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)

In view of the potential role of free radicals in the genesis of cardiac abnormalities under different pathophysiological conditions and the importance of contractile proteins in determining heart function, this study was undertaken to examine the effects of oxygen free radicals on the rat heart myofibrils. Xanthine plus xanthine oxidase (X + XO) which is known to generate superoxide anions (O2-) and hydrogen peroxide (H2O2), an activated species of oxygen, was found to decrease Ca(2+)-stimulated ATPase activity, increase Mg(2+)-ATPase activity and reduce sulfhydryl (SH) group contents in myofibrils; these effects were completely prevented by superoxide dismutase (SOD) plus catalase (CAT). Both H2O2 and hypochlorous acid (HOCl), an oxidant, produced actions on cardiac myofibrils similar to those observed by X + XO. The effects of H2O2 and HOCl were prevented by CAT and L-methionine, respectively. N-ethylmaleimide (NEM) and 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), inhibitors of SH groups, also produced effects similar to those seen with X + XO. Dithiothreitol (DTT), a well known sulfhydryl-reducing agent, prevented the actions of X + XO, H2O2, HOCl, NEM and DTNB. These results suggest that marked changes in myofibrillar ATPase activities by different species of oxygen free radicals may be mediated by the oxidation of SH groups.
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PMID:Alterations in cardiac contractile proteins due to oxygen free radicals. 164 33

The goat spermatozoa membranes isolated after treatment with octa (ethylene glycol) mono n-dodecyl ether (C12E8) followed by discontinuous sucrose density gradient centrifugation have been found to contain an ATPase that is stimulated by externally added Ca2+ only. The membrane fraction has also found to contain Mg(2+)-dependent Ca(2+)-ATPase activity, however the former activity is about 2 fold higher than the latter. The molecular weight of the enzyme is found to be about 97,000 on SDS-polyacrylamide gel. The optimum concentration of Ca2+ required for maximum activity is 3 mM for both Mg(2+)-dependent and Mg(2+)-independent Ca(2+)-ATPase. Histidine and imidazole buffers are found to be the most suitable for dependent and independent enzyme activities respectively. ATP with an optimum concentration of 4 mM is observed to be the best substrate than any other nucleotides. The inhibitors like trifluoperazine and vanadate and group specific probes e.g. DTNB and TNBS inhibit these two enzymes but at different rates. Ca(2+)-uptake study shows that the uptake in the presence of Ca2+ and ATP is higher than in the presence of Mg2+, Ca2+ and ATP. The findings lead us to believe that the Mg(2+)-independent Ca(2+)-ATPase has some role in Ca2+ transport like Mg(2+)-dependent enzyme.
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PMID:Biochemical characterization of a calcium ion stimulated-ATPase from goat spermatozoa. 183 Jan 26

Treatment of beef-heart mitochondrial F1 ATPase with 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) results in the incorporation of 1 mol DTNB/mol F1 without loss of ATPase activity. Incorporation is not prevented by ATP. Labeling occurs predominantly on an alpha-subunit, but also with a significant degree of modification of gamma- and epsilon-subunits. It is suggested that the modified sulfhydryl groups of the alpha-, gamma- and epsilon-subunits are in proximity so that only one can be modified by the reagent. Guanidine hydrochloride (0.3 M) dissociates F1 into its subunits. Eight sulfhydryl groups/mol F1 can be modified under these conditions. Guanidine hydrochloride does not cause dissociation of F1 in the presence of 30% (v/v) dimethylsulfoxide (Me2SO) and 2 mM ATP. Under these conditions a second molecule of DTNB is incorporated into F1 with nearly equal modification of the epsilon-subunit and an alpha-subunit. It is proposed that Me2SO and ATP induce a more stable conformation of F1, which is resistant to dissociation by guanidine hydrochloride, but in which the site of reaction with DTNB is made more accessible by the guanidine hydrochloride to permit the simultaneous modification of an alpha-subunit and the epsilon-subunit. This conformation is probably that which occurs during ATP synthesis by F1 in the presence of Me2SO.
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PMID:Conformational change in beef-heart mitochondrial F1 ATPase to ATP synthesis mode induced by dimethylsulfoxide and ATP revealed by sulfhydryl group labeling. 252 68

