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:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Inhibition of glutamate transport is a potential indirect cause of excitotoxic damage by glutamate in the CNS. The mercuric ion, the form in which metallic mercury vapor is believed to exert its neurotoxic action, is a known inhibitor of amino acid transport. This study examines the specificity with which HgCl2 inhibits glutamate transport in mouse cerebral astrocytes by means of comparative measurements of 2-deoxyglucose uptake. Uptake of 2-deoxyglucose is an index of glucose utilization that reflects the function of Na+,K+-ATPase and hexokinase, and is sensitive to Na+ entry. The kinetic parameters, ionic dependence, and substrate specificity of glutamate transport in these astrocyte cultures were consistent with the commonly occurring system designated X-AG. Acute exposure to 0.5 microM HgCl2 inhibited by 50% the initial rate of glutamate transport but did not affect 2-deoxyglucose uptake. Glutamate transport was not detectably inhibited by Al2+, Pb2+, Co2+, Sr2+, Cd2+, or Zn2+ (10 microM as chlorides). The inhibitory action of 0.5 microM HgCl2 on glutamate transport was rapidly reversible. The action of 1-2 microM HgCl2 was progressive when exposures were extended to 1-3 h, and was more slowly reversible. These results suggest that Hg2+ can impair glial glutamate transport reversibly at exposure levels that do not compromise some other vital cell functions.
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PMID:Specificity and reversibility of the inhibition by HgCl2 of glutamate transport in astrocyte cultures. 289 9

A casein kinase activity, which copurifies with the H+-ATPase activity during isolation of plasma membranes Saccharomyces cerevisiae and during centrifugation of the solubilized membrane extract through a sucrose gradient, is separated from the Mr = 100,000 ATPase catalytic polypeptide by subsequent DEAE-cellulose chromatography. The purified casein kinase activity exhibits a low Km of 12 microM MgATP, is maximally stimulated by 6 mM free Mg2+, and is 50% inhibited by 300 microM Zn2+, by 7.5 micrograms of heparin/ml, and by 300 microM orthovanadate. It phosphorylates only seryl residues. The purified casein kinase contains two polypeptides of Mr = 45,000 and 39,000 which yield antibodies which do not cross-react to each other. The two polypeptides seem to originate from a precursor of Mr = 85,000 which is detected by both antibodies in partly purified fractions. In the absence of casein, a zinc and heparin-sensitive phosphorylation of the ATPase polypeptide is observed in partly purified ATPase fractions, and a peptide of similar mobility is phosphorylated, among others, in isolated plasma membranes. The purified ATPase activity is markedly inhibited by incubation in the presence of acid phosphatase. In agreement with a recent report that the purified active ATPase molecule is largely phosphorylated (Yanagita, Y., Abdel-Ghany, M., Raden, D., Nelson, N., and Racker, E. (1987) Proc. Natl. Acad. Sci. U. S. A. 894, 925-929) this data suggests that dephosphorylation leads to deactivation of ATPase activity.
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PMID:Characterization of a protein serine kinase from yeast plasma membrane. 289 78

The Mr 170,000 to 180,000 membrane glycoprotein associated with multidrug resistance (P-glycoprotein) is involved in drug transport mechanisms across the plasma membrane of multidrug-resistant cells. We have recently reported the purification of P-glycoprotein. The purified P-glycoprotein was found to have an ATPase activity, which might be coupled with the active efflux of anticancer drugs. In the present study, we have further studied the properties of the P-glycoprotein ATPase activity by an immobilized enzyme assay procedure using a P-glycoprotein-antibody-Protein A-Sepharose complex. GTP was also hydrolyzed by the P-glycoprotein, although less efficiently than ATP. The ATPase activity of P-glycoprotein had an optimal pH range around neutrality (pH 6.5-7.4). The detergent concentration of 3-[(3-cholamidopropyl)dimethyl-ammonio]-1-propane sulfonate used for protein solubilization was essential for enzyme recovery. Maximum activity was obtained when 0.1-0.2% 3-[(3-cholamidopropyl)dimethyl-ammonio]-propane sulfonate was used, while higher concentrations markedly inhibited the ATPase activity. The ATPase activity was dependent on Mg2+; maximum activity was obtained at 2-10 mM. Manganese and cobalt could substitute for magnesium as ionic cofactors. Divalent cations such as Ca2+, Zn2+, Ni2+, Cd2+, and Cu2+ inhibited the Mg2+-catalyzed ATP hydrolysis. N-Ethylmaleimide and vanadate inhibited the ATPase activity, while sodium azide or ouabain had no effect. Anticancer agents such as vincristine and Adriamycin did not affect the enzyme activity. In contrast, verapamil and trifluoperazine, agents which inhibit active drug efflux and restore drug sensitivity in resistant cells, caused an increase in the P-glycoprotein ATPase activity suggesting that P-glycoprotein might be the target molecule of these agents.
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PMID:Characterization of the ATPase activity of the Mr 170,000 to 180,000 membrane glycoprotein (P-glycoprotein) associated with multidrug resistance in K562/ADM cells. 290 Jun 77

