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)

Purified plasma membranes were obtained from five transplantable human tumors, a grade IV astrocytoma, an oat cell carcinoma, and three melanomas. Plasma membrane fractions were isolated from tumor homogenates by differential and discontinuous sucrose gradient centrifugation. Determination of enzyme activities indicated that the plasma membranes were enriched 10- to 20-fold with respect to 5'-nucleotidase, nicotinamide adenine dinucleotide glycohydrolase, Mg2+-activated nucleoside triphosphatase, and sialic acid. Specific activities of nearly all the enzymes varied with the individual tumors, even among tumors of the same type, i.e., the melanomas. Electron micrographs of the plasma membrane fractions showed smooth single-membrane vesicles with slight contamination by lysosomes. Therefore, these membranes are suitable for comparative biochemical studies and for the preparation of tumor-specific monoclonal antibodies. Plasma membranes from all five tumors contained very high Mg2+-adenosine triphosphatase (ATPase) activities. The Na+-K+-ATPase was a minor component of the total ATPase of these membranes (less than 30%). The major component was an ATPase exhibiting similar activity toward several nucleoside triphosphates. The activity of such a nucleoside triphosphatase has been correlated with tumorigenicity in cultured liver epithelial cells. The nucleoside triphosphatase of the plasma membranes of astrocytoma and oat cell carcinoma was stimulated from 50 to 1005 by concanavalin A, whereas ATPase of the melanoma plasma membranes was not or only slightly stimulated. The different response to concanavalin A could be due to differences in the ATPase molecules of the individual tumors or to the different environment of the ATPase.
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PMID:Isolation and characterization of plasma membranes from transplantable human astrocytoma, oat cell carcinoma, and melanomas. 611 38

Electrophorus electroplax microsomes were examined for Ca2+- and Mg2+-dependent ATPase activity. In addition to the previously reported low-affinity ATPase, a high-affinity (Ca2+,Mg2+)-ATPase was found. At low ATP and Mg2+ concentrations (200 microM or less), the high-affinity (Ca2+,Mg2+)-ATPase exhibits an activity of 18 nmol Pi mg-1 min-1 with 0.58 microM Ca2+. At higher ATP concentrations (3 mM), the low-affinity Ca2+-ATPase predominates, with an activity of 28 nmol Pi mg-1 min-1 with 1 mM Ca2+. In addition, Mg2+ can also activate the low-affinity ATPase (18 nmol Pi mg-1 min-1). The high-affinity ATPase hydrolyzes ATP at a greater rate than it does GTP, ITP, or UTP and is insensitive to ouabain, oligomycin, or dicyclohexylcarbodiimide inhibition. The high-affinity enzyme is inhibited by vanadate, trifluoperazine, and N-ethylmaleimide. Added calmodulin does not significantly stimulate enzyme activity; rinsing the microsomes with EGTA does not confer calmodulin sensitivity. Thus the high-affinity ATPase from electroplax microsomes is similar to the (Ca2+,Mg2+)-ATPase reported to be associated with Ca2+ transport, based on its affinity for calcium and its response to inhibitors. The low-affinity enzyme hydrolyzes all tested nucleoside triphosphates, as well as diphosphates, but not AMP. Vanadate and N-ethylmaleimide do not inhibit the low-affinity enzymes. The low-affinity enzyme reflects a nonspecific nucleoside triphosphatase, probably an ectoenzyme.
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PMID:Characterization of the Ca2+- and Mg2+-dependent ATPases in Electrophorus electroplax microsomes. 613 30

The principle organelle marker enzymes and various adenosine triphosphatase (ATPase) activities were studied in human skeletal muscle. The reproducibility of each assay was established under optimal and linear assay conditions. Whole homogenates of normal human quadriceps muscle were fractionated by centrifugation on a continuous sucrose density gradient. Gradient fractions were assayed for organelle marker enzymes and frequency-density histograms were constructed for each enzyme. Good resolution of the principal organelles was obtained. Adenosine triphosphatase (ATPase) was assayed under conditions of maximal stimulation by Ca2+, or Mg2+ or Na2+, K+ + Mg2+. The distribution of these activities was compared with those of the organelle marker enzymes. Both Ca2+-ATPase and Mg2+-ATPase were distributed to both the mitochondrial and myofibrillar fractions but could be distinguished by the inhibition of mitochondrial ATPase with sodium azide. The distribution of Na+, K+-activated, Mg2+-dependent ATPase (Na+, K+ ATPase) activity suggested a sarcolemmal localization. The results of electron microscopy of gradient fractions were consistent with the organelle content of the fractions as determined by enzymic analyses. These studies provide reference information for the subsequent investigation of organelle pathology of human muscle disorders.
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PMID:Analytical subcellular fractionation of normal human skeletal muscle by sucrose density gradient centrifugation. 613 12

