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Query: UNIPROT:P20020 (adenosine triphosphatase)
 3,299 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The membrane-bound adenosine triphosphatase (ATPase) activity of Acholeplasma laidlawii B differs in many respects from the common (Mg2+, Ca2+)-ATPase activity of higher bacteria, most notably in that it is specifically activated by Mg2+ and strongly and specifically stimulated by Na+ (or Li+). Various inhibitors diminish the ATPase activity with a concentration dependence which suggests that a single enzyme species is responsible for all of the observed ATP hydrolytic activity (both basal and Na+ stimulated). The Km for ATP is influenced by temperature but not by membrane lipid fatty acid composition. Vmax is influenced by both of these factors, showing a break in Arrhenius plots which falls below the lipid phase transition midpoint but well above the lower boundary when a phase transition occurs within the temperature range studied. The apparent energy of activation for Vmax is strongly influenced by lipid fatty acid composition both above and below the break. When whole cells of A. laidlawii B are incubated in KCl or NaCl buffers, they rapidly swell and lyse if deprived of an energy source or treated with ATPase inhibitors at concentrations which significantly inhibit enzyme activity in isolated membranes, whereas in sucrose or MgSO4 buffers of equal osmolarity, the cells are stable under these conditions. These results suggest that the membrane ATPase of A. laidlawii B is intimately associated with the membrane lipids and that it functions as a monovalent cation pump which regulates intracellular osmolarity as the (Na+, K+)-ATPase does in eucaryotes.
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PMID:Physiological role and membrane lipid modulation of the membrane-bound (Mg2+, na+)-adenosine triphosphatase activity in Acholeplasma laidlawii. 3 51

Cardiac myosin obtained from atria had a higher Ca2+-activated ATPase activity than did cardiac myosin from ventricles in various species of animals and in humans. The increased specific activity of Ca2+-activated adenosine triphosphatase (ATPase) of atrial myosin appeared to correlate with the level of the activity of ventricular myosin ATPase in the animal, since the same order in ATPase activity, as observed in ventricular myosins from various animals, was noted in atrial myosins. The enzymatic properties of atrial myosin also were characterized by no activation by N-ethylmaleimide, low activating energy, and a lower rate of inactivation at alkaline pH compared with the same properties of ventricular myosin. These findings suggest a difference in the myosin molecule at or near the active site, involving some sulfhydryl groups, between the two types of cardiac myosin. The Mg2+-activated ATPase activity, both in the presence and absence of actin (which is thought to be closely related to the basic contraction mechanism), also was enhanced in atrial myosin. Thus, the ATPase activities of atrial and ventricular myosins were different with special reference to the reaction pathway involving calcium and magnesium ions and appear to account for the difference in the velocity of contraction between the atria and the ventricles.
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PMID:Cardiac atrial myosin adenosine triphosphatase of animals and humans: distinctive enzymatic properties compared with cardiac ventricular myosin. 3 14

Growth of Clostridium perfringens was inhibited by compounds which dissipate or prevent the formation of electrochemical proton gradients. Membrane vesicles prepared from this organism exhibited Mg2+-dependent adenosine triphosphatase (ATPase) activity sensitive to N,N'-dicyclohexylcarbodiimide. Mg2+-ATPase activity was optimal of 50 degrees C, but no discrete pH optimum was observed. Adenosine triphosphate-dependent quenching of the fluorescence of the weak base quinacrine by everted membrane vesicles suggested that the Mg2+-ATPase is a proton pump capable of generating an electrochemical proton gradient. Adenosine triphosphate-dependent transport of Ca2+ by everted vesicles was sensitive to uncouplers and inhibitors of the Mg2+-ATPase.
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PMID:Properties and function of the proton-translocating adenosine triphosphatase of Clostridium perfringens. 4 Sep 63

