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

Acyclovir [9-[(2-hydroxyethoxy)methyl]guanine] is an acyclic guanine nucleoside analogue that is widely used clinically as an antiherpetic agent. Its limited absorption in humans after oral administration prompted the search for prodrugs. A congener, referred to as 6- deoxyacyclovir [2-amino-9-[(2-hydroxyethoxy)methyl]-9H-purine], was synthesized and found to be 18 times more water soluble than was acyclovir. Surprisingly, this congener was readily oxidized to acyclovir by xanthine oxidase (EC 1.2.3.2). It was also oxidized by aldehyde oxidase (EC 1.2.3.1) largely to 8-hydroxy-6- deoxyacyclovir [2-amino-8-hydroxy-9-[(2-hydroxyethoxy)methyl]-9H-purine] and then to 8- hydroxyacyclovir [2-amino-6,8-dihydroxy-9[(2-hydroxyethoxy)methyl]-9H-purine]. 6- Deoxyacyclovir and the major products of its oxidation by aldehyde oxidase lacked appreciable activity against herpes simplex type I in vitro. On the basis of these results, it was apparent that the success of 6- deoxyacyclovir as a prodrug in vivo would depend upon how well its desired activation by xanthine oxidase competed with the nonactivating oxidations by aldehyde oxidase. In rats dosed orally with 6- deoxyacyclovir , absorption was extensive and the major urinary metabolite was acyclovir. In two human volunteers, urinary excretions of acyclovir were 5-6 times greater than those typically observed after administration of equivalent doses of acyclovir itself. The areas under the plasma concentration-time curves for acyclovir were also 5-6 times greater. Plasma levels of acyclovir peaked soon after ingestion of the prodrug, indicating rapid absorption and metabolic conversion. These results suggested that 6- deoxyacyclovir might have clinical usefulness as a prodrug of acyclovir suitable for oral administration.
 ...
PMID:6-Deoxyacyclovir: a xanthine oxidase-activated prodrug of acyclovir. 658 47

Molybdenum cofactor was extracted from membranes of Proteus mirabilis by three methods: acidification, heat treatment and heat treatment in the presence of sodium-dodecylsulphate (SDS). Extracts prepared by the latter method contained the highest concentration of molybdenum cofactor. In these extracts molybdenum cofactor was present in a low molecular weight form. It could not penetrate an YM-2 membrane during ultrafiltration suggesting a molecular weight above 1000. During aerobic incubation of cofactor extracts from membranes at least four fluorescent species were formed as observed in a reversed-phase high performance liquid chromatography (HPLC) system. The species in the first peak was inhomogeneous while the species in the others seem to be homogeneous. In water, all fluorescent products had an excitation maximum at 380 nm and an emission maximum at 455 nm. Their absorption spectra showed maxima at around 270 nm and 400 nm. Fluorescent compounds present in the first peak could penetrate an YM-2 membrane during ultrafiltration, whereas the compounds in the other peaks hardly did. Using xanthine oxidase from milk as source of molybdenum cofactor apparently identical cofactor species were found. Cytoplasmic nor membrane extracts of the chlorate resistant mutant chl S 556 of P. mirabilis could complement nitrate reductase of Neurospora crassa nit-1 in the presence of 20 mM molybdate. However, fluorescent species with identical properties as found for the wild-type were formed during aerobic incubation of extracts from membranes of this mutant.
 ...
PMID:Molybdenum cofactor from the cytoplasmic membrane of Proteus mirabilis. 676 9

