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

Nucleotides have at least two functions in eukaryotic cilia and flagella. ATP, originating in the cells, is utilized for motility by energy-transducing protein(s) called dynein, and the binding of guanine nucleotides to tubulin, and probably certain transformations of the bound nucleotides, are prerequisites for the assembly of microtubules. Besides dynein, which can be solubulized from Chlamydomonas flagella as a heterogeneous, Mg2+ or Ca2+-activated ATPase, we have purified and characterized five other flagellar enzymes involved in nucleotide transformations. A homogeneous, low molecular weight, Ca2+-specific adenosine triphosphatase was isolated, which was inhibited by Mg2+ and was not specific for ATP. This enzyme was not formed by treating purified dynein with proteases. It was absent from extracts of Tetrahymena cilia. Its function might be an auxiliary energy transducer, or in steering or tactic responses. Two species of adenylate kinase were isolated, one of which was much elevated in regenerating flagella; the latter was also present in cell bodies. A large part of flagellar nucleoside diphosphokinase activity could not be solubilized. Two soluble enzyme species were identified, one of which was also present in cell bodies. Since these enzymes are of interest because they might function in microtubule assembly, we studied the extent to which brain nucleoside diphosphokinase co-polymerizes with tubulin purified by repeated cycles of polymerization. Arginine kinase was not detected in Chlamydomonas flagellar extracts.
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PMID:Nucleotide-metabolizing enzymes in Chlamydomonas flagella. 0 Mar 97

1. Tributyltin at concentrations of approx. 1nmol/mg of protein induces respiratory control and lessens the protein permeability of coupling-factor-deficient submitochondrial particles. 2. At these concentrations or lower, it increases the P/O ratio of the particles to a small extent and inhibits the adenosine triphosphatase activity without greatly increasing its sensitivity to uncoupling agents. 3. It fails to stimulate ATP-driven reversed electron transport or transhydrogenase, but stimulates the transhydrogenase driven by aerobic succinate oxidation. 4. The results indicate that, unlike oligomycin, tributyltin does not discriminate between damaged and intact ATP-synthesizing complexes. 5. The relationship between the oligomycin- and tributyltin-binding sites is discussed.
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PMID:The action of tributyltin on energy coupling in coupling-factor-deficient submitochondrial particles. 0 63

The purpose of this work was in investigate the capability of cell extracts of Escherichia coli and E. coli treated with colicin K to catalyze the following energy-dependent reverse transhydrogenase reaction: NADP + NADH + ATP in equilibrium NADPH + NAD +ADP + Pi. Under anaerobic conditions this reaction requires the presence of a specific portion of the electron transport chain, a functional energy coupling system, including an adenosine triphosphatase, enzyme, and ATP as energy source. The ATP-linked reaction was partially inhibited in French press extracts of E. coli K-12 C600 cells that had been pretreated with colicin K but not in extracts from similarly treated cells of a colicin-tolerant mutant. Ultracentrifugation of extracts yielded particulate fractions competent in catalyzing the reaction; this reaction is substantially inhibited in fractions from colicin-treated cells. The extent of inhibition increased with increasing concentration of colicin. Supernatants also supported ATP-linked formation of NADPH, but this reaction was insensitive to the colicin effect. A comparison between the requirement of the reaction in supernatant and particulate fractions suggests that the reaction in the supernatant is different from the one inhibited by colicin. The ATP-hydrolyzing ability of particulate fractions from the control or treated bacteria was identical. Likewise, the electron transport chain was not affected by colicin treatment, as evidenced from lack of effect on NADH oxidase, succinic dehydrogenase, and NADPH-NAD transhydrogenase. It is concluded that colicin K interferes with the coupling of ATP the utilization of the intermediate for the ATP-linked transdehydrogenase reaction.
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PMID:Effect of colicin K on a membrane-associated, energy-linked function. 0 29

