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)

A natural DNA-intercalator plant benzo-c-phenanthridine alkaloid sanguinarine is more toxic for mouse transformed fibroblast L-cells in culture than synthetic DNA-intercalator ethidium bromide (EtB) and alkaloid berberine. Dimidium bromide is also an inhibitor of the L-cell growth. In assay conditions, growth of L-cells is stopped by 1.5 x 10(-5) M of sanguinarine. Lebr-625 cells, resistant to 25 micrograms/ml of EtB, have sanguinarine sensitivity close to that of L-cells, but Lebr-625 cells are resistant to dimidium bromide. Sanguinarine is more toxic for L-cells in culture than the anticancer drug cis-PtNH3)2Cl2. Trans-Pt(NH3)2Cl2 is less toxic for these cells. The strong toxicity of sanguinarine for L- and Lebr-625 cells in culture, as compared to other DNA-complexing drugs, seems to be associated with the wide range of potential cell targets for sanguinarine influence. Besides the inhibition of nucleic acid metabolism reactions, characteristic of DNA-intercalators, and disruption the mitochondrial ATP synthesis, also characteristic of organic heterocyclic cationic molecules of DNA-intercalators, sanguinarine can modify the thiol groups of enzymes including SH-sensitive membrane-bound Na+, K(+)-ATPase of cerebral cortex and Ca2(+)-ATPase of skeletal muscle sarcoplasmic reticulum fragments.
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PMID:[The toxicity of sanguinarine compared to a number of other DNA-tropic compounds for ethidium bromide-sensitive and -resistant transformed murine fibroblasts in culture]. 262 83

The MgATP complex analogue cobalt-tetrammine-ATP [Co(NH3)4ATP] inactivates (Na+ + K+)-ATPase at 37 degrees C slowly in the absence of univalent cations. This inactivation occurs concomitantly with incorporation of radioactivity from [alpha-32P]Co(NH3)4ATP and from [gamma-32P]Co(NH3)4ATP into the alpha subunit. The kinetics of inactivation are consistent with the formation of a dissociable complex of Co(NH3)4ATP with the enzyme (E) followed by the phosphorylation of the enzyme: (Formula: see text). The dissociation constant of the enzyme-MgATP analogue complex at 37 degrees C is Kd = 500 microM, the inactivation rate constant k2 = 0.05 min-1. ATP protects the enzyme against the inactivation by Co(NH3)4ATP due to binding at a site from which it dissociates with a Kd of 360 microM. It is concluded, therefore, that Co(NH3)4ATP binds to the low-affinity ATP binding site of the E2 conformational state. K+, Na+ and Mg2+ protect the enzyme against the inactivation by Co(NH3)4ATP. Whilst Na+ or Mg2+ decrease the inactivation rate constant k2, K+ exerts its protective effect by increasing the dissociation constant of the enzyme.Co(NH3)4ATP complex. The Co(NH3)4ATP-inactivated (Na+ + K+)-ATPase, in contrast to the non-inactivated enzyme, incorporates [3H]ouabain. This indicates that the Co(NH3)4ATP-inactivated enzyme is stabilized in the E2 conformational state. Despite the inactivation of (Na+ + K+)-ATPase by Co(NH3)4ATP from the low-affinity ATP binding site, there is no change in the capacity of the high-affinity ATP binding site (Kd = 0.9 microM) nor of its capability to phosphorylate the enzyme Na+-dependently. Since (Na+ + K+)-ATPase is phosphorylated Na+-dependently from the high-affinity ATP binding site although the catalytic cycle is arrested in the E2 conformational state by specific modification of the low-affinity ATP binding site, it is concluded that both ATP binding sites coexist at the same time in the working sodium pump. This demonstration of interacting catalytic subunits in the E1 and E2 conformational states excludes the proposal that a single catalytic subunit catalyzes (Na+ + K+)-transport.
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PMID:Demonstration of cooperating alpha subunits in working (Na+ + K+)-ATPase by the use of the MgATP complex analogue cobalt tetrammine ATP. 282

1H nuclear magnetic relaxation measurements have been used to determine the three-dimensional conformation of an ATP analogue, Co(NH3)4ATP, at the active site of sheep kidney Na,K-ATPase. Previous studies have shown that Co(NH3)4ATP is a competitive inhibitor with respect to MnATP for the Na,K-ATPase [Klevickis, C., & Grisham, C. M. (1982) Biochemistry 21, 6979; Gantzer, M. L., Klevickis, C., & Grisham, C. M. (1982) Biochemistry 21, 4083] and that Mn2+ bound to a single, high-affinity site on the ATPase can be an effective paramagnetic probe for nuclear relaxation studies of the Na,K-ATPase [O'Connor, S. E., & Grisham, C. M. (1979) Biochemistry 18, 2315]. From the paramagnetic effect of Mn2+ bound to the ATPase on the longitudinal relaxation rates of the protons of Co(NH3)4ATP at the substrate site (at 300 and 361 MHz), Mn-H distances to seven protons on the bound nucleotide were determined. Taken together with previous 31P nuclear relaxation data, these measurements are consistent with a single nucleotide conformation at the active site. The nucleotide adopts a bent configuration, in which the triphosphate chain lies nearly parallel to the adenine moiety. The glycosidic torsion angle is 35 degrees, and the conformation of the ribose ring is slightly N-type (C2'-exo, C3'-endo). The delta and gamma torsional angles in this conformation are 100 degrees and 178 degrees, respectively. The bound Mn2+ lies above and in the plane of the adenine ring. The distances from Mn2+ to N6 and N7 are too large for first coordination sphere complexes but are appropriate for second-sphere complexes involving, for example, intervening hydrogen-bonded water molecules.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:1H nuclear magnetic resonance studies of the conformation of an ATP analogue at the active site of Na,K-ATPase from kidney medulla. 284 41

