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)

Purified ferredoxin-(cytochrome c)-NADP+ oxidoreductase and xanthine oxidase were found to catalyse the reduction of nitrofurantoin to the free radical. Under aerobic conditions, the nitrofurantoin radical underwent autoxidation to regenerate the parent compound with the concomitant production of superoxide and eventually hydrogen peroxide. The nitrofurantoin radical was also shown to react with hydrogen peroxide to generate a highly reactive species which was capable of oxidising methionine to ethylene. This active oxygen radical appeared to be identical with the crypto-OH . radical, previously proposed as being formed from the analogous reaction of the methyl viologen radical with hydrogen peroxide [R.J. Youngman and E.F. Elstner, FEBS Lett. 129, 265 (1981)]. Catalase inhibited nitrofurantoin-dependent ethylene formation in both enzyme systems, whereas superoxide dismutase was only inhibitory in the xanthine oxidase mediated reaction. Although the primary function of the respective enzyme systems is to generate the nitrofurantoin radical, the xanthine oxidase reaction is markedly more complex than that of ferredoxin-(cytochrome c)-NADP+ oxidoreductase. The differences between the two enzyme reactions appear to be due to the endogenous autoxidation of xanthine oxidase. The aerobic activation of nitrofurantoin by xanthine oxidase involved the superoxide anion as an intermediate, whereas the nitrofuran was directly reduced by ferredoxin-(cytochrome c)-NADP+ oxidoreductase without a requirement for active oxygen species.
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PMID:Mechanisms of oxygen activation by nitrofurantoin and relevance to its toxicity. 629 96

The desulfo form of milk xanthine oxidase (xanthine: oxygen oxidoreductase, EC 1.2.3.2) was reactivated by incubation with rhodanese (thiosulfate: cyanide sulfurtransferase, EC 2.8.1.1), thiosulfate, and sulfhydryl reagent; 50% of full activity was recovered. No further reactivation occurred with additional incubation. It was also found that native enzyme in the sulfo form with full activity was inactivated by incubation with the same system, down to half of full activity and no further inactivation occurred. After these incubations the enzyme was found to be a mixture of functional and nonfunctional enzymes based on spectral changes with xanthine, on [14C]oxipurinol equilibration, and on steady-state kinetics. The 35S of [35S]thiosulfate was incorporated into desulfo xanthine oxidase in parallel with an increase in catalytic activity. Most of the 35S was cyanolysable but was protected from cyanolysis by pretreatment with allopurinol. The 35S was released from 35S-labeled reconstituted xanthine oxidase upon incubation with the rhodanese system containing unlabeled thiosulfate. However, catalytic activity remained unchanged, indicating that the sulfur atom was exchanged during the incubation.
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PMID:Reversible interconversion between sulfo and desulfo xanthine oxidase in a system containing rhodanese, thiosulfate, and sulfhydryl reagent. 657 44

Fractionation of cell organelles of nitrogen-fixing nodules of cowpea (Vigna unguiculata L. Walp) by discontinuous and continuous sucrose density centrifugation indicated that starch-containing plastids possessed the complete pathway for purine nucleotide synthesis together with significant activities of some other enzymes associated with the provision of substrates in purine synthesis; triosephosphate isomerase (EC 5.3.1.1), NADH-glutamate synthase (EC 2.6.1.53), aspartate aminotransferase (EC 2.6.1.1), phosphoglycerate oxidoreductase (EC 1.1.1.95), and methylene tetrahydrofolate oxidoreductase (EC 1.5.1.5). Enzymes of purine oxidation, xanthine oxidoreductase (EC 1.2.3.2), and urate oxidase (EC 1.7.3.3) were recovered in the soluble fraction; glutamine synthetase (EC 6.3.1.2) occurred in bacteroids and in the cytosol. Intact, infected (bacteroid-containing) and uninfected cells were prepared by enzymatic maceration of the central zone of the nodule and partially separated by centrifugation on discontinuous sucrose gradients. Glutamine synthetase was largely restricted to infected cells whereas plastid enzymes, de novo purine synthesis, and urate oxidase were present in both cell types. Although the levels of all enzymes assayed were higher in infected cells, both cell types possessed the necessary enzyme complement for ureide formation. A model for the cellular and subcellular organization of nitrogen metabolism and the transport of nitrogenous solutes in cowpea nodules is proposed.
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PMID:Cellular and subcellular organization of pathways of ammonia assimilation and ureide synthesis in nodules of cowpea (Vigna unguiculata L. Walp.). 687 Feb 68

