UNIPROT:P20020 - FACTA Search

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Query: UNIPROT:P20020 (adenosine triphosphatase)
3,299 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Exposing micro-dissected pancreatic islets of non-inbred ob/ob mice to 2-5 mM-alloxan for 10 min decreased the ability of the islets to accumulate Rb+. Rb+ accumulation in pieces of exocrine pancreas was unaffected by alloxan. When islets were treated with alloxan in the presence of 2-20 mM-D-glucose, the Rb+-accumulating ability was protected in a dose-dependent manner. The protective action of D-glucose was reproduced with 3-O-methyl-D-glucose but not with L-glucose or D-mannoheptulose; mannoheptulose prevented D-glucose from exerting its protective action. The inhibition of Rb+ accumulation was due to a decreased inward pumping, since alloxan did not affect Rb+ efflux from pre-loaded islets. The inhibitory effect of alloxan had a latency of about 1 min, as revealed by experiments with dispersed islet cells in suspension. Alloxan-treated islets showed only a marginal decrease in ATP and no change in glucose 6-phosphate concentration. Although alloxan slightly decreased the hydrolysis of ATP in a subcellular fraction enriched in plasma membranes, this effect could not be attributed to a ouabain-sensitive adenosine triphosphatase. The plasma membranes exhibited a K+-activated hydrolysis of p-nitrophenyl phosphate; this enzyme activity too was insensitive to alloxan. Glucose may protect the univalent-cation pump by preventing permeation of alloxan via a path coupled to the hexose-transport system. Inhibition of the pump may be fundamental to the induction of alloxan-diabetes.
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PMID:Alloxan cytotoxicity in vitro. Inhibition of rubidium ion pumping in pancreatic beta-cells. 19 15

Inorganic lead ion in micromolar concentrations inhibits Electrophorus electroplax microsomal (Na+ + K+)-adenosine triphosphatase ((Na+ + K+)-ATPase) and K+-p-nitrophenylphosphatase (NPPase). Under the same conditions, the same concentrations of PbCl2 that inhibit ATPase activity also stimulate the phosphorylation of electroplax microsomes in the absence of added Na+. Enzyme activity is protected from inhibition by increasing concentrations of microsomes, ATP, and other metal ion chelators. The kinetics follow the pattern of a reversible noncompetitive inhibitor. No kinetic evidence is elicited for interactions of Pb2+ with Na+, K+, Mg2+, ATP, or p-nitrophenylphosphate. Na+- ATPase, in the absence of K+, and (Na+ + K+)-NPPase activity at low [K+] are also inhibited. ATP inhibition of NPPase is not reversed by Pb2+. The calculated concentrations of free [Pb2+] that produce 50% inhibition are similar for ATPase and NPPase activities. Pb2+ may act at a single independent binding site to produce both stimulation of the kinase and inhibition of the phosphatase activities.
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PMID:Inhibition by lead ion of Electrophorus electroplax (Na+ + K+)-adenosine triphosphatase and K+-p-nitrophenylphosphatase. 19 41

A phosphorylation potential deltaGp, where deltaGp = deltaGo' + RT2.303 log ([ATP]/([ADP][Pi])), of approx. 44.3 kJ.mol-1 (10.6 kcal.mol-1) was generated by submitochondrial particles that were oxidizing either NADH or succinate. Addition of adenylyl imidodiphosphate, which should suppress adenosine triphosphatase activity of any uncoupled particles, did not raise the phosphorylation potential. Raising the Pi concentration slightly increased the magnitude of the value for [ATP]/[ADP], but this did not fully compensate for the increased Pi concentration, so that the phosphorylation potential decreased slightly as the Pi concentration was raised. The phosphorylation potential developed by submitochondrial particles is lower than that generated by phosphorylating membrane vesicles from some bacteria, and is also less than that developed externally by mitochondria, but is strikingly close to the phosphorylation potential that is generated internally by mitochondria.
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PMID:The phosphorylation potential generated by respiring bovine heart submitochondrial particles. 20 65

