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)

1. While much is now known about the Na-K-ATPase and the posttetanic hyperpolarization of nervous tissue, they have yet to be studied together in the same preparation. 2. The post-tetanic hyperpolarization was studied in desheathed garfish olfactory nerve. The rate constant of decay of the post-tetanic hyperpolarization was determined by monitoring difference potentials after stimulation at 1/sec for 2-3 min. 3. In membrane fractions prepared from these nerves, the ouabain-sensitive ATPase activity (Na-K-ATPase) was determined by spectrophotometric measurements. 4. Both the post-tetanic hyperpolarization and the Na-K-ATPase showed a similar sigmoidal dependence on K+ concentration. The sequence of cation specificities measured at the K-site of the enzyme was the same as that determined by post-tetanic hyperpolarization measurements in whole nerve. 5. The rate constants of the enzyme showed a dependence on Na+ concentration that paralleled the way in which the post-tetanic hyperpolarization rate constants varied as a function of the number of impulses. When Na+ was completely replaced by Li+, neither enzyme activity nor post-tetanic hyperpolarization could be measured. 6. The pH optimum for enzyme activity was between pH 7-0 and 7-8, while the optimal pH for post-tetanic hyperpolarization was above pH 8-0. 7. Metabolite levels in preparations of this nerve studied in vitro correspond to levels found in vivo. 8. High energy phosphate levels were measured fluorometrically in extracts of nerve samples that had been stimulated in air at 1/sec for various intervals. 9. During the first 2 min of stimulation, there was a significant accumulation of inorganic phosphate, and the ATP/ADP.Pi ratio dropped appreciably. 10. The accumulation of ATPase products was commensurate with the approach of post-tetanic hyperpolarization rate constants to their maximum level. This provides direct evidence for an ATPase functioning in active Na+ transport in nerve. 11. The garfish Na-K-ATPase is sensitive to the ATP/ADP ratio of the incubating medium, but is relatively insensitive to orthophosphate, Pi. The fall in post-tetanic hyperpolarization rate constants observed with continued nerve stimulation may have been partially due to the falling ATP/ADP ratio measured in nerve under similar conditions.
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PMID:Post-tetanic hyperpolarization, sodium-potassium-activated adenosine triphosphatase and high energy phosphate levels in garfish olfactory nerve. 13 26

ATPase (ATP phosphohydrolase, EC 3.6.1.3) was detected in the membrane fraction of the strict anaerobic bacterium, Clostridium pasteurianum. About 70% of the total activity was found in the particulate fraction. The enzyme was Mg2+ dependent; Co2+ and Mn2+ but not Ca2+ could replace Mg2+ to some extent; the activation by Mg2+ was slightly antagonized by Ca2+. Even in the presence of Mg2+, Na+ or K+ had no stimulatory effect. The ATPase reaction was effectively inhibited by one of its products, ADP, and only slightly by the other product, inorganic phosphate. Of the nucleoside triphosphates tested ATP was hydrolyzed with highest affinity ([S]0.5 v = 1.3 mM) and maximal activity (120 U/g). The ATPase activity could be nearly completely solubilized by treatment of the membranes with 2 M LiCl in the absence of Mg2+. Solubilization, however, led to instability of the enzyme. The clostridial solubilized and membrane-bound ATPase showed different properties similar to the "allotopic" properties of mitochondrial and other bacterial ATPases. The membrane-bound ATPase in contrast to the soluble ATPase was sensitive to the ATPase inhibitor dicyclohexylcarbodiimide (DCCD). DCCD, at 10(-4) M, led to 80% inhibition of the membrane-bound enzyme; oligomycin ouabain, or NaN3 had no effect. The membrane-bound ATPase could not be stimulated by trypsin pretreatment. Since none of the mono- or divalent cations had any truly stimulatory effect, and since a pH gradient (interior alkaline), which was sensitive to the ATPase inhibitor DCCD, was maintained during growth of C. pasteurianum, it was concluded that the function of the clostridial ATPase was the same as that of the rather similar mitochondrial enzyme, namely H+ translocation. A H+-translocating, ATP-consuming ATPase appears to be intrinsic equipment of all prolaryotic cells and as such to be phylogenetically very old; in the course of evolution the enzyme might have been developed to a H+-(re)translocating, ATP-forming ATPase as probably realized in aerobic bacteria, mitochondria and chloroplasts.
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PMID:Properties and function of clostridial membrane ATPase. 13 64