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 effects of monovalent cations on calcium uptake by fragmented sarcoplasmic reticulum have been clarified. Homogenization of muscle tissue in salt-containing solutions leads to contamination of this subcellular fraction with actomyosin and mitochondrial membranes. When, in addition, inorganic cations are contributed by the microsomal suspension and in association with nucleotide triphosphate substrates there is an apparent inhibition of the calcium transport system by potassium and other cations. However, when purified preparations were obtained after homogenization in sucrose medium followed by centrifugation on a sucrose density gradient in a zonal rotor, calcium uptake and the associated adenosine triphosphatase activity were considerably activated by potassium and other univalent cations. When plotted against the log of the free calcium concentration there was only a slight increase in calcium uptake and ATPase activity in the absence of potassium ions but sigmoid-shaped curves were obtained in 100 mM K+ with half-maximal stimulation occurring at 2 muM Ca2+ for both calcium uptake and ATPase activity. The augmentation in calcium uptake was not due to an ionic strength effect as Tris cation at pH 6.6 was shown to be inactive in this respect. Other monovalent cations were effective in the order K+ greater than Na+ greater than NH4+=Rb+=Cs+ greater than Li+ with half-maximal stimulation in 11 mM K+, 16 mM Na+, 25 mM NH4+, Rb+, and Cs+ and in 50 mM Li+. There was nos synergistic action between K+ AND Na+ ions and both calcium uptak and associated ATPase were insensitive to ouabain. Thallous ions stimulate many K+-requiring enzymes and at one-tenth the concentration were nearly as effective as K+ ions in promoting calcium uptake. The ratio of Ca2+ ions transported to P1 released remained unchanged at 2 after addition of K+ ions indicating an effect on the rate of calcium uptake rather than an increased efficiency of uptake. In support of this it was found that during the stimulation of calcium uptake by Na+ ions there was a reduction in the steady state concentration of phosphorylated intermediate formed from [gamma-32P]ATP. It is considered that there is a physiological requirement for potassium ions in the relaxation process.
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PMID:Caclium uptake and associated adenosine triphosphatase activity in fragmented sarcoplasmic reticulum. Requirement for potassium ions. 1 56

1. Isolated outer membranes from rat spleen mitochondria can be stored in liquid N(2) for several weeks without significant loss of ATPase (adenosine triphosphatase) activity. 2. The ATPase reaction has a broad pH optimum centering on neutral pH, with little significant activity above pH9.0 or below pH5.5. 3. A sigmoidal response of the ATPase activity to temperature is observed between 0 and 55 degrees C, with complete inactivation at 60 degrees C. The Arrhenius plot shows that the activation energy above the transition temperature (22 degrees C) (E(a)=144kJ/mol) is one-third of that calculated for below the transition temperature (E'(a)=408kJ/mol). 4. The outer-membrane ATPase (K(m) for MgATP=50mum) is inactive unless Mg(2+) is added, whereas the inner-membrane ATPase (K(m) for ATP=11mum) is active without added Mg(2+) unless the mitochondria have been depleted of all endogenous Mg(2+) (by using ionophore A23187). 5. The substrate for the outer-membrane ATPase is a bivalent metal ion-nucleoside triphosphate complex in which Mg(2+) (K(m)=50mum) can be replaced effectively by Ca(2+) (K(m)=6.7mum) or Mn(2+), and ATP by ITP. Cu(2+), Co(2+), Sr(2+), Ba(2+), Ni(2+), Cd(2+) and Zn(2+) support very little ATP hydrolysis. 6. Univalent metal ions (Na(+), K(+), Rb(+), Cs(+) and NH(4) (+), but not Li(+)) stimulate the MgATPase activity (<10%) at low concentrations (50mm), but, except for K(+), are slightly inhibitory (20-30%) at higher concentrations (500mm). 7. The Mg(2+)-stimulated ATPase activity is significantly inhibited by Cu(2+) (K(i)=90mum), Ni(2+) (K(i)=510mum), Zn(2+) (K(i)=680mum) and Co(2+) (K(i)=1020mum), but not by Mg(2+), Ca(2+), Ba(2+) or Sr(2+). 8. The outer-membrane ATPase is insensitive to the inhibitors oligomycin, NN'-dicyclohexylcarbodiimide, NaN(3), ouabain and thiol-specific reagents. A significant inhibition is observed at high concentrations of AgNO(3) (0.5mm) and NaF (10mm). 9. The activity towards MgATP is competitively inhibited by the product MgADP (K(i)=0.7mm) but not by the second product P(i) or by 5'-AMP.
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PMID:Kinetic properties of a magnesium ion- and calcium ion-stimulated adenosine triphosphatase from the outer-membrane fraction of rat spleen mitochondria. 2 56

The effect of inhibitors and uncouplers on the osmotic shock-sensitive transport systems for glutamine and galactose (by the beta-methyl galactoside permease) was compared to their effect on the osmotic shock-resistant proline and galactose permease systems in cytochrome-deficient cells of Salmonella typhimurium SASY28. Both osmotic shock-sensitive and -resistant systems were sensitive to uncouplers and to inhibitors of the membrane-bound Ca2+, Mg2+-activated adenosine triphosphatase. This suggests that uptake by both types of systems is energized in these cells by an electrochemical gradient of protons formed by ATP hydrolysis through the ATPase.
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PMID:Energetics of galactose, proline, and glutamine transport in a cytochrome-deficient mutant of Salmonella typhimurium. 2 79