1. The properties of membrane vesicles from the extreme thermophile Bacillus caldolyticus were investigated. 2. Vesicles prepared by exposure of spheroplasts to ultrasound contained cytochromes a, b and c, and at 50 degrees C they rapidly oxidized NADH and ascorbate in the presence of tetramethyl-p-phenylenediamine. Succinate and l-malate were oxidized more slowly, and dl-lactate, l-alanine and glycerol 1-phosphate were not oxidized. 3. In the absence of proton-conducting uncouplers the oxidation of NADH was accompanied by a net translocation of H(+) into the vesicles. Hydrolysis of ATP by a dicyclohexylcarbodi-imide-sensitive adenosine triphosphatase was accompanied by a similarly directed net translocation of H(+). 4. Uncouplers (carbonyl cyanide p-trifluoromethoxyphenylhydrazone or valinomycin plus NH(4) (+)) prevented net H(+) translocation but stimulated ATP hydrolysis, NADH oxidation and ascorbate oxidation. The last result suggested an energy-conserving site in the respiratory chain between cytochrome c and oxygen. 5. Under anaerobic conditions the reduction of cytochrome b by ascorbate (with tetramethyl-p-phenylenediamine) was stimulated by ATP hydrolysis, indicating an energy-conserving site between cytochrome b and cytochrome c. However, no reduction of NAD(+) supported by oxidation of succinate, malate or ascorbate occurred, neither did it with these substrates in the presence of ATP under anaerobic conditions, suggesting that there was no energy-conserving site between NADH and cytochrome b. 6. Succinate oxidation, in contrast with that of NADH and ascorbate, was strongly inhibited by uncouplers and stimulated by ATP hydrolysis. These effects were not observed when phenazine methosulphate, which transfers electrons from succinate dehydrogenase directly to oxygen, was present. It was concluded that in these vesicles the oxidation of succinate was energy-dependent and that the reoxidation of reduced succinate dehydrogenase was dependent on the outward movement of H(+) by the protonmotive force. 7. In support of the foregoing conclusion it was shown that the reduction of fumarate by NADH was an energy-conserving process. 8. If the activities of vesicles accurately represent those of the intact organism it appears that in B. caldolyticus the reduction of fumarate to succinate at the expense of reducing equivalents from NADH is energetically favoured over succinate oxidation even under aerobic conditions. This may be related to the need for an ample supply of succinate for haem synthesis in order to provide cytochromes for the organism.
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PMID:The oxidative activities of membrane vesicles from Bacillus caldolyticus. Energy-dependence of succinate oxidation. 20 11

In order to study the action of the divalent cation which is essential for phosphorylation of sodium- and potassium-transport adenosine triphosphatase, magnesium ion, the normal ligand, was replaced with calcium ion, which had properties diffeerent from those of Mg2+, Mn2+, Fe2+, Co2+, Ni2+, or Zn2+. Phosphorylation of the enzyme from ATP at pH 7.4 in the presence of Na+ and Ca2+ yielded a Ca.phosphoenzyme (60% of the maximal level) with a normal rate of dephosphorylation following a chase with unlabeled Ca.ATP (PK = 0.092S-1 at 0 degrees C). In contrast, after a chase by a chelator, namely ethylenediaminetetraacetic acid, 1,2-cyclohexylenedinitrilotetraacetic acid, or ethylene glycol bis-(beta-aminoethyl ether)N,N'-tetraacetic acid, dephosphorylation slowed within 5 s and half of the initial phosphoenzyme remained with a stability about 5-fold greater than normal. Three states of the phosphoenzyme were distinguished according to their relative sensitivity to ADP or to K+ added during a chase. Normally prepared Mg.phosphoenzyme was sensitive to K+ but not to ADP; Ca.phosphoenzyme was sensitive either to ADP or to K+; and the stabilized phosphoenzyme prepared from Ca.phosphoenzyme by addition of a chelator was sensitive neither to ADP nor to K+ nor to both together. Addition of Ca2+ to the stabilized phosphoenzyme restored the reactivity to that of Ca.phosphoenzyme. Addition of Mg2+ to the stabilized phosphoenzyme changed the reactivity to that of Mg.phosphoenzyme. Therefore, this unreactive, stabilized state of the phosphoenzyme appeared to be a divalent cation-free phosphoenzyme. With respect to sensitivity to ouabain, Ca.phosphoenzyme was as sensitive as Mg.phosphoenzyme but calcium-free phosphoenzyme was much less sensitive. It was concluded that the divalent cation required for phosphorylation normally remains tightly bound to the phosphoenzyme and is required for normal reactivity. Calcium ion was almost unique in dissociating relatively easily from the phosphoenzyme. Strontium ion appeared to act similarly to Ca2+.
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PMID:Binding of divalent cation to phosphoenzyme of sodium- and potassium-transport adenosine triphosphatase. 21 Nov 32

