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)

In Halobacterium halobium, proton pumping driven by light or by respiration generates an electrochemical potential difference across the membrane. Energy storage in this form is only transient. Cellular energy transducers competing with proton leaks stabilize this free energy as high energy phosphate bonds, electrochemical potential of other ions, and chemical potential of amino acids and possibly other chemical species. The pH changes induced by light or by respiration in cell suspensions are complicated by proton flows associated with the functioning of the cellular energy transducers. Dominant is the proton inflow coupled to the synthesis of ATP, which has been kinetically resolved. A proton-per-ATP ratio of about 3 is calculated from simultaneous measurements of photophosphorylation and the proton inflow. This value is compatible with the chemiosmotic coupling hypothesis. The time course of the light-induced changes in membrane potential indicates that light-driven pumping increases a dark preexisting potential of about 130 mV only by a small amount (20-30 mV). The complex kinetic features of the membrane potential changes do not closely follow those of the pH changes, indicating that flows of ions other than protons are involved. A qualitative model consistent with the available data is presented. A salient feature of this model is a sudden relaxation of the protonmotive force by a proton inflow through the ATPase when the preexisting protonmotive force is increased by light or respiration and reaches a critical value. The trigger could be either the proton-motive force, the pH gradient, or possibly the internal pH.
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PMID:Light energy conservation processes in Halobacterium halobium cells. 1 79

gamma-Glutamylcysteine synthetase was purified from rat liver by an improved method involving chromatography on Sepharose-aminohexyl-ATP to a specific activity of about 1600 units/mg, or approximately twice that previously obtained; it is thus the most active preparation of this enzyme thus far isolated. The earlier preparation, which is homogeneous on polyacrylamide gel electrophoresis, exhibits "half of the sites" reactivity in that it binds a maximum of 0.5 mol of the inhibitor L-methionine-S-sulfoximine phosphate per mol of enzyme. In contrast, the present enzyme preparation binds 1 mol of methionine sulfoximine phosphate per mol of enzyme; it also differs from the enzyme obtained earlier in exhibiting much less ATPase activity and less activity in catalyzing ATP-dependent cyclization of glutamate. gamma-Glutamylcysteine synthetase dissociates in sodium dodecyl sulfate into two nonidentical subunits of apparent molecular weights 74,000 and 24,000; after cross-linking with dimethyl-suberimidate, a species having a molecular weight of about 100,000 was found on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. New information has been obtained about the interaction of the enzyme with glutamate analogs; thus, the enzyme is active with such glutamate analogs as beta-glutamate, N-methyl-L-glutamate, and threo-beta-hydroxy-L-glutanate, and it is effectively inhibited by cis-1-amino-1,3-dicarboxycyclonexane, 2-amino-4-phosphonobutyrate, and gamma-methylglutamate.
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PMID:gamma-Glutamylcysteine synthetase. Further purification, "half of the sites" reactivity, subunits, and specificity. 1 92

Methylxanthines (MX) inhibit cell division in sea urchin and clam eggs. This inhibitory effect is not mediated via cAMP. MX also inhibit respiration in marine eggs, at concentrations which inhibit cleavage. Studies showed that no changes occurred in ATP and ADP levels in the presence of inhibitory concentrations of MX, indicating an extra-mitochondrial site of action for the drug. Subsequent studies revealed decreased levels of NADP+ and NADPH, when eggs were incubated with inhibitory concentrations of MX, but no change in levels of NAD+ and NADH. MX did not affect the pentose phosphate shunt pathway and did not have any effect on the enzyme NAD+ -kinase. Further studies showed a marked inhibitory effect on the glutathione reductase activity of MX-treated eggs. Reduced glutathione (GSH) could reverse the cleavage inhibitory effect of MX. Moreover, diamide, a thiol-oxidizing agent specific for GSH in living cells, caused inhibition of cell division in sea urchin eggs. Diamide added to eggs containing mitotic apparatus (MA) could prevent cleavage by causing a dissolution of the formed MA. Both MX and diamide inhibit a Ca2+-activated ATPase in whole eggs. The enzyme can be reactivated by sulfhydryl reducing agents added in the assay mixture. In addition, diamide causes an inhibition of microtubule polymerization, reversible with dithioerythritol. All experimental evidence so far suggests that inhibition of mitosis in sea urchin eggs by MX is mediated by perturbations of the in vivo thiol-disulfide status of target systems, with a primary effect on glutathione levels.
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PMID:Effects of caffeine and other methylxanthines on the development and metabolism of sea urchin eggs. Involvement of NADP and glutathione. 1 15

The stoichiometry of H+ ejection by mitochondria during hydrolysis of a small pulse of ATP (the H+/ATP ratio) has been reexamined in the light of our recent observation that the stoichiometry of H+ ejection during mitochondrial electron transport (the H+/site ratio) was previously underestimated. We show that earlier estimates of the H+/ATP ratio in intact mitochondria were based upon an invalid correction for scaler H+ production and describe a modified method for determination of this ratio which utilizes mersalyl or N-ethylmaleimide to prevent complicating transmembrane movements of phosphate and H+. This method gives a value for the H+/ATP ratio of 2.0 without the need for questionable corrections, compared with a value of 3.0 for the H+/site ratio also obtained by pulse methods. A modified version of the chemiosmotic theory is presented, in which 3 H+ are ejected per pair of electrons traversing each energy-conserving site of the respiratory chain. Of these, 2 H+ return to the matrix through the ATPase to form ATP from ADP and phosphate, and 1 H+ returns through the combined action of the phosphate and adenine nucleotide exchange carriers of the inner membrane to allow the energy-requiring influx of Pi and ADP3- and efflux of ATP4-. Thus, up to one-third of the energy input into synthesis of extramitochondrial ATP may be required for transport work. Since other methods suggest that the H+/site significantly exceeds 3.0, an alternative possibility is that 4 h+ are ejected per site, followed by return of 3 H+ through the ATPase and 1 H+ through the operation of the proton-coupled membrane transport systems.
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PMID:H+/ATP ratio during ATP hydrolysis by mitochondria: modification of the chemiosmotic theory. 1 16

