Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.6.1.25 (triphosphatase)
1,529 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

When isolated rat mesenteric small arteries were submitted to 2 s of sonication, a nucleoside triphosphatase activity was released to the medium, mainly from the plasma membrane of the vascular smooth muscle cells. The activity was kinetically characterized: It hydrolysed ATP, UTP and GTP with the same substrate affinity and the same specific activity. CaATP, as well as MgATP were substrates for the enzyme with an apparent Km in the micromolar range. ATPase inhibitors: ouabain, vanadate, AlF4-, oligomycin and N-ethylmaleimide were without effect on the hydrolytic activity. Among other modifiers tested only N,N'-dicyclohexylcarbodiimide caused significant (greater than 30%) inhibition. In the presence of micromolecular concentrations of Ca2+ and Mg2+, small (less than 20 mM) concentrations of Na+, K+, Rb+, Cs+ and choline+, irrespective of the nature of the anion, activated the hydrolysis with an equilibrium ordered pattern, but concentrations of monovalent cation salts above 20 mM decreased the hydrolysis rate. No activation by monovalent cation salts was seen at millimolar concentrations of divalent cations and substrate. On the basis of the results a standard mixture is proposed, which allows a sensitive assay of the specific enzyme activity.
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PMID:Characterisation of Ca2+ or Mg(2+)-dependent nucleoside triphosphatase from rat mesenteric small arteries. 165 84

1. Thiamine triphosphatase activity in particulate fraction, but not in soluble, of rat skeletal muscle was stimulated by several anions. 2. The stimulative effect of anions was dependent on pH of reaction medium and was reversible. 3. The activities of ATPase in rat muscle particulate preparation and thiamine triphosphatase in the brain were inhibited by the anions.
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PMID:Membrane-associated thiamine triphosphatase in rat skeletal muscle. 166 9

Addition of ATP or ATP analog to the incubation media is shown to result in cell death in experiments with different cultured cell lines as evidenced by the results of several independent assays, both in the absence or presence of extracellular Ca2+. Cytolytic T-lymphocyte (CTL) clone itself was not only resistant to cytolytic effects of ATP, but was able to "rescue" antigen-nonbearing 51Cr-labeled cells from lytic effects of extracellular ATP (but not from lytic effects of adenosine 5'-thiotriphosphate) when present during assay. To test whether the resistance of CTL to ATP is due to a high activity of ecto-ATPase, four independent assays of ATPase activity were utilized to demonstrate the presence and relatively high activity of the ecto-ATPase(s) on CTL surface. Studies of substrate specificity of CTL ecto-ATPase suggest that there is more than one nucleoside 5'-triphosphatase on the surface of CTL. The enzyme(s) activity is Ca2+- and Mg2+-dependent and in this respect is similar to recently described hepatic cells ecto-ATPase. We tested effects of known ATP-binding site-specific reagents fluorescein 5'-isothiocyanate (FITC) and 5'-fluorosulfonylbenzoyladenosine (FSBA) to find covalent modification procedures to be used in studies of functional role of ecto-ATPase. FSBA, but not FITC, inhibits lymphocyte ecto-ATPase but addition of ATP together with FSBA protects ecto-ATPase activity. Inactivation of CTL ecto-ATPase by pretreatment with FSBA makes CTL susceptible to lytic effects of extracellular ATP, as was hypothesized for the functional role of this enzyme in CTL.
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PMID:Ecto-ATPase activity in cytolytic T-lymphocytes. Protection from the cytolytic effects of extracellular ATP. 213 37

Chromobindin A is a large, multisubunit protein that binds to chromaffin granule membranes in a Ca2+- and ATP-regulated manner. Ca2+ stimulates binding to the membrane, whereas ATP, in the the absence of Ca2+, is required for release of the protein from the membrane. We now report that spectral and HPLC data indicate that nucleotides are associated with the native chromobindin A complex and that the protein can bind two molecules of [3H]ATP in vitro. Chromobindin A also appears to be a novel nucleotide triphosphatase. ATPase activity was detected in fractions containing chromobindin A isolated by affinity chromatography, gel filtration, or ion exchange chromatography. Kinetic studies indicated that the Vmax is 44 nmol of Pi/mg/min and the Km is 0.115 mM, whereas the nonhydrolyzable ATP analog 5'-adenylylimidodiphosphate acts as a competitive inhibitor of this reaction with a Ki of 0.08 mM. The activity was found to be sensitive to protease treatment or to preincubation at 65 degrees C and was inhibited by Ca2+ or low pH. The ATPase activity was not inhibited by N-ethylmaleimide, N,N'-dicyclohexylcarbodiimide, vanadate, oligomycin, or azide.
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PMID:Interactions of the complex secretory vesicle binding protein chromobindin A with nucleotides. 213 61

