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)

The flexibility of the tertiary structure around the active site of myosin ATPase [EC 3.6.1.3] was studied using the reactivity of two specific thiol groups, S1 and S2, as a structural probe. The following four maleimide derivatives were used as thiol-directed reagents: N-ethylmaleimide (NEM), N-(4-methoxy-2-benzimidazolyl methyl) maleimide (MBM), N-(p-(2-benzimidazolyl)phenyl)maleimide (BIPM) and N-(4-dimethyl-amino-3,5-dinitrophenyl)maleimide (DDPM). 1. All the maleimide derivatives used activated the Ca2+-ATPase activity and inhibited the EDTA-ATPase activity, like NEM, indicating that they modified S1. The rate of modification of S1 by NEM and BIPM increased with increasing pH, while that by DDPM decreased. BIPM simultaneously modified S1 and S2. 2. S1 showed much higher reactivity toward the maleimides, except for BIPM, than did N-acetylcysteine (N-Ac-Cys) a low molecular-weight model compound. The extremely small pKa value of S1, 6.28, accounted for this high reactivity. In addition, the ATP-induced increase in its reactivity inducated that S1 was in a buried state. Kinetic analysis showed that the teritiary structure around S1 at alkaline pH differed from that at acidic pH. 3. The apparent rate constant of S2-modification with NEM was approximately one seven-hundredth and one four-hundredth of those of S1 and N-Ac-Cys, respectively. Fluorimetric studies using BIPM revealed that S2 in the buried state was exposed upon adding ATP; this was compensated by the burying of some other thiol group(s) (Sp). Non-linearity of the Arrhenius plots of the reaction rate of S2 suggested that the S2 region of myosin had different conformations at high and low temperatures, the transition temperature being 10--15degrees. This non-linearity completely disappeared in the presence of Mg2+-ATP. On the other hand, Arrhenius plots for the thiols reactive to BIPM did not show non-linearity in the presence or absence of ATP.
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PMID:Thiols of myosin. IV. "Abnormal" reactivity of S1 thiol and the conformational changes around S2 thiol. 0 75

A method is described for the preparation of high purity myosin from the left ventricle of pig heart. The purified myosin was free from nucleic acid, actin, tropomyosin, troponin, the 150,000 molecular weight protein and other contaminants. Analyses of subunits in the purified myosin were carried out on 3.5% acrylamide gel with 0.1% SDS. Of the total protein present in myosin, 11.3% was in the light chains; light chain 1 (LC1), 5.9% and light chain 2 (LC2), 5.4%. Urea gel electrophoresis of the purified myosin showed three closely spaced bands corresponding to the 20,000 dalton, the charge-modified 20,000 dalton and the phosphorylated 20,000 dalton components. The properties of the Ca2+-activated and K+-activated ATPases [EC 3.6.1.3] of the purified myosin were also studied. The Km values were 27 and 55 muM and the Vmax values were 0.263 and 0.317 mumole P1/mg/min for the Ca2+-activated and K+-activated ATPases, respectively. The pH-activity profiles and the effects of SH modification were of the skeletal myosin type except that the activities were lower.
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PMID:Cardiac myosin from pig heart ventricle. Purification and enzymatic properties. 1 Feb 92