CTP synthetase from Escherichia coli catalyzes exchange of 18O from the beta gamma-bridge position of [gamma-18O4] ATP into the beta-nonbridge position. This positional isotope exchange occurs in the presence of UTP and MgCl2 but in the absence of NH3. The enzyme also has an ATPase activity in the presence of UTP that occurs under conditions that are identical to those used in the positional isotope exchange experiments. These data provide evidence for the stepwise nature of the reactions catalyzed by CTP synthetase with the initial step involving phosphorylation of UTP by ATP. The relative rate of the isotope exchange reaction is approximately 3 times faster than the ATPase reaction, but the isotope exchange rate is approximately 3% of the overall rate in the presence of NH3. These results are consistent with the ATPase reaction involving attack of water on the phosphorylated intermediate (4-phospho-UTP). The positional isotope exchange reaction is independent of the UTP concentration above saturating levels of UTP demonstrating that the order of addition of substrates is UTP followed by ATP and then NH3.
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PMID:Mechanistic investigations of Escherichia coli cytidine-5'-triphosphate synthetase. Detection of an intermediate by positional isotope exchange experiments. 293 96

A Ca++-dependent secretion of norepinephrine ([3H]NE) was evoked in adrenergic nerve endings in rat heart ventricle slices incubated in a modified Krebs-HCO3 medium containing choline Cl as the replacement for NaCl (Ch+-Ca++). Exogenous ATP inhibited secretion and lithium ion, a known inhibitor of NE uptake dependent upon Mg++-ATPase activity in vesicles (but not ouabain) prevented the response to ATP (Bogdanski, 1983,1986). It was suggested that vesicles attached to the axolemma recaptured [3H]NE from the extracellular fluid. This report indicates that other known inhibitors of uptake in isolated vesicles also inhibited the response to ATP in the attached vesicles. Included were two inhibitors of Mg++-ATPase activity, N-ethylmaleimide (NEM) and dicyclohexylcarbodiimide (DCCD), and the proton transporters 2,4-dinitrophenol (2,4-DNP 1.0 mM) and chlorpromazine (CPZ). Potassium ionophores (valinomycin with 2,4-DNP 0.1 mM, and nigericin) and a pH neutralizing reagent for vesicles (NH3 from ammonium sulfate in solution) were also effective. The uptake inhibitors, except 2,4-DNP, could also increase the rate of depletion of stored NE and its deamination in nonsecreting nerve endings incubated in Krebs-HCO3 (KRB) medium. Valinomycin by itself stimulated uptake in the presence of ATP. It is suggested that mechanisms of uptake and retention of NE in isolated vesicles (symposium (1982) Fed. Proc. 41:2742-2780) apply to the axoplasmic vesicles as well. Thus, the activity of Mg++-ATPase drives proton transport to establish the electrochemical gradients of H+, which drive the transport of NE. A lowering of the gradients can mobilize amines and evoke secretion.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Norepinephrine uptake dependent upon apparent Mg++-ATPase activity and proton transport in storage vesicles in axoplasm. 297 43

Excretion of acid (or generation of bicarbonate) by the kidneys is necessary for acid-base homeostasis. Most of this acid is excreted in the form of ammonia and titratable acid, the latter representing the amount of acid required to titrate the urine buffers from the plasma pH to urine pH. The transport of ammonia in the kidney is now recognized to entail more than simple nonionic diffusion of NH3 and trapping of NH4+. NH4+ transport in the kidney probably occurs by passive diffusion and by transport on the Na+-H+ exchanger, the Na+-K+-2Cl- transporter and on Na+-K+-ATPase. NH3 diffusion is stimulated by an acid disequilibrium pH in various nephron segments. Also, diffusion equilibrium of NH3 in various regions of the kidney has now been disproved. These various mechanisms of ammonia transport are considered in terms of their possible changes with acid-base disturbances. Phosphate is the most predominant urine buffer; its urinary excretion increases with acidosis. The mechanisms probably involve a decrease in the preferentially transported species, HPO4(2-), and a direct effect of pH on proximal tubule apical phosphate transport. With chronic acidosis, changes in the activity of the apical Na+-phosphate transporter occur. These effects of systemic acid-base balance interact with parathyroid hormone and dietary phosphate status to alter phosphate reabsorption. Citrate transport in the kidney is analyzed because of its sensitivity to systemic pH and because of the possible influence on systemic acid-base status in certain circumstances. Alterations in citrate excretion with acid-base disturbances depend on changes in the concentration of the transported species, citrate2-, and on changes in renal metabolism.
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PMID:Roles and mechanisms of urinary buffer excretion. 331 Jun 62