Adenosine triphosphatase activity and nucleotide binding affinity of isolated beta-subunit preparations from Escherichia coli F1F0-ATP synthase were studied. The aim was to find out whether isolated beta-subunit would provide an experimental model in which effects of mutations on catalysis per se, unencumbered by complications due to their effects on positive catalytic cooperativity, could be studied. Three types of purified, isolated beta-subunit preparations were studied. Type I-beta was from a strain lacking all F1F0 subunits except beta and epsilon. Type II-beta was from F1 carrying the alpha S375F mutation which blocks positive catalytic cooperativity. Type III-beta was from normal F1. Type I- and II-beta had very low ATPase activity (less than 10(-4) s-1) which was azide-insensitive, aurovertin-insensitive, and unaffected by anti-beta antibody. Type I-beta activity was EDTA-insensitive. We conclude that isolated beta-subunit from E. coli F1F0 has zero or at most very low intrinsic ATPase activity. Type III-beta had low ATPase activity (8.4 x 10(-5) s-1 to 1.1 x 10(-3) s-1 in seven different preparations). This activity was aurovertin-sensitive, but varied in azide sensitivity from 0 to 34% inhibited. The azide-sensitive component, like F1 and alpha 3 beta 3 gamma oligomer, was inhibited by anti-beta and anti-alpha antibodies. The azide-insensitive component was stimulated by anti-beta and unaffected by anti-alpha. We show here that (alpha beta)-oligomer has ATPase activity which is azide-insensitive, aurovertin-sensitive, stimulated by anti-beta, and unaffected by anti-alpha. The intrinsic ATPase activity of Type III-beta could be due to contaminating (alpha beta)-oligomer plus alpha 3 beta 3 gamma-oligomer. Isolated beta had very low affinity for nucleotide as compared to the first catalytic site on F1. Taken together with the very low ATPase activity of isolated beta (even if real), the work shows that isolated beta is not a good experimental model of F1 catalysis.
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PMID:Adenosine triphosphatase and nucleotide binding activity of isolated beta-subunit preparations from Escherichia coli F1F0-ATP synthase. 215 22

Polyoma virus large tumor antigen (PyV T antigen) has been purified to near homogeneity by immunoaffinity column chromatography. We have detected DNA helicase and ATPase (nucleoside-5'-triphosphatase) activities in the purified PyV T antigen fraction and characterized these activities. The ATPase activity was stimulated about 2-fold by poly(dT), which was the most effective stimulator among the synthetic polynucleotides tested. Natural nucleic acids, such as calf thymus native and heat-denatured DNA, and single-stranded circular fd DNA were also effective, but the degree of stimulation was less than 1.5-fold. The basal and poly(dT)-stimulated ATPase activities showed similar preference for nucleoside 5'-triphosphates, requirement for divalent cations, and pH optima. The preference for nucleoside 5'-triphosphates was ATP, dATP greater than CTP, UTP much greater than GTP. The only difference observed between the two activities was salt sensitivity. The basal ATPase activity was resistant to KC1 up to 300 mM. In contrast, poly-(dT)-stimulated activity was reduced to the level of basal activity at 300 mM KC1. DNA helicase activity required divalent cations and was dependent on hydrolysis of ATP. The activity showed similar preference for nucleoside 5'-triphosphates, requirement for divalent cations, and pH optimum as the two ATPase activities, and the salt sensitivity of DNA helicase activity was similar to that of poly(dT)-stimulated ATPase activity. The helicase activity was inhibited competitively by the addition of single-stranded or double-stranded DNA, and a relatively high inhibitory activity was observed with poly [d(A-T)]. The PyV T antigen helicase was found to migrate in the 3' to 5' direction along the DNA strand to which the protein bound.
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PMID:DNA helicase and nucleoside-5'-triphosphatase activities of polyoma virus large tumor antigen. 216 Feb 69

Intraperitoneal administration of mitomycin C (40 micrograms/100 g body weight) to male Wistar rats increased the ATPase activity in hypotonic extracts of liver cell nuclei for 4 days after injection. Partially purified ATPase, obtained by the DEAE-cellulose column chromatography of these extracts, showed a 14 times higher specific activity than that found in normal rat liver nuclei. The enzymatic activity was strongly enhanced by the addition of polynucleotides, especially poly A and poly I, to the assay mixture, but was inhibited by GTP, a chelating agent, heparin and thiol-group inhibitors. Quercetin and oligomycin were less effective, and ouabain showed no inhibitory effect. Mg2+ ions were essential, but neither Ca2+, Na+ nor K+ ions were required for the manifestation of the activity. These characteristic properties of the enzyme are similar to those of a nucleoside triphosphatase found in the nuclear matrix and envelope, suggesting that some energy-providing mechanisms involved in the repair processes of DNA damage or cellular injury are induced by mitomycin C administration.
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PMID:Enhanced ATPase activity in liver cell nuclei induced by administration of mitomycin C to rats. 253 22

