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:1.17.3.2 (xanthine oxidase)
8,383 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

MnO2 reacted with desferrioxamine B yielding a green, water-soluble complex, with absorption maxima at 315 and 635 nm whose extinction coefficients were 925 and 60 M-1 cm-1, respectively. Increasing the proportion of ligand to metal increased both color yield and ability to scavenge O2-, with maximal color yield and activity being achieved at a 1:1 ratio. The complex catalyzed the dismutation of O2- and 1 microM was equivalent to 1 unit of superoxide dismutase activity in the xanthine oxidase-cytochrome c assay. The complex thus exhibited approximately 0.1% as much activity as did the manganese-containing superoxide dismutase, on the basis of manganese content. The activity of the complex was not suppressed by bovine serum albumin or by the soluble proteins extracted from Lactobacillus plantarum. In contrast, the activities of Cu(II) complexes of salicylate or Gly-His-Lys were suppressed by these proteins.
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PMID:A mimic of superoxide dismutase activity based upon desferrioxamine B and manganese(IV). 282 13

The superoxide dismutase (SOD) mimetic reactivity of Cu(II)EDTA was studied in the pH range of 6.0 to 8.0. Cu(II)EDTA disproportionated superoxide without inhibiting superoxide production by xanthine oxidase, as a result of bonding sites becoming available on the copper complex with increasing acidity. This disproportionation by Cu(II)EDTA is offered as evidence that the addition of EDTA to biological preparations for the purpose of complexing copper and thereby inhibiting copper-dependent superoxide disproportionation and promoting superoxide-dependent reactions is not a valid practice.
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PMID:Copper(II)ethylenediaminetetraacetate does disproportionate superoxide. 282 69

Cytochrome a1c1 (nitrite-cytochrome c oxidoreductase) purified from Nitrobacter winogradskyi (formerly N. agilis) contained molybdenum, non-heme iron, and acid-labile sulfur in addition to hemes a and c; it contained 1 mol of heme a, 4-5 g atoms of non-heme iron, 2-5 g atoms of acid-labile sulfur, and 1-2 g atoms of molybdenum per mol of heme c, but did not contain copper. The fluorescence spectra of the molybdenum cofactor derivative prepared from cytochrome a1c1 were very similar to those of the cofactor derivative from xanthine oxidase, and the aponitrate reductase of nit-1 mutant of Neurospora crassa was complemented by addition of the molybdenum cofactor derived from the cytochrome. Further, the ESR spectrum of cytochrome a1c1 was similar to that of liver sulfite oxidase. The content of cytochrome a1 in the cells cultivated with the medium in which tungsten was substituted for molybdenum markedly decreased as compared with that in the cells cultivated in the molybdenum-supplemented medium. These results indicate that cytochrome a1c1 is an iron-sulfur molybdoenzyme which contains hemes a and c.
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PMID:Nitrobacter winogradskyi cytochrome a1c1 is an iron-sulfur molybdoenzyme having hemes a and c. 282 43

Exposure of isolated SENCAR mouse epidermal cells to the tumor promoter 12-0-tetradecanoylphorbol-13-acetate (TPA) in vitro resulted in the production of oxidant species detected as chemiluminescence. This oxidant response can be inhibited by superoxide dismutase and copper complexes but not catalase or scavengers of hydroxyl radical or singlet oxygen, suggesting that the oxidant is superoxide anion. Inhibitors of various parts of the arachidonate cascade affect the TPA-induced oxidant response in a manner that corresponds to their effects on in vivo tumor promotion experiments. Agents that inhibit lipoxygenase activity, i.e. nordihydroguaiaretic acid, benoxaprofen, but not agents that are cyclooxygenase inhibitors, i.e. indomethacin, are effective in suppressing the oxidant response to TPA. Phospholipase C but not phospholipase A2 or D produced an oxidant response kinetically similar to that elicited by TPA. The inhibitors of TPA-induced oxidants inhibited the phospholipase C response to the same extent, suggesting that TPA and phospholipase C may produce an oxidant species through a common mechanism, via phospholipid turnover-protein kinase C activation. The relevance of oxidant production to the tumor promotion process is suggested by the ability of exogenous xanthine/xanthine oxidase, a superoxide anion-generating system, to induce ornithine decarboxylase, a characteristic of TPA-treated cells. In addition, oxidant production is significantly lower in cells from the TPA-promotion resistant C57BL/6J mouse. These studies provide further support for a role for reactive oxygens in the tumor promotion process.
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PMID:Reactive oxygen in the tumor promotion stage of skin carcinogenesis. 284 22