The conversion of xanthine dehydrogenase to xanthine oxidase that produces oxygen radicals has been implicated in the ischemic injury to the myocardium and to the kidney. Xanthine dehydrogenase uses NAD as the electron acceptor to catalyze a reaction which does not produce any oxygen free radicals and may depress the conversion of xanthine dehydrogenase to xanthine oxidase. Nicotinamide is the preferred precursor for NAD. This study was conducted to examine the effect of an 18% casein diet supplemented with 0.5% nicotinamide on the activity of oxidoreductase and its two enzyme forms, xanthine dehydrogenase and xanthine oxidase, in kidney, heart and liver of female obese Zucker rats that spontaneously develop glomerulosclerosis, cardiomegaly and fatty liver. Lean litter mates were used as controls. Nicotinamide supplementation had no effect on the activities of these enzyme forms in the liver of either obese rats or lean rats. Obese rats fed the nicotinamide supplemented diet had higher activities of these enzyme forms in kidneys and hearts than unsupplemented diet fed obese rats, but this difference was not observed in lean rats. In unsupplemented rats, xanthine oxidase activity in the kidney was greater in lean rats than obese rats. Thus, the abnormalities observed in obese rats are unlikely attributable to the xanthine oxidase-mediated oxidant stress.
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PMID:Dietary nicotinamide supplementation increases xanthine oxidoreductase activity in the kidney and heart but not liver of obese Zucker rats. 761 99

The ability of O2 metabolites derived from the xanthine-xanthine oxidase system to inhibit mitochondrial function was examined using freshly isolated rat liver mitochondria. Under 2,4-dinitrophenol-uncoupled conditions, mitochondria exposed to free radicals exhibited a significant decrease in O2 consumption supported by NAD(+)-linked substrates, but showed almost no change in O2 consumption in the presence of succinate and ascorbate. Oxidative stress caused the loss of intramitochondrial nicotinamide nucleotides, and addition of NAD+ fully prevented any fall in O2 consumption with NAD(+)-linked substrates. The activity of electron-transfer complex I (NADH oxidase and NADH-cytochrome c oxidoreductase) and the energy-dependent reduction of NAD+ by succinate were unaltered by oxidative stress. Exposure to free radicals also had an uncoupling effect at all three coupling sites. The degree of mitochondrial swelling was closely correlated with the inhibition of State-3 oxidation of site-I substrates and with the increase in State-4 oxidation of succinate. The immunosuppressive agent cyclosporin A completely prevented the mitochondrial damage induced by oxygen free radicals (swelling, Ca2+ release, sucrose trapping, uncoupling and selective inhibition of the mitochondrial respiration of site-I substrates). The same protective effect was found when Ca2+ cycling was prevented, either by chelating Ca2+ with EGTA or by inhibiting Ca2+ reuptake with Ruthenium Red. These findings suggest that the deleterious effect of free radicals on mitochondria in the present experimental system was triggered by the cyclosporin A-sensitive and Ca(2+)-dependent membrane transition, and not by direct impairment of the mitochondrial inner-membrane enzymes.
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PMID:Oxidative damage to mitochondria is mediated by the Ca(2+)-dependent inner-membrane permeability transition. 769 Oct 56