Rat testicular microsomal membrane fraction contains both Mg+2-dependent and Mg+2-independent Ca+2-ATPase activity. The latter activity is about two times higher than the former. Calcium ion required for maximum activation of Mg+2-independent Ca+2-ATPase in 3.0 mM, whereas for the dependent one it is 2.5 mM. Both the enzymes are resistant to cold shock upto seven days. Histidine and imidazole buffers are found to be the most suitable for dependent and independent enzyme activities, respectively. The pH optima for dependent one is 7.5, whereas for the independent one it is 8.5. Temperature optima for the former is 37 degrees C and for latter one it is 40 degrees C. Among all the nucleotides tested, ATP is found to be the best substrate for both the enzymes. The optimum concentration of ATP for dependent and independent enzyme activities are 3.0 mM and 1.5 mM respectively. Divalent metal ions like Zn+2, Ba+2 and Mn+2 have been found to inhibit Mg+2-dependent Ca+2-ATPase activity whereas Mg+2-independent Ca+2-ATPase activity is inhibited by the divalent ions except zinc which is found to stimulate the enzyme activity. Both the enzymes are inhibited by vanadate, EDTA and EGTA. I50, for vanadate is 0.05 and 0.125 mM for dependent and independent activities, respectively. Sulfhydryl groups modifying agents e.g., NEM, DTNB and chlorpromazine are found to affect the enzyme activities in different ways. Thus NEM and chlorpromazine are found to inhibit and DTNB stimulate the enzyme activities in both the cases.
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PMID:Identification and characterization of a Mg2+-dependent and an independent Ca+2-ATPase in microsomal membranes of rat testis. 296 51

A light chain of 18 000 daltons of native actomyosin isolated from rabbit skeletal muscle was removed by DTNB-treatment. Investigated were the differences in superprecipitation and ATPase activity of LC2-deficient and control actomyosin. The superprecipitation of control actomyosin develops in two phases, with high amplitude and kinetics dependent on the Ca++ concentration. On the other hand, superprecipitation of treated actomyosin develops in a single phase, with low amplitude and a kinetics independent of the Ca++ concentration. The partial lack of LC2 leads to the loss of Ca++-sensitivity of ATPase activity. On the basis of the results, LC2 has been assumed to fix that conformation state of myosin heads which is required for the functioning of the troponin system on the one hand, and a cooperation between myosin heads on the other. The regulatory function of LC2 is manifest in controlling the actin-myosin-ATP interaction, at the activated state of the troponin system, in an extent depending on the actual Ca++ concentration.
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PMID:Effect of DTNB-treatment on Ca++-sensitivity of superprecipitation and ATPase activity of actomyosin. 316 Feb 18

Previous experiments demonstrated that two thiols of skeletal myosin subfragment 1 (SF1) could be oxidized to a disulfide bond by treatment with a 2-fold excess of 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) in the presence of MgADP [Wells, J. A., & Yount, R. G. (1980) Biochemistry 19, 1711-1717]. The resulting characteristic changes in the ATPase activities of SF1 and the fact that MgADP was stably trapped at the active site [Wells, J. A., & Yount, R. G. (1979) Proc. Natl. Acad. Sci. U.S.A. 76, 4966-4970] suggested that the two thiols cross-linked were SH1 (Cys-707) and SH2 (Cys-697) from the myosin heavy chain. To verify this suggestion, SF1, after DTNB treatment as above, was treated with an excess of N-ethylmaleimide to block all accessible thiols. The single protein disulfide produced by DTNB oxidation was reduced with dithioerythritol and the modified SF1 internally cross-linked with equimolar [14C]p-phenylenedimaleimide (pPDM) in the presence of MgADP. After extensive trypsinization, the major 14C-labeled peptide was isolated, characterized, and shown to be Cys-Asn-Gly-Val-Leu-Gly-Ile-Arg-Ile-Cys-Arg, in which the two cysteines were cross-linked by pPDM. This peptide is known to contain SH2 and SH1 in this order and to come from residues 697-708 in the rabbit skeletal myosin heavy chain [Elzinga, M., & Collins, J. (1977) Proc. Natl. Acad. Sci. U.S.A. 74, 4281-4284; M. Elzinga, personal communication].(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Flexibility of the myosin heavy chain: direct evidence that the region containing SH1 and SH2 can move 10 A under the influence of nucleotide binding. 323 15