Cardiac and skeletal muscle myosins have been treated by N-ethylmaleimide in presence or absence of Mg-ADP. The variations of Ca2+ and K+-ATPase activities and the incorporation of N-[14C]ethylmaleimide into the whole myosin molecule and into its separated subunits (heavy and light chains) have been measured with N-ethylmaleimide treatment for different lengths of time. The results reported here show the following: 1. The Ca2+-ATPase activity of cardiac myosin is activated by N-ethylmaleimide treatment to a lesser extent than that of skeletal myosin. 2. The K+-ATPase activity of both myosins is inhibited in the same quantitative way. 3. The cardiac light chain L1 contains one highly reactive thiol group which is absent from the skeletal light chains. 4. The labelling of three SH-groups localized in the heavy subunits of both myosins induced the same degree of inactivation. 5. The difference observed between the degree of inhibition of the Ca2+-ATPase activity for the two types of myosin with longer treatments appears to be due to differences in the reactivity of the fourth--SH group labelled on the heavy chains.
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PMID:A comparative study of reactive--SH groups of cardiac and skeletal muscle myosins. 13 24

Stomach wall Mg2+-Na+-K+-dependent ATPase, ATP, and ADP were studied in rats, at 4, 7, 17, and 24 hr after pylorus ligation, in order to relate H+ secretion and ulcer development. It was observed, in both parts of forestomach and corpus + antrum, that the stomach wall Mg2+-Na+-K+-dependent ATPase significantly increased at 4 and 7 hr, while it significantly decreased at 24 hr, after pylorus ligation. Contrary to this, stomach-wall ATP decreased at 4 hr, relatively increased at 7 hr, thereafter significantly decreased in forestomach and corpus + antrum. Ouabain inhibited the H+ secretion, ulcer development, and stomach wall Mg2+-Na+-K+-dependent ATPase activity. The possible causal interrelationships between the examined parameters are studied.
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PMID:Examination of stomach wall Mg2+-Na+-K+-dependent ATPase, ATP, and ADP in pylorus-ligated rats. 13 8

The properties of a Ca2+ activated adenosine triphosphatase shown to be present in homogenates of purified rat peritoneal mast cells were investigated. The enzyme was activated by Ca2+, Mg2+, and to a lesser extent by Mn2+ and Co2+. Ca2+ alone was necessary for full activity and the further addition of Mg2+ did not have any effect. The chelating agents EGTA (ethanedioxybis(ethylamine)tetra-acetate) and EDTA completely inhibited the reaction. The pH optimum was 7.8. Reduced glutathione, cysteine, dithiothreitol, N-ethylmaleimide, urea, ADP, NaF, increasing ionic strength and Triton X-100 all inhibited the reaction. On subcellular fractionation of mast-cell homogenates by density-gradient centrifugation, the distribution of Ca2+ activated adenosine triphosphatase resembled that of 5'-nucleotidase, but differed from that of the other markers used, suggesting localization in the plasma membrane. Further experiments indicated that the enzyme is present on the external surface of the plasma membrane.
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PMID:Characterization of calcium-ion-activated adenosine triphosphatase in the plasma membrane of rat mast cells. 13 82

Comparison between the effects on various rat liver mitochondrial functions of ethacrynate, a thiol reagent inhibitor of oxidative phosphorylations [3, 4] and those of dihydroethacrynate its saturated derivative which is not a thiol reagent, has been performed. Both, ethacrynate and dihydroethacrynate increase oxygen consumption by mitochondria in state 4 (succinate as substrate) in a concentration dependent way (from 1 to 5 X 10(-4) M EA or DHEA). This activation is followed, only with ethacrynate, by an inhibition appearing sooner with higher concentrations. After preincubation or mitochondria with ethacrynate (1 to 5 X 10(-4) M), the stimulation of respiration by (ADP + Pi) is completely inhibited whereas it is only weakly affected by dihydroethacrynate at the same concentrations. Ethacrynate and dihydroethacrynate provoke variations of intramitochondrial Mg2+ and K+ levels which need energy from the respiratory chain. These are affected by Pi or (Pi + ADP) in a different way with ethacrynate and with dihydroethacrynate. After preincubation with mitochondria, ethacrynate and to a smaller extent dihydroethacrynate, inhibit partially ADP translocation; ADP increases the inhibitory effect of EA on translocation and not that of dihydroethacrynate. Ethacrynate increases the oligomycin sensitive ATPase activity and dihydroethacrynate still more. After a ten minutes preincubation with mitochondria, ethacrynate and dihydroethacrynate hardly affect the 2.4 DNP stimulated ATPase activity. Preincubation with succinate or ADP strongly increases the ethacrynate inhibition whereas it decreases dihydroethacrynate inhibition. Ethacrynate and dihydroethacrynate do not affect the efflux of Pi produced by ATP hydrolysis but ethacrynate enforces the inhibitory effect of mersalyl (Mg2+ containing medium). After ten minutes of preincubation with mitochondria, ethacrynate binds 25 nmoles of -SH/mg protein (DTNB titration) and dihydroethacrynate has no effect. These results show an effect of ethacrynate on two types of thiols linked with energy conservation mechanisms and ADP translocation. These thiols could be unmasked or made accessible by conformational modifications of the inner membrane upon energization or addition of ADP.
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PMID:Thiols related to mitochondrial ATPase and transports: unmasking upon conformational changes supported by the comparative effects of ethacrynate and dihydroethacrynate. 13 33

