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

Adenosine 5'-triphosphate (ATP) synthesis driven by an artificially imposed membrane potential in right-side-out membrane vesicles of Escherichia coli was investigated. Membrane vesicles prepared in the presence of adenosine diphosphate were loaded with K+ by incubation with 0.5 M potassium phosphate. Addition of valinomycin resulted in the synthesis of 0.2 to 0.3 nmol of ATP/mg of membrane protein, whereas no synthesis was observed after addition of nigericin. Addition of K+, dicyclohexylcarbodiimide, carbonylcyanide p-trifluoromethoxyphenylhydrazone, or azide to the assay buffer inhibited ATP synthesis. Adenosine diphosphate and Mg2+ were found to be required. Ca2+, which can replace Mg2+ for the hydrolytic activity of the Mg2+-adenosine triphosphatase (ATPase) (EC 3.6.1.3), could not replace Mg2+ in the synthetic reaction and, in fact, inhibited ATP synthesis even in the presence of Mg2+. Strain NR-70, a mutant lacking the Mg2+-ATPase, was unable to synthesize ATP using an artificially imposed membrane potential. Additionally, the Mg2+-ATPase was found to contain tightly bound ATP.
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PMID:Adenosine 5'-triphosphate synthesis energized by an artificially imposed membrane potential in membrane vesicles of Escherichia coli. 0 30

Membrane vesicles from Azotobacter vinelandii O prepared by osmotic lysis of spheroplasts in tris (hydroxymethyl) aminomethane/acetate buffer (pH 7.8) contain a latent adenosine triphosphatase (ATPase). The ATPase can be activated when the vesicles are incubated in the presence of an electron donor (D-lactate) and a mixture of adenosine diphosphate and inorganic phosphate or by controlled treatment with trypsin. After the ATPase is activated, the membrane vesicles in the presence of adenosine triphosphate accumulate calcium but not glucose or rubidium (in the presence of valinomycin). ATP-dependent calcium uptake follows Michaelis-Menten kinetics with a Km of 48 muM and a Vmax of 20 nmol/min/mg of membrane protein and is highly specific for calcium over cations magnesium, barium, lanthanum, sodium, potassium, and lithium. The calcium accumulated in the presence of ATP is freely exchangeable with external calcium and is rapidly released in the presenceof uncouplers or ATPase inhibitors. Calcium uptake in the presenceof ATP is blocked by dicyclohexylcarbodiimide, ADP, p-chloromercuriphenylsulfonate, by the proton-conducting ionophores m-chlorophenylcarbonylcyanide hydrazone, nigericin, monensin, and gramicidin D, but not by potassium cyanide, anoxia, or valinomycin (in the presence of potassium). Measurements of the external pH of vesicle suspensions reveal that protons are actively taken up by the membranes during hydrolysis of ATP. These results suggest that vesicles prepared under these conditions have a topology which is inverted with respect to the intact cell and that calcium is accumulated by means of proton antiport.
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PMID:ATP-dependent calcium transport in isolated membrane vesicles from Azotobacter vinelandii. 0 92

The early kinetic steps of actomyosin subfragment 1 (acto-S1) adenosine triphosphatase have been investigated by simultaneous monitoring of fluorescence and light scattering and also by observation of the time course of the production of phosphate. The results show that fluorescence enhancement occurs after the dissociation of actomyosin and that the rate of enhancement is similar to the maximum rate of enhancement for S1 alone, under similar conditions of pH and temperature. The maximum rate of the phosphate burst for acto S1 is also approximately the same as that for S1 alone. The maximum rates for fluorescence enhancement or phosphate formation are reached at much lower adenosine triphosphate concentrations for acto-S1 than for S1. An extension of the actomyosin scheme is presented which accounts for these results.
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PMID:Intermediate states of actomyosin adenosine triphosphatase. 1 92

