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)

Acute myocardial ischemia results in a decrease in developed tension and an increase in resting tension. A breakdown of the excitation-contraction coupling system can explain the behavior of the ischemic muscle at a subcellular level. We have identified a specific defect in the sarcoplasmic reticulum (SR) from the ischemic myocardium; i.e., the uncoupling of calcium transport from ATP hydrolysis. The mediators of this excitation-contraction uncoupling process have not been identified. It is now established that the intracellular pH of the ischemic myocardium is in the range of 6.4 but the role of protons and potential role of free radicals have not been identified. We have hypothesized that protons and free radicals may interact to produce the excitation-contraction uncoupling of the ischemic myocardium. Cardiac SR was isolated from the wall of canine left ventricle and calcium uptake velocity and Ca2+ stimulated-Mg2+ dependent ATPase activity determined. Increasing proton concentration between pH 7.0 and 6.4 significantly reduced calcium uptake rates (pH 7.0 = 0.95 +/- 0.02; 6.4 = 0.50 +/- 0.02 mumoles Ca2+/mg-min; p less than 0.01) with no effect on ATPase activity. Calculated coupling ratios (mumoles Ca2+/mumoles Pi) decreased from 0.87 +/- 0.06 at pH 7.0 to 0.51 +/- 0.05 at pH 6.4. At pH 7.0, the generation of exogenous free radicals from the xanthine-xanthine oxidase system significantly depressed both calcium uptake rates (Control = 0.95 +/- 0.02; X+XO = 0.15 +/- 0.02) and ATPase activity (Control = 1.05 +/- 0.02; X+XO + 0.30 +/- 0.01 mumoles Pi/mg-min; p less than 0.01). The decreases in calcium uptake and in ATPase activity were completely reversible with superoxide dismutase (SOD). At pH 6.4 in the presence of xanthine and xanthine oxidase, there is a further depression of calcium uptake rates (Control = 0.50 +/- 0.02; X+XO = 0.11 +/- 0.01; p less than 0.05) but there is no SOD reversible component. The addition of SOD + 20mM mannitol normalized calcium transport at pH 6.4. The calculated coupling ratio at pH 6.4 in the presence of free radicals was 0.13. In contrast sarcoplasmic reticulum isolated from ischemic myocardium demonstrated a significant depression of calcium uptake rates at pH 7.1 which was further accentuated at pH 6.4. Ca2+-ATPase was significantly depressed at pH 7.1 but there was no accentuation at pH 6.4. It is concluded that no single species of free radical can explain the intracellular excitation-contraction uncoupling of the ischemic myocardium. The system can be explained by the interaction of hydrogen ions and superoxide anions producing both injury to the sarcoplasmic reticulum and the formation of lipid free radicals with hydroxyl-like activity.
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PMID:Mediation of sarcoplasmic reticulum disruption in the ischemic myocardium: proposed mechanism by the interaction of hydrogen ions and oxygen free radicals. 630 8

The inhibition of the activity of bovine xanthine oxidase (XO) by divalent mercury and other metal ions has been investigated by optical spectroscopy and stop-flow kinetic measurements. The study shows that Hg2+ ion completely inhibits the activity of XO, while other metal ions such as Zn2+, Mg2+, Co2+, and Ni2+ inhibit the activity only marginally (approximately 10%). The inhibition by the Hg2+ ion was found to be monophasic and noncompetitive with strong affinity for binding to XO. The pH-dependent study of the inhibition indicates that at least two ionizing groups of XO are involved in the binding of the Hg2+ ion.
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PMID:The inhibition of bovine xanthine oxidase activity by Hg2+ and other metal ions. 867 4