In the presence of adenosine 5'-triphosphate (ATP) and 1-10 mM MgCl2, the relative viscosity (eta rel) of dephosphorylated gizzard myosin is reduced markedly over a range of KCl from 0.35 to 0.15 M. Sedimentation patterns show that the decrease in eta rel is due to the conversion of the 6S to 10S forms of myosin. Under similar conditions, eta rel of phosphorylated myosin is not altered, and at 0.2 M KCl, the 10S form is not observed. In 1 and 2 mM MgCl2 and less than 0.2 M KCl, 10S can be formed from both phosphorylated myosin plus ATP and dephosphorylated myosin minus ATP. In the presence of ethylenediaminetetraacetic acid (EDTA), the decrease of eta rel and corresponding change in sedimentation pattern are independent of ATP and show only a dependence on KCl. Therefore, ATP and dephosphorylation are not obligatory for the 6S to 10S transition. In all instances, the 6S-10S transition of monomeric myosin is paralleled by an alteration of adenosine-5'-triphosphatase (ATPase) activity; i.e., the KCl dependence of the two processes is the same. Transition from 6S to 10S causes a decrease in Mg2+-and Ca2+-ATPase activity of myosin and an increase in K+-EDTA-ATPase activity. The relationship between myosin shape and the ATP dependence of Mg2+-ATPase activity also is consistent with this generalization. The phosphorylation dependence of the viscosity transition from 6S to 10S is not linear, and phosphorylation of both heads is required for the complete transition. In contrast, the ATP dependence of the transition is linear, and the binding of 2 mol of ATP/myosin is required for maximum effect.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Correlation of enzymatic properties and conformation of smooth muscle myosin. 613 93

The properties of a cell surface nucleoside 5'-triphosphatase have been studied in small, intact, frog skeletal muscles, as a means of distinguishing the enzyme from other adenosine 5'-triphosphatases and of understanding its behaviour in the muscle membrane. The ectoenzyme in situ was shown to be a Ca2+- or Mg2+-activated ATPase liberating 7.5 +/- 0.4 (mean +/- SEM, n = 30) mumol of inorganic phosphate/g of muscle per 20 min, when the muscle was exposed to 2 mM ATP and 2 mM Ca2+ in Ringer's solution. The apparent Km for Mg2+ was 0.74 mM and for Ca2+ was 0.23 mM. A residual ATPase activity (20%) was found in the complete absence of divalent cations suggesting the existence of two ATPase types. A broad specificity toward nucleoside 5'-triphosphates was exhibited by the ecto-ATPase, but there was no nonspecific phosphatase activity. The enzyme was inhibited by La3+ and Cd2+, but was insensitive to ouabain, 2,4-dinitrophenol, oligomycin, and ruthenium red. Thus the ectoenzyme was not a Na+, K+-transport ATPase, was not an ATPase of mitochondrial origin, or a Ca2+-transport enzyme. Insulin had no effect. Inhibition by mersalyl, carbodiimide, and polar and cross-linking nonpolar nitrobenzene derivatives suggested that, for maximum activity, this membrane-bound enzyme required free sulfhydryl groups, certain free carboxyls, and an appreciable degree of hydrophobicity in its microenvironment.
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PMID:Characteristics of skeletal muscle ecto-ATPase in situ. 615 Jul 52

The Ca2+-Mg2+ adenosine-5'-triphosphatase (ATPase) in sarcoplasmic reticulum has been covalently labeled with the phosphorescent triplet probe erythrosinyl 5-isothiocyanate. The rotational diffusion of the protein in the membrane at 25 degrees C was examined by measuring the time dependence of the phosphorescence emission anisotropy. Detailed analysis of both the total emission S(t) = Iv(t) + 2IH(t) and anisotropy R(t) = [Iv(t) - IH(t)]/[Iv(t) + 2IH(t)] curves shows the presence of multiple components. The latter is incompatible with a simple model of protein movement. The experimental data are consistent with a model in which the sum of four exponential components defines the phosphorescence decay. The anisotropy decay corresponds to a model in which the phosphor itself or a small phosphor-bearing segment reorients on a sub-microsecond time scale about an axis attached to a larger segment, which in turn reorients on a time scale of a few microseconds about an axis fixed in the frame of the ATPase. A fraction of the protein molecules rotate on a time scale of 100-200 microseconds about the normal to the bilayer, while the rest are rotationally stationary, at least on a sub-millisecond time scale.
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PMID:Rotational diffusion of calcium-dependent adenosine-5'-triphosphatase in sarcoplasmic reticulum: a detailed study. 615 81

