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)

The teleostean gill is characterized by an exceptionally low permeability to water. Water moves along the osmotic gradient across the gill, being gained in fresh water and lost in sea water. Coupling of water movement to solute movement has not been reported. In fresh water, the gill is the site of independent active uptake of sodium and chloride. Na+ uptake is coupled to H+ or NH4+ excretion, Cl- uptake to HCO3- excretion. Amiloride blocks sodium transport and thiocyanate inhibits the chloride pump. In sea water, sodium and chloride exchanges across the gill are about 100 times faster than in fresh water, up to 100% of the internal sodium or chloride being exchanged per hour. Chloride is actively excreted, while sodium movement may well be passive. The chloride pump is associated with a mechanism for Na/K exchange; both pump and Na/K exchange are blocked by thiocyanate and possibly by ouabain. Three enzymes are involved in the ionic pumps: carbonate dehydratase (EC 4.2.1.1; carbonic anhydrase), sodium/potassium-stimulated adenosine-triphosphatase (EC 3.6.1.3, ATPase) and anion-stimulated ATPase. Specialized cells ('chloride cells') are presumably the site of the active transport.
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PMID:Transport of ions and water across the epithelium of fish gills. 0 38

Adenosine triphosphatase enzymatic activity was investigated in human approximatively normal, dysplastic and neoplastic mammary tissue, by three different methods. Staining intensity varied within wide limits; myoepithelial cells and blood vessels showed similar enzymatic activity. Epithelial cells reacted only faintly, or not at all; carcinoma cells were never labelled. Stromal response was highly variable. The calcium-cobalt method of Padykula and Herman gave more intense reactions than the lead-nitrate procedure of Wachstein and Meisel, either in the original form or according to the modifications recommended by Russo and Wells. With the latter method the sharpness of stain deposits on the different structures was markedly enhanced. The functional significance of ATPase activity is discussed.
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PMID:ATPase activity in the breast: a comparison between three methods. 9 Dec 95

Adenosine triphosphatase activity not dependent on sodium or potassium but inhibited by thiocyanate is present in broken-cell homogenates of eel gill and rat kidney. This enzymatic property is predominantly associated with mitochondria, although thiocyanate-inhibited ATPase can also be detected in microsomes with little or no mitochondrial contamination as measured by the activity of the mitochondrial marker enzyme succinic dehydrogenase. When eels are transferred from fresh to salf water, thus increasing active outward transport of chloride across the gill, the thiocyanate-inhibited ATPase of gill microsomes does not change, though the activities of succinic dehydrogenase and Na-K-ATPase in gill homogenates are augmented. The thiocyanate-inhibited ATPase of homogenates of outer renal medulla does not differ from that of renal cortex, in contrast to Na-k-atpase which is higher in renal medulla than in cortex. The data do not support a role for thiocyanate-inhibited ATPase in active chloride transport by epithelial tissues.
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PMID:Thiocyanate inhibition of ATPase and its relationship to anion transport. 12 12

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

The nucleoside triphosphatase [EC 3.6.1.15] activity of actomysin and that of myosin are measured by varying the concentration of nucleoside triphosphate and that of CaCl2 or MgGl2. The results thus obtained are examined by asking a question of which is responsbile for the activity, the true substrate and the active enzyme in terms of the reaction scheme shown in p. 719. The answers found for the above question are summarized in Table I (see p. 720). It is emphasized that the summmary (Table I) corresponds very well to the fact that myosin alone does not superprecipitate in the presence of either calcium or magnesium ions, whereas actomyosin does superprecipitate in the presence of magnesium ions and not in the presence of calcium ions. Obviously, the true substrate type of reaction scheme represents a kinetic property characteristic of the superprecipitation-coupled nucleoside-triphosphatase. It is also noted of the summary (Table I) that actin is capable of not only activating Mg-nucleoside-triphosphatase but also switiching the reaction scheme from the active enzyme type to the true substrate type. It is known that trinitrophenylation of myosin results in activation of the Mg-ATPase activity of myosin. However, it is now found that trinitrophenylation is not capable of switiching the reaction scheme, that is to say that the Mg-ATPase reaction of trinitrophenyl-myosin stays with the active enzyme type of reaction scheme and that of acto-trinitrophenyl-myosin with the true substrate type of reaction scheme. Effect of actin on the function of myosin seems, therefore, very unique.
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PMID:A new kinetic property characteristic of the actomyosin-nucleoside-triphosphatase. 17 88

When photosynthetic membranes from Rhodospirillum rubrum, devoid of loosely bound small molecules and proteins, were passed through a French-pressure cell, the enzyme adenosine-5'-triphosphatase (EC 3.6.1.3.) (ATPase) was released into the soluble fraction. The solubilized ATPase was purified to homogeneity. In many respects it behaved like the enzyme purified by other workers, but it also hydrolyzed Mg-ATP with a small, but significant rate. Furthermore, it was much more stable. Maximal restoration of photophosphorylation in ATPase-depleted membranes was achieved by addition of about 1 mg purified ATPase per mg bacteriochlorophyll. For reconstitution of NAD+-photoreduction, about half of this amount was saturating.
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PMID:Coupling factor adenosine-5'-triphosphatase from Rhodospirillum rubrum: a simple and rapid procedure for its purification. 18 8