The adenosine triphosphatase (ATPase) activities of human polymorphonuclear leukocytes (PMNL) were studied with an assay that monitored the release of 32P-labeled inorganic pyrophosphate (32P1) from gamma-[32P]adenosine 5'-triphosphate (ATP). In cell homogenates, (Na+ + K+)-sensitive, ouabain-inhibitable ATPase comprised an insignificant fraction of the total ATPase activity. Additions of p-nitrophenyl phosphate and beta-glycerophosphate (substrates for nonspecific acid and alkaline phosphatases) and of tartrate (inhibitor of acid phosphatase) gave no indication of inhibition. This suggested that the assay was relatively specific for ATP hydrolysis. The activity was found to have a pH optimum of 8.7 and a Km for ATP of 0.6 mM. There was an absolute requirement for Mg2+, with other divalent cations substituting less efficiently. When the Mg2+-dependent ATPase activity of intact cells was compared with that in homogenized cells, no significant difference was observed. The activity in intact cells was linear with respect to incubation time up to at least l0 min. Trypan blue staining and lactate dehydrogenase assays revealed that greater than 92% of the PMNL remained intact and viable during the assay. No soluble ATPase was released from the cells under assay conditions. In following the distribution of gamma[32P]ATP and 32P2 counts became cell associated. Since the experimental evidence supports the observation that PMNL remain intact and viable and that ATP does not penetrate the cell under assay conditions, it is proposed that greater than 90% of the Mg2+-dependent ATPase of the human PMNL is associated with a plasma membrnae enzyme. This would qualify the enzyme for the role of a plasma membrane marker for future fractionation and isolation attempts.
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PMID:Magnesium-dependent adenosine triphosphatase as a marker enzyme for the plasma membrane of human polymorphonuclear leukocytes. 1 92

A simple method for isolation of adenosine triphosphatase (EC 3.6.1.3) from mitochondria is described. The enzyme is released from mitochondrial Lubrol particles by drastic sonication and purified by gel filtration on Sepharose 6-B. The described procedure is effective in isolating adenosine triphosphatase from rat liver as it is from beef heart mitochondria. The enzyme isolated from beef heart has a specific activity of 120 mumol P/min per mg protein and enzyme isolated from rat liver has a specific activity of 70 mumol P/min per mg protein when measured as a release of inorganic phosphate.
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PMID:A simple procedure for isolating adenosine triphosphatase from mitochondria. 1 70

p-Nitrophenyl phosphate hydrolysis was studied at neutral pH with tissue preparations of the rat secretory and maturation enamel organs and dental pulp. By introduction of inhibitors to nonspecific alkaline phosphatase activity and stimulants to the K+-stimulated and ouabain-sensitive p-nitrophenyl phosphatase activity, the latter enzyme activity could be demonstrated. This enzyme activity is generally held to be representative of the enzyme sodium- and potassium-stimulated adenosine triphosphatase. The K+-stimulated activity was magnesium dependent and highly sensitive to fluoride. It was inhibited completely by 3 mM fluoride in the incubation medium and about 1 mM produced half the maximum inhibition. The K+-independent enzyme activity was inhibited 50-60% by fluoride in concentrations between 3 and 15 mM. The high fluoride sensitivity of the K+-stimulated activity may perhaps help to explain the vulnerability of dental tissues to fluoride.
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PMID:Demonstration of a K+-stimulated and ouabain-sensitive p-nitrophenyl phosphatase activity in enamel-and dentin-forming tissues in the rat. 2 90

Exposure of male rats to parathion (2.6 mg/kg), lindane (17.6 mg/kg), or their combination through oral intubation daily for a period of 90 days produced histological and biochemical alterations in the liver and testis. The focal necrosis of the liver, although observed in all the treatments, was very prominent in the animals exposed to lindane alone. The kidney and epididymis, however, did not show any significant histological lesions. The activity of acetylcholine esterase in blood and brain decreased markedly, whereas that of succinic dehydrogenase, adenosine triphosphatase, and the alkaline and acid phosphate in liver and testis showed significant alterations for all three treatments.
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PMID:Comparative response of male rats to parathion and lindane: histopathological and biochemical studies. 9 96

Lactobacillus casei cells can accumulate folate to an intracellular concentration in excess of 500 muM and to concentration gradients (relative to the extracellular compartment) of several thousand-fold. Maximum rates of folate transport are achieved rapidly (t(1/2) < 1 min) after the addition of glucose to energy-depleted cells and occur at intracellular adenosine 5'-triphosphate concentrations above 625 muM. The rate of folate transport and the adenosine 5'-triphosphate content of cells are both extremely sensitive to arsenate and decrease in parallel with increasing concentrations of the inhibitor, indicating a requirement for phosphate-bond energy in the transport process. The energy source is not a membrane potential or a pH gradient generated via the membrane-bound adenosine triphosphatase, since dicyclohexylcarbodiimide (an adenosine triphosphatase inhibitor) and carbonyl cyanide m-chlorophenylhydrazone (a proton conductor) have little effect on the uptake process. The K(+)-ionophore, valinomycin, is an inhibitor of folate transport, but does not act via a mechanism involving dissipation of the membrane potential. This can be deduced from the facts that the inhibition by valinomycin is relatively insensitive to pH, is considerably greater in Na(+)- than in K(+)-containing buffers, and is not enhanced by the addition of proton conductors. Folate efflux is not affected by valinomycin, glucose, or various metabolic inhibitors, although a rapid release of the accumulated vitamin can be achieved by the addition of unlabeled folate together with an energy source (glucose). These results suggest that the active transport of folate into L. casei is energized by adenosine 5'-triphosphate or an equivalent energy-rich compound, and that coupling occurs not via the membrane-bound adenosine triphosphatase but by direct interaction of the energy source with a component of the transport system.
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PMID:Coupling of energy to folate transport in Lactobacillus casei. 11 Jul 91

