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

[3H]Proline and [3H]uridine were injected into both eyes of the goldfish. 1 h before and after this injection 3X10)-6)M ouabain was administrated unilaterally to the retina. 8 h and 24 h after tracer injection the radioactivity in the retina, optic nerve and tectum was measured. It is suggested that the inhibition of the neuronal Na+-K+-ATPase inside the retina is responsible for the reduction of the labelled material transported into the optic nerve.
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PMID:Evidence for the involvement of the Na+-K+-ATPase in the mechanism of axonal protein and nucleoside transport. 6 59

The ability of five nucleotides in the presence of excess divalent cations to inhibit UDPglucuronosyltransferase in sealed or leaky liver microsomal vesicles was studied. Two nucleotides inhibited potently while three others were weak inhibitors. At low concentration, both of the potent inhibitors, uridine tri- and diphosphates tended to inhibit more in sealed microsomal vesicles than in leaky microsomes, while the weak inhibitors, uridine diphosphate glucose and adenosine triphosphate behaved in the opposite manner and inhibited less in sealed than in leaky microsomes. At physiological concentrations of UDPglucuronic acid (0.4 mM) quite extensive inhibition of oestradiol glucuronidation could be achieved with physiological concentrations of uridine tri- or diphosphates (0.2 or 0.4 mM). In sealed or leaky microsomes, beta, gamma-methylene-interrupted uridine triphosphate, which is resistant to hydrolysis by nucleoside triphosphatase, inhibited much less than did uridine triphosphate.
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PMID:Studies on the inhibition of hepatic microsomal glucuronidation by uridine nucleotides or adenosine triphosphate. 11 13

Showdomycin [2-(beta-D-ribofuranosyl)maleimide] is a nucleoside antibiotic containing a maleimide ring and which is structurally related to uridine. Showdomycin inhibited rat brain (Na+ + K+)-ATPase irreversibly by an apparently bimolecular reaction with a rate constant of about 11.01-mol- minus 1-min- minus 1. Micromolar concentrations of ATP protected against this inhibition but uridine triphosphate or uridine were much less effective. In the presence of K+, 100 MUM ATP was unable to protect against inhibition by showdomycin. These observations show that showdomycin inhibits (Na+ + K+)-ATPase by reacting with a specific chemical group or groups at the nucleotide-binding site on this enzyme. Inhibition by showdomycin appears to be more selective for this site than that due to tetrathionate or N-ethylmaleimide. Since tetrathionate is a specific reactant for sulfhydryl groups it appears likely that the reactive groups are sulfhydryl groups. The data thus show that showdomycin is a relatively selective nucleotide-site-directed inhibitor of (Na+ + K+)-ATPase and inhibiton is likely due to the reaction of showdomycin with sulfhydryl group(s) at the nucleotide-binding site on this enzyme.
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PMID:Showdomycin, a nucleotide-site-directed inhibitor of (Na+ + K+)-ATPase. 12 87

A new procedure for the isolation of membrane vesicles from Acholeplasma laidlawii cells is described. The membrane vesicles are completely free from contaminations of whole cells and cell debris and represent a homogeneous fraction as shown by electron microscopy, Ficoll density-gradient centrifugation, and titration on agar plate. Absence of cytoplasmic contaminations was confirmed by double-labelling of membranes with 3H-oleic acid and 14C-uridine, as well as by distribution of specific marker enzymes of membranes and cytoplasm. On the basis of light-scattering and electron microscopy, the vesicular nature of these membranes was established. The vesicles had the same orientation as intact cells (absence on membrane vesicles of ATPase and NADH dehydrogenase activities, localized in the inner surface of membrane). The respiratory activity of the membrane vesicles was low and was not stimulated by exogenous substrates, the respiratory chain of the vesicles being reduced and terminated by flavoproteins. The ability of membrane vesicles to take up carbohydrates was shown.
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PMID:Transport properties of membrane vesicles from Acholeplasma laidlawii. I. Isolation and general characteristics. 12 39

