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)

The ecto-ATPase activity of washed human platelets has been characterized by a higher-performance liquid chromatographic method. Mg++ was found to stimulate ecto-ATPase activity more strongly than Ca++. The combination of Mg++ and Ca++ at increasing concentrations caused diminishing activity levels. Elevated ecto-ATPase activity was also found in platelets incubated with prostaglandin E1 (PGE1) or potassium cyanide (KCN). It is proposed that the increase of ecto-ATPase activity is related to the extrusion or exposure of plasma membrane containing a ouabain-insensitive ATPase. The role of ecto-ATPase in platelet aggregation is discussed in light of these findings.
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PMID:Platelet aggregation and the ouabain-insensitive ATPase. Ecto-ATPase, reflection of membrane integrity. 14 Dec 4

Intact spermatozoa from rat cauda epididymis possess a Mg2+-dependent ATPase activity that hydrolyses externally added [gamma-32P]ATP. The ATPase reaction was linear with time for approx. 6 min and there was no detectable uptake of ATP by these cells. The ATPase activity of the whole spermatozoa was not due to leakage of the intracellular enzymic activity, contamination of the broken cells or any possible cell damage during incubation and isolation of spermatozoa. The activity of the enzyme was strongly inhibited (approx. 85%) by p-chloromercuribenzenesulphonic acid (50 microM) or the diazonium salt of sulphanilic acid (50 microM), which are believed not to enter the cells, whereas ouabain (0.5 mM), NaF (10 mM), NaN3 (2.5 mM) and oligomycin (5 microM) had no appreciable effect on the activity of the spermatozoal APTase. There was little loss of ATPase activity from the cells when washed with 0.5 mM-EDTA and an iso-osmotic or hyperosmotic medium. These data are consistent with the view that the observed ATPase activity is located on the external surface of spermatozoa. The sperm ecto-ATPase activity is resistant to the action of proteinases (50 micrograms/ml), namely trypsin, chymotrypsin and Pronase. Studies with various unlabelled phosphate esters indicate that the sperm ecto-ATPase is not a non-specific phosphatase and it has high degree of substrate specificity for ATP.
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PMID:Evidence for the occurrence of an ecto-(adenosine triphosphatase) in rat epididymal spermatozoa. 23 71

Hydrolysis of extracellular ATP and other nucleoside phosphates by A-431 human epidermoidal carcinoma cells was studied. The hydrolysis of extracellular ATP by these cells required either Mg2+ or Ca2+, and either cation could be replaced by Co2+, Fe2+, or Mn2+. Nucleoside triphosphates (ATP, GTP, CTP, UTP, and dTTP), but not nucleoside diphosphates, were hydrolyzed by the cells with Km and Vmax values similar to those for ATP (0.9-1.1 mmol/l and 6-10 nmol Pi formed/10(6) cells, respectively). The hydrolysis of ATP was inhibited strongly by ATP-gamma S and AMPPNP, and weakly by AMPCPP and ADP-beta S, but not by AMPCPP or AMPCP. Since the hydrolysis of [gamma-32P]ATP was inhibited by all these nucleoside triphosphates, the binding site for ATP is presumed to be the same as that for the other nucleoside triphosphates. All these results indicate that ecto-ATPase activity associated with A-431 cells is due to ecto-nucleoside triphosphatase. The nucleotide specificity shown in the present study indicates that ecto-nucleoside triphosphatase associated with A-431 cells is a molecule different from P2-purinergic receptors which can be stimulated specifically with nucleoside phosphates like ATP, ADP, UTP, UDP, and GTP, but not by other nucleotides.
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PMID:Characterization of ecto-nucleoside triphosphatase on A-431 human epidermoidal carcinoma cells. 129 31