Sources of superoxide anion (O2-.) production in calf pulmonary artery smooth muscle homogenate and subcellular fractions were examined in this study by measurement of the chemiluminescence produced by the reaction of O2-. with 50 microM lucigenin, because recent evidence suggests that endogenously produced reactive O2 species appear to mediate certain vascular responses. In the homogenate fraction, an NADH (0.1 mM)-dependent oxidoreductase activity was the major detected source of chemiluminescence. NADPH (0.1 mM) produced only 3% of the O2-. observed with NADH. Quantitation of certain other potential sources of O2-. (under optimized conditions), including xanthine oxidase (0.1 mM hypoxanthine), mitochondria (5 mM succinate + 30 microM antimycin), cyclooxygenase/lipoxygenase (1 microM arachidonic acid + 0.1 mM NADPH), or autooxidation (0.1 mg/ml superoxide dismutase), resulted in the detection of minimal amounts (< 3% of NADH) of chemiluminescence. Estimation of mitochondrial O2-. production from tissue respiration rates suggests that lucigenin is a poor detector of intramitochondrial O2-.. These observations were confirmed by examination of chemiluminescence produced by subcellular fractions, where the major activity detected was an NADH oxidoreductase, which fractionated in a manner closely matching the activity of the microsomal marker enzyme rotenone-insensitive NADH-cytochrome c reductase. Because this NADH oxidoreductase appears to be a major vascular smooth muscle-derived source of O2-. production, this system has the potential to be an important endogenous source for the generation of vasoactive reactive O2 species.
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PMID:Sites of superoxide anion production detected by lucigenin in calf pulmonary artery smooth muscle. 781 Jun 85

Serratia marcecens 2CC-1 utilizes quinaldic acid (quinoline 2-carboxylic acid) as sole source of carbon, nitrogen and energy. Growth of strain 2CC-1 on quinaldic acid as well as on nicotinic acid and hypoxanthine was inhibited completely by the molybdate antagonist tungstate, whereas growth on kynurenic acid and 6-hydroxynicotinic acid was not affected by tungstate. The synthesis of the molybdenum-containing hydroxylases quinaldic acid 4-oxidoreductase and nicotinic acid 6-oxidoreductase was found to be inducible. In addition, Serratia marcescens 2CC-1 produced a constitutively expressed xanthine oxidoreductase. Quinaldic acid 4-oxidoreductase was purified 1075-fold with a recovery of 5%. For catalytic activity, artificial electron acceptors were necessary. The 95-100-kDa enzyme was a heterodimer with subunit molecular masses of 75-80 kDa and 18-19 kDa. Quinaldic acid 4-oxidoreductase contained 2.3-3.7 g atom of iron and 0.5-0.6 g atom of molybdenum per mol of enzyme. The absorption spectrum exhibited maxima at 280 nm, 334 nm, 480 nm and a shoulder at 550 nm, with A280/A334 = 4.8, A280/A450 = 10.0, A280/A480 = 9.4, and A450/A550 = 1.6, suggesting the absence of a flavin cofactor. Acridine, quinacrine, ethylenediaminetetraacetate, 2,2'-dipyridyl, 1,10-phenanthroline and iodoacetate did not affect enzyme activity. p-Hydroxymercuribenzoate, m-arsenite, cyanide and methanol were effective inhibitors of quinaldic acid 4-oxidoreductase. Cyanide-inhibited enzyme was reactivated by treatment with S2-, indicating the presence of a pterin molybdenum cofactor with a monooxo-monosulfidotype molybdenum center. Quinaldic acid 4-oxidoreductase showed a very high substrate specificity, quinaldic acid being the only substrate found to be transformed significantly.
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PMID:Microbial metabolism of quinoline and related compounds. XVIII. Purification and some properties of the molybdenum- and iron-containing quinaldic acid 4-oxidoreductase from Serratia marcescens 2CC-1. 835 32

