Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P47989 (xanthine oxidase)
 8,633 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of cortical tissue preparations (CTP) from human brain on the production of reactive oxygen species (ROS) has been investigated with several biochemical model reactions. As indicators for ROS, fragmentation of the methionine derivatives, alpha-keto-gamma-methylthiobutyric acid (KMB) or 1-amino-cyclopropane-1-carboxylic acid (ACC), yielding ethene have been used. With these systems we have shown that production of OH-radical-type oxidants by the xanthine oxidase (XOD)-system is strongly stimulated by CTP. This activity is due to intrinsic iron ions since ethene formation from KMB is stimulated by EDTA, inhibited by desferrioxamine (Desferal) and also visible with heat-denatured CTP. CTP by themselves have no XOD activity. 3-Hydroxykynurenine (3HK) is another possible substrate for XOD but produces H2O2 without XOD-catalysis, whereas allopurinol is not inhibiting. CTP contain measurable NAD(P)H oxidoreductase activity, producing OH- radical- type oxidants at the expense of NADPH and (to a lesser extent) NADH as electron donors, shown as redox-cycling of 2-methyl-5-hydroxy-1,4-naphthoquinone, plumbagin. Ethene formation from KMB is also driven by both morpholinosydnonimine (SIN) or ONOOH. The reaction driven by SIN is stimulated by CTP and inhibited by catalase, SOD and hemoglobin. Since ethene release from KMB driven by ONOOH is inhibited by CTP the mechanisms driving KMB fragmentation are different for SIN and ONOOH. Furthermore CTP contain approx. 4 U catalase activity per mg protein and very weak peroxidase (POD) activity shown as ACC fragmentation yielding ethene in the presence of both H2O2 and KBr or NaCl. Since ACC binds to CTP and both compounds, ACC and KMB are natural products, present in food (ACC) or synthesized from methionine in vivo (KMB), these compounds may represent protecting agents in systems where reactive oxygen species are formed. One might even speculate that the production of ethene at these membrane receptor sites may have biological functions, since ethene is known to possess anaesthetic activities.
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PMID:Pro- and antioxidative properties of cortical tissue preparations from human brain exhibiting NMDA-receptor characteristics. 1043 95

Available evidence for oxidative stress after angioplasty is indirect or ambiguous. We sought to characterize the pattern, time course, and possible sources of free radical generation early after arterial balloon injury. Ex vivo injury performed in arterial rings in buffer with lucigenin yielded a massive oxygen-dependent peak of luminescence that decayed exponentially and was proportional to the degree of injury. Signals for injured vs. control arteries were 207. 1 +/- 17.9 (n = 13) vs 4.1 +/- 0.7 (n = 22) cpm x 10(3)/mg/min (p <. 001). Data obtained with 0.25 mmol/l lucigenin were validated with 0. 005-0.05 mmol/l lucigenin or the novel superoxide-sensitive probe coelenterazine (5 micromol/l). Gentle removal of endothelium prior to injury scarcely affected the amount of luminescence. Lucigenin signals were amplified 5- to 20-fold by exogenous NAD(P)H, and were >85% inhibited by diphenyliodonium (DPI, a flavoenzyme inhibitor). Antagonists of several other potential free radical sources, including xanthine oxidase, nitric oxide synthase, and mitochondrial electron transport, were without effect. Overdistension of intact rabbit iliac arteries in vivo (n = 7) induced 72% fall in intracellular reduced glutathione and 68% increase in oxidized glutathione, so that GSH/GSSG ratio changed from 7.93 +/- 2.14 to 0. 81 +/- 0.16 (p <.005). There was also 28.7% loss of the glutathione pool. Further studies were performed with electron paramagnetic resonance spectroscopy. Rabbit aortas submitted to ex vivo overdistension in the presence of the spin trap DEPMPO (5-diethoxy-phosphoryl-5-methyl-1-pyrroline-N-oxide, 100 mmol/l, n = 5) showed formation of radical adduct spectra, abolished by DPI or superoxide dismutase. Computer simulation indicated a mixture of hydroxyl and carbon-centered radical adducts, likely due to decay of superoxide adduct. Electrical mobility shift assays for NF-kappaB activation were performed in nuclear protein extracts from intact or previously injured rabbit aortas. Balloon injury induced early NF-kappaB activation, which was decreased by DPI. In conclusion, our data show unambiguously that arterial injury induces an immediate profound vascular oxidative stress. Such redox imbalance is likely accounted for by activation of vessel wall NAD(P)H oxidoreductase(s), generating radical species potentially involved in tissue repair.
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PMID:Vascular oxidant stress early after balloon injury: evidence for increased NAD(P)H oxidoreductase activity. 1088 53