Membrane phosphorylation and nucleoside triphosphatase activity of sarcoplasmic reticulum vesicles isolated from rabbit skeletal muscle were studied using ATP and ITP as substrates. The Ca2+ concentration was varied over a range large enough to saturate either the high affinity Ca2+-binding site or both high and low affinity binding sites. In intact vesicles, which are able to accumulate Ca2+, the steady state level of enzyme phosphorylated by either ATP or ITP is already high in 0.02 mM Ca2+ and does not vary as the Ca2+ concentration is increased to 10 mM. Essentially the same pattern of membrane phosphorylation by ATP is observed when leaky vesicles, which are unable to accumulate Ca2+, are used. However, for leaky vesicles, when ITP is used as substrate, the phosphoenzyme level increases 3- to 4-fold when the Ca2+ concentration is raised from 0.02 to 20 mM. When Mg2+ is omitted from the assay medum, the degree of membrane phosphorylation by ATP varies with Ca2+ in the same way as when ITP is used in the presence of Mg2+. Membrane phosphorylation of leaky vesicles by either ATP or ITP is observed in the absence of added Mg2+. When these vesicles are incubated in media containing ITP and 0.1 mM Ca2+, addition of Mg2+ up to 10 mM simultaneously decreases the steady state level of phosphoenzyme and increases the rate of ITP hydrolysis. When ATP is used, the addition of 10 mM Mg2+ increases both the steady state level of phosphoenzyme and the rate of ATP hydrolysis. When the Ca2+ concentration is raised to 10 or 20 mM, the degree of membrane phosphorylation by either ATP or ITP is maximal even in the absence of added Mg2+ and does not vary with the addition of 10 mM Mg2+. In these conditions the ATPase and ITPase activities are activated by Mg2+, although not to the level observed in 0.1 mM Ca2+. An excess of Mg2+ inhibits both the rate of hydrolysis and membrane phosphorylation by either ATP or ITP.
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PMID:Calcium and magnesium regulation of phosphorylation by ATP and ITP in sarcoplasmic reticulum vesicles. 18 11

Mitochondria were isolated from Euglena gracilis strain Z by pressure-breakage of the cells and sucrose-cushion centrifugation. Multiple peaks (2-4) were observed in the rate of phosphorylation with Mg-ADP-phosphate concentration curves. The phosphorylative and oxidative activities were highest with NADH as the substrate, moderate with succinate, and lowest with glutamate. Inhibition of phosphorylation with 2,4-dinitrophenol and carbonyl cyanide, m-chlorophenylhydrazone gave sigmoidal concentration curves, with the extent of inhibition by DNP depending on the substrate used. Inhibition of phosphorylation by valinomycin, atractyloside, or carboxyatractyloside was only approximately 60%. Oligomycin inhibited phosphorylation in 2 phases at low and high concentrations; it inhibited Mg-ATPase in a sigmoidal fashion. Both phosphorylation and oxidation had discontinuities in Arrhenius plots at 34 C and 18 C. The relative Mg2+-dependent nucleoside triphosphatase activity was: 1 for ATP and GTP, 0.6 for ITP, 0.15 for CTP and UTP; with Ca2+ in place pf Mg2+ this activity was 0.35. Both DNP and CCCP stimulated the Mg-ATPase 50-200%. The optimal pH for the stimulation was approximately 7 regardless of the uncoupler used, and approximately 8 without the uncouplers. The few differences observed between mitochodria from Euglena and those from other sources are probably due to the fragmentation of the reticular mitochondrial structure during isolation and not to unique characteristics of these mitochondria.
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PMID:Some biochemical properties of mitochondria isolated from Euglena gracilis. 19 37

The acitvities of sodium-potassium-activated adenosine triphosphatase (Na+,K+-activated ATPase) and ouabain-inhibited, sodium-potassium-activated adensoine triphosphatase (Na+,K+-ATPase) in subcellular fractions of guinea-pig and rat vasa deferentia were compared to determine whether the ineffectiveness of ouabain and reduced extracellular potassium in the rat vas deferens observed in the preceding paper occurs because of a relatively low level of Na+,K+-ATPase and/or an insensitivity to ouabain. The results indicate that the specific and total activities of Na+,K+-activated ATPase and Na+,K+-ATPase (i.e., the transport enzyme) in the individual subcellular fractions and in the tissue were higher in the vas deferens of the rat than in the guinea pig. The percentage of inhibition of Na+,K+-activated activity by ouabain (8 x 10(-5) M) varied in the subcellular fractions; it was higher in the guinea-pig (range 31--87%) than in the rat (nonsignificant effect to 40%). A greater percentage of total Na+K+- activated ATPase activity was inhibited in the vas deferens of the guinea pig (56%) than the rat (30%). Differences in the effects of lowered extracellular potassium concentration or ouabain on resting membrane potential (preceding paper) are apparently unrelated to the amount of transport enzyme in the vasa deferentia or the two species, or to its relative sensitivity to ouabain.
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PMID:Species differences in sodium-potassium adenosine triphosphatase activity in the smooth muscle of the guinea-pig and rat vas deferens. 21 53

Histamine stimulation of gastric acid secretion has for a long time been known to be mediated by an H2-type receptor located on the parietal cell surface, but the biochemical nature of this receptor has only very recently been elucidated. It is a 70-kDa glycoprotein showing structural analogies with the beta 2-adrenergic receptor and the other seven membrane-spanning domains/G protein-coupled receptors. It activates adenylated cyclase through a cholera toxin-sensitive, pertussis toxin-insensitive, guanosine 5'-triphosphatase-binding regulatory Gs protein. The cAMP thereby produced is believed to play a crucial role in the opening of the Cl- channel associated with the (H+,K+)-ATPase in the secretory membrane. However, other sites of action are likely to be involved, since several histamine- or cAMP-dependent phosphoproteins have been detected in the parietal cell. In addition to its action on cAMP production, histamine was found to produce a transient increase in the intracellular Ca2+ concentration, but this effect remains unexplained. On the other hand, the intervention of an H3-type histamine receptor in the regulation of gastric acid secretion has recently been documented, but the cellular location of this new receptor has not been yet investigated.
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PMID:Receptors regulating acid secretion. 164 88


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