Native solium and potassium adenosine triphosphatase from guinea pig kidney accepted a phosphate group from radioactive inorganic phosphate to form an acyl phosphate bond at the active site in the presence or absence of sodium ion. Magnesium ion was always required. In the presence of sodium ion and absence of adenosine triphosphate, there was no phosphorylation by inorganic phosphate. Addition of unlabeled adenosine triphosphate produced a potassium-sensitive phosphoenzyme which exchanged its phosphate-group with radioactive inorganic phosphate. The dephosphoenzyme was an intermediate in this exchange. The rate constant for dephosphorylation was about 0.05 per second. Addition of rubidium ion, a congener of potassium ion, to the potassium-sensitive phosphoenzyme produced a phosphoenzyme labeled from inorganic phosphate with a corresponding rate constant of 0.26 per s. This was a rubidium-complexed phosphoenzyme. Addition of magnesium ion to potassium-sensitive phosphoenzyme converted it into insensitive phosphoenzyme, the splitting of which was not accelerated by potassium ion or by adenosine diphosphate. Its rate constant was 0.07 per s. In the absence of sodium ion and adenosine triphosphate, inorganic phosphate was incorporated directly into a similar insensitive phosphoenzyme. In the presence of potassium ion or rubidium ion, inorganic phosphate was incorporated into a potassium-complexed or rubidium-complexed phosphoenzyme which exchanged 32-P with inorganic phosphate completely in less than 3 s. Incorporation of inorganic phosphate into a complex of the enzyme with the inhibitor, ouabain, is already described in the literature. Its rate constant was about 0.02 per s. Thus there appear to be at least four reactive states of the phosphoenzyme which equilibrate measurably with inorganic phosphate, namely, potassium-sensitive phosphoenzyme, potassium-complexed phosphoenzyme, insensitive phosphoenzyme, and ouabain phosphoenzyme. Two of these reactive states are functional intermediates in native sodium and potassium ion transport adenosine triphosphatase. The results are compatible with control of the reactivity of the active site by conformational changes in the surrounding active center and with regulation of the energy level of the phosphate group according to the kind of monovalent cation bound to the enzyme.
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PMID:Phosphorylation by inorganic phosphate of sodium plus potassium ion transport adenosine triphosphatase. Four reactive states. 12 73

Radioactive adenosine triphosphate was synthesized transiently from adenosine diphosphate and radioactive inorganic phosphate by sodium and potassium adenosine triphosphatase from guinea pig kidney. In a first step, K+-sensitive phosphoenzyme was formed from radioactive inorganic phosphate in the presence of magnesium ion and 16 mM sodium ion. In a second step the addition to the phosphoenzyme of adenosine diphosphate with a higher concentration of sodium ion produced adenosine triphosphate. Recovery of adenosine triphosphate from the phosphoenzyme was 10 to 100% in the presence of 96 to 1200 mM sodium ion, respectively. Potassium ion (16mM) inhibited synthesis if added before or simultaneously with the high concentration of sodium ion but had no effect afterward. The half-maximal concentration for adenosine diphosphate was about 12 muM. Ouabain inhibited synthesis. The ionophore gramicidin had no significant effect on the level of phosphoenzyme nor on the rate nor on the extent of synthesis of adenosine triphosphate. The detergent Lubrol WX reduced the rate of phosphoenzyme break-down and the rate of synthesis but did not affect the final recovery. Phospholipase A treatment inhibited synthesis. In a steady state, the enzyme catalzyed a slow ouabain-sensitive incorporation or inorganic phosphate into adenosine triphosphate. These results and other suggest that binding of sodium ion to a low affinity site on phosphoenzyme formed from inorganic phosphate is sufficient to induce a conformational change in the active center which permits transfer of the phosphate group to adenosine diphosphate.
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PMID:Synthesis of adenosine triphosphate and exchange between inorganic phosphate and adenosine triphosphate in sodium and potassium ion transport adenosine triphosphatase. 12 28


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