The nature and mechanism of the inhibition of the oxidoreductase activity of milk xanthine oxidase (XO) by Cu(2+), Hg(2+) and Ag(+) ions has been studied by steady state and stopped flow transient kinetic measurements. The results show that the nature of the inhibition is noncompetitive. The inhibition constants for Cu(2+) and Hg(2+) are in the micromolar and that for Ag(+) is in the nanomolar range. This suggests that the metal ions have strong affinity towards XO. pH dependence studies of the inhibition indicate that at least two ionisable groups of XO are involved in the binding of these metal ions. The effect of the interaction of the metal ions on the reductive and oxidative half reactions of XO has been investigated, and it is observed that the kinetic parameters of the reductive half reaction are not affected by these metal ions. However, the interaction of these metal ions with XO significantly affects the kinetic parameters of the oxidative half reaction. It is suggested that this may be the main cause for the inhibition of XO activity by the metal ions.
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PMID:Mechanism of the inhibition of milk xanthine oxidase activity by metal ions: a transient kinetic study. 1100 70

Archaeoglobus fulgidus is a hyperthermophilic sulphate-reducing archaeon. It has an optimum growth temperature of 83 degrees C and is described as a strict anaerobe. Its genome lacks any homologue of canonical superoxide (O2.-) dismutases. In this work, we show that neelaredoxin (Nlr) is the main O2.- scavenger in A. fulgidus, by studying both the wild-type and recombinant proteins. Nlr is a 125-amino-acid blue-coloured protein containing a single iron atom/molecule, which in the oxidized state is high spin ferric. This iron centre has a reduction potential of +230 mV at pH 7.0. Nitroblue tetrazolium-stained gel assays of cell-soluble extracts show that Nlr is the main protein from A. fulgidus which is reactive towards O2.-. Furthermore, it is shown that Nlr is able to both reduce and dismutate O2.-, thus having a bifunctional reactivity towards O2.-. Kinetic and spectroscopic studies indicate that Nlr's superoxide reductase activity may allow the cell to eliminate O2.- quickly in a NAD(P)H-dependent pathway. On the other hand, Nlr's superoxide dismutation activity will allow the cell to detoxify O2.- independently of the cell redox status. Its superoxide dismutase activity was estimated to be 59 U mg-1 by the xanthine/xanthine oxidase assay at 25 degrees C. Pulse radiolysis studies with the isolated and reduced Nlr proved unambiguously that it has superoxide dismutase activity; at pH 7.1 and 83 degrees C, the rate constant is 5 x 106 M-1 s-1. Besides the superoxide dismutase activity, soluble cell extracts of A. fulgidus also exhibit catalase and NAD(P)H/oxygen oxidoreductase activities. By putting these findings together with the entire genomic data available, a possible oxygen detoxification mechanism in A. fulgidus is discussed.
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PMID:Oxygen detoxification in the strict anaerobic archaeon Archaeoglobus fulgidus: superoxide scavenging by neelaredoxin. 1106 58

Since xanthine oxidase (XO, Xanthine:oxidoreductase, E.C.1.2.3.22) is a key enzyme in reactive oxygen specie formation which plays a major role in cell oxidative stress, the availability of a sensitive and simple assay useful to detect its activity in monolayer cell cultures is worthwhile. In order to achieve this, we developed a method in which the conversion of pterine into isoxanthopterin is monitored fluorimetrically. Temperature assay was 50 degrees C. The activity of XO was detected in cerebellar granule cells exposed to glutamate. Since XO is formed from protease-dependent xanthine dehydrogenase processing, its activity appearance was found to be prevented by the protease inhibitor, leupeptin, as well as the glutamate NMDA-receptor inhibitor, MK-801, and the Ca(++) complexing agent, EGTA. The reported novel protocol, at variance with a conventional method, is shown to be a simple, fast, sensitive and relatively cheap method to assay XO activity. In addition, the reported assay can be applied to any cell type in culture.
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PMID:A sensitive method to assay the xanthine oxidase activity in primary cultures of cerebellar granule cells. 1108 57