1. The magnitude of the protonmotive force in phosphorylating membrane vesicles from Paracoccus denitrificans was estimated. The membrane potential component was determined from the uptake of S(14)CN(-), and the transmembrane pH gradient component from the uptake of [(14)C]methylamine. In each case a flow-dialysis technique was used to monitor uptake. 2. With NADH as substrate, the membrane potential was about 145mV and the pH gradient was below 0.5 pH unit. The membrane potential was decreased by approx. 15mV during ATP synthesis, and was abolished on addition of carbonyl cyanide p-trifluoromethoxyphenylhydrazone. In the presence of KCl plus valinomycin the membrane potential was replaced by a pH gradient of 1.5 units. 3. Succinate oxidation generated a membrane potential of approx. 125mV and the pH gradient was below 0.5 pH unit. Oxidation of ascorbate (in the presence of antimycin) with either 2,3,5,6-tetramethyl-p-phenylenediamine or NNN'N'-tetramethyl-p-phenylenediamine as electron mediator usually generated a membrane potential of approx. 90mV. On occasion, ascorbate oxidation did not generate a membrane potential, suggesting that the presence of a third energy-coupling site in P. denitrificans vesicles is variable. 4. With NADH or succinate as substrate, the phosphorylation potential (DeltaG(p)=DeltaG(0)'+RTln[ATP]/ [ADP][P(i)]) was approx. 53.6kJ/mol (12.8kcal/mol). Comparison of this value with the protonmotive force indicates that more than 3 protons need to be translocated via the adenosine triphosphatase of P. denitrificans for each molecule of ATP synthesized by a chemiosmotic mechanism. In the presence of 10mm-KNO(3) the protonmotive force was not detectable (<60mV) but DeltaG(p) was not altered. This result may indicate either that there is no relationship between the protonmotive force and DeltaG(p), or that for an unidentified reason the equilibration of SCN(-) or methylamine with the membrane potential and the pH gradient is prevented by NO(3) (-) in this system.
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PMID:The protonmotive force in phosphorylating membrane vesicles from Paracoccus denitrificans. Magnitude, sites of generation and comparison with the phosphorylation potential. 21 22

Pb2+-stimulated phosphorylation of Electrophorus electricus electroplax (Na+ + K+)-adenosine triphosphatase is prevented by stoichiometric quantities of 2,3-dimercaptopropanol. The chelator in the same low concentrations does not block Na+-dependent phosphorylation. Both Pb2+-and Na+-dependent phosphorylation reactions show the same dependence on MgCl2. Phosphorylation in the presence of both Na+ and Pb2+ is cumulative suggesting that Pb2+ and Na+ bind at separate, independent sites. The enthalpy change due to binding of Pb2+ is about -1.76 kcal/mol. 32P-phosphopeptides obtained from pronase or pepsin digests of Pb2+-and Na+-dependent phosphoproteins are electrophoretically identical. Pb2+ does not stimulate but does inhibit ATP-ADP exchange activity under the conditions in which this activity is stimulated by Na+. Since the phosphorylation sites are identical, it is concluded that the differences in reactivity of the Na+- and Pb2+-phosphoenzymes are due to different conformational changes produced by binding of Na+ and Pb2+. The Pb2+-sensitive conformation is critical for Na+ specificity of phosphorylation, reversibility of phosphorylation, and for phosphatase activity but not for acceptor site phosphorylation by ATP. These findings have implications for enzyme reaction models.
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PMID:Characteristics of lead ion-stimulated phosphorylation of Electrophorus electricus electroplax (Na+ + K+)-adenosine triphosphatase and inhibition of ATP-ADP exchange. 21 19

