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

---

Query: EC:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

After incorporation of the purified Na(+)-translocating F0F1-ATPase from Propionigenium modestum into preformed phospholipid vesicles the synthesis of ATP from ADP and inorganic phosphate could be observed under conditions where a valinomycin-mediated K+ diffusion potential (delta psi) and/or a Na+ concentration gradient (delta pNa) were imposed. This reaction was not inhibited by the protonophore carbonyl cyanide p-tri-fluoromethoxyphenylhydrazone (FCCP). Furthermore, the delta pNa-driven ATP synthesis was stimulated by FCCP. In contrast, the addition of the Na+/H+ antiporter monensin or of the F0F1 inhibitors N,N'-dicyclohexylcarbodiimide and venturicidin abolished the synthesis of ATP completely. Finally, delta pNa alone was able to elicit ATP synthesis, when a Na+ concentration gradient of sufficient magnitude was applied. In this case ATP synthesis occurred above a threshold level of approximately 120 mV and, furthermore, delta psi and delta pNa appear to be equivalent as driving forces for this process. Therefore, the data provide firm evidence for the concept that delta"mu Na+ is the primary driving force for the synthesis of ATP in P. modestum.
...
PMID:ATP synthesis energized by delta pNa and delta psi in proteoliposomes containing the F0F1-ATPase from Propionigenium modestum. 832 55

We have investigated the role of intracellular pH (pHi) in early plant development using ion-selective microelectrodes to record from eggs and embryos of the brown alga Pelvetia. Temporal changes in pHi were investigated by recording from zygotes at all stages of the first cell cycle. pHi was 7.57 +/- 0.09 in recently fertilized eggs, but decreased by approximately 0.2 units a few hours postfertilization. Proton motive force (pmf) was also monitored and found to be less than -50 mV throughout the first cell cycle. Because of the low pmf values, we suggest that secondary active transport is probably not coupled to H+, and instead we propose that solute transport is driven by the Na+ electrochemical potential. Zygotes strictly regulated pHi over a wide range of extracellular pH (pHo); pHi varied by less than 0.2 units over pHo values from 6.2 to 9.2. Inhibitor studies were conducted to investigate the mechanism of regulation. Agents known to inhibit the H(+)-ATPase (antimycin A, KCN, carbonylcyanide m-chlorophenylhydrazone, N,N'-dicyclohexylcarbodiimide, and erythrosin B) caused marked cytoplasmic acidification. Addition of amiloride, an inhibitor of Na+/H+ antiport, also resulted in acidification, as did removal of NaCl from the medium. By contrast, increasing extracellular NaCl concentration caused transient alkalinization of the cytoplasm. Taken together, these results indicate that proton pumping by an H(+)-ATPase and Na+/H+ antiporter contribute to pH regulation.
...
PMID:Intracellular pH and its regulation in Pelvetia zygotes. 838 34

In inverted subcellular vesicles of Escherichia coli grown at high delta mu H+ (neutral pH, no protonophorous uncoupler), ATP-driven Na+ transport and oxidative phosphorylation are completely inhibited by the protonophore CCCP. If E. coli was grown at low delta mu H+, i.e. at high pH or in the presence of uncoupler, some oxidative phosphorylation was observed in the vesicles even in CCCP-containing medium, and Na+ transport was actually stimulated by CCCP. The CCCP-resistant transport and phosphorylation were absent from the unc mutant lacking F0F1 ATPase. Both processes proved to be sensitive to (i) the Na+/H+ antiporter monensin, (ii) the Na+ uniporter ETH 157, (iii) the F0 inhibitors DCCD and venturicidin, and (iv) the F1 inhibitor aurovertin. The CCCP-resistant oxidative phosphorylation was stimulated by Na+ and arrested by oppositely directed delta pNa. These data are consistent with the assumption that, under appropriate growth conditions, the F0F1-type ATPase of E. coli becomes competent in transporting Na+ ions.
...
PMID:ATP-driven Na+ transport and Na(+)-dependent ATP synthesis in Escherichia coli grown at low delta mu H+. 842 16

In chromaffin granule ghosts, the Na+/Ca2+ exchanger in the granule membrane can provide a high affinity (Km 1-3 microM) and high capacity (Vmax 50-100 nmol mg min-2) mechanism for Ca2+ accumulation. The activity of the Na+/H+ antiporter can be used to couple Ca2+ uptake via Na+/Ca2+ exchange to ATP-dependent proton translocation via the granule membrane H(+)-ATPase. Therefore, Ca2+ uptake can be indirectly linked to the proton pump. However, under conditions designed to mimic the environment of a granule in the cytosol of a chromaffin cell, measured rates of Ca2+ uptake are low, a free Ca2+ concentration of about 5 microM in the ghost matrix being attained. Under such circumstances, the granules seem unlikely to play a major role in calcium homeostasis in the intact cell.
...
PMID:Indirect coupling of calcium transport in chromaffin granule ghosts to the proton pump. 851 42