A marked increase in water permeability can be induced in Xenopus oocytes by injection of mRNA from tissues that express water channels, suggesting that the water channel is a protein. In view of this and previous reports which showed that proteinases may interfere with mercurial inhibition of water transport in red blood cells (RBC), we examined the influence of trypsin, chymotrypsin, papain, pronase, subtilisin and thermolysin on water permeability as well as on ATPase activity, H(+)-pump, passive H+ conductance, and Na+/H+ exchange in apical brush-border vesicles (BBMV) and endosomal (EV) vesicles from rat renal cortex. H+ transport was measured by Acridine orange fluorescence quenching and water transport by stopped-flow light scattering. As measured by potential-driven H+ accumulation in BBMV and EV, proteinase treatment had little effect on vesicle integrity. In BBMV, ecto-ATPase activity was inhibited by 15-30%, Na+/H+ exchange by 20-55%, and H+ conductance was unchanged. Osmotic water permeability (Pf) was 570 microns/s and was inhibited 85-90% by 0.6 mM HgCl2; proteinase treatment did not affect Pf or the HgCl2 inhibition. In EV, NEM-sensitive H+ accumulation and ATPase activity were inhibited by greater than 95%. Pf (140 microns/s) and HgCl2 inhibition (75-85%) were not influenced by proteinase treatment. SDS-PAGE showed selective digestion of multiple polypeptides by proteinases. These results confirm the presence of water channels in BBMV and EV and demonstrate selective inhibition of ATPase function and Na+/H+ exchange by proteinase digestion. The lack of effect of proteinases on water transport by mercurials. We conclude that the water channel may be a small integral membrane protein which, unlike the H(+)-ATPase and Na+/H+ exchanger, has no functionally important membrane domains that are sensitive to proteolysis.
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PMID:Proteinases inhibit H(+)-ATPase and Na+/H+ exchange but not water transport in apical and endosomal membranes from rat proximal tubule. 130 58

Brush-border (BBMV) and basolateral membrane vesicles (BLMV) from rat renal cortex exhibit an ecto-ATPase activity that is distinct from other ATPases. We have examined the cellular and regional distribution of this enzyme in rat kidney using antibodies against rat liver ecto-ATPase. In isolated vesicles, the distribution shown by biochemical assays of ATPase activity was confirmed by immunocytochemistry and Western blotting. Indirect immunofluorescence and immunogold labeling showed that brush borders of the S1 and S3 segments of the proximal tubule (PT) were stained, but the S2 segment was negative. Staining was most intense in the S3 segment. The luminal membrane of the initial part of the thin descending limb of Henle also showed a marked staining. Surprisingly, basolateral plasma membranes of PT had no detectable staining. However, the plasma membrane of endothelial cells was heavily stained, both in larger vessels and in peritubular capillaries. Using an antibody against rat thrombomodulin, a marker for endothelial cell plasma membranes, we showed that preparations of BBMV, BLMV, and endocytic vesicles are all contaminated with these membranes. This may explain, at least partially, the biochemically measured ecto-ATPase activity in renal cortical membrane vesicles. Finally, no specific staining in the kidney was found using polyclonal antipeptide antibodies against the "long form" of liver ecto-ATPase, either by immunocytochemistry or by Western blotting. This indicates either that there is no long isoform of the ecto-ATPase in the kidney or that the intracellular domains of the long form are different in the two tissues.
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PMID:Localization of ecto-ATPase in rat kidney and isolated renal cortical membrane vesicles. 131 23

A molecule which is immobilized, oriented or tumbling more slowly than the frequency of a periodic field, may interact with the field to produce chemical effects that are uncommon in a homogeneous solution. Among these effects are the alteration of the rate of a chemical reaction and the exchange of energy between the oscillating field and the conformation of the molecule. When certain conditions are satisfied, this exchange allows the molecule to absorb and couple the energy of the field to drive an endergonic reaction. The efficiency of energy coupling depends on field strength and frequency and on the ligand concentration. There are windows of these parameters to achieve efficient coupling. These windows can be expressed in terms of the rate constants and equilibrium constants of the catalytic reactions, and the amplitude and frequency of the periodic field. This mechanism allows cells to receive, process and transmit energy of high and medium level periodic potentials by means of membrane enzymes or receptors. A theory for the transduction of electric energy, electroconformational coupling (ECC) will be discussed. The electric field induced cation pumping activities of Na,K-ATPase and Ca-ATPase of human erythrocytes and the ATP synthetic activity of beef heart mitochondrial ATPase will then be used to test an ECC membrane transport model. For the processing of low level periodic signals, a theory of an oscillatory activation barrier (OAB), which considers resonance transduction between an oscillating field and the activation barrier of the rate limiting step in an enzymic reaction, will be discussed. The OAB mechanism successfully interprets the AC stimulated ATP hydrolysis activity of Ecto-ATPase from chicken oviduct and F0F1-ATPase from beef heart. We propose that mechanisms similar to an OAB model are adopted by cells to sense weak electric, acoustic, mechanical, concentration (i.e., chemical potential) and other types of signals, and to communicate with other cells by these signals. The experimental data and mechanistic information presented in this communication give us a glimpse of the molecular electronic designs in living cells. This information is also relevant with respect to environmental issues. Environmental electromagnetic fields and sonic pollutants may interfere with normal communications of cells and organisms. Their benefit, if any, and detrimental effects can be assessed and dealt with only if we fully understand mechanisms of cellular interactions with these fields and pollutants, at the molecular level.
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PMID:Molecular recognition and processing of periodic signals in cells: study of activation of membrane ATPases by alternating electric fields. 153 30