1. The mechanism underlying the raised leucocyte sodium content in fulminant hepatic failure was studied by measurement of sodium fluxes, (Na+ + K+)-dependent adenosine triphosphatase activity, and leucocyte ATP content. 2. The rate constant for sodium efflux in the leucocytes was significantly reduced, and attributable to reduced activity of the enzyme (Na+ + K+)-ATPase. Leucocyte ATP content was not significantly different from that of control cells. 3. Incubation of cells from patients in the sera of normal subjects resulted in a reversal of these changes. Inhibition of the leucocyte sodium efflux rate constants and (Na+ +K+)-ATPase of normal cells was achieved by incubation in sera from patients. 4. We suggest that the raised sodium content of leucocytes in fulminant hepatic failure is attributable to a defective sodium pumping mechanism, possibly due to a circulating toxin.
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PMID:A study in vitro of the sodium pump in fulminant hepatic failure. 21 31

We have studied the effect of 3,5,3'-triiodothyronine (T3) on the respiration of adult rat hepatocytes in primary monolayer culture prepared from hypothyroid rat liver. After addition of T3 to the culture medium at a concentration of 2 x 10(-7) M, oxygen consumption of the cultured cells increased detectably at 24 h and was maximal at 72--96 h, relative to control cultures (38.0 +/- 1.8 vs. 25.0 +/- 1.5 microliter/h.mg protein). The thyroid-responsive enzymes, Na+ + K+-activated adenosine triphosphatase (NaK-ATPase) and alpha-glycerophosphate dehydrogenase (GPD), each exhibited increased activity in response to T3, in parallel with the change in oxygen consumption, whereas the activity of Mg-dependent ATPase was unaffected. These responses to T3 were dose dependent over similar concentration ranges, the half-maximal response for each occurring at ca 8 x 10(-10) M. In thyroid-treated cells, the observed increase in respiration was almost completely (90%) inhibited after addition of ouabain (10(-3) M) to the culture medium. It was found also that a 4-h exposure of the cultured hepatocytes to T3 was sufficient to elicit a significant thermogenic response, measured at a time (48 h later) when T3 was no longer present in the medium. The response to T3 occurred in fully defined culture medium and was independent of the presence or absence of hypothyroid rat serum, corticosterone, or insulin, and cellular ATP was unaffected by T3 in concentrations up to 2 x 10(-7) M. The findings document that adult rat hepatocytes in primary monolayer culture respond directly to thyroid hormone; the increases in respiration and NaK-ATPase activity elicited by T3 were cotemporal and apparently coordinate.
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PMID:Thyroid thermogenesis in adult rat hepatocytes in primary monolayer culture: direct action of thyroid hormone in vitro. 22 Mar 77

A method is described for preparation of membrane vesicles (diameter 80nm) capable of respiration-linked ATP synthesis. Vesicles prepared from succinate-grown bacteria oxidized NADH, succinate and ascorbate plus NNN'N'-tetramethylphenylenediamine; vesicles prepared from methanol-grown bacteria also oxidized methanol and formaldehyde, but they were otherwise identical. The uncoupling agent carbonyl cyanide chlorophenylhydrazone and the adenosine triphosphatase inhibitor dicyclohexylcarbodi-imide both inhibited ATP synthesis, whereas they had no effect on the rate of respiration. Rotenone inhibited ATP synthesis and respiration with NADH as substrate; antimycin A inhibited with succinate as substrate, and cyanide inhibited with all substrates. P/O ratios were usually 0.7-1.3 with NADH, 0.6-1.0 with succinate and 0.2-0.6 with reduced NNN'N'-tetramethylphenylenediamine or methanol as respiratory substrate. When 2,6-dichlorophenol-indophenol was used as an alternative electron acceptor to O(2) (NADH as donor) the P/2e ratio was 1.65. Although these P/O ratios are minimum values, because they do not take into account unknown amounts of uncoupled O(2) consumption, they are consistent with previous proposals [O'Keeffe & Anthony (1978) Biochem, J.170, 561-567] based on measurements of proton translocation in whole cells. The results also confirm that methanol dehydrogenase and cytochromes c and a/a(3) are arranged so that the first step in methanol oxidation is coupled to synthesis of ATP.
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PMID:The microbial metabolism of C1 compounds. Oxidative phosphorylation in membrane preparations of Pseudomonas AM1. 22 Sep 60

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