Seminal plasma from 22 men attending an infertility clinic was subjected to preparative ultracentrifugation for 2 h at 105,000 g. The pelleted material as well as the supernatant thus obtained were investigated with regard to prostasome membrane-linked enzyme activities in relation to other semen parameters. The mean activity of Zn2+-dependent adenosine triphosphatase in the sedimented prostasome fraction was 1.45 +/- 1.02 mumol (range 0.29-4.79) orthophosphate released per milligram protein and 20 min, while the corresponding figures for the supernatant were 0.56 +/- 0.30 (range 0.12-1.29). Hence, 72% of the specific activity was sedimented, and 28% remained in the supernatant. The same pattern was recognized with regard to the other two enzymes investigated, although they displayed individual characteristics with regard to distribution after ultracentrifugation. The pelleted prostasome-linked mean aminopeptidase activity was 0.39 U/mg protein (81.9%), with only 0.087 U (18.1%) remaining in the supernatant. The corresponding figures for gamma-glutamyltransferase were 7.89 (60.4%) and 5.17 (39.6%) mu kat/g protein, respectively. The different enzyme activities in the prostasome fraction and supernatant, respectively, were interrelated to each other and correlated significantly with r values between 0.73 and 0.93 (p less than 0.001). It was concluded that a minor fraction of prostasomes remained in the supernatant after ultracentrifugation. A relationship existed between prostasomes and semen volume revealing a rather consistent pattern in that small volumes favoured the presence of comparatively more prostasomes in the supernatant and less prostasomes in the pelleted fraction than large volumes. In addition, the sperm concentration seemed to be another determinant of the distribution of prostasomes in seminal plasma on subsequent ultracentrifugation.
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PMID:Prostasome membrane associated enzyme activities and semen parameters in men attending an infertility clinic. 290 7

A procedure is described for the isolation of intact hippocampal mossy fiber synaptosomes. Electron microscopic examination revealed numerous synaptosomal profiles which are clearly of mossy fiber origin, indicated by their large size (2-6 micron diameter) and characteristic morphology. Furthermore, this fraction is enriched in zinc and dynorphin B which appear to be concentrated in mossy fiber terminals in vivo. Synaptosomes isolated by this procedure accumulated 2-deoxyglucose and retained 88% of total lactate dehydrogenase activity after incubation at 30 degrees C for 60 minutes, indicating a high degree of membrane integrity. Oxygen consumption was stimulated 4-fold by veratridine (0.1 mM) and inhibited 90% by ouabain (1 mM), suggesting that synaptosomal metabolism remained tightly coupled to ouabain-sensitive ATPase activity. Potassium-stimulated (45 mM) release of dynorphin B was completely dependent upon the presence of extrasynaptosomal calcium, while only 30% of the evoked release of glutamate was calcium-dependent. D-aspartate, which exchanges glutamate out of the cytoplasmic pool, virtually eliminated the calcium-independent component of glutamate release. This synaptosomal preparation will be useful in identifying the factors that modulate the release of amino acid and opioid neurotransmitters from hippocampal nerve terminals and in the investigation of their presynaptic mechanisms of action.
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PMID:Glutamate and dynorphin release from a subcellular fraction enriched in hippocampal mossy fiber synaptosomes. 290 27

The microsomal Mg-ATPase from various rat tissues was compared. After fractionating the microsomal vesicles by sucrose gradient centrifugation, the highest specific activity of the Mg-ATPase was found in the low-density vesicles which contained plasma membrane. A large fraction (25-90%) of the microsomal Ca-independent Mg-ATPase found in each tissue had the following properties: (1) the Km for ATP was 0.2 mM; (2) the rate of ATP hydrolysis by the Mg-ATPase was nonlinear due to an ATP-stimulated inactivation of the enzyme; (3) wheat germ agglutinin, concanavalin A, glutaraldehyde, and antiserum prevented inactivation induced by ATP or AdoPP[NH]P; (4) detergents at relatively low detergent:protein ratios increased the rate of inactivation with little change in the initial rate of ATP hydrolysis; (5) the Mg-ATPase was inactivated by irradiation in the presence of 8-azido ATP. (6) in addition to ATP, the Mg-ATPase was able to hydrolyze CTP, GTP, UTP, ITP, and GTP but was unable to hydrolyze any of the 10 nonnucleotide phosphocompounds which were tested; (7) the bivalent cation requirement of the Mg-ATPase could be provided by Mg2+, Ca2+, Mn2+, Zn2+, or Co2+ but the enzyme was inactive in the presence of Cu2+, Sr2+, Ba2+, or Be2+; (8) the Mg-ATPase activity was not altered by ionophores or inhibitors of the Na,K-ATPase, the Ca,Mg-ATPase or the mitochondrial F1ATPase. These data suggest that a major portion of the microsomal, basal Mg-ATPase activity is due to one unique enzyme found in most if not all tissues.
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PMID:Comparison of the rat microsomal Mg-ATPase of various tissues. 293 82

