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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)

The isolated nuclei of wheat embryo possess the ATPase activity. The addition of Mg2+ and Ca2+ significantly increases the activities of nuclear ATPases, whereas Hg2+, Cu2+ and Mn2+ inhibit the activity. The activating effect of Mg2+ is enhanced by an addition of Na and K ions. The activity of wheat embryo nuclear Mg-ATPase is higher than its Ca-ATPase activity; both ATPases also differ in their pH optima. Separation of total nuclear protein according to the solubility of its individual protein components in wheat and strong salt solutions, using the detergents, as well as ammonium sulfate precipitation and dialysis do not result in separation of Mg-activated and Ca-activated ATPases, although their levels of activities and ratios change in the course of fractionation. The Mg- and Ca-ATPase activities of the wheat embryo nuclei were found in the nuclear fraction of albumin, in nonhistone proteins and nuclear membranes. In the albumin nuclear fraction and subfractions of non-histone proteins the higher level of activity is observed in Ca-ATPase, whereas in the nuclei and soluble fractions of residual proteins in Mg-ATPase.
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PMID:[Properties and localization of Mg- and Ca-ATpase activities in wheat embryo cell nuclei]. 14 25

The interrelated temperature induced structural changes in the protein and lipid fractions of the Na+, K+-ATPase preparations were studied. A spin-labelled analog of ATP (ATP) was used, where the paramagnetic fragment was attached to the 2' (3')-OH ribose group. It is shown that the rotational mobility of ATP changes with the temperature in a discontinuous way. This correlates with the behaviour of the enzymatic activity of Na+, K+-ATPase and with the state of lipids in the enzyme preparations, both being characterized by a break in the 20-23 degrees C temperature region. When the Mn2+ ions were substituted by Mn2+ a strong magnetic dipolar interaction between the spin label in ATP and the Mn2+ ion was observed, which proves that the complex E-ATP--Mn2+ is formed before the hydrolysis of ATP. The structural changes which occur near 20 degrees C were also observed in the neighbourhood of the SH-groups modified by spin label X, an analog of maleimide. The structural changes observed support the idea that the protein-lipid interactions in the Na+, K+-ATPase provide the relaxation of the system from the unstable state during hydrolysis of ATP and cation transport.
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PMID:The lipid-protein interaction in the membrane-bound Na+, K+-ATPase: a spin label study. 14 11

The effects of manganese and ethanol interaction on some chemical constituents of the liver and serum of rats were investigated in order to assess the influence of these substances in inducing susceptibility to manganese poisoning. Manganese and ethanol alone or in combination were administered to the rats as drinking solutions for a period of 30 days. Both the chemicals had a synergistic effect in altering the activity of SDH and ATPase in the liver of rats. The combined treatment also produced significant increase in the activity of adenosine deaminase and alpha-amylase in the liver and serum respectively. Furthermore, the accumulation of manganese in the liver and the increase in the calcium content of the serum were significantly greater after combined ethanol and manganese administration--than either of them alone. These alterations indicate that the toxic effects of manganese are enhanced when the metal and ethanol interact in the biological system.
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PMID:The interaction between manganese and ethanol in rats. 15 83

The dicyclohexylcarbodiimide-sensitive ATPase from spinach chloroplast has been isolated. On sodium dodecyl sulfate gels, seven different polypeptides were seen. Five of these polypeptides coincided with the CF1 subunits, a 7,500-dalton peptide was identified as the proteolipid which interacts with [14C]dicyclohexylcarbodiimide, and there was a 15,500-dalton hydrophobic polypeptide with unknown function. In two-dimentional gels, two additional peptides were resolved, one 17,500 daltons (co-migrating in sodium dodecyl sulfate gels with subunit delta) and one 13,500 daltons (co-migrating with subunit epsilon). Reconstitution was obtained by freezing and thawing the complex with a crude mixture of phospholipids. After reconstitution the complex catalyzed 32P1-ATP exchange (rates of 200 to 400 nmoles x mg-1 x min-1) and ATP formation during acid-to-base transition. These reactions were inhibited by dicyclohexylcarbodiimide and uncouplers. Uncouplers at low concentrations stimulated and at high concentrations inhibited the Mg2+-ATPase activity. ATP hydrolysis and 32P1-ATP exchange were catalyzed by the complex in the presence of either Mg2+ or Mn2+ but not with Ca2+ or Co2+. ATP and GTP were substrates for the exchange reaction but not ADP or CTP.
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PMID:Purification and reconstitution of the N,N'-dicyclohexylcarbodiimide-sensitive ATPase complex from spinach chloroplasts. 15 58

