimulated both ATP hydrolysis by the purified ATPase and H(+) pumping by the reconstituted ATPase in the presence of K(+) and valinomycin. Hence, our results support the idea that the vacuolar H(+)-pumping ATPase from oat, unlike some animal vacuolar ATPases, could be regulated directly by cytoplasmic Cl(-) concentration. The purified and reconstituted H(+)-ATPase was composed of 10 polypeptides of 70, 60, 44, 42, 36, 32, 29, 16, 13, and 12 kilodaltons. These results demonstrate conclusively that the purified vacuolar ATPase is a functional electrogenic H(+) pump and that a set of 10 polypeptides is sufficient for coupled ATP hydrolysis and H(+) translocation.
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PMID:Proton Transport Activity of the Purified Vacuolar H-ATPase from Oats : Direct Stimulation by Cl. 1666 20

Chloride-transporting proteins play fundamental roles in many tissues in the plasma membrane as well as in intracellular membranes. They have received increasing attention in the last years because crucial, and often unexpected and novel, physiological functions have been disclosed with gene-targeting approaches, X-ray crystallography, and biophysical analysis. CLC proteins form a gene family that comprises nine members in mammals, at least four of which are involved in human genetic diseases. The X-ray structure of the bacterial CLC homolog, ClC-ec1, revealed a complex fold and confirmed the anticipated homodimeric double-barreled architecture of CLC-proteins with two separate Cl-ion transport pathways, one in each subunit. Four of the mammalian CLC proteins, ClC-1, ClC-2, ClC-Ka, and ClC-Kb, are chloride ion channels that fulfill their functional roles-stabilization of the membrane potential, transepithelial salt transport, and ion homeostasisin the plasma membrane. The other five CLC proteins are predominantly expressed in intracellular organelles like endosomes and lysosomes, where they are probably important for a proper luminal acidification, in concert with the V-type H+-ATPase. Surprisingly, ClC-4, ClC-5, and probably also ClC-3, are not Cl- ion channels but exhibit significant Cl-/H+ antiporter activity, as does the bacterial homolog ClC-ec1 and the plant homolog AtCLCa. The physiological significance of the Cl-/H+ antiport activity remains to be established.
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PMID:CLC chloride channels and transporters: a biophysical and physiological perspective. 1772 41

Chloride homeostasis in Saccharomyces cerevisiae has been characterized with the goal of identifying new Cl- transport and regulatory pathways. Steady-state cellular Cl- contents ( approximately 0.2 mEq/liter cell water) differ by less than threefold in yeast grown in media containing 0.003-5 mM Cl-. Therefore, yeast have a potent mechanism for maintaining constant cellular Cl- over a wide range of extracellular Cl-. The cell water:medium [Cl-] ratio is >20 in media containing 0.01 mM Cl- and results in part from sequestration of Cl- in organelles, as shown by the effect of deleting genes involved in vacuolar acidification. Organellar sequestration cannot account entirely for the Cl- accumulation, however, because the cell water:medium [Cl-] ratio in low Cl- medium is approximately 10 at extracellular pH 4.0 even in vma1 yeast, which lack the vacuolar H(+)-ATPase. Cellular Cl- accumulation is ATP dependent in both wild type and vma1 strains. The initial (36)Cl- influx is a saturable function of extracellular [(36)Cl-] with K(1/2) of 0.02 mM at pH 4.0 and >0.2 mM at pH 7, indicating the presence of a high affinity Cl- transporter in the plasma membrane. The transporter can exchange (36)Cl- for either Cl- or Br- far more rapidly than SO4=, phosphate, formate, HCO3-, or NO3-. High affinity Cl- influx is not affected by deletion of any of several genes for possible Cl- transporters. The high affinity Cl- transporter is activated over a period of approximately 45 min after shifting cells from high-Cl- to low-Cl- media. Deletion of ORF YHL008c (formate-nitrite transporter family) strongly reduces the rate of activation of the flux. Therefore, Yhl008cp may be part of a Cl(-)-sensing mechanism that activates the high affinity transporter in a low Cl- medium. This is the first example of a biological system that can regulate cellular Cl- at concentrations far below 1 mM.
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PMID:Chloride homeostasis in Saccharomyces cerevisiae: high affinity influx, V-ATPase-dependent sequestration, and identification of a candidate Cl- sensor. 1837


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