The relation between ESR-detectable Cu(II) and Cu,Zn-superoxide dismutase activity was examined. The Cu(II) spin numbers per one unit of SOD were 6.26 X 10(12) (+/- 0.51 X 10(12] spins in several preparations of recombinant human Cu,Zn-SOD, native placental, and erythrocyte SOD. Measurement could be performed over a wide range of pH (4.0-10.0), preferably at temperatures below -40 degrees C. The data obtained by this method correlated well to the results obtained by the method of Fridovich et al. using the xanthine-xanthine oxidase system (correlation coefficient 0.995). The specific activity of SOD was proportional to the Cu(II) content measured by ESR, but not to the total Cu content measured by atomic absorption. This indicates that it is important to measure the Cu(II) content for determining Cu,Zn-SOD activity.
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PMID:Relation between ESR-detectable Cu(II) and superoxide dismutase activity. 285 62

Mixed-function oxidation systems comprised of Fe3+, O2, and electron donors such as thiol compounds, ascorbate, NAD(P)H/NAD(P)H oxidase, and xanthine oxidase/hypoxanthine, catalyze the inactivation of many enzymes. This report describes the isolation and purification of a soluble protein from Saccharomyces cerevisiae, which specifically inhibits the inactivation of various enzymes by a nonenzymatic Fe3+/O2/thiol mixed-function oxidase system. When thiol is replaced with another electron donor (e.g. ascorbate), this specific protein no longer protects against iron (or copper)/O2-dependent radical-induced enzyme inactivation. Purification steps included a polyethylene glycol precipitation followed sequentially by a chromatography on DE52 and high pressure liquid chromatography on phenyl, DEAE, and gel-filtrated columns. The final gel filtration step yielded two protein peaks exhibiting protector activity and possessing a Mr of 500,000 and 90,000. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of these two fractions gave a single band at 27 kDa suggesting that these protein species simply represent different oligomeric structures. The protector protein did not possess catalase, glutathione peroxidase, superoxide dismutase, or iron chelation activities. Since the protection activity reported herein is specific for mixed-function oxidation systems containing thiols, we propose that the protector protein functions as a sulfur radical scavenger.
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PMID:The isolation and purification of a specific "protector" protein which inhibits enzyme inactivation by a thiol/Fe(III)/O2 mixed-function oxidation system. 289 5

Na-Ca exchange activity in bovine cardiac sarcolemmal vesicles was stimulated up to 10-fold by preincubating the vesicles with 1 microM FeSO4 plus 1 mM dithiothreitol (DTT) in a NaCl medium. The increase in activity was not reversed upon removing the Fe and DTT. Stimulation of exchange activity under these conditions was completely blocked by 0.1 mM EDTA or o-phenanthroline; this suggests that the production of reduced oxygen species (H2O2, O2-.,.OH) during Fecatalyzed DTT oxidation might be involved in stimulating exchange activity. In agreement with this hypothesis, the increase in exchange activity in the presence of Fe-DTT was inhibited 80% by anaerobiosis and 60% by catalase. H2O2 (0.1 mM) potentiated the stimulation of Na-Ca exchange by Fe-DTT under both aerobic and anaerobic conditions; H2O2 also produced an increase in activity in the presence of either FeSO4 (1 microM) or DTT (1 mM), but it had no effect on activity by itself. Superoxide dismutase did not block the effects of Fe-DTT on exchange activity; however, the generation of O2-. by xanthine oxidase in the presence of an oxidizable substrate stimulated activity more than 2-fold. Hydroxyl radical scavenging agents (mannitol, sodium formate, sodium benzoate) did not attenuate the stimulation of activity observed with Fe-H2O2. Exchange activity was also stimulated by the simultaneous presence of glutathione (GSH; 1-2 mM) and glutathione disulfide (GSSG; 1-2 mM). Neither GSH nor GSSG was effective by itself and either 0.1 mM EDTA or o-phenanthroline blocked the effects on transport activity of the combination of GSH + GSSG. Treatment of the GSH and GSSG solutions with Chelex ion-exchange resin to remove contaminating transition metal ions reduced (by 40%) the degree of stimulation observed with GSH + GSSG. Full stimulating activity was restored to the Chelex-treated GSH and GSSG solutions by the addition of 1 microM Fe2+; Cu2+ was less effective than Fe2+ whereas Co2+ and Mn2+ were without effect. In the presence of 1 microM Fe2+, GSH alone produced a slight increase in transport activity, but this was markedly enhanced by the addition of Chelex-treated GSSG. The results indicate that stimulation of exchange activity requires the presence of both a reducing agent (DTT, GSH, O-.2, or Fe2+) and an oxidizing agent (H2O2, GSSG, and perhaps O2) and that the effects of these agents are mediated by metal ions (e.g. Fe2+).(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Redox modification of sodium-calcium exchange activity in cardiac sarcolemmal vesicles. 300 82