A crude plasma membrane fraction from the homogenate of purified rat mast cells demonstrates a high degree of Ca2+-dependent and Mg2+-dependent adenosine triphosphatase (ATPase) activity. The microsomal and mitochondrial fractions show negligible amounts of the Ca2+ and Mg2+-activated ATPases. The broad ATPase inhibitor, ethacrynic acid, effectively blocks the mast cell ATPase activity while ouabain demonstrates little inhibitory effect. Correspondingly, ethacrynic acid inhibits histamine release from antigen-challenged mast cells while ouabain does not. Both ATPase inhibition and histamine release inhibition by ethacrynic acid require the presence of the olefinic bond in the ethacrynic acid molecule.
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PMID:Ethacrynic acid inhibitable Ca2+ and Mg2+-activated membrane adenosine triphosphatase in rat mast cells. 7 76

Sodium glycocholate was shown to remove a Ca2+-activated adenosine triphosphatase from the external surface of the rat mast cell without causing lysis. Sensitized mast cells pretreated with sodium glycocholate showed a decrease in histamine-releasing capacity when triggered with antigen, Synacthen and ATP. Release induced by calcium ionophore A23187 was unaffected.
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PMID:Effect of removal of calcium-activated adenosine triphosphatase from rat mast cells by treatment with sodium glycocholate. 7 27

Embryonal rhabdomyosarcomas from the nasopharynx of two children were examined by histochemical methods commonly applied to muscle biopsies. These stains included nicotinamide adenine dinucleotide-tetrazolium reductase (NADH-TR), succinate dehydrogenase (SDH), PAS, PAS-diastase, myophosphorylase, calcium-mediated adenosine triphosphatase (ATPase) preincubated at high and low pH, and oil red O. Myofibrils were easily identified with ATPase and blood vessel walls were also stained. NADH-TR clearly showed longitudinal and cross-striations that were not seen with H&E or PTAH stains. The modified Gomori trichrome stain additionally contributed to the recognition of myofibrils. Some techniques of muscle histochemistry applied to fresh frozen sections of tumor tissue may provide evidence of muscular differentiation in otherwise poorly differentiated sarcomas for a more accurate diagnosis of rhabdomyosarcoma.
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PMID:Diagnostic value of histochemistry in embryonal rhabdomyosarcoma. 9 52

Ca2+ accumulation and endogenous respiration of sporulating Bacillus megaterium are inhibited to the same extent by electron-transport of inhibitors and the uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone, suggesting that Ca2+ is accumulated by an active transport process. Forespores isolated in stage V of sporulation demonstrated Ca2+-specific carrier-mediated Ca2+ uptake, consistent with downhill transfer [Hogarth & Ellar (1978) Biochem. J. 176, 197-203]. In the present studies forespore Ca2+ uptake was unaffected by carbonyl cyanide p-trifluoromethoxyphenylhydrazone and by concentrations of respiratory inhibitor that inhibited forespore endogenous respiration by 85%. These data suggest that Ca2+ enters the isolated forespore by facilitated diffusion. Ca2+ uptake into sporulating protoplasts was completely inhibited by concentrations of respiratory inhibitors that had no effect on either Ca2+ uptake or respiration of stage-V forespores, but which resulted in inhibition of mother-cell membrane NADH oxidase. These results indicate that the mother-cell membrane is a site for active transport of Ca2+ into the sporulating cell. The effects of the adenosine triphosphatase inhibitor dicyclohexylcarbodi-imide on mother-cell membrane adenosine triphosphatase, NADH oxidase and protoplast Ca2+ uptake were examined.
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PMID:Energy-dependence of calcium accumulation during sporulation of Bacillus megaterium KM. 11 Mar 19

