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)

Plasma membrane vesicles were isolated from a subline of L929 mouse fibroblasts grown on defined medium in the absence of serum. These vesicles were not significantly contaminated by mitochondria or endoplasmic reticulum. The isolation procedure, a modification of that originally developed by McKeel and Jarett (McKeel, D.W., and Jarett, L. (1970) J. Cell Biol. 44, 417-432) employs mechanical homogenization in isotonic medium followed by differential centrifugation. The resultant plasma membrane vesicles take up radioactivity when exposed to uniformly labeled nucleosides. Two subfractions of the plasma membrane were isolated, distinguished by their differing activity of 5'-nucleotidase and (Na+,K+)-stimulated ATPase, two well known plasma membrane enzyme markers. Uptake of nucleoside radioactivity was extensively studied in one subfraction; it was linear with time and membrane concentration over ranges used for the studies. Apparent Km values for uptake of radioactivity from adenosine, inosine, and uridine were 7.1 +/- 26 muM, respectively. Uptake of radioactivity from all three nucleosides exhibits a broad pH optimum from pH 7 to pH 9, but falls off rapidly at lower pH. N-Ethylmaleimide was an effective inhibitor of uptake of radioactivity from all three nucleosides; uptake of radioactivity from uridine is more sensitive than uptake of radioactivity from the purine nucleosides. Adenosine inhibited uptake of radioactivity from inosine more than from uridine. Inosine inhibited the uptake of radioactivity from adenosine, but uridine did not. Caffeine and 6-methylaminopurine riboside (6-N-methyladenosine differentially inhibit uptake of radioactivity from adenosine and inosine, and thus the vesicles apparently possess seperate transport systems for uptake of radioactivity from purine nucleosides and from uridine.
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PMID:Transport mechanisms in isolated plasma membranes. Nucleoside processing by membrane vesicles from mouse fibroblast cells grown in defined medium. 0 4

A protein has been studied which spontaneously precipitates from stored fractions of platelet soluble phase prepared by density gradient centrifugation. It is rich in a Ca2+ ATPase activity which displays an activity/pH profile resembling that of skeletal muscle myosin. Adjustment of freshly prepared soluble phase fractions to 0.6 M with respect to KCl and dilution 1 in 3 results in the precipitations of a protein fraction with essentially the same enzymatic properties as the spontaneously precipitable protein. These two similar proteins represent between 9 and 13% of the soluble phase total protein and each account for almost the whole of divalent cation activated ATPase activity of the soluble phases from which they were derived. The Mg2+ ATPase activity is only about twice purified with respect to the soluble phase enzyme activity, but the Ca2+ ATPase shows a 10-13-fold enrichment. Synthetic actomyosins can be prepared from the two proteins by addition of either platelet or skeletal muscle actin. These show significant increases in Mg2+ ATPase at the most favourable combination ratios. The ratio between the yield of soluble phase protein obtained by dilution precipitation and the lactate dehydrogenase activity of the soluble phase remains constant under a wide range of homogenization and sonication conditions applied to the original whole platelet suspensions. This confirms our earlier view that the soluble phase is a valid intracellular compartment for a considerable proportion of the platelet contractile protein and that in the complex the myosin-like component predominates.
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PMID:The identification and subcellular localization of thrombosthenin "M", the myosin-like component of pig platelets. 0 43

The pH optimum was the same in canine tissue for cardiac and skeletal muscle myosin; when myosin was activated by monovalent cations, the pH optimum was 7.5 while activation of myosin by divalent cations gave a pH optimum of 5.5. Protons were needed for divalent cation activation of myosin. With changes in pH there were concomitant changes in the apparent affinity of enzyme for substrate (S 0.5), such that with a decrease in pH there was an elevation in K+- or NH4+ -activated myosin's apparent affinity for adenosine triphosphate (ATP), and at the same time a decrease in Vmax values of myosin. The converse was true with the divalent cations, Ca++ and Mn++; here with a decrease in pH there was a concomitant decrease in apparent affinity of myosin for ATP, and at the same time an increase in the enzymatic Vmax values. It appeared that hydrogen ions affected the apparent affinity of myosin for substrate and this in turn affected the rate-limiting step in ATPase reaction. Addition of monovalent cations to the divalent cation activating system lowered the activity of myosin, and the converse was true: divalent cations lowered the activity of myosin when activated by monovalent ones in a monovalent cation activating system.
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PMID:Effect of variations in pH on kinetics of myosin. 0 60