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

1. Preincubation with N-ethylmaleimide inhibits the overall activity of highly purified (Na+ +K+)-ATPase (ATP phosphohydrolase, EC 3.6.1.3) preparations of rabbit kidney outer medulla. 2. This inhibition is decreased by addition of ATP or 4-nitrophenylphosphate under non-phosphorylating conditions, and also by addition of ADP or adenylylimidodiphosphate. 3. N-ethylmaleimide treatment leads to inhibition of K+-stimulated 4-nitrophenylphosphatase activity, Na+-stimulated ATPase activity, and phosphorylation by ATP as well as by inorganic phosphate. These inhibitions strictly parallel that of the overal (Na+ +K+)-ATPase reaction. 4. N-ethylmaleimide lowers the number of sites which are phosphorylated by inorganic phosphate, without affecting the dissociation constant of the enzyme-phosphate complex. 5. N-ethylmaleimide does not affect the relative stimulation by ATP of the K+-stimulated 4-nitrophenylphosphatase activity. 6. These effects of N-ethylmaleimide can be explained as a complete loss of active enzyme, either by reaction of N-ethylmaleimide inside the active center, or by alterations in the quaternary structure through reactions outside the active center.
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PMID:Studies on (Na+ +K+) activated ATPase. XLI. Effects of N-ethylmaleimide on overall and partial reactions. 1 94

Ciliary 30S dynein of Tetrahymena was investigated with regard to modification of the ATPase activity with N-ethylmaleimide (NEM) in the presence of ATP. The elevation of enzyme activity due to the modification was largely repressed by addition of ATP at a concentration of 1 mM or more during preincubation of 20 h at 0 degrees C. The repression was highly specific for ATP, though ADP and AMPPNP showed slight repressive effects. After complete hydrolysis of ATP added to the preincubation mixture, however, elevation of 30S dynein ATPase activity occurred. It is suggested that the repression by ATP of NEM-induced elevation of 30S dynein ATPase activity is simply due to a protecting effect of ATP on certain SH group(s) (probably SH1-type group(s)) around the active center of 30S dynein. When 30S dynein was maximally activated by modification with NEM, ATP or ADP did not significantly promote the inactivation of the modified enzyme upon further treatment with NEM, indicating that 30S dynein lacks the characteristics of SH2-type groups. On the other hand, ATP also showed a protective effect against inhibition of native 30S dynein by high concentrations of NEM. High concentrations of ADP and AMPPNP were inhibitory to 30S dynein ATPase activity but inorganic phosphate did not inhibit 14S or 30S dynein ATPase activities at all.
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PMID:Effects of adenosine triphosphate on N-ethylmaleimide-induced modification of 30S dynein from Tetrahymena cilia. 1 51

The activity of calcium-stimulated ATPase (E.C. 3.6.1.3) in homogenates of the secretory enamel organ of rat incisors was studied biochemically. ATP hydrolysis was estimated from the amount of inorganic phosphate liberated. An analysis of the total degradation of ATP was initially performed to ensure that the enzyme assays pertained to the original substrate, ATP, and were not influenced by reaction products formed. Standard incubations were run in tris-maleate buffer, pH 8.2, with 3 mM ATP, 3 mM Ca2+ and 0.5 mM R 8231 at 37 degrees C. The presence of R 8231 was necessary to inhibit nonspecific alkaline phosphatase. The calcium-stimulated ATPase was completely inhibited when heated at 55-60 degrees C for 5 min. The pH optimum was found to be 8.2. The hydrolysis was substantially dependent on Ca2+ and was fastest when the ATP:Ca2+ ratio was 1:1. High substrate concentrations inhibited the hydrolysis. The addition of 1 mM Zn2+ and Ni2+ to the incubation medium markedly inhibited the hydrolysis as did, though less strongly, p-hydroxymercuribenzoate, oligomycin, EDTA and ruthenium red. l-Cysteine, mercaptoethanol, iodoacetic acid and sodium azide were without effect. F- was without effect unless added to a final concentration above 15 mM to media where Ca2+ had first been allowed to react with ATP.
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PMID:Calcium-stimulated ATPase activity in homogenates of the secretory enamel organ in the rat. 2 89

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

An enzyme capable to split adenosine triphosphate (ATP) was shown to be firmly associated with mature herpes simplex virus particles purified from infected rabbit lung (ZP) cells. The enzyme localized in the viral envelope was markedly activated by bivalent cations, to the largest degree by Mg2+ at a pH optimum of 7.8--8.0. Na+ and K+ ions neither separately nor together showed any activating effect. Enzyme activity was not sensitive to the action of ouabain. No adenosine diphosphatase (ADPase) and adenosine monophosphatase (AMPase) activities were observed. ATPase activity was competitively inhibited by ADP. AMP and inorganic phosphate were without effect. The ATPase of nuclear membranes isolated from ZP cells exhibited similar properties but behaved differently to the action of sodium dithionite, dinitrophenol, oligomycin and gramicidin, as well as on heat inactivation. The origin of the virus enzyme is discussed.
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PMID:Some properties of the adenosine triphosphatase associated with herpes simplex virus and nuclear membrane of host cells. 2 4


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