A Ca(2+)-ATPase with an apparent Km for free Ca2+ = 0.23 microM and Vmax = 44 nmol Pi/mg/min was detected in a rat parotid plasma membrane-enriched fraction. This Ca(2+)-ATPase could be stimulated without added Mg2+. However, the enzyme may require submicromolar concentrations of Mg2+ for its activation in the presence of Ca2+. On the other hand, Mg2+ could substitute for Ca2+. The lack of a requirement for added Mg2+ distinguished this Ca(2+)-ATPase from the Ca(2+)-transporter ATPase in the plasma membranes and the mitochondrial Ca(2+)-ATPase. The enzyme was not inhibited by several ATPase inhibitors and was not stimulated by calmodulin. An antibody which was raised against the rat liver plasma membrane ecto-ATPase, was able to deplete this Ca(2+)-ATPase activity from detergent solubilized rat parotid plasma membranes, in an antibody concentration-dependent manner. Immunoblotting analysis of the pellet with the ecto-ATPase antibody revealed the presence of a 100,000 molecular weight protein band, in agreement with the reported ecto-ATPase relative molecular mass. These data demonstrate the presence of a Ca(2+)-ATPase, with high affinity for Ca2+, in the rat parotid gland plasma membranes. It is distinct from the Ca(2+)-transporter, and immunologically indistinguishable from the plasma membrane ecto-ATPase.
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PMID:A Ca(2+)-ATPase from rat parotid gland plasma membranes has the characteristics of an ecto-ATPase. 153 8

The overall rate of an enzyme catalyzed reaction is determined by the activation barrier of a rate-limiting step. If the barrier is oscillatory due to the intrinsic properties of a fluctuating enzyme, this enzymatic reaction will be influenced by a low level periodic electric field through the resonance transduction between the applied field and the oscillatory activation barrier. The ATP hydrolysis activity of a highly purified, detergent solubilized Ecto-ATPase from chicken oviduct was used to test the above concept. At 37 degrees C, this activity (1,800 mumols mg-1 min-1) was stimulated up to 47% (to 2,650 mumols mg-1 min-1) by an alternating electric field (AC), with a frequency window at 10 kHz. The maximal stimulation occurred at 5.0 V (peak-to-peak) cm-1. The potential drop across the dimension of the enzyme was approximately 10 microV (micelle diameter 20 nm). The activation barrier, or the Arrhenius activation energy, of the ATP splitting was measured to be 30 kT and the maximal barrier oscillation was calculated to be approximately 2.5 kT according to the oscillatory activation barrier (OAB) model. With the optimal AC field, full impact of the electric stimulation could be effected in much less than a second. The OAB model is many orders of magnitude more sensitive for deciphering low level periodic signals than the electroconformational coupling (ECC) model, although the latter has the ability to actively transduce energy while the former does not. By the OAB mechanism, the detecting limit of an external electric field by the ATPase, in a cell 20 micro m in diameter,would be 5 mV cm-1, but could be much lower for other membrane enzymes or receptors (e.g., nV cm-1). We propose that mechanisms similar to the OAB model could explain how a weak electromagnetic field or acoustic noises can exert its effects on an organism or a living cell.
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PMID:Resonance transduction of low level periodic signals by an enzyme: an oscillatory activation barrier model. 153 97