The human intrafusal fibers were found to consist of two morphological and three histochemical (ATPase reaction) types. Two types of nuclear bag fibers were seen. Type A showed alkali stable and acid labile and Type B showed acid and alkali stable ATPase reaction. The nuclear chain fibers showed only alkali stable ATPase reaction. In the lower motor neuron atrophy, muscle spindle showed thickening of the capsule, atrophy of the nuclear chain fibers, and splitting of the nuclear bag fibers. ATPase reaction showed targetoid Type B nuclear bag fibers and 2 types of nuclear chain fibers. Oxidative enzymes also showed targetoid nuclear bag and chain fibers. In upper motor neuron atrophy the spindle showed no changes.
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PMID:Histochemical and morphological changes in human muscle spindle in upper and lower motor neuron lesions. 0 85

Arrhenius plots of a membrane (Na+ + K+)-dependent ATPase (adenosine triphosphatase) activity showed characteristic discontinuities, whereas those of the associated K+-dependent phosphatase activity did not. These findings support the contention that the phosphatase activity does not depend on phospholipid in the same way as does the ATPase activity.
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PMID:Differential effects of temperature on a membrane adenosine triphosphatase and associated phosphatase. 0 69

The biochemical properties of the electrically excitable sodium channels in the electroplaque of Electrophorus electricus were investigated using tritiated tetrodotoxin (TTX) as a specific membrane probe. Membrane fragments from the electroplaque were isolated essentially by differential centrifugation and characterized with respect to the plasma membrane markers acetylcholine receptors, acetylcholinesterase, (Na+ + K+)ATPase, and [3H]TTX binding. Equilibrium binding studies showed that [3H]TTX bound to a single population of noninteracting receptor sites with an apparent dissociation constant of 6 +/- 1 X 10(-9) M. The toxin-membrane complex dissociated with a first-order rate constant of 0.012 sec-1. Studies on the pH dependence of complex formation demonstrated the requirement for an ionizable, functional group with a pK of 5.3 and this group has been shown to be a carboxyl. Treatment of the membranes with trimethyloxonium tetrafluoroborate, a carboxyl group modifying reagent, resulted in an irreversible loss in the binding of [3H]TTX, which could be prevented by low concentrations of TTX or saxitoxin. This decrease was due to a reduction in the total number of binding sites and not to a decrease in toxin binding affinities. The relative binding affinities of various monovalent alkali metal and polyatomic cations for the TTX-receptor site showed that this site displayed cation discrimination properties which were similar to those reported previously for the electrically excitable sodium channel in intact nerve fibers. A possible role for this site in the ion selectivity of the sodium channel is proposed.
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PMID:Properties of the tetrodotoxin binding component in plasma membranes isolated from Electrophorus electricus. 0 13

The proton circuit devised by Mitchell in the chemiosmotic theory was subjected to analysis using the formalism of irreversible thermodynamics. The phenomenological coefficients and the degree of coupling relating co-permeant flows were derived from anion/H+, substrate/H+, cation/H+ and anion/anion biporter models. Linearity and equality of the cross-coefficients in Onsager relations were always satisfied. Macroscopic flows leading to charges splitting, such as oxido-reduction, hydro-dehydratation and transhydrogenase, are driven by a composite thermodynamic force which includes the proton-motive component. Multiple coupling occurs in the circuit when it is assumed that the net inward flux of protons becomes zero, i.e. when the circulation of protons reaches a stationary state. Under these conditions, oxidative phosphorylation, ATPase- or respiration-linked transhydrogenase and uptake of anion or cation against their electrochemical gradient may be predicted, in agreement with known experimental evidence.
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PMID:A non-equilibrium thermodynamics analysis of active transport within the framework of the chemiosotic theory. 0 23