Glutamate kills sensitive neurons through several steps downstream to receptor activation: increased free Ca2+ levels, activation of various enzymes and accumulation of reactive oxygen species (ROS). We have evaluated in a well established model of neuronal cultures the neuroprotective effects of blocking these mechanisms, either singularly or by combining multiple enzyme inhibition and/or ROS scavenging. In vitro cultures of cerebellar granule cells exposed to a toxic concentration of glutamate (100 microM for 15 min in the absence of Mg2+) combined with several pharmacological treatments. Inhibition of nitric oxide synthase (NOS) and phospholipase A2 (PLA2) were effective in decreasing cell death and the combined treatments showed some degree of additivity. By contrast, inhibition of xanthine oxidase (XO) with allopurinol was uneffective. Antioxidants (in particular vitamin e or vitamin E analogs). protected neurons up to more than 50%. A synergistic effect was demonstrated by the combination of vitamin E and C. On the other hand, antioxidants did not increase the protection granted by enzyme inhibitors, suggesting that they act downstream to NOS and PLA2. In conclusion, NOS and PLA2 activated by Ca2+ influx give rise to reactive oxygen species whose deleterious action can be counteracted either by inhibiting these enzymes or by scavenging the excess of free radicals produced by them. Finally, a moderate protection was obtained by blocking protein synthesis with cycloheximide, suggesting a partial contribution of apoptotic mechanisms to the excitotoxic cell death.
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PMID:Inhibition of free radical production or free radical scavenging protects from the excitotoxic cell death mediated by glutamate in cultures of cerebellar granule neurons. 886 90

The mechanism for formation of high-affinity binding of 1-(2,6-dichlorobenzylidene-amino)-3-hydroxyguanidine (guanoxabenz) to alpha2-adrenoceptors was studied in particulate fractions from the rat spleen. The proportion of apparent high versus low-affinity alpha2-adrenoceptor binding sites increased with increasing incubation time and was also augmented by Mg2+ ions. The formation of high-affinity guanoxabenz binding seemed to be inhibited by a series of N-hydroxyguanidine analogs to guanoxabenz, as well as by a series of metabolic inhibitors that included allopurinol, 1-chloro-2,4-dinitrobenzene, 5,5'-dithiobis-(2-nitrobenzoic acid), cibacron blue, phenyl-p-benzoquinone, didox, and trimidox. The formation of guanoxabenz high-affinity binding was also inhibited in a time- and concentration-dependent fashion by preincubating the membranes with the LW03 N-hydroxyguanidine analogue of guanoxabenz. Moreover, when the spleen membranes were extensively washed for 30 min with buffers at 25 degrees, the guanoxabenz high-affinity binding disappeared. However, when these washed membranes were supplemented with xanthine, the apparent affinity of guanoxabenz increased four to five-fold. Taken together, all data were compatible with the theory that the formation of high-affinity binding was dependent on the generation of a guanoxabenz metabolite that showed an approximate 100-fold greater affinity for the alpha2-adrenoceptors than guanoxabenz itself. Because the most potent blocker of the formation of high-affinity binding was allopurinol (apart from some N-hydroxyguanidine analogs to guanoxabenz) and since the activity could be restored with xanthine, a likely candidate responsible for the metabolic activation is xanthine oxidase.
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PMID:Characterization of the enzymatic activity for biphasic competition by guanoxabenz (1-(2,6-dichlorobenzylidene-amino)-3-hydroxyguanidine) at alpha2-adrenoceptors. I. Description of an enzymatic activity in spleen membranes. 980 20

The sulfate-reducing bacterium aldehyde oxidoreductase from Desulfovibrio gigas (MOP) is a member of the xanthine oxidase family of enzymes. It has 907 residues on a single polypeptide chain, a molybdopterin cytosine dinucleotide (MCD) cofactor and two [2Fe-2S] iron-sulfur clusters. Synchrotron data to almost atomic resolution were collected for improved cryo-cooled crystals of this enzyme in the oxidized form. The cell constants of a=b=141.78 A and c=160.87 A are about 2% shorter than those of room temperature data, yielding 233,755 unique reflections in space group P6(1)22, at 1.28 A resolution. Throughout the entire refinement the full gradient least-squares method was used, leading to a final R factor of 14.5 and Rfree factor of 19.3 (4sigma cut-off) with "riding" H-atoms at their calculated positions. The model contains 8146 non-hydrogen atoms described by anisotropic displacement parameters with an observations/parameters ratio of 4.4. It includes alternate conformations for 17 amino acid residues. At 1.28 A resolution, three Cl- and two Mg2+ ions from the crystallization solution were clearly identified. With the exception of one Cl- which is buried and 8 A distant from the Mo atom, the other ions are close to the molecular surface and may contribute to crystal packing. The overall structure has not changed in comparison to the lower resolution model apart from local corrections that included some loop adjustments and alternate side-chain conformations. Based on the estimated errors of bond distances obtained by blocked least-squares matrix inversion, a more detailed analysis of the three redox centres was possible. For the MCD cofactor, the resulting geometric parameters confirmed its reduction state as a tetrahydropterin. At the Mo centre, estimated corrections calculated for the Fourier ripples artefact are very small when compared to the experimental associated errors, supporting the suggestion that the fifth ligand is a water molecule rather than a hydroxide. Concerning the two iron-sulfur centres, asymmetry in the Fe-S distances as well as differences in the pattern of NH.S hydrogen-bonding interactions was observed, which influences the electron distribution upon reduction and causes non-equivalence of the individual Fe atoms in each cluster.
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PMID:Structure refinement of the aldehyde oxidoreductase from Desulfovibrio gigas (MOP) at 1.28 A. 1171 86