A stable and homogeneous adenosine-5'-triphosphatase (ATPase, EC 3.6.1.3) has been solubilized from Rhodospirillum rubrum (R. rubrum) chromatophores by chloroform extraction. Purification of the Ca2+-dependent ATPase activity was 200-fold. Ca2+ can be replaced by Mg2+, Cd2+, and Mn2+. The Km for Ca-ATP (0.17 mM) is increased about 5-fold during solubilization of the enzyme, whereas the Km values for Mg-ATP (0.029 mM) and Cd-ATP (0.014 mM) are not affected. The chloroform-released ATPase has a molecular weight of 400,000 +/- 30,000 and consists of the following subunits (molecular weights in parenthesis): alpha(58,000), beta(53,500), gamma(39,000), delta(18,500), and epsilon(14,000). The amino acid composition and the fluorescence spectra are presented. Besides the chloroform-released ATPase complex three other Ca2+-dependent ATPase forms have been isolated from R. rubrum chromatophores by other methods for comparison. Ultrasonication of the membranes leads to the release of an ATPase complex which is mainly composed of alpha, beta, and gamma-subunits. From an acetone powder extract an ATPase complex could be purified by affinity chromatography which is composed of four kinds of subunits (alpha, beta, gamma, delta). The same acetone powder yields an ATPase consisting of only three different types of subunits (alpha, beta, gamma) if the final purification step is preparative disc electrophoresis on 6% polyacrylamide gels instead of affinity chromatography.
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PMID:Purification, subunit structure, and kinetics of the chloroform-released F1ATPase complex from Rhodospirillum rubrum and its comparison with F1ATPase forms isolated by other methods. 15 49

A DNA-dependent ATPase has been purified from calf thymus. The enzyme hydrolyses ATP and dATP in the presence of heat-denatured DNA. It does not hydrolyse the corresponding nucleoside triphosphates of guanine, uridine and cytosine. The Km values for ATP and dATP are both 0.62 mM. The enzyme requires magnesium or manganese ions. Its sedimentation coefficient is about 4.4 S. The catalytic activity is inhibited by N-ethylmaleimide but is not sensitive to novobiocin and nalidixic acid which are potent inhibitors of bacterial DNA gyrase. In some cases, during purification, chromatographically distinct additional DNA-dependent ATPase activities were detected. Limited proteolysis or covalent modification of the enzyme in the tissues, or during the first steps of its extraction, are probably responsible for the appearance of these chromatographically distinct forms.
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PMID:A DNA-dependent ATPase of calf-thymus. 15 29

Tightly bound magnesium was found in soluble, purified ATPase (F1) from beef heart mitochondria in the amount of 1 mol/mol of F1. Iron, zinc, cobalt, manganese, calcium, sodium, copper, and potassium were not tightly bound at stoichiometric levels. Removal of magnesium by chelating agents caused loss of ATPase activity. Removal of tightly bound nucleotide by gel filtration in 50% glycerol- or 60 mM K2SO4-containing buffers did not remove magnesium. Cold dissociation did release magnesium when complete denaturation was accomplished. The results suggest that magnesium is an integral part of F1, that it is required for activity, and that magnesium and nucleotides are tightly bound at separate sites. The idea that the tightly bound nucleotides are not complexed with cations suggests certain structural requirements at their binding sites which might account for the unusual properties of the sites.
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PMID:Tightly bound magnesium in mitochondrial adenosine triphosphatase from beef heart. 15 99

Phosphoryl group transfer from ATP to ADP occurred in the isolated membrane of catecholamine storage vesicles. The reaction was accelerated by extraction of the membranes with 50% (v/v) acetone and by treatment with 1% (v/v) Triton X-100. The phosphoryl group transfer reaction was activated by Mg2+ and by Mn2+. The activation profile differed from that obtained for the ATPase activity. The Michaelis-Menten kinetics of the phosphoryl transfer reaction were not entirely linear. From the linear parts of the double reciprocal plots KmATP approximately equal to 1 mM and KmADP approximately equal to 0.4 mM was obtained. All lines of the double reciprocal plots intersected indicating a sequential reaction mechanism. The reaction exhibited a narrow specificity for nucleoside diphospate and a broader one for nucleoside triphosphate indicating that ADP was the true substrate. The transfer reaction was slightly inhibited by AMP, orthophosphate and P1, P5-di(adenosine-5')pentaphosphate. The thiol reagents, N-ethylmaleimide and para-chloromercuribenzoate (PCMB), affected the ATPase activity and the phosphoryl transfer activity differently: with the blockade of 2.4 essential thiol equivalents by N-ethylmaleimide the ATPase was inhibited 50% and net uptake of catecholamine ceased, while the phosphoryl transfer remained unimpaired. PCMB affected both, the ATPase activity and phosphoryl transfer reaction. Treatment of the membranes with dithioerythritol prevented the PCMB-induced inhibition of the phosphoryl transfer, but was ineffective in protecting the ATPase activity, indicating that different thiol groups must be involved in the both enzymatic activities.
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PMID:Partial characterization of a phosphoryl group transferring enzyme in the membrane of catecholamine storage vesicles. 16 May 8