An electrochemical potential difference for hydrogen ions ( a protonmotive force) was artifically imposed across the membrane of the anaerobic bacterium Streptococcus lactis. When cells were exposed to the ionophore, valinomycin, the electrical gradient was established by a potassium diffusion potential. A chemical gradient of protons was established by manipulating the transmembrane pH gradient. When the protonmotive force attained a value of 215 mV or greater, net ATP synthesis was catalyzed by the membrane-bound Ca++, Mg++ -stimulated ATPase. This was true whether the protonmotive force was dominated by the membrane potential (negative inside) or the pH gradient (alkaline inside). Under these conditions, ATP synthesis could be blocked by the ATPase inhibitor, dicyclohexylcarbodiimide, or by ionophores which rendered the membrane specifically permeable to protons. These observations provide strong evidence in support of the chemiosmotic hypothesis, which states that the membrane-bound ATPase couples the inward movement of protons to the synthesis of ATP.
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PMID:ATP synthesis driven by a protonmotive force in Streptococcus lactis. 0 50

Active buffer transport, e.g. H+ -secretion by stomach and kidney and HCO3--secretion by pancreas and salivary glands, is linked with the presence of a HCO3-stimulated ATP-Phosphohydrolase. In contrast to (Na+ -k+)-ATPase which is considered to be equivalent to the Na+ pump, the HCO3--ATPase requires only one ion for activation and is insensitive to ouabain. The HCO3--ATPase is found in the plasma membrane of the epithelia, but in contrast to the (Na+ -k+)-ATPase it is located in the luminal cell border. The activity of the HCO3--ATPase changes in parallel along with the rate of active buffer transport, a finding which underlines its importance as a transport enzyme. Several disorders of buffer transport are described which are possibly associated with a defect of the HCO3--ATPase system.
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PMID:[The role of HCO3- ATPase in H+ /HCO3-Secretion (author's transl)]. 0 81

1. A soluble protein with a molecular weight of 11-12-10(3) has been isolated from bovine-heart mitochondria, which stimulates the following ATP-dependent reactions of submitochondrial particles treated with 0.6 mM EDTA and 1 M NH4OH: reverse electron transfer from succinate to NAD, transhydrogenation from NADH to NADP, and ATP-Pi exchange. The factor has no effect on the NADH oxidase, succinate oxidase and ATPase activities of the particles. 2. The stimulatory effect of the factor in the ATP-dependent reduction of NAD by succinate is 12 mumol-min-1-mg-1 of the factor protein. However, the NH4OH-EDTA treated particles are saturated for maximal activation of the above reaction by very small amounts of the factor (about 20-40 mug factor per mg particle). 3. Electrophoresis of the factor preparation on polyacrylamide gels showed a single protein band plus a nonprotein material which moved at the dye front and was weakly stained with Coomassie Blue. The protein was shown to be required for activation of the particles; whether the fast-moving, nonprotein material is also required is not known. 4. The factor is inhibited by mercurials and N-ethylmaleimide. The former, but not the latter, inhibition is completely reversed by 1,4-dithiothreitol. 5. The NH4OH-EDTA treated particles are also stimulated by rutamycin up to about 0.1 nmol of rutamycin per mg particle; higher rutamycin concentrations inhibit. Depending on the particle preparation, the factor stimulates up to about 3 nmol per mg particle, but does not inhibit at higher concentrations. In addition, under certain conditions in which appropriate concentrations of rutamycin fail to stimulate the particles, the factor still does.
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PMID:Purification and properties of a low molecular weight protein factor of mitochondrial energy-linked functions. 0 97


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