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)

We have studied the mechanism by which liver Golgi apparatus maintains the acidity of its contents, using a subcellular fraction from rat liver highly enriched in Golgi marker enzymes. Proton accumulation (measured by quenching of acridine-orange fluorescence) and anion-dependent ATPase were characterized and compared. Maximal ATPase and proton accumulation required ATP; GTP and other nucleotides gave 10% to 30% of maximal activity. Among anions, Cl- and Br- approximately doubled the activities; others were much less effective. Half-maximal increase of ATPase and H+ uptake required 55 mmol/L and 27 mmol/L Cl-, respectively. In predominantly chloride media, SCN- and NO3- markedly inhibited H+ uptake. Nitrate competitively inhibited both the chloride-dependent ATPase (apparent Ki 6 mmol/L) and proton uptake (apparent Ki 2 mmol/L). Nitrate and SCN- also inhibited uptake of 36Cl. Replacing K+ with Na+ had no effect on the initial rate of proton uptake but somewhat reduced the steady state attained. Replacement of K+ with NH4+ and choline reduced proton uptake without affecting ATPase. The ATPase and H+ uptake were supported equally well by Mg2+ or Mn2+. The ATPase was competitively inhibited by 4-acetamido-4'-isothiocyano-stilbene-2,2'-disulfonic acid (apparent Ki 39 mumol/L). Other agents inhibiting both H+ uptake and ATPase were N-ethylmaleimide, N,N'-dicyclohexylcarbodiimide, chlorpromazine, diethylstilbestrol, Zn2+, Co2+ and Cu2+. In the Cl- medium, accumulated protons were released by ionophores at the relative rates, monensin = nigericin greater than valinomycin greater than carbonyl cyanide mchlorophenylhydrazone; the last of these also reduced ATPase activity. In the absence of Cl-, monensin and valinomycin both stimulated the ATPase. These results show a close association between ATPase activity and acidification of liver Golgi vesicles. They support a role for Cl- that depends on its uptake as a counter ion for H+ and suggest that it may also stimulate proton transport by a more direct effect on a component of the transport system.
...
PMID:Proton accumulation and ATPase activity in Golgi apparatus-enriched vesicles from rat liver. 184 95

The mutT nucleoside triphosphatase, which prevents AT----CG transversions during DNA replication, has been crystallized from ammonium sulfate utilizing a novel technique involving vapor diffusion in capillaries. X-ray diffraction analysis has revealed that the crystals are monoclinic, space group P2(1), with cell constants a = 34.14, b = 72.54, c = 56.38, and beta = 98.90. The Vm value of 2.31 A3/Da is consistent with two molecules of enzyme per asymmetric unit. The crystals are reasonably stable in the x-ray beam, and a data set to 2.5 A resolution has been collected for native protein. There is evidence that the crystals diffract to at least 2.1 A.
...
PMID:Crystallization and preliminary X-ray diffraction studies on the mutT nucleoside triphosphate pyrophosphohydrolase of Escherichia coli. 185 Nov 63

The molecular mechanisms surrounding the toxicity and high mortality rate that accompany the release of bacterial lipopolysaccharide (LPS) are unclear, although its potent activity suggests that an amplification system is involved. Because previous studies suggest that a guanine-nucleotide-binding protein (G-protein) may participate in LPS action, we have evaluated the effects of LPS on GTPase activity in membranes isolated from macrophage (RAW 264.7) and fibroblast (B82L) cell lines. LPS induced substantial GTPase activation (200-300% above basal), and kinetic analyses indicated that the maximal LPS-stimulated increase in velocity is observed within 15 min, that it is a low-Km (for GTP) activity, that it can be enhanced by ammonium sulphate, and that it appears to be pertussis toxin-insensitive. Moreover, the LPS-enhanced GTPase activity was not antagonized by phosphatase/ATPase inhibitors such as p-nitrophenyl phosphate, ouabain, bafilomycin or N-ethylmaleimide, and in fact was potentiated by the addition of ATP or ADP. Conversely, the LPS precursor, lipid X, which can decrease the lethal effects of LPS, was found to dose-dependently inhibit the LPS-mediated stimulation of GTPase activity. Half-maximal inhibition was seen at the same lipid X/LPS ratio known to be effective in vivo, i.e. 1:1(w/w). These effects appear to be specific because other phospholipids, detergents and glycosides neither stimulated basal, nor inhibited LPS-induced, GTPase activity. These data suggest the involvement of a GTPase in LPS action, and indicate that lipid X may act to directly antagonize LPS at this level.
...
PMID:Bacterial lipopolysaccharide-stimulated GTPase activity in RAW 264.7 macrophage membranes. 185 66