Beef brain cortex adenylate cyclase (ATP pyrophosphate-lyase (cyclizing) EC 4.6.1.1) activity is 84--88% inhibited by 5 - 10(-5) M ethyleneglycol-bis-(beta-aminoethyl ether)N,N'-tetraacetic acid in the absence of F- but only 50--60% inhibited by 5 - 10(-5) M ethyleneglycol-bis-(beta-aminoethyl ether)N,N'-tetraacetic acid in the presence of F-. In either case, further increase in EGTA concentration did not alter the degree of inhibition. The inhibition can be completely reversed in both cases by addition of 3 - 10(-5) M Ca2+, (yielding a [free Ca2+] of approximately 2 - 10(-6) M) and 5 - 10(-5) M Mn2+ or Co2+ and partially by 5 - 10(-5) M Sr2+ but not by addition of 5 - 10(-5) M Ba2+, Zn2+, Ni2+ or Fe2+. A [free Ca2+] of 7.2 - 10(-5) M markedly inhibited cyclase activity in the presence of F-. Solubilization by 1.8% Triton X-100 resulted in an enzyme preparation no longer stimulated by NaF and 100% inhibited by the addition of 5 - 10(-5) M ethyleneglycol-bis-(beta-aminoethyl ether)N,N'-tetraacetic acid either in the absence or presence of NaF. However, in contrast to ethyleneglycol-bis-(beta-aminoethyl ether)N,N'-TETRAACETIC ACID, EDTA had no measurable effect on adenylate cyclase either in the presence or absence of NaF and ethyleneglycol-bis-(beta-aminoethyl ether)N,N'-tetraacetic acid did not affect ATPase or phosphodiesterase activities. The data is rationalized by the postulation of two independent enzyme components in brain cortex: one component is about six-fold activated by NaF and the NaF effect is enhanced by low concentrations of Ca2+ and Mg2+. A second component is totally Ca2+ dependent and inhibited by high concentrations of F-. Mn2+, Co2+ and Sr2+ appear to be in vitro Ca2+ substitutes for both enzyme systems. On this basis, Triton X-100 treatment results in about a three-fold increase in specific activity of the Ca2+ dependent cyclase component but a complete abolition of the NaF stimulated component.
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PMID:Differentiation of fluorides-stimulated and non-fluoride-stimulated components of beef brain cortex adenylate cyclase cy calcium ions, ethyleneglycol-bis-(beta-aminoethyl ether) N,N'-tetraacetic acid and Triton X-100. 16 52

EPR and water proton relaxation rate (1/T1) studies of partially (40%) and "fully" (90%) purified preparations of membrane-bound (Na+ + K+) activated ATPase from sheep kidney indicate one tight binding site for Mn2+ per enzyme dimer, with a dissociation constant (KD = 0.88 muM) in agreement with the kinetically determined activator constant, identifying this Mn2+-binding site as the active site of the ATPase. Competition studies indicate that Mg2+ binds at this site with a dissociation constant of 1 mM in agreement with its activator constant. Inorganic phosphate and methylphosphonate bind to the enzyme-Mn2+ complex with similar high affinities and decrease 1/T1 of water protons due to a decrease from four to three in the number of rapidly exchanging water protons in the coordination sphere of enzyme-bound Mn2+. The relative effectiveness of Na+ and K+ in facilitating ternary complex formation with HPO2-4 and CH3PO2-3 as a function of pH indicates that Na+ induces the phosphate monoanion to interact with enzyme-bound Mn2+. Thus protonation of an enzyme-bound phosphoryl group would convert a K+-binding site to a Na+-binding site. Dissociation constants for K+ and Na+, estimated from NMR titrations, agreed with kinetically determined activator constants of these ions consistent with binding to the active site. Parallel 32Pi-binding studies show negligible formation (less than 7%) of a covalent E-P complex under these conditions, indicating that the NMR method has detected an additional noncovalent intermediate in ion transport. Ouabain, which increases the extent of phosphorylation of the enzyme to 24% at pH 7.8 and to 106% at pH 6.1, produced further decreases in 1/T1 of water protons. Preliminary 31P- relaxation studies of CH3PO2-3 in the presence of ATPase and Mn2+ yield an Mn to P distance (6.9 +/- 0.5 A) suggesting a second sphere enzyme-Mn-ligand-CH3PO2-3 complex. Previous kinetic studies have shown that T1+ substitutes for K+ in the activation of the enzyme but competes with Na+ at higher levels. From the paramagnetic effect of Mn2+ at the active site on the enzyme on I/T1 of 205T1 bound at the Na+ site, a Mn2+ to T1+ distance of 4.0 +/- 0.1 A is calculated, suggesting the sharing of a common ligand atomy by Mn2+ and T1+ on the ATPase. Addition of Pi increases this distance to 5.4 A consistent with the insertion of P between Mn2+ and T1+. These results are consistent with a mechanism for the (Na+ + K+)-ATPase and for ion transport in which the ionization state of Pi at a single enzyme active site controls the binding and transport of Na+ and K+, and indicate that the transport site for monovalent cations is very near the catalytic site of the ATPase. Our mechanism also accounts for the order of magnitude weaker binding of Na+ compared to K+.
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PMID:Magnetic resonance and kinetic studies of the mechanism of membrane-bound sodium and potassium ion- activated adenosine triphosphatase. 17 21


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