Ischemia is a major cause of brain damage, and patient management is complicated by the paradoxical injury that results from reoxygenation. We have now explored the generation of reactive oxygen species (ROS) in hippocampal and cortical neurons in culture in response to oxygen and glucose deprivation or metabolic inhibition and reoxygenation. Fluorescence microscopy was used to measure the rate of ROS generation using hydroethidine, dicarboxyfluorescein diacetate, or MitoSOX. ROS generation was correlated with changing mitochondrial potential (rhodamine 123), [Ca2+]c (fluo-4, fura-2, or Indo-1), or ATP consumption, indicated by increased [Mg2+]c. We found that three distinct mechanisms contribute to neuronal injury by generating ROS and oxidative stress, each operating at a different stage of ischemia and reperfusion. In response to hypoxia, mitochondria generate an initial burst of ROS, which is curtailed once mitochondria depolarize or prevented by previous depolarization with uncoupler. A second phase of ROS generation that followed after a delay was blocked by the xanthine oxidase (XO) inhibitor oxypurinol. This phase correlated with a rise in [Mg2+]c, suggesting XO activation by accumulating products of ATP consumption. A third phase of ROS generation appeared at reoxygenation. This was blocked by NADPH oxidase inhibitors and was absent in cells from gp91(phox-/-) knock-out mice. It was Ca2+ dependent, suggesting activation by increased [Ca2+]c during anoxia, itself partly attributable to glutamate release. Inhibition of either the NADPH oxidase or XO was significantly neuroprotective. Thus, oxidative stress contributes to cell death over and above the injury attributable to energy deprivation.
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PMID:Three distinct mechanisms generate oxygen free radicals in neurons and contribute to cell death during anoxia and reoxygenation. 1726 68

In this study we investigated the superoxide radicals scavenging effect and xanthine oxidase inhibitory activity by magnesium lithospermate B, which was originally isolated from the roots of Salvia miltiorrhiza (also named Danshen or Dansham), an important herb in Oriental medicine. Superoxide radicals were generated both in beta-NADH/PMS system and xanthine/ xanthine oxidase system. Magnesium lithospermate B significantly inhibited the reduction of NBT induced by superoxide radicals with an IC(50) of 29.8 microg/mL and 4.06 microg/mL respectively in the two systems. Further study suggested that magnesium lithospermate B can directly inhibit xanthine oxidase and exhibits competitive inhibition. Magnesium lithospermate B was also found to have the hypouricemic activity in vivo against potassium oxonate-induced hyperuricaemia in mice. After oral administration of magnesium lithospermate B at doses of 10, 20 and 30 mg/kg, there was a significant decrease in the serum urate level when compared to the hyperuricemia control. In addition, magnesium lithospermate B significantly protected HL-60 cells from superoxide radicals-induced apoptosis in the xanthine/ xanthine oxidase reactions. This study provided evidence that magnesium lithospermate B exhibits direct superoxide radicals scavenging and xanthine oxidase inhibitory activity.
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PMID:Superoxide radicals scavenging and xanthine oxidase inhibitory activity of magnesium lithospermate B from Salvia miltiorrhiza. 1868 36


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