The aim of this work was to characterize the products of metabolic activation of the antitumor drug ledakrin (Nitracrine) in model metabolic systems, where formation of drug-DNA adducts was previously discovered. The metabolic products obtained in different biological systems were compared with those obtained in experiments where chemical reducing agents were applied. Therefore, activation products were obtained in the presence of the microsomal fraction of rat liver and in the experiments with the reducing agents dithiothreitol, hydrazine hydrate, and SnCl(2). Furthermore, transformations of the drug with oxidoreductase enzymes DT-diaphorase and xanthine oxidase were observed. The ledakrin transformation products were separated and analyzed by HPLC with diode array detection. Structural studies of the products were performed by means of ESI-MS and NMR. Proton, carbon, and nitrogen assignments were made based upon DQF-COSY, ROESY, TOCSY, HSQC, and HMBC experiments. It was demonstrated during the reduction of ledakrin that a key metabolite, a compound with an additional five-membered ring attached to positions 1 and 9 of the acridine core and with the retained 9-aminoalkyl side chain, was formed in all the systems that were studied. It was determined that the reactive nitrogen atoms of this additional ring underwent further transformations resulting in the formation of a six-membered ring produced by the addition of a carbon atom to the dihydropyrazoloacridine ring. Furthermore, it was observed that positions 2 and 4 of ledakrin's acridine ring are susceptible to nucleophilic substitution as revealed by the studies with dithiothreitol. Additionally, although most products from the reduction of ledakrin were extremely unstable, 1-aminoacridinone, produced enzymatically and with dithiothreitol, exhibited persistent stability under the studied conditions.
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PMID:Products of metabolic activation of the antitumor drug ledakrin (nitracrine) in vitro. 1117 May 2

Tirapazamine (1) is a promising antitumor agent that selectively causes DNA damage in hypoxic tumor cells, following one-electron bioreductive activation. Surprisingly, after more than 10 years of study, the products arising from bioreductive metabolism of tirapazamine have not been completely characterized. The two previously characterized metabolites are 3-amino-1,2,4-benzotriazine 1-oxide (3) and 3-amino-1,2,4-benzotriazine (5). In this work, 3-amino-1,2,4-benzotriazine 4-oxide (4) is identified for the first time as a product resulting from one-electron activation of the antitumor agent tirapazamine by the enzymes xanthine/xanthine oxidase and NADPH:cytochrome P450 oxidoreductase. As part of this work, the novel N-oxide (4) was unambiguously synthesized and characterized using NMR spectroscopy, UV-vis spectroscopy, LC/MS, and X-ray crystallography. Under conditions where the parent drug tirapazamine is enzymatically activated, the metabolite 4 is produced but readily undergoes further reduction to the benzotriazine (5). Thus, under circumstances where extensive reductive metabolism occurs, the yield of the 4-oxide (4) decreases. In contrast, the isomeric two-electron reduction product 3-amino-1,2,4-benzotriazine 1-oxide (3) does not readily undergo enzymatic reduction and, therefore, is found as a major bioreductive metabolite under all conditions. Finally, the ability of the 4-oxide metabolite (4) to participate in tirapazamine-mediated DNA damage is considered.
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PMID:3-amino-1,2,4-benzotriazine 4-oxide: characterization of a new metabolite arising from bioreductive processing of the antitumor agent 3-amino-1,2,4-benzotriazine 1,4-dioxide (tirapazamine). 1142 85