The brush border of intestinal epithelial cells consists of an array of tightly packed microvilli. Within each microvillus is a bundle of 20-30 actin filaments. The basal ends of the filament bundles are embedded in and interconected by a filamentous meshwork, the terminal web, which lies directly beneath the microvilli. When calcium and ATP are added to isolated brush borders that have been treated with the detergent, Triton X-100, the microvillar filament bundles rapidly retract into and through the terminal web region. Biochemical studies of brush border contractile proteins suggest that the observed microvillar contraction is actomyosin mediated. We have shown previously that the major protein of the brush border's actin (Tilney, L. G., and M. S. Mooseker. 1971. Proc. Natl. Acad. Sci. U. S. A. 68:2611-2615). The brush border also contains a protein with the same molecular weight as the heavy chain subunit of myosin (200, 000 daltons). In addition, preparations of demembranated brush borders exhibit potassium-EDTA ATPase activity of 0.02 mumol phosphate/mg-min (22 degrees C); this assay is diagnostic for myosin-like ATPase isolated from vertebrate sources. Other proteins of the brush border include a 30,000 dalton protein with properties similar to those of tropomyosin, and a protein with the same molecular weight as the Z band protein, alpha-actinin (95,000 daltons). How these observations bear on the basis for microvillar movements in vivo is discussed within the framework of our recent model for the organization of actin and myosin in the brush border (Mooseker, M. S., and L. G. Tilney. 1975. J. Cell Biol. 67:725-743).
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PMID:Brush border motility. Microvillar contraction in triton-treated brush borders isolated from intestinal epithelium. 1 Dec 22

Myosin was extracted and partially purified from the head portion of spermatozoa of the starfish, Asterias amurensis. The sperm myosin showed a specific Ca2+-activated ATPase [EC 3.6.1.3] activity of 0.2 mumoles Pi/min/mg at high ionic strength and pH 6.5. It resembled egg myosin in forming thick filaments, becoming attached to actin filaments. subunit composition, and serological properties.
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PMID:Isolation of myosin from starfish sperm heads. 1 47

The inhibition of guinea-pig heart (Na+ + K+)-ATPase (ATP phosphohydrolase EC 3.6.1.3) by calcium has been studied at pH 7.4, 6.8 and 6.4. 1. A decrease in pH reduced the threshold inhibitory concentration of calcium and the calcium concentration producing an inhibition of 50% of the enzyme activity. 2. Calcium reduced the apparent affinity of the enzyme of Na+, this effect occurred only at pH 7.4. 3. Calcium increased the apparent affinity of the enzyme for K+, this effect was enhanced at acidic pH. 4. Activation of the enzyme by Na+ for a constant Na+ : K+ ratio has been studied at pH 7.4 and at pH 6.8 in the absence and in the presence of 3.10(-4) M Ca 2+; the results of this experiment indicate that Ca2+ effect at pH 7.4 was not influenced by Na+ -- K+ competition and was probably due to a Na+ -- Ca2+ interaction. 5. At pH 7.4, the calcium inhibitory threshold concentration and the concentration producing 50% inhibition were reduced when Na+ was low; at pH 6.8, the calcium inhibition was not markedly modified by the change of Na+ concentration. 6. The Ca2+ -activated ATPase of myosin B which is related to the contractile behaviour of muscle and the Ca2+ -ATPase of the sarcoplasmic reticulum which is related to the ability of this structure to accumulate calcium were activated in a range of calcium concentration producing an inhibition of (Na2+ + K+) -ATPase. The present results indicate that the increase by acidity of the (Na2+ + K+) -ATPase sensitivity to calcium might be due to a suppression of a Na+ -Ca2+ interaction. On the basis of these observations, it is proposed that calcium might inhibit the Na+ -pump during the repolarization phase of the action potential and that, by this effect, it might control cell excitability.
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PMID:Influence of pH and sodium on the inhibition of guinea-pig heart (Na+ + K+)-ATPase by calcium. 1 90

It is found that dinitrophenol, octanol and toluene produce similar effects on pH-dependence of ATPase of myosin and heavy meromyosin (HMM), i.e. they decrease or remove the neutral suppression of ATPase activity. The appearance of pH-dependence curves is simplified and approaches the form, which is characteristic for the ionisation curve of one; in the last resort two groups, participating in the enzyme activity. The activity of HMM is higher and the zone of the neutral suppression is diminished at low ionic strength, the activation by the modifiers being observed at the significantly lesser degree. CaATPase activation by dinitrophenol, octanol and toluene is suggested to be of the same nature and is accounted for the masking of "the inhibiting" ionizable group of the enzyme with near to neutral pK. This masking may be the result of the conformational changes occuring at the deformation of hydrofobic regions. The ionization of "the activity inhibiting" group of the enzyme depends directly or indirectly on the concentration of potassium chloride and the increase of KCl concentration bring to the inhibition of ATPase activity.
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PMID:[Influence of dinitrophenol, octanol and toluene upon pH-dependence of ca-ATPase activity of heavy meromyosin]. 1 25