We have described the overall process that is responsible for the efficient transfer of ammonium from its production site in the proximal tubule cells to the final urine. The mechanism depends on direct NH4+ transport at a number of sites. There appears to be a predominance of NH3 over NH4+ transport in net total ammonia transport only in the collecting ducts and possibly the descending limbs of Henle's loop. Several examples of physiologically important direct NH4+ transport in the kidney were described. First, coupled Na/NH4/2Cl transport across the apical membrane of the thick ascending limb of Henle's loop mediates secondary active transport of ammonium, which drives countercurrent multiplication of ammonium in the renal medulla. Second, part of the NH4+ uptake across the apical membrane of the thick ascending limb may occur as a result of penetration by NH4+ through apical K+ channels. It is unknown whether NH4+ penetrates K+ channels in other tubule segments. Third, NH4+ can be actively transported into cells by substitution of NH4+ for K+ on the Na-K-ATPase. This NH4+ transport process is likely to be rapid enough to be physiologically significant only in the inner medulla, where NH4+ concentrations are high enough to successfully compete with K+. Fourth, NH4+ penetrates the paracellular pathway in some nephron segments such as the proximal tubule and thick ascending limb. Simple passive diffusion of NH4+ via the paracellular pathway is thought to be physiologically important in the thick ascending limb where it contributes to net NH4+ absorption.
...
PMID:NH4+ transport in the kidney. 189 Aug 4

Multidrug-resistant P388 cells were found to be resistant also to a variety of ammonium, phosphonium and arsonium compounds. As previously shown for anthracyclines and vinca alkaloids, the resistance to the permanently charged lipophilic cationic compounds could be circumvented by verapamil. Relative to drug-sensitive cells, K+ uptake and plasma membrane Mg-ATPase activity in multidrug-resistant cells are ouabain resistant. The intracellular K+ concentration in drug-resistant cells is maintained at a normal level by increased activity of the furosemide sensitive transport system. It is suggested that the reduced activity of the electrogenic Na(+)-K+ pump in multidrug-resistant, cells could result in a lower transmembrane potential and therefore reduced accumulation of cationic lipophilic compounds.
...
PMID:Reduced ouabain-sensitive potassium entry as a possible mechanism of multidrug-resistance in P388 cells. 193 Feb 95

To define proton transport mechanisms involved in the regulation of intracellular pH (pHi) in cells of the inner medullary collecting duct (IMCD), pHi and cell membrane potential were estimated by using the fluorescent dyes 2,7-biscarboxyethyl-5(6)-carboxyfluorescein and 3,3'-dipropylthiadicarbocyanine iodide, respectively, in suspensions of freshly isolated rabbit IMCD cells. The resting pHi of IMCD cells in nonbicarbonate Ringer's solution (pH 7.4) was 7.21 +/- 0.03 (mean +/- SE). When cells were acidified by ammonium withdrawal, the initial pHi recovery rate was 0.33 +/- 0.02 pH unit/min; replacement of extracellular Na+ (130 mM) with N-methyl-D-glucamine+ reduced the pHi recovery rate to 0.08 +/- 0.02 pH unit/min, while addition of 0.1 mM amiloride in the presence of extracellular Na+ reduced the rate of pHi recovery to 0.02 +/- 0.02 pH unit/min. Similar results were obtained in cells acid loaded with HCl. Cells recovering from acidification exhibited 22Na+ uptake rates threefold higher than did nonacidified cells. The rate of Na(+)-dependent pHi recovery was independent of the cell membrane potential. In the absence of extracellular Na+, depolarizing cell membrane potential in a stepwise manner by increasing extracellular K+ concentrations from 1 to 130 mM resulted in graded increments in the rate of pHi recovery. In the presence of 130 mM K+, the pHi recovery rate in acidified cells was dependent on cellular ATP levels, sensitive to 1 mM N-ethylmaleimide, and insensitive to 0.01 mM oligomycin in the presence of glucose (control, 0.24 +/- 0.01; ATP-depleted, 0.13 +/- 0.02; addition of N-ethylmaleimide, 0.16 +/- 0.01; addition of oligomycin, 0.27 +/- 0.02 pH unit/min). ATP depletion markedly inhibited H+ extrusion from IMCD cells measured by using a pH stat. These results provide direct evidence in freshly isolated IMCD cells that both a Na+:H+ antiporter and a rheogenic H(+)-ATPase participate in pHi regulation.
...
PMID:Intracellular pH regulation in freshly isolated suspensions of rabbit inner medullary collecting duct cells: role of Na+:H+ antiporter and H(+)-ATPase. 196 25

Active accumulation of neurotransmitters by synaptic vesicles is an essential component of the synaptic transmission cycle. Isolated vesicles show energy-dependent uptake of several transmitters by processes which are apparently mediated by a proton electrochemical potential across the vesicle membrane. Although this energy gradient is probably generated by a proton ATPase, the functional separation of ATP cleavage and transmitter uptake activity has only been shown clearly for monoamine transport. We report here that the light-driven proton pump, bacteriorhodopsin, can replace the endogenous proton ATPase in proteoliposomes reconstituted from vesicular detergent extracts. The system shows light-dependent uptake of glutamate with properties very similar to those observed in intact vesicles, e.g. chloride dependence or stimulation by NH4+. Our experiments show that the proton pump and the glutamate transporter are separate entities and provide a powerful tool for further characterization of the glutamate carrier.
...
PMID:Bacteriorhodopsin drives the glutamate transporter of synaptic vesicles after co-reconstitution. 197 Feb 94