The cytochemical localization and intensity of adenosine triphosphatase (ATPase) activity in the spermatozoa from fertile and infertile human ejaculate were observed by an electron microscope. Sperm from fertile and infertile human ejaculate were fixed in 1% glutaraldehyde and treated histochemically to demonstrate calcium- and magnesium-dependent ATPase (Ca++- and Mg++-dependent). Furthermore, as substrates, ADP, AMP, and beta-glycerophosphate were used. The localization of Ca++-activated ATPase was not different from that of Mg++-activated ATPase. In the fertile human ejaculated sperm, ATPase activity was found on the surface of the acrosome and mitochondria consisting of the mitochondrial sheath, around the outer coarse fibers and in the axial filament complex. Compared with the result with fertile specimens, in the infertile human ejaculated sperm, ATPase activity on the motile structures, the outer coarse fibers, and the axial filament complex were considerably weaker and occasionally not recognized. From this study, it may be considered that ATPase around the outer coarse fibers and in the axial filament complex of sperm may serve to mediate contraction of the axonemal elements during motility. (Author's Modified)
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PMID:[The cytochemical localization of ATPase activity in the spermatozoa from fertile and infertile human ejaculate by electron microscope (author's transl)]. 13 69

Na+-dependent ADP/ATP exchange activity, of a (Na++K+)-dependent ATPase preparation from eel electric organ, was measured in terms of the incorporation of 14C into ATP during incubations with labeled ATP and [14C]ADP. Estimates of initial rates of exchange were possible by keeping changes in nucleotide concentrations, from both exchange and extraneous hydrolytic processes, to less than 10%. Under these conditions, increases in MgC12 concentration, from 0.2 to 3 mM, generally inhibited this exchange activity. The concentrations of free Mg2+, Mg-ATP, and Mg-adp present, with a range of MgC12, ATP, and ADP concentrations, were calculated from measured dissociation constants. Inhibition was associated with Mg-ATP as well as with Mg2+, at concentrations from 0.4 to 1 mM (Mg-ADP, in the same concentration range, probably inhibited also). The affinity of the enzyme for these inhibitors is in fair correspondence with demonstrated affinties for Mg2+, Mg-atp, and Mg-ADP at low affinity substrate sites, measured kinetically. These observations are considered in terms of a dimeric enzyme with high and low affinity substrates sites: ADP/ATP exchange being catalyzed at the high affinity sites, with inhibition occurring through occupancy by Mg2+, Mg-ATP, or Mg-ADP, of the low affinity sites, thereby pulling the reaction process away from those steps involved in exchange.
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PMID:The (Na + K+)-dependent ATPase. Mode of inhibition of ADP/ATP exchange activity by MgC12. 13 46

1. The effect was studied of local anesthetics (tetracaine, dibucaine, procaine and xylocaine) on the forward and the backward reactions of the calcium pump of skeletal muscle sarcoplasmic reticulum. 2. The inhibition of the rate of calcium uptake, the rate of calcium-dependent ATP splitting and the rate of calcium-dependent ATP-ADP phosphate exchange by sarcoplasmic reticulum in the presence of the above drugs is at least partially due to the inhibition of the phosphoprotein formation from ATP. 3. The rate of the ADP-induced calcium release from sarcoplasmic reticulum and the rate of ATP synthesis driven by the calcium efflux are inhibited on account of a reduction of the phosphoprotein formation by orthophosphate. 4. The phosphorylation of calcium transport ATPase by either ATP or orthophosphate is diminished by the local anesthetics owing to a reduction in the apparent calcium affinity of sarcoplasmic reticulum emmbranes on the outside and on the inside, respectively. 5. The drug-induced calcium efflux from calcium-preloaded sarcoplasmic reticulum vesicles, a reaction not requiring ADP, is probably not mediated by calcium transport ATPase.
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PMID:Aspects of the mechanism of action of local anesthetics on the sarcoplasmic reticulum of skeletal muscle. 13 47

1. Evidence is presented that the ATPase activity detected in cell extracts of Chlorobium thiosulfatophilum is bound to the cytoplasmic membrane rather than to the chlorobium vesicles. 2. The activity of this ATPase is inhibited in vitro by various carbodiimides, phloridzin and sodium azide. 3. The apparent Km for ATP is approximately 0.2 mM and the enzyme shows product inhibition by ADP. 4. Photophosphorylation, characterized in vivo, is inhibited by many of the compounds that inhibit the ATPase.
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PMID:Localization and possible role of an adenosine triphosphatase in Chlorobium thiosulfatophilum. 13 90


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