The halophyte Mesembryanthemum crystallinum is an inducible crassulacean acid metabolism (CAM) plant native to seasonally arid coastal environments that has been widely used to study plant responses to environmental stress. On exposure of plants to salt, the activities of both the tonoplast (vacuolar) H(+)-ATPase (V-ATPase) and Na+/H+ antiporter increase in leaf cells, thereby energizing vacuolar salt accumulation. To investigate the molecular basis of this response, a cDNA (Vmac1) encoding the H(+)-conducting c subunit (16.6 kDa) of an M. crystallinum V-ATPase has been cloned. Northern analysis of RNA from leaves of plants treated with NaCl or with isoosmotic mannitol solutions demonstrated (i) that NaCl increased steady-state transcript levels for the V-ATPase c subunit, and (ii) that this effect was caused by the ionic rather than the osmotic component of salt stress. Southern analysis of genomic DNA suggested the probable existence of more than one gene for this subunit of the V-ATPase in M. crystallinum. Expression studies using the 3'-untranslated region of the Vmac1 cDNa as a probe showed that the corresponding salt-inducible transcript was preferentially expressed in leaves. Induction by salt was also observed in juvenile plants in addition to adult ones. These findings, as well as the inability of mannitol to upregulate mRNA levels for this gene, clearly differentiate between the induction of transcript for the V-ATPase c subunit and for genes involved in the CAM pathway in M. crystallinum. Further, the plant growth regulator abscisic acid (ABA) was able to mimic the effect of salt on transcript levels for the V-ATPase c subunit, suggesting the possible involvement of ABA in a distinct signal-transduction pathway linked to vacuolar salt accumulation in this highly salt-tolerant species.
...
PMID:Salt regulation of transcript levels for the c subunit of a leaf vacuolar H(+)-ATPase in the halophyte Mesembryanthemum crystallinum. 865 19

In the proximal tubule in vivo, glomerulotubular balance requires that tubule epithelial cells accommodate a twofold variation in Na+ reabsorption through the Na+/H+ exchanger of the luminal membrane. In a mathematical model of proximal tubule, in which permeability coefficients are fixed, doubling flux through the Na+/H+ antiporter produces a substantial increase in cell volume and cytosolic HCO3-. In this model, it is possible to vary peritubular K+ permeability with changes in luminal Na+ entry, so that cell volume is constrained to be constant. In these calculations, the model predicts that peritubular hyperpolarization and nearly constant cytosolic HCO3- will accompany increases in luminal Na+ entry. Realistic models of variable peritubular K+ permeability might include a functional dependence on flux through the Na(+)-K(+)-adenosinetriphosphatase, cytosolic pH, or cell volume. When K+ permeability is represented as a function of any of these variables, homeostatic control of cell volume and pH can be obtained over a physiological variation of Na+/H+ flux. However, when luminal Na+ entry is via Na(+)-glucose cotransport, volume homeostasis is best when peritubular K+ permeability depends on the rate of active Na+ transport. For any modulator of K+ permeability, realistic constraints on the value of this parameter suggest that peritubular K+ permeability is, by itself, not sufficient to maintain cell volume within narrow limits. Parallel activation of another exit pathway, such as peritubular Na(+)-3 HCO3- cotransport, may be required to achieve the necessary homeostasis.
...
PMID:Coupling of entry to exit by peritubular K+ permeability in a mathematical model of rat proximal tubule. 876 Feb 57

Palytoxin (PTx) at nanomolar concentrations enhances the permeability of mammalian cell membranes to both Na+ and Ca2+. In basal human osteoblast-like Saos-2 cells, PTx (8 nM) caused a persistent decrease in cytosolic pH (pHi) of about 0.2 units, which required the presence of extracellular Ca2+ (Cae2+) and Na+ (Nae+). We acidified Saos-2 cells by incubation with nigericin to examine the action of PTx in cells with an activated Na+/H+ antiporter. Under these conditions, PTx increased the pHi without requiring Cae2+ or Nae+, and the alkalinization was unaffected by hexamethylene amiloride. We conclude that the PTx-induced rise in pHi did not involve the Na+/H+ antiporter. PTx increased the rate of 86Rb+ efflux. We propose that PTx induced alkalinization in nigericin-acidified cells by collapsing the K+ gradient. Exposure to ouabain had no effect on pHi, but it prevented the actions of PTx on PHi in both basal and nigericin-acidified cells. Ouabain-resistant mutant cells were less sensitive to PTx in extruding 86Rb+ than their ouabain-sensitive parents. We conclude that PTx interacts with the Na(+)-K(+)-adenosinetriphosphatase to regulate pHi in both basal and nigericin-acidified Saos-2 cells.
...
PMID:Palytoxin modulates cytosolic pH in human osteoblast-like Saos-2 cells via an interaction with Na(+)-K(+)-ATPase. 896 26