Nitroreductase enzymes generally catalyze the reduction of nitroaromatic compounds to the corresponding amines. In contrast, ferredoxin NADP oxidoreductase (FNR), glutathione reductase, xanthine oxidase, and cytochrome c reductase catalyze the NADPH dependent elimination of the nitramine nitro group from 2,4,6-trinitrophenylmethylnitramine to form N-methylpicramide (NMP). Nitrite elimination was inhibited under aerobic conditions. Our results suggest that under aerobic conditions, tetryl is enzymatically reduced to the nitroanion radical which is then involved in the reduction of molecular oxygen. Under anaerobic conditions, the radical is reduced to NMP and nitrite is eliminated.
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PMID:Elimination of nitrite from the explosive 2,4,6-trinitrophenylmethylnitramine (tetryl) catalyzed by ferredoxin NADP oxidoreductase from spinach. 860 4

Transcriptional control of the nitrogen fixation (nif) genes in response to oxygen in Azotobacter vinelandii is mediated by nitrogen fixation regulatory protein L (NifL), a regulatory flavoprotein that modulates the activity of the transcriptional activator nitrogen fixation regulatory protein A (NifA). CD spectra of purified NifL indicate that FAD is bound to NifL in an asymmetric environment and the protein is predominantly alpha-helical. The redox potential of NifL is -226 mV at pH 8 as determined by the enzymic reduction of NifL by xanthine oxidase/xanthine in the presence of appropriate mediators. The reduction of NifL by xanthine oxidase prevented NifL from acting as an inhibitor of NifA. In the absence of electron mediators NifL could also be reduced by Escherichia coli flavohaemoprotein (Hmp) with NADH as reductant. Hmp contains a globin-like domain with haem B as prosthetic group and an FAD-containing oxidoreductase module. The carboxyferrohaem form of Hmp was competent to reduce NifL, suggesting that electron donation to NifL originates from the flavin in Hmp rather than by direct electron transfer from the haem. Spinach ferredoxin:NAD(P) oxidoreductase, which adopts a folding similar to the FAD- and NAD-binding domains of Hmp, also reduced NifL with NADH as reductant. Re-oxidation of NifL occurs rapidly in the presence of air, raising the possibility that NifL might sense intracellular oxygen. We propose a physiological redox cycle in which the oxidation of NifL by oxygen and hence the activation of its inhibitory properties occurs rapidly, in contrast with the switch from the active to the reduced form of NifL, which occurs more slowly.
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PMID:Electron donation to the flavoprotein NifL, a redox-sensing transcriptional regulator. 960 Oct 70

Xanthine oxidase (xanthine: oxygen oxidoreductase, EC 1.1.3.22), a molybdenum-containing hydroxylase that produces superoxide and uric acid from purine substrates and molecular oxygen, is involved in the oxidative stress underlying several human pathologies including lung diseases. An enzymatic activity similar to xanthine oxidase was previously reported in bronchoalveolar lavage fluid of patients with chronic obstructive pulmonary disease (COPD-BAL), by fluorometric analysis of DNA unwinding and cytochrome c reduction kinetics. Here we report the detection of xanthine oxidase activity products by electron paramagnetic resonance (EPR) in presence of the spin-trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and reversed-phase high-performance liquid chromatography (RP-HPLC) in COPD-BAL (n = 14, average age of patients 65 years, range 38-81) and BAL from healthy nonsmoker controls (n = 6, average age 64 years, range 44-73). Superoxide DMPO adducts were detected in COPD-BAL and in an in vitro system containing xanthine and xanthine oxidase (XA/XO), but not in BAL controls and when superoxide dismutase (SOD, 1000 I.U./ml) was added to COPD-BAL. The HPLC analyses after addition of xanthine showed production of uric acid in COPD-BAL and in the XA/XO system but not in BAL controls. These results support the involvement of xanthine oxidase in the mechanisms of superoxide production by BAL supernatant, which increases oxidative stress in chronic obstructive pulmonary disease.
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PMID:Detection of xanthine oxidase activity products by EPR and HPLC in bronchoalveolar lavage fluid from patients with chronic obstructive pulmonary disease. 982 42


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