We have cloned and sequenced over 9 kb of the mitochondrial genome from the sea star Pisaster ochraceus. Within a continuous 8.0-kb fragment are located the genes for NADH dehydrogenase subunits 1, 2, 3, and 4L (ND1, ND2, ND3, and ND4L), cytochrome oxidase subunits I, II, and III (COI, COII, and COIII), and adenosine triphosphatase subunits 6 and 8 (ATPase 6 and ATPase 8). This large fragment also contains a cluster of 13 tRNA genes between ND1 and COI as well as the genes for isoleucine tRNA between ND1 and ND2, arginine tRNA between COI and ND4L, lysine tRNA between COII and ATPase 8, and the serine (UCN) tRNA between COIII and ND3. The genes for the other five tRNAs lie outside this fragment. The gene for phenylalanine tRNA is located between cytochrome b and the 12S ribosomal genes. The genes for tRNA(glu) and tRNA(thr) are 3' to 12S ribosomal gene. The tRNAs for histidine and serine (AGN) are adjacent to each other and lie between ND4 and ND5. These data confirm the novel gene order in mitochondrial DNA (mtDNA) of sea stars and delineate additional distinctions between the sea star and other mtDNA molecules.
...
PMID:Nucleotide sequence of nine protein-coding genes and 22 tRNAs in the mitochondrial DNA of the sea star Pisaster ochraceus. 197 16

The effects of altering the availability of sodium ions (Na+) on contractility of the guinea-pig isolated trachealis was examined using regimens which are reported to inhibit Na+/K+ ATPase activity (ouabain), Na+/H+ exchange (amiloride, ammonium ion (NH4+)) or Na+/Ca2+ exchange (reduced extracellular Na+). Inhibition of Na+/K+ ATPase and reversal of Na+/Ca2+ exchange resulted in increased 45Ca uptake and contraction of the trachealis by voltage-sensitive and voltage-insensitive mechanisms respectively. When Na+/H+ exchange was inhibited by amiloride the tissues relaxed to below their baseline tension. The relaxation was not due to reduced Ca2+ influx. Treatment with NH4+ produced a contractile response. Reduced extracellular Na+ caused a transient contraction as a result of reversal of the normal Na+/Ca2+ exchange process leading to accumulation of Ca2+ within the cell. Since the effects of amiloride and reduced extracellular sodium were different, it is unlikely that amiloride is acting primarily by inhibiting Na+/Ca2+ exchange. Amiloride reduced tissue sensitivity to methacholine and KCl without affecting Ca2+ influx. This may involve a secondary stimulation of Na+/Ca2+ exchange following changes in [Na+]i. Ouabain also reduced tissue sensitivity to methacholine and KCl. These findings suggest that Na+ are important in determining smooth muscle contractility. If NH4+ is altering pH then, at the concentrations used, the changes in [H+] were not sufficient to alter responses to the spasmogens.
...
PMID:Effects of altered availability of Na+ on guinea-pig airway smooth muscle contractility. 213 15

Examination of retinal tissue homogenates indicated the presence of a [Ca2+ + Mg2+]-dependent adenosinetriphosphatase activity that exhibited high affinity for Ca2+ (K0.5 = 0.17 microM) and moderately high affinity for Mg2+ and ATP (K0.5 = 12.5 microM and Km = 22.8 microM, respectively). Maximum ATP hydrolysis occurred at pH 7.4. Under conditions of optimal substrate, cation and hydrogen ion concentrations, specific activity ranged from 15 to 18 nmol phosphate released min-1 mg-1 protein. Although the retinal [Ca2+ + Mg2+] adenosinetriphosphatase hydrolyzes both ATP and dATP, other nucleotides (CTP, GTP, ITP and UTP) were not hydrolyzed to any great extent. The monovalent cations, Li+, K+ and Na+, had no effect upon hydrolysis of ATP; whereas Cs+ and NH4+ ions were moderately (approximately 30%) inhibitory. All divalent cations tested were stimulatory. With the exception of rotenone which inhibited ATP hydrolysis approximately 25%; retinal adenosinetriphosphatase activity was insensitive to mitochondrial inhibitors (NaN3, KCN, ruthenium red and oligomycin). Adenosinetriphosphatase activity was observed to be very sensitive to low concentrations (I50 approximately 2 microM) of vanadate; whereas, lanthanum administration resulted in no inhibition. Removal of calmodulin (80%) resulted in reducing adenosinetriphosphatase activity 60% but addition of exogenous calmodulin back to calmodulin deficient membranes did not restore activity to starting levels. Calmodulin antagonists trifluoperazine and calmidazolium reduced significantly Ca2+ stimulated, Mg2+ dependent ATP hydrolysis. We conclude that the [Ca2+ + Mg2+]-dependent adenosinetriphosphatase of bovine retina is a non-mitochondrial protein exhibiting very high affinity for Ca2+ and appears to require calmodulin for maximum activity. Because of its high affinity for Ca2+, this protein may play an important role in reducing intracellular Ca2+ to nanomolar levels.
...
PMID:Partial characterization of a high affinity [Ca2+ + Mg2+]-dependent adenosinetriphosphatase from bovine retina. 213 89


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---