One of the cell-adhesion molecules (CAMs) responsible for rat hepatocyte aggregation has been described as a glycoprotein having an Mr of 105,000 (cell-CAM105). The Mr and localization of cell-CAM105 in liver membranes are very similar to those of liver ecto-ATPase, an ATPase with its nucleotide-hydrolysing site localized on the outside of the cell membrane. The protein sequence of the ecto-ATPase has been deduced from cDNA cloning. Structural analysis of the sequence indicates that the ecto-ATPase has immunoglobulin-like domains and is a member of the immunoglobulin superfamily. Since a group of proteins in the immunoglobulin superfamily has been shown to have functions related to cell adhesion, the structural characteristics of the ecto-ATPase further led to the possibility that the ecto-ATPase may have functions related to cell adhesion. In this paper, using the cDNA for the ecto-ATPase, the anti-peptide antibodies produced against peptides derived from the ecto-ATPase cDNA sequence and monoclonal antibodies against the cell-CAM105, we present evidence of identity between cell-CAM105 and ecto-ATPase. First, in Western immunoblots, two anti-cell-CAM105 monoclonal antibodies cross-reacted with the purified ecto-ATPase. Secondly, in immunodepletion experiments, antibodies against the ecto-ATPase depleted the same protein recognized by the anti-cell-CAM105 antibodies. Thirdly, in two-dimensional gel-electrophoretic analysis, anti-peptide antibodies generated against an extracellular N-terminal peptide and the intracellular C-terminal peptides of the ecto-ATPase immunoprecipitated proteins of similar isoelectric points and Mr values to those of the cell-CAM105. Fourthly, proteins immunoprecipitated by anti-ecto-ATPase antibodies and anti-cell-CAM105 antibodies have similar V8-proteinase-digest peptide maps. Finally, monoclonal antibodies against the cell-CAM105 specifically recognized the protein expressed in COS cells transfected with the ecto-ATPase cDNA. These results indicate that the ecto-ATPase cDNA codes for a protein that is identical with the cell-CAM105. Since the ecto-ATPase has structural features of immunoglobulin domains, the identity of cell-CAM105 with ecto-ATPase leads to the conclusion that this liver CAM, similarly to neuronal CAM, is also a member of the immunoglobulin supergene family. Furthermore, immunological studies indicate that the cell-CAM105/ecto-ATPase is composed of two isoforms of different C-terminal sequences. The association of ATPase activity with cell-CAM105 raises the possibility that extracellular nucleotides may play important roles in regulating cell adhesion.
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PMID:Immunochemical characterization of two isoforms of rat liver ecto-ATPase that show an immunological and structural identity with a glycoprotein cell-adhesion molecule with Mr 105,000. 183 73

An ATP diphosphohydrolase (EC 3.6.1.5) is an enzyme hydrolyzing pyrophosphate bonds in nucleoside di- and triphosphates with broad substrate specificity in the presence of divalent cations. The ATPase and ADPase activities in the enzyme purified to homogeneity from bovine aortic vessel wall were insensitive to oligomycin, ouabain, and various protease treatments, and sensitive to azide and Ap5A. Bovine aorta endothelial and smooth muscle cells were cultured separately to characterize the ectonucleotidase activities. The activities were dependent on the addition of divalent cations and had broad substrate specificity. The ecto-ATPase and -ADPase activities were insensitive to oligomycin, ouabain, and protease treatments, and sensitive to azide and Ap5A. No enzyme degrading only ADP was found in the aortic vessel wall. Moreover, antiserum raised against purified ATP diphosphohydrolase inhibited the ecto-ATPase and -ADPase activities. These results indicated that ecto-ATPase and ecto-ADPase are not separate enzymes but are expressed by one enzyme, ATP diphosphohydrolase.
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PMID:ATP diphosphohydrolase is responsible for ecto-ATPase and ecto-ADPase activities in bovine aorta endothelial and smooth muscle cells. 183 87


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