Metal ion-activated acid ATPase was present in chicken liver lysosomes. The enzyme catalyzed the hydrolysis of nucleoside tri-, di-, and monophosphates and cleaved the phosphodiester linkage. Among the substrates studied, ATP was hydrolyzed at the highest rate at pH 5.4. The enzyme activity was stimulated 3.5 approximately 7.5-fold by divalent cations such as Ca2+, Mg2+, and Zn2+, but inhibited by EDTA or Hg2+.
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PMID:Acid ATPase from chicken liver lysosomes. II. Presence of metal ion-activated enzyme. 293 47

Purified goblet cell apical membranes from Manduca sexta larval midgut exhibit a specific ATPase activity approx. 20-fold higher than that in the 100 000 X g pellet of a midgut homogenate. The already substantial ATPase activity in this plasma membrane segment is doubled in the presence of 20-50 mM KCl. At ATP concentrations ranging from 0.1 to 3.0 mM, the presence of 20 mM KCl leads to a 10-fold increase in the enzyme's affinity for ATP. ATPase activity is greatest at a pH of approx. 8. In addition to ATP, GTP serves as a substrate, but CTP, ADP, AMP and p-nitrophenyl phosphate do not. Either Mg2+ or Mn2+ is required for activity and cannot be replaced by Ca2+ or Zn2+. The ATPase activity of goblet cell apical membranes is inhibited by neither the typical (Na+ + K+)-ATPase inhibitors, ouabain and orthovanadate, nor by the typical mitochondrial F1F0-ATPase inhibitors, azide and oligomycin. Although 1.5 microM DCCD is ineffective, 150 microM DCCD leads to total inhibition of ATPase activity. The ATPase activity of goblet cell apical membranes is stimulated not only by K+, but also, in order of decreasing effectiveness, by Rb+, Li+, Na+ and even Mg2+. Replacement of Cl- by Br-, F- and HCO3- has less influence than variation of the cations. However, replacement of Cl- by NO3- inhibits strongly this ATPase activity. The ATPase activity described above is characteristic of the alkali metal ion pump containing apical membranes of goblet cells and is not enhanced to a similar degree in other purified midgut epithelial cell plasma membrane segments. Its localization, its broad cation specificity and its insensitivity to ouabain all mimic properties of active ion transport by the lepidopteran midgut and suggest this ATPase as a possible key component of the lepidopteran electrogenic alkali metal ion pump.
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PMID:Cation-stimulated ATPase activity in purified plasma membranes from tobacco hornworm midgut. 293 79

A metal ion-activated acid ATPase was present in chicken liver lysosomes. We used Zn2+ as an activator. Lysosomal extract containing octylglucoside from chicken liver was centrifuged at 100,000 xg for 60 min. The supernatant was analyzed by gel filtration on a Sepharose 6B column. Two peaks of metal ion-activated acid ATPase activities were obtained according to the distribution patterns. Each of the two active fractions was incubated with phosphatidylinositol-specific phospholipase C at 37 degrees C for 60 min. The resulting solution was analyzed by gel filtration on a smaller size column of Sepharose 6B again. Molecular weight of the major peak was altered from approx. 1,600,000 to 130,000, whereas that of the minor one, 700,000, remained unchanged.
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PMID:Acid ATPase from chicken liver lysosomes. III. A metal ion-activated ATPase combines with membranous phosphatidylinositol. 294 83

The ATPase activity of native dynein 1 from sea urchin sperm flagella is activated reversibly by inorganic monovalent chlorides with the magnitude of activation being nearly independent of the cation below 0.3 M. At higher concentrations, activation increases in the order LiCl greater than NH4Cl greater than NaCl greater than KCl, with the maximum occurring at about 0.8 M in all cases. The sodium halides activate reversibly in the order NaI greater than NaBr greater than NaCl, but NaF is strongly inhibitory. The presence of the organic anions formate, acetate, or propionate favors the native low ATPase activity state, with lithium acetate giving little activation at up to 1 M and sodium acetate partially reversing the activation due to simultaneous presence of 0.6 M NaCl. The sedimentation rate of the dynein does not change between 0.2 and 0.8 M NaCl or sodium acetate, suggesting that the effects of the anions on ATPase activity are due to local changes near the catalytic site, rather than to large-scale changes in the molecular structure. All the agents that activate the dynein ATPase, either reversibly (halides) or irreversibly (Triton X-100), decrease its sensitivity to inhibition by vanadate, consistent with ATPase activation being the result of a decreased stability of the dynein. ADP.Pi kinetic intermediate that is thought to bind vanadate at the gamma-Pi site and act as a dead-end kinetic block. Although many divalent cations, including Mg2+, Mn2+, Fe2+, Co2+, Ni2+, Zn2+, Ca2+, and Sr2+, can support dynein ATPase activity, the magnitude of ATPase increase observed upon treatment with Triton X-100 is greatest with Mg2+ and Mn2+, which are also the only cations capable of supporting the motility of demembranated flagella at rates similar to those observed in vivo.
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PMID:Activation of dynein 1 adenosine triphosphatase by monovalent salts and inhibition by vanadate. 294 15


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