Adenosine triphosphatase (ATPase) activity stimulated by Ca2+ or Mg2+ was characterized in spinal nerve and spinal sensory ganglion of bullfrog. Enzyme activity of homogenates from both sources reached a maximum at a 1-2 mM concentration of either cation, although the level of maximal activity in nerve trunks was approximately twice that in ganglia. Enzyme activation was not observed with 2 mM-Sr2+ or Ba2+. Co2+ or Mn2+, at 2 mM, depressed Ca2+ activation of the enzyme by 50-60% in nerve but had no inhibitory effect on ganglia activity. In intact spinal ganglion/spinal nerve preparations, incubated for 20 h in medium containing 0.2 mM-Co2+, no effect was detected on Ca2+/Mg2+ ATPase activity in ganglia or nerve trunks whereas fast axonal transport was inhibited by 80%. Incubation in medium containing 0.02 mM-Hg2+ depressed enzyme activity in ganglia by 64% and in nerve trunks by 44%, whereas fast transport was again inhibited by 80%. When only nerve trunks were exposed to these ions, Hg2+ but not Co2+ was observed to slow the rate of fast axonal transport. The divalent cation specificity of the Ca2+/Mg2+ ATPase activity is distinct from the ion specificities, determined in previous work, of the Ca2+ requirement during initiation of fast axonal transport in the soma, and of the Ca2+ requirement during translocation in the axon. Thus, previous observations of Ca2+-dependent events in fast axonal transport cannot be taken per se to suggest the involvement of Ca2+/Mg+ ATPase in the transport process.
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PMID:Ca2+- or Mg2+-stimulated ATPase activity in bullfrog spinal nerve: relation to Ca2+ requirements for fast axonal transport. 616 13

The in vitro system of RNA transport containing isolated nuclei of Djungarian hamster cells transformed by SV-40 virus was studied. A functional test for cytoplasmic contaminations of the nuclei was proposed. The release of the newly synthesized RNA was found to be dependent on the duration of incubation, temperature and pH of the incubation medium as well as on the presence of spermine, spermidine, dithiothreitol, Mg2+, EDTA, exogenous RNA, nucleoside triphosphates and cytosol. The results obtained indicate that RNA release is an active process with activation energy of 12 kcal/mol. ATP, GTP, CTP and UTP have equal ability to serve as energy sources for the release of RNA. The nucleoside triphosphatase activity of the nuclei was the same in the presence of these four nucleoside triphosphates.
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PMID:[RNA transport from isolated nuclei of cultured Djungarian hamster cells]. 617 80

1. A procedure for the isolation of tightly coupled mitochondria from human early placenta is described. 2. Mitochondria obtained by this method were able to oxidize Krebs cycle intermediates, pyruvate, glutamate, glutamine, palmitoyl-carnitine, alpha-glycerophosphate and beta-hydroxybutyrate. 3. These mitochondria incubated in the medium containing ethylene diamine tetraacetic acid and bovine serum albumin and no added Mg2+ ions exhibited a high respiratory control and adenosine diphosphate:oxygen (ADP:O) ratios corresponding to the theoretical values for all substrates tested. Addition of Mg2+ ions markedly reduced the respiratory control index and ADP:O ratio. 4. Adenosine triphosphatase (ATPase) activity in the obtained mitochondrial preparation was stimulated about tenfold by Mg2+. Oligomycin inhibited Mg2+-stimulated ATPase activity by about 25 per cent, but completely inhibited this activity in the absence of Mg2+ ions. 5. It is concluded that the effect of Mg2+ ions on the respiratory control and ADP:O ratio reported in this paper is exerted mainly through the Mg/+-stimulated oligomycin-insensitive ATPase activity.
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PMID:Tightly coupled mitochondria from human early placenta. 621 76

Adenosine triphosphatase (ATPase) activity of flagella isolated from ejaculated bull sperm was solubilized by 5 min exposure to 0.6 M KCl at 4 degrees C. ATPase activity in the flagellar extract was characterized with respect to enzyme, substrate, activator ion, salt, and hydrogen ion concentration. Flagellar extract required the presence of a divalent cation for activity: Mg2+, Ca2+, or Mn2+ could function as activator, but Zn2+ or Cd2+ could not. Magnesium-activated ATPase was maximal in the presence of Mg2+ and ATP in equimolar concentrations and at alkaline pH. Calcium activated ATPase was maximal over a wide range of Ca2+:ATP ratios and at pH 8.0. The presence of increasing concentrations of Na+ and/or K+ ions in the assay medium (0.5-300 mM) had no effect on the ATPase activity of flagellar extract.
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PMID:Studies on the flagellar ATPase of bull spermatozoa: extraction and characterization. 622 99


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