Isolated perfused medullary thick ascending limbs from rabbits were studied to determine the mechanism of ammonium ion absorption. Under control conditions, thick ascending limbs spontaneously absorbed NH4+ and generated a lumen-positive potential. When these tubules were chemically voltage clamped to lumen-negative potentials by lowering the bath NaCl concentration, NH4+ absorption persisted. Thus NH4+ was absorbed against an electrochemical gradient. The active flux accounts for most of the net flux under control conditions, the remainder being due to passive paracellular NH4+ diffusion. The NH4+ permeability, measured in separate experiments, was high (1.50 +/- 0.25 x 10(-4) cm/s) compared with values in other segments. The NH3 permeability was relatively low (3.1 +/- 0.5 x 10(-3) cm/s). Luminal furosemide (10(-4) M) eliminated most of the active NH4+ flux, indicating that a major fraction of the active flux is dependent on apical entry of NH4+ via the Na+ -K+ -2Cl- cotransporter (presumably by substitution for K+). The remaining active flux was completely inhibited by 10(-4) M ouabain in the bath. Active chloride absorption was maintained when NH4+ entirely replaced K+ in bath and perfusate, indicating that NH4+ substitutes for K+ on the apical cotransporter and the basolateral Na+ -K+ -ATPase. Ammonium absorption provides an active "single effect" for countercurrent multiplication of NH4+ in the renal medulla.
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PMID:Active NH4+ absorption by the thick ascending limb. 339 13

We present evidence that cysteine 269 of the small subunit of Escherichia coli carbamyl phosphate synthetase is essential for the hydrolysis of glutamine. When cysteine 269 is replaced with glycine or with serine by site-directed mutagenesis of the carA gene, the resulting enzymes are unable to catalyze carbamyl phosphate synthesis with glutamine as nitrogen donor. Even though the glycine 269, and particularly the serine 269 enzyme bind significant amounts of glutamine, neither glycine 269 nor serine 269 can hydrolyze glutamine. The mutations at cysteine 269 do not affect carbamyl phosphate synthesis with NH3 as substrate. The NH3-dependent activity of the mutant enzymes was equal to that of wild-type. Measurements of Km indicate that the enzyme uses unionized NH3 rather than ammonium ion as substrate. The apparent Km for NH3 of the wild-type enzyme is calculated to be about 5 mM, independent of pH. The substitution of cysteine 269 with glycine or with serine results in a decrease of the apparent Km value for NH3 from 5 mM with the wild-type to 3.9 mM with the glycine, and 2.9 mM with the serine enzyme. Neither the glycine nor the serine mutation at position 269 affects the ability of the enzyme to catalyze ATP synthesis from ADP and carbamyl phosphate. Allosteric properties of the large subunit are also unaffected. However, substitution of cysteine 269 with glycine or with serine causes an 8- and 18-fold stimulation of HCO-3 -dependent ATPase activity, respectively. The increase in ATPase activity and the decrease in apparent Km for NH3 provide additional evidence for an interaction of the glutamine binding domain of the small subunit with one of the two known ATP sites of the large subunit.
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PMID:Catalytic domains of carbamyl phosphate synthetase. Glutamine-hydrolyzing site of Escherichia coli carbamyl phosphate synthetase. 352 65

Electrophysiological studies were performed on slowly adapting cells of the crayfish (Astacus astacus) stretch receptor to examine some aspects of the operation of the sodium pump. Intracellular sodium activity (aiNa) and pH (pHi) were measured with liquid ion exchanger microelectrodes and the effects of NH3/NH+4 were observed. In cells in which the sodium pump was inhibited by K+-free solution, NH+4 induced a decrease of aiNa that can be explained only in Na+ extrusion is assumed. pHi measurements provide indirect evidence that NH+4 was taken up at the same time as Na+ was extruded. Ouabain blocks the operation of the sodium pump in the presence of K+ and NH+4. This result suggests that the ammonium-mediated decrease in aiNa in K+-free solution was caused by activation of the sodium pump. The results obtained by electrophysiological methods in a living cell are qualitatively in good agreement when compared with biochemical investigations on assays of crustacean Na+-K+ ATPase.
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PMID:Electrophysiological evidence for ammonium as a substitute for potassium in activating the sodium pump in a crayfish sensory neuron. 356 30

The alkali light chain, A2, in subfragment-1 (S-1) was exchanged with A1 added externally in NH4 + -NH3 buffer (pH 9.9). The exchange yield was higher than 80% using only 2-fold molar excess of A1 over S-1 containing A2. The ATPase activities of the exchanged S-1 (A1) were the same as those of untreated S-1 (A1). The method was also applicable to exchanging the alkali light chains in myosin.
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PMID:An efficient exchange method for alkali light chain in myosin subfragment. 623 54


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