Gill epithelial cells of euryhaline crustaceans demonstrate net inward transport of sodium ions, possibly via apical Na+/H+ antiporters, Na+/K+/2Cl- cotransporters or Na+ channels working in series with the basolateral Na(+) + K(+)-ATPase. We have identified and sequenced the cDNA coding for a crustacean Na+/H+ antiporter, starting with mRNA isolated from gills of the euryhaline green shore crab Carcinus maenas. The complete 2595-base-pair cDNA includes an open reading frame coding for a 673-amino-acid protein. A search of GenBank revealed more than 20 high-scoring matches, all Na+/H+ antiporter sequences from mammalian, amphibian, teleost and nematode species. Injection of Xenopus laevis oocytes with cRNA transcribed from the cloned crab sequence substantially enhanced Na(+)-dependent H+ efflux from the oocytes. Analysis of crab tissue antiporter mRNA levels by semi-quantitative reverse transcription-polymerase chain reaction revealed that posterior and anterior gills of Carcinus maenas expressed this antiporter the most strongly, followed in decreasing order by skeletal muscle, hepatopancreas, hypodermis and heart. Hydropathy and transmembrane alpha-helix analysis suggested a 10-helix membrane-spanning topology of the antiporter protein. It is clear from this study that Carcinus maenas gills vigorously transcribe a gene coding for a Na+/H+ antiporter. Whether these gills also express a gene coding for an epithelial Na+ channel or Na+/K+/2Cl- cotransporter remains to be demonstrated.
...
PMID:Sodium/proton antiporter in the euryhaline crab Carcinus maenas: molecular cloning, expression and tissue distribution. 910 80

Distal tubules (DT) from sham or five-sixths nephrectomized (Nx) rats were perfused in vivo to evaluate the hypothesis that, after Nx, endogenous angiotensin II (ANG II) modulates DT in vivo bicarbonate reabsorption (JtCO2) via H(+)-adenosinetriphosphatase (H(+)-ATPase) and Na+/H+ exchange. In Nx rats JtCO2 was increased (65 +/- 7 vs. -24 +/- 21 pmol.min-1.mm-1, P < 0.01). Both luminal and intravenous AT1-receptor blockade by losartan reduced Nx DT JtCO2 (41 +/- 6 and 34 +/- 4 pmol.min-1.min-1, respectively, P < 0.05), whereas neither 10(-9) M nor 10(-11) M ANG II luminal perfusion increased JtCO2, suggesting preexisting high endogenous ANG II levels. The Na+/H+ antiporter inhibitors 5-(N-ethyl-N-isopropyl)-amiloride and 5-(N,N-dimethyl)-amiloride were without effect. Luminal perfusion of 5 nM concanamycin A, a V-type H(+)-ATPase inhibitor, reduced Nx DT JtCO2 (45 +/- 8 pmol.min-1.mm-1, P < 0.05). In Nx A-type intercalated cells, we demonstrated cellular hypertrophy, elaboration of apical microplicae, and enhanced expression/apical polarization of H(+)-ATPase. Thus ANG II is an important determinant in sustaining brisk DT JtCO2 following Nx and is associated with enhanced expression and A-type intercalated cell apical polarization of H(+)-ATPase.
...
PMID:ANG II-dependent HCO3- reabsorption in surviving rat distal tubules: expression/activation of H(+)-ATPase. 922 42

The proton transport processes in the upper part of the descending limb of the long-looped nephron (LDLu) from hamsters were studied using a fluorescent dye, 2',7'-bis(carboxyethyl)carboxyfluorescein (BCECF) in microperfused single nephron preparations. Intracellular pH (pHi), as assessed by the measurement of the fluorescence of BCECF trapped in the cytoplasm, was 7.23 +/- 0.05 (n = 18) under nominally HCO3--free conditions. Ouabain, when added to the bath, decreased pHi by 0.22 units. After an NH4Cl prepulse, the initial proton extrusion rate was 1.23 +/- 0.26 (n = 9) pH units/min, and was retarded in the presence of 1 mM amiloride either in the bath or in the lumen. pHi failed to recover when Na+ was eliminated from ambient solutions. These observations suggest that Na+/H+ antiporters exist both in the apical and basolateral cell membranes. By measuring tubular fluid pH (pHt) under stopped flow conditions, we examined whether the hamster LDLu has the capacity to generate and maintain a transmural H+ gradient. After the tubular outflow was obstructed, the luminal fluid was rapidly acidified, reaching a steady-state pH of 6.84 +/- 0.09 (n = 7). The steady-state pH was influenced by bath pH. Tubular fluid acidification was not observed in the absence of Na+ and was prevented by ouabain. We conclude that the hamster LDLu has the capability to generate and maintain a transmural proton gradient by proton secretion via a luminal Na+/H+ antiporter which is secondarily driven by the Na+-K+ ATPase in the basolateral membrane.
...
PMID:Proton secretion in the upper part of the descending limb of long-looped nephron from hamsters. 930 4


<< Previous 1 2 3 4 5 6 7 8 9 Next >>

---