I-protein inhibited theMg-activated ATPase [EC 3.6.1.3] activity of actinomyosin by approximately 50% at low ionic strength. Concomitantly, the onset of superprecipitation was retarded. I-protein was found to bind to myosin, but not to F-actin. The inhibitory action of I-protein occurred only in the absence of Ca ions in the troponintropomyosin-actin myosin system. Addition of Ca ions abolished the effect. Thus, it is very likely that I-protein prevents unnecessary hydrolysis of ATP in the relaxed state of muscle.
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PMID:I-protein, a new regulatory protein from vertebrate skeletal muscle. III. Function. 1 32

Study of pH-dependence of Ca-ATPase activity of heavy meromyosin (HMM) at low and high ionic strength showed essential differences in the modifying effect of two sulfhydryl reagents, p-CMB and silver. Silver ions in conditions studied independently on pH and KCl concentration produce an inhibition of ATP hydrolysis by myosin and HMM, the shape of the pH-dependence curve remaining similar to that of the native enzyme up to 40% of blocking free sulfhydryl groups. At the same degree of binding of sulfhydryl groups with p-CMB at 0,5 M KCl the pH-dependence curve due to activation at neutral pH changes it's shape and becomes similar to that for dissociation of two ionizable groups (at neutral and alkaline regions). In contrast to this, a low or zero concentrations of KCl no activation was observed for the enzyme with 40-50% of SH-Groups modified by p-CMB and Ca-ATPase in this case seemed to be independent of pH. The data obtained suggest that SH-Groups are not included into the active site of myosin, and the activating effect observed for some sulfhydryl reagents, is due to conformational changes and it can be the result of the penetrance of the organic part of the reagent molecule into hydrophobic region of the protein.
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PMID:[pH-dependence characteristics of Ca-ATPase activity of heavy meromyosin with modified SH-groups]. 1 1

Myosin from rabbit stomach was highly purified by ammonium sulfate fractionation in the presence of ATP and MgCl2, ultracentrifugation and Sepharose 4B chromatography. The myosin composed of one heavy and two light chains as determined by SDS-gel electrophoresis. The molecular weights of the light chains were the same as those of gizzard myosin, about 20,000 and 17,000, respectively. The pH-activity curve and the KCl concentration dependency of Ca-ATPase of the stomach myosin were similar to those of other smooth muscle myosins. The stomach myosin was more resistant to pepsin digestion than skeletal myosin. Other proteolytic enzymes, trypsin, chymotrypsin, papain, and nagarse, digested the myosin in the same way as skeletal myosin.
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PMID:Purification and some properties of rabbit stomach myosin. 1 37

Curves of V pH-dependence for Ca ATPase of myosin and heavy meromyosin are demonstrated to be well modelled with theoretical curves for the case of proton dissociation at three groups of enzyme-substrate complex with the loss of the activity at some intermediate ionization stage. Variation of pK values for these three groups and the degree of inhibition for intermediate forms of enzyme-substrate complex are found to be sufficient to reproduce main varieties of described in the literature and obtained in this work multiformity of pH-dependence curves of different nucleoside triphosphates hydrolysis by both native and modified enzymes. Calculated pK values and modification data suggest a significant importance of the dissociation of two imidazole groups ("activating" and "inhibitory") and cisteine sulhydryl group for the catalytic activity of myosin. Inhibition of ATPase activity by increasing of KCl concentrations is found to be due first of all to a shift in pK values of "inhibitory" imidazole and sulhydryl groups.
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PMID:[Kinetic study of the pH-dependence of maximal rate of Ca-ATP hydrolysis by myosin]. 2 83


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