Limited tryptic digestion of Escherichia coli transcription termination factor rho [an RNA-dependent nucleoside triphosphatase (NTPase)] yields predominantly two fragments (f1 and f2) when the protein is bound to both poly(C) and ATP. The apparent molecular masses of the two fragments are 31 kDa for f1 and 15 kDa for f2, adding up to the molecular mass of the intact rho polypeptide chain (46 kDa). Sequence analysis of the amino termini demonstrates that f1 is derived from the amino-terminal portion of rho and that the trypsin cleavage that defines f2 occurs at lysine-283. These results suggest that, in the liganded (activated) form, the native rho protein monomer is organized into two distinct structural domains that are separable by a single proteolytic cleavage. The f1 fragment, purified from NaDodSO4/polyacrylamide gels and renatured, binds poly(C) but the f2 fragment does not; neither regains any ATPase activity. ATP- and polynucleotide-dependent changes in the rate of proteolysis and in the character of the fragments produced suggest that rho undergoes a series of conformational transitions as a consequence of RNA binding, NTP binding and NTP hydrolysis. The rate of loss of rho ATPase activity and of intact rho monomers is slower in the presence of adenosine 5'-[gamma-thio]triphosphate than in the presence of either ATP or ADP, indicating that the hydrolysis of ATP may result in different conformational effects than does the binding of this ligand. These findings are discussed within the context of recent models of rho-dependent transcription termination.
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PMID:Escherichia coli transcription termination factor rho has a two-domain structure in its activated form. 258 Mar 3

1. In broken red cell membranes, Mg2+ inhibition of Na+,K+-adenosine-5'-triphosphatase (Na+,K+-ATPase) activity was partially competitive with MgATP. Mg2+ inhibition of Na+,K+-ATPase activity was uncompetitive with K+ in broken red cell membranes, and Mg2+ inhibition of ouabain-sensitive K+ influx in K+-free resealed ghosts was uncompetitive with external K+. 2. When Na+,K+-ATPase activity was measured at relatively high K+ concentration, Mg2+ inhibition was partially competitive with Na+. Mg2+ inhibition of ouabain-sensitive K+ influx in K+-free resealed ghosts was competitive with cell Na+. Magnesium was a more effective inhibitor of the uncoupled Na+ efflux in low-Na+ ghosts than in high-Na+ ghosts. 3. These findings indicate that Mg2+ inhibition results from combination of the ion with the enzyme form E2K at high intracellular Na+ and K+, and from combination with the form E1 at low intracellular Na+ and K+. 4. In ghosts containing high concentrations of MgPO4, inhibition of the K+-K+ exchange by Mg2+ was more effective at high than at low nucleotide concentrations. At high MgPO4 and low Mg2+ concentration the activity of the exchange increased monotonically with nucleotide concentration, but at a higher Mg2+ concentration, nucleotide activation of the exchange was biphasic: the K+-K+ exchange rate increased, reached a maximum, and then decreased with increasing nucleotide concentration.
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PMID:Interaction of magnesium with the sodium pump of the human red cell. 284 41

The inhibitory effect of dicyclohexylcarbodiimide (DCCD) on the activity of the adenosine-triphosphatase of Escherichia coli (ECF1) has been examined in detail. DCCD reacted with ECF1 predominantly in beta subunits with a maximum of 2 mol of reagent per mole of ECF1 being incorporated in these subunits. Ninety-five percent inhibition of steady-state or multistate ATPase activity required incorporation of 1 mol of DCCD per mole of enzyme into beta subunits. Seventy-five percent inhibition of the initial rate of unisite catalysis was only obtained after incorporation of 2 mol of DCCD per mole of ECF1 into beta subunits. Analyses of the kinetics of unisite catalysis and nucleotide binding experiments both indicate that DCCD binds outside the substrate ATP binding site. Inhibition by this reagent appears to be due in part to an effect on the catalytic sites but mainly to the blocking of cooperativity between these sites.
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PMID:Effect of dicyclohexylcarbodiimide on unisite and multisite catalytic activities of the adenosinetriphosphatase of Escherichia coli. 286 53


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