Phosphate was reported to be an inhibitor of copper- and zinc-containing superoxide dismutase (SOD) [de Freitas, D.M., & Valentine, J.S. (1984) Biochemistry 23, 2079-2082]. Thus SOD activity, in 50 mM 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) (pH 7.4), was decreased by approximately 50% when the assay was made 10 mM in phosphate, and the ionic strength was adjusted with sodium fluoride. The inhibitory effect of phosphate was attributed to the neutralization of the positive charge on the guanidino residue of Arg-141. We have reexamined the effects of phosphate inhibition of SOD and found that the enzyme has identical activity in phosphate or HEPES buffer when the ionic strength is adjusted with NaBr. The putative inhibitory effect of phosphate appears to have been due to fluoride inhibition of the superoxide generating system of xanthine/xanthine oxidase. We have confirmed this result by using a photochemical generation of O2- in addition to the enzymatic generation of O2-. Chemical modification of the lysine residues to homoarginines does not affect the activity of the enzyme and does not impart a phosphate sensitivity. Chemical modification with phenylglyoxal caused approximately 80% inactivation of the native enzyme and 90% inactivation of the O-methylisourea-modified enzyme. Our results suggest that phosphate does not inhibit the copper- and zinc-containing superoxide dismutase (Cu,Zn-SOD) beyond the expectations of its effect on ionic strength.
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PMID:Phosphate inhibition of the copper- and zinc-containing superoxide dismutase: a reexamination. 302

Citrate-Fe3+, reportedly a physiological chelate, exhibits superoxide dismutaselike activity, as evidenced by the inhibition of xanthine oxidase-dependent cytochrome c reduction; the dismutation of xanthine oxidase-generated superoxide to hydrogen peroxide and oxygen, and the enhanced disproportionation of potassium superoxide. The catalytic activity of citrate-Fe3+ corresponds, on a molar basis, to 0.03% of that of copper- and zinc-containing superoxide dismutase. Although weak, this activity enables citrate-Fe3+ to inhibit superoxide and ADP-Fe3+ -dependent peroxidation of extracted microsomal lipids. Also, the dismutase activity of citrate-Fe3+ interferes with its ability to promote lipid peroxidation. It is proposed that chelation of Fe3+ by citrate may represent a protective mechanism against the deleterious consequences of superoxide generation.
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PMID:Superoxide-dependent redox cycling of citrate-Fe3+: evidence for a superoxide dismutaselike activity. 302 73

When Chinese hamster fibroblasts were exposed to hydrogen peroxide or to a system consisting of xanthine oxidase and hypoxanthine, which generates superoxide anion plus hydrogen peroxide, sister-chromatid exchanges (SCEs) were formed in a dose-dependent manner. When the iron-complexing agent o-phenanthroline was present in the medium, however, the production of these SCEs was completely inhibited. This fact indicates that the Fenton reaction: Fe2+ + H2O2----OH0 + OH- + Fe3+ is responsible for the production of SCEs. When O2- and H2O2 were generated inside the cell by incubation with menadione, the production of SCE was prevented by co-incubation with copper diisopropylsalicylate, a superoxide dismutase mimetic agent. The most likely role of O2- is as a reducing agent of Fe3+: O2- + Fe3+----Fe2+ + O2, so that the sum of this and the Fenton reaction, i.e., the iron-catalyzed Haber-Weiss reaction, provides an explanation for the active oxygen species-induced SCE: H2O2 + O2(-)----OH- + OH0 + O2. According to this view, the OH radical thus produced is the agent which ultimately causes SCE. These results are discussed in comparison with other mechanisms previously proposed for induction of SCE by active oxygen species.
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PMID:Iron-mediated induction of sister-chromatid exchanges by hydrogen peroxide and superoxide anion. 303 88


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