A myosin was isolated from the clonal rat glial cell strain C-6 and compared with rat skeletal muscle myosin. After cell extracts were subjected to gel filtration chromatography in the presence of KI and magnesium pyrophosphate the C-6 myosin was rapidly purified by a procedure similar to that used for skeletal muscle myosin. The C-6 myosin resembles muscle myosin both physically and enzymatically. It contains heavy chains of 200,000 daltons and two classes of light chains of 17,000 and 19,000 daltons in approximately equal molar ratios. This myosin forms bipolar thick filaments in 0.1 M KCl and binds reversibly to skeletal muscle F-actin, the binding being inhibited by MgATP. Skeletal muscle F-actin stimulates the C-6 myosin adenosine triphosphatase 2- to 3-fold in the presence of KCl and Mg2+. The action activation of muscle myosin ATPase at low ionic strength is 10-fold greater than that of C-6 myosin. Ca2+ and EDTA stimulated the ATPase activities of both enzymes. When assayed in the presence of 0.6 M KCl and 1 mM EDTA the skeletal muscle myocin ATPase demonstrates substrate saturation while the C-6 myosin enzyme activity is stimulated by ATP concentrations above 2.5 mM.
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PMID:Purification and characterization of myosin from the clonal rat glial cell strain C-6. 12 31

A Mg2+- and Ca2+-stimulated adenosine triphosphatase (ATPase) at the outer surface of intact Ehrlich ascites tumor cells is described. A surface-bound adenosine triphosphate (ATP)-splitting activity at a lower rate was also demonstrated in the absence of Ca2+ but with Mg2+, Na+, and K+ present in the isotonic medium. Hence, when part of the Mg2+ was exchanged for Ca2+, a marked increase of the ATP-splitting activity was observed. The stimulatory effect of Ca2+ was seen only if both Na+ and K+ were present in the isotonic incubation medium. Thus, the enzyme activity was Mg2+- and Ca2+-dependent. Ca2+, together with the monovalent cations was inhibitory compared with Mg2+ under similar conditions. The apparent Km for ATP for the Mg2+-stimulated ATPase is 0.05 mM, while that of the Mg2+- and Ca2+-stimulated enzyme is 0.10 mM. The Vmax of the former is 0.8 mu-mole per 100 mg Schneider protein per 30 sec compared with 1.92 mu-moles per 100 mg Schneider protein per 30 sec for the latter. The calculated Km for the Mg2+- and Ca2+-stimulated ATPase after subtraction of the Mg2+-stimulated part is 0.22 mM. Ethacrynic acid and N-ethylmaleimide both inhibited the Mg2+- and Ca2+-stimulated ATPase by about 10 percent, while the ouabain inhibition was 15 percent. Cytochalasin B did not influence the enzyme activity, whereas La3+ had a slight stimulatory effect.
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PMID:A Mg2+- and Ca2+-stimulated adenosine triphosphatase at the outer surface of Ehrlich ascites tumor cells. 12 5

The specificity of the histochemical localization of the calcium activated adenosine triphosphatase (ATPase) activity of the sarcoplasmic reticulum (SR) at pH 7.4 was studied using a calcium-citro-phosphate technique. The latter involves the splitting of ATP by ATPase producing phosphate ions which then react with calcium and citrate to form an insoluble reaction product. This reaction product was detected by both light and electron microscopy. Light microscopic examination showed a darkly stained continuous reticular pattern of reaction product which surrounded individual myofibrils. This reticular pattern of reaction product was distinctly dissimilar to that found when the histochemical reactions for mitochondrial or myofibrillar ATPase were performed. Ultrastructural investigations demonstrated the presence of discrete foci of electron dense reaction product in close association with the membranes of the SR in striated muscle fibres. Only occasional flecks were seen in the vicinity of mitochondria or myofilaments. The possibility is considered that the reticular pattern of staining achieved by the calcium-citro-phosphate technique may reflect the distribution of the "extra ATPase" of the SR, an enzyme implicated in the process of calcium uptake and muscle relaxation.
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PMID:On the specificity of the histochemical technique for sarcoplasmic reticular adenosine triphosphatase: a light and electron microscopic study. 12 15


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