We have compared the adenosine triphosphatase (ATPase) activity of mitochondria prepared from wild-type Neurospora crassa and from poky, a maternally inherited mutant known to possess defective mitochondrial ribosomes and reduced amounts of cytochromes aa3 and b. poky contains two distinct forms of mitochondrial ATPase. The first is normal in its Km for ATP, specificity for nucleotides and divalent cations, pH optimum, cold stability, and sensitivity to inhibitors (oligomycin, N,N-dicyclohexyl carbodiimide, and adenylyl imidodiphosphate). The fact that membrane-bound, cold-stable, oligomycin-sensitive ATPase activity is present in poky (with an activity of 1.93 +/- 0.03 mumol/min-mg of protein compared with 1.33 +/- 0.07 mumol/min-mg of protein in the wild-type strain) and also in chloramphenicol-grown wild-type cells suggests that products of mitochondrial protein synthesis play only a limited role in the attachment of the mitochondrial ATPase to the membrane in Neurospora. poky also contains a second form of mitochondrial ATPase, which has an activity of 1.5 +/- 0.2 mumol/min-mg of protein, is oligomycin sensitive but cold labile, and presumably is attached less firmly to the mitochondrial membrane. The two forms, added together, represent a substantial overproduction of mitochondrial ATPase by poky.
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PMID:Mitochondrial adenosine triphosphatase of wild-type and poky Neurospora crassa. 2 38

The localization of alkaline phosphatases in dentinogenically active rat incisor odontoblasts was studied by means of subcellular fractionation and electron microscopical histochemistry. Subcellular fractionation revealed the predominant phosphatase activity to be present in the microsome fraction and to a lesser extent in the mitochondrial fraction. Adenosine triphosphate degrading enzyme activity was determined in the presence or absence of (+/-)-6(m-bromophenyl)-5, 6-dihydroimidazo(le) (2,1-b) thiazole oxalate (R 8231). Before the histochemical study, the effects on phosphatase activities by aldehyde fixation were studied by biochemical assay. A method of fixation for optimal preservation of phosphatase activity is presented. Phosphatase electron microscopic histochemistry was performed by using ATP as a substrate and with or without addition of the inhibitor R 82319 Precipitates were seen in the membranes of vesicles present in the odontoblast process and the Golgi region. When there were signs of insufficient fixation, precipitates were also seen in the outer membranes of mitochondria. No phosphatase activity was seen in the cell membrane. ATP degrading enzyme activities mediated by nonspecific alkaline phosphatase (APase) and Ca2+ -adenosine triphosphatase thus have the same morphological localization. This close association is consistent with earlier biochemical studies.
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PMID:Ultrastructural localization of alkaline phosphatases in rat incisor odontoblasts. 2 17

Patulin (4-hydroxy-4H-furo[3,2-c]pyran-2(6H)-one), a carcinogenic lactone produced as a major metabolite by several fungi, inhibited the Mg++-dependent Na+-K+ activated adenosine triphosphatase (ATPase) activity of mouse brain microsomal fractions with an estimated IC50 of 3.0 X 10(-4) M. Inhibition was concentration dependent. Hydrolysis of ATP was linear with both time and enzyme concentration either with or without patulin in reaction mixtures. Altered pH and activity curves for Na+-K+ ATPase demonstrated comparable inhibition by patulin in buffered acidic ranges through an optimum of 7.5, followed by a reduction of toxicity to this system at higher alkaline pH. Kinetic studies of cationic-substrate activation of Na+-K+ ATPase indicated noncompetitive inhibition with respect to ATP (at low affinity nucleotide-directed sites) and Na+ (in the presence of low, noninterfering concentrations of K+). Competitive inhibition with respect to activation of the Na+-k+-stimulated activity and K+-stimulated p-nitrophenyl phosphatase activity of the enzyme system was indicated by altered binding site parameters without change in apparent Vmax in the presence of patulin. Activity was partially restored by washing. Preincubation of patulin with dithiothreitol or glutathione protected the enzyme from inhibition. Results suggest that patulin exerted its effect on Na+-K+ ATPase either directly by interfering with K+ binding or indirectly by inducing a conformational change in the enzyme.
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PMID:Effects of patulin on the kinetics of substrate and cationic ligand activation of adenosine triphosphatase in mouse brain. 2 94


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