Adenosine triphosphate (ATP) hydrolysis catalyzed by the plasma membrane (Na+,K+)ATPase isolated from several sources was inhibited by Mg+, provided that K+ and ATP were also present. Phosphorylation of the adenosine triphosphatase (ATPase) by ATP and by inorganic phosphate was also inhibited, as was p-nitrophenyl phosphatase activity. (Ethylenedinitrilo)tetraacetic acid (EDTA) and catecholamines protected from and reversed the inhibition of ATP hydrolysis by Mg2+, K+ and ATP. EDTA was protected by chelation of Mg2+ but catecholamines acted by some other mechanism. The specificities of various nucleotides as inhibitors (in conjunction with Mg2+ and K+) and as substrates for the (Na+, K+) ATPase were strikingly different. ATP, ADP, beta,gamma-CH2-ATP and alpha,beta-CH2-ADP were active as inhibitors, whereas inosine, cytidine, uridine, and guanosine triphosphates (ITP, CTP, UTP, and GTP) and adenosine monophosphate (AMP) were not. On the other hand, ATP and CTP were substrates and beta,gamma-NH-ATP was a competitive inhibitor of ATP hydrolysis, but not an inhibitor in conjunction with Mg2+ and K+. The Ca2+-ATPase from sarcoplasmic reticulum and F1, the Mg2+-ATPase from the inner mitochondrial membrane, were also inhibited by Mg2+. Catecholamines reversed inhibition of the Ca2+-ATPase, but not that of F1.
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PMID:Reversible inhibition of (Na+, K+) ATPase by Mg2+, adenosine triphosphate, and K+. 13 42

1H nuclear magnetic resonance techniques were used to study the binding of uridine 5'-triphosphate to the Ca2+-transport ATPase (EC 3.6.1.3) of sarcoplasmic reticulum vesicles from rabbit skeletal muscle. The nuclear spin relaxation times determined for the bound nucleotide are used to characterize the rotational motion of the ATPase to which the nucleotide is bound. The results, assuming an anisotropic model for the motion of the ATPase in the membrane, place a low upper limit on the rotational correlation time of the ATPase. This indicates that the motion of the ATPase in the membrane is quite rapid when compared, for example, with the motion found for other membrane-bound proteins such as rhodopsin.
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PMID:Rapid anisotropic motion of the Ca2+-transport ATPase of the rabbit skeletal muscle sarcoplasmic reticulum. 14 71

Under the effect of acetylcholine and vagal stimulation on the donor frog myocardium, a uridine polyphosphate-like substance (X-factor) is released. It intensifies contractions of the isolated heart-recipient and decreases the heart's sensitivity to acetylcholine and vagal stimulation. Acetylcholine (1-10(-4)-1-10(-5 g/ml) decreases UTPase activity (by 20-25%) and ATPase activity (by 15%) in isolated ventricle of the frog heart. When acetylcholine is washed away, UTPase activity is almost completely restored. Suppression of UTPase activity by acetylcholine seems to be one of the mechanisms responsible for the accumulation and release and uridine polyphosphates in the heart muscle.
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PMID:[Role of nucleoside triphosphatase in the formation of factor-X in frog myocardium following exposure to acetylcholine]. 14 28

In Saccharomyces cerevisiae the uptake of cytosine, uracil and uridine is mediated by three permeases. Using mutants blocked in the metabolic utilization of these three compounds we were able to study their specific uptake. Cytosine and uridine show simple saturation kinetics, whereas uracil uptake is a biphasic process. A comparison of the effects of several inhibitors of energy metabolism on these uptake systems was made. Striking differences were found. 2,4-Dinitrophenol (10(-3) M) and NaN3 (10(-2) M) inhibit the entry of the three compounds to similar extent, but chlorhexidine (10(-5) M) and Dio 9 (50 microgram/ml) which are ATPase inhibitors in vitro strongly impaired cytosine and uridine entry and remained without effect on uracil uptake. We provisionally conclude that these systems may be energized by different mechanisms. In the case of cytosine and uridine permease, a membrane ATPase is possibly involved in the process of energetic coupling whereas this does not seem to be so for uracil.
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PMID:Properties of three distinct pyrimide transport systems in yeast. Evidence for distinct energy coupling. 15 49

A DNA-dependent ATPase has been purified from calf thymus. The enzyme hydrolyses ATP and dATP in the presence of heat-denatured DNA. It does not hydrolyse the corresponding nucleoside triphosphates of guanine, uridine and cytosine. The Km values for ATP and dATP are both 0.62 mM. The enzyme requires magnesium or manganese ions. Its sedimentation coefficient is about 4.4 S. The catalytic activity is inhibited by N-ethylmaleimide but is not sensitive to novobiocin and nalidixic acid which are potent inhibitors of bacterial DNA gyrase. In some cases, during purification, chromatographically distinct additional DNA-dependent ATPase activities were detected. Limited proteolysis or covalent modification of the enzyme in the tissues, or during the first steps of its extraction, are probably responsible for the appearance of these chromatographically distinct forms.
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PMID:A DNA-dependent ATPase of calf-thymus. 15 29


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