Evidence now exists for the phosphorylation of all the major proteins of the myofibril with the exception of troponin C. Although uncertainty exists in most cases about the role of phosphorylation of the myofibrillar proteins, there is substantial evidence that phosphorylation of serine 20 of rabbit cardiac troponin I leads to a lowering of the sensitivity of the actomyosin ATPase to Ca2+. This process is of special importance in the physiological response of the heart to adrenalin. A well defined enzymic system involving a specific kinase and a phosphatase is present in most muscles for the phosphorylation and dephosphorylation of the P light chain (regulatory, L2 or DTNB light chain) of myosin. Myosin light-chain kinase is very active in fast skeletal muscles, and although it is unlikely that phosphorylation followed by dephosphorylation of the P light chain occurs fast enough to be synchronous with the contractile cycle, phosphorylation may have a modulatory role in this tissue. Both post-tetanic potentiation and the reduced actomyosin ATPase turnover rate observed in fast-twitch muscle as a consequence of sustained forceful contraction have been suggested by different investigators to be consequences of P light chain phosphorylation. Nevertheless, unequivocal evidence associating either of these effects with phosphorylation is not yet available. Kinase activity is also high in vertebrate smooth muscle and it has been suggested that phosphorylation of the P light chain is the process that activates the actomyosin ATPase in this tissue. Evidence from a number of studies indicates, however, that regulation of smooth muscle actomyosin ATPase may not be a simple phosphorylation-dephosphorylation process.
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PMID:Phosphorylation of the myofibrillar proteins and the regulation of contractile activity in muscle. 613 9

Two different hybrid myosins were obtained by combining "desensitized" myosin (DM) of Akazara scallop striated adductor with rabbit skeletal DTNB-light chains (DTNB-LC) and with chicken gizzard regulatory light chains (GR-LC). Using the two hybrid myosins, the following were found: (a) DTNB-LC has an inhibitory effect on the Mg-ATPase activities of Akazara DM and acto-DM both in the absence of calcium and in its presence. (b) DTNB-LC also has an enhancing effect on the superprecipitation activity of acto-DM. (c) The Mg-ATPase activities of DM and acto-DM are made sensitive to calcium by GR-LC, regardless of whether GR-LC is phosphorylated or unphosphorylated. (d) However, the Mg-ATPase activity of acto-myosin hybridized with phosphorylated GR-LC is definitely higher than that of acto-myosin hybridized with unphosphorylated GR-LC.
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PMID:Akazara scallop myosins hybridized with DTNB-light chains of skeletal myosin and with regulatory light chains of gizzard myosin. 613 82

Mg2+-ATPase activity was identified in the cytosol of human erythrocytes. A partial purification of this activity was achieved by an initial DEAE-Sephadex column chromatography, followed by gel filtration on Sephadex G-100 and then a second DEAE-Sephadex chromatography procedure. The enzyme appeared in the void volume of the Sephadex G-100 column and was retained on an Amicon XM100A ultrafiltration membrane. The molecular weight of the enzyme was estimated to be 113 000 from SD gels. The above purification protocol yielded an enzyme with an optimal pH between 7.6 and 8.2. The enzyme activity increased linearly between 30 and 44 degrees C. It was stable for several months at -20 degrees C. Magnesium was essential for activity, but the rate attainable with Mn2+ was at least as great as that due to Mg2+. No other divalent cation was able to substitute for Mg2+ or Mn2+. Neither low nor high Ca2+ concentrations significantly affected the enzymatic activity. Substrate specificity studies showed that ATP was the preferred substrate followed by CTP (46% of the rate produced by ATP). Hydrolysis of GTP, UTP, ITP and ADP was less than 10% of the rate seen with ATP. No phosphatase, pyrophosphatase, phosphodiesterase, hexokinase, phosphofructokinase or adenylate cyclase activity could be detected in this enzyme preparation. Calmodulin, which stimulates the (Ca2+ + Mg2+)-ATPase of the human erythrocyte membrane, failed to enhance the Mg2+-ATPase activity. Of considerable interest, the activity of this Mg2+-ATPase was enhanced approximately 5-fold by low concentrations of mercuric ion, p-hydroxymercuribenzoate and DTNB, but was much less sensitive to iodoacetamide.
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PMID:Partial purification and characterization of a novel Mg2+-dependent ATPase present in the cytosol from human erythrocytes. 615 Jul 30

The cation dye acridine orange (AO) was shown to inhibit ATPase activity of myosin, DTNB-myosin and heavy meromyosin and not to influence that of EDTA-S-1 at low ionic force. The inhibiting effect is concerned with the presence of KCl in solution. The allosteric influence of AO on myosin ATPase activity is discussed and dependence of this effect on charge distribution on the surface of the protein molecule is considered.
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PMID:[Acridine orange inhibition of the ATPase activity of myosin and its fragments]. 621 85


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