Milk xanthine oxidase (xanthine: oxygen oxidoreductase; XO; EC 1.1.3.22) was found to catalyze the conversion of retinaldehyde to retinoic acid. The ability of XO to synthesize all trans-retinoic acid efficiently was assessed by its turnover number of 31.56 min-1, determined at pH 7.0 with 1 nM XO and all trans-retinaldehyde varying between 0.05 to 2 microM. The determination of both retinoid and purine content in milk was also considered in order to correlate their concentrations with kinetic parameters of retinaldehyde oxidase activity. The velocity of the reaction was dependent on the isomeric form of the substrate, the all trans- and 9-cis-forms being the preferred substrates rather than 13-cis-retinaldehyde. The enzyme was able to oxidize retinaldehyde in the presence of oxygen with NAD or without NAD addition. In this latter condition the catalytic efficiency of the enzyme was higher. The synthesis of retinoic acid was inhibited 87% and 54% by 4 microM and 2 microM allopurinol respectively and inhibited 48% by 10 microM xanthine in enzyme assays performed at 2 microM all trans-retinaldehyde. The Ki value determined for xanthine as an inhibitor of retinaldehyde oxidase activity was 4 microM.
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PMID:Xanthine oxidase catalyzes the synthesis of retinoic acid. 1169 48

Low-density lipoprotein (LDL) and its oxidized derivatives are hypothesized to impair vascular function by increasing superoxide anion (O.). To investigate mechanisms in situ, isolated carotid arteries were incubated with native LDL (nLDL) or minimally oxidized LDL (mmLDL). With the use of en face fluorescent confocal microscopy and hydroethidine, an oxidant-sensitive fluorescent probe, we found that nLDL increased O. in vascular endothelium greater than fourfold by an N(omega)-nitro-L-arginine methyl ester (L-NAME)-inhibitable mechanism. In contrast, mmLDL increased O. in vascular endothelium greater than eightfold by mechanisms that were partially inhibited by L-NAME and allopurinol and essentially ablated by diphenyleneiodium. These data indicate that both nLDL and mmLDL uncouple endothelial nitric oxide synthase (eNOS) activity and that mmLDL also activates xanthine oxidase and NADPH oxidoreductase to induce greater increases in O. generation than nLDL. Western analysis revealed that both lipoproteins inhibited A-23187-stimulated association of heat shock protein 90 (HSP90) with eNOS without inhibiting phosphorylation of eNOS at serine-1179 (phospho-eNOS), an immunological index of electron flow through the enzyme. As HSP90 mediates the balance of.NO and O. generation by eNOS, these data provide new insight into the mechanisms by which oxidative stress, induced by nLDL and mmLDL, uncouple eNOS activity to increase endothelial O. generation.
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PMID:Native LDL and minimally oxidized LDL differentially regulate superoxide anion in vascular endothelium in situ. 1212 24

Hypertension, a disease with a high incidence in the population, affects all parts of the cardiovascular system. Studying the alteration of vasomotor responses of microvessels of hypertensive animals or responses of vessels following short-term increases in hemodynamic forces helps us to better understand the underlying cellular signaling events responsible for their functional adaptation. These adaptations are likely to precede the structural remodeling of arterioles, resulting in irreversible increases in peripheral vascular resistance in hypertension. Although malfunction of several mechanisms can lead to the development of hypertension, hemodynamic forces (such as pressure and shear stress) are increased in all forms of hypertension. Thus, local mechanisms that sense the level of these forces and transduce the signals into vasomotor responses must be affected in all forms of hypertension. The endothelium has a central role in the early functional adaptations. Pressure-induced myogenic constriction is enhanced due to the augmented release of endothelium-derived constrictor factors that modulate arteriolar smooth muscle sensitivity to Ca(2+). In contrast, flow/shear stress-induced dilation of arterioles is reduced in hypertension, due to the impaired mediation of the response by nitric oxide (NO). The magnitude of impairment is gender specific, primarily due to an estrogen-dependent enhancement of NO release in females. It is proposed that the elevated hemodynamic forces present in hypertension may themselves initiate these alterations, probably by enhancing the release of reactive oxygen species (ROS; produced by xanthine oxidase, NAD(P)H oxidoreductase, eNOS, etc.), which then interfere with the synthesis and/or action of endothelium-derived mediators. Interfering early on with these mechanisms may prevent the development of irreversible structural changes of the microcirculation observed in hypertension.
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PMID:Signaling pathways of mechanotransduction in arteriolar endothelium and smooth muscle cells in hypertension. 1215 4


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