The microsomal oxidation of ethanol or 1-butanol was increased by ferrous ammonium sulfate-ethylenediaminetetraacetic acid (1:2) (Fe-EDTA) (3.4-50 microM). The increase was blocked by hydroxyl radical scavenging agents such as dimethyl sulfoxide or mannitol. The activities of aminopyrine demethylase or aniline hydroxylase were not affected by Fe-EDTA. The accumulation of H2O2 was decreased in the presence of Fe-EDTA, consistent with an increased utilization of H2O2. Other investigators have shown that Fe-EDTA increases the formation of hydroxyl radicals in systems where superoxide radicals are generated. The stimulation by Fe-EDTA appears to represent a pathway involving hydroxyl radicals rather than catalase because (1) stimulation occurred in the presence of azide, which inhibits catalase, (2) stimulation occurred in the presence of 1-butanol, which is not an effective substrate for catalase, and (3) stimulation was blocked by hydroxyl radical scavenging agents, which do not affect catalase-mediated oxidation of ethanol. A possible role for contaminating iron in the H2O or buffers could be ruled out since similar results were obtained with or without chelex-100 treatment of these solutions. The stimulatory effect by Fe-EDTA required microsomal electron transfer with NADPH, and H2O2 could not replace the NADPH-generating system. In the absence of microsomes or catalase, Fe-EDTA also stimulated the coupled oxidation of ethanol during the oxidation of xanthine by xanthine oxidase. These results suggest that during microsomal electrom transfer, conditions may be appropriate for a Fenton type or a modified Haber-Weiss type of reaction to occur, leading to the production of hydroxyl radicals.
 ...
PMID:Role of hydroxyl radicals in the iron-ethylenediaminetetraacetic acid mediated stimulation of microsomal oxidation of ethanol. 677 47

The role of xanthine oxidase in thyroid function was studied in the rat in vivo by different approaches. Allopurinol, an inhibitor of xanthine oxidase, was administered by mixing it with a powdered diet (16 mg/100 g body wt per day for 10 days). This treatment significantly reduced the total uptake of iodide and inhibited the organification of iodide in the rat thyroid gland. Thyroid xanthine oxidase and dehydrogenase were almost completely inactivated by tungstate, which was given to rats (100 p.p.m./animal per day in drinking water for 10 days) maintained on a purified diet containing low levels of molybdenum. Under these conditions, no inhibitory effect was observed on synthesis of thyroid hormones. It therefore seemed reasonable to assume that the suppressive effect of allopurinol on the biosynthesis of thyroid hormones is not mediated by xanthine oxidase.
 ...
PMID:Thyroid xanthine oxidase and its role in thyroid iodine metabolism in the rat: difference between effects of allopurinol and tungstate. 695 31

A new spectrophotometric method for the determination of adenosine deaminase is described. Adenosine is deaminated to inosine, the latter is cleaved by an inosine-guanosine specific nucleoside phosphorylase to hypoxanthine and ribose-1-phosphate. Hypoxanthine can be oxidized further to uric acid by xanthine oxidase or to allantoin by xanthine oxidase and uricase. The hydrogen peroxide formed in these reactions is reduced by catalase to water. In the presence of high concentrations of ethanol, equivalent amounts of acetaldehyde are produced. The acetaldehyde is oxidized NAD(P) dependent and the production rate of NAD(P)H is recorded at 334 nm. The new method is suitable for the detection of adenosine deaminase in whole blood, lymphocytes, sera and tissues.
 ...
PMID:A new spectrophotometric assay for enzymes of purine metabolism. IV. Determination of adenosine deaminase. 736 76

We examined the effects of FK506, an immunosuppressive agent, on the genesis of water immersion stress-induced gastric lesions in rats. Using high-performance liquid chromatography, four kinds of prostaglandins, ie, 6-keto-prostaglandin F1 alpha, prostaglandin F2 alpha, prostaglandin E2, and prostaglandin D2, were detected, and no leukotrienes were detected in gastric mucosa in rats without stress. After 6 hr of stress, gastric lesions developed with decreases in all prostaglandin contents, and the emergence of peptide leukotrienes was observed. Intramuscular administration of FK506 (0.1, 0.25, 0.5, 1.0, and 2.0 mg/kg) reduced lesion index dose-dependently. Administration of FK506 at doses over 0.25 mg/kg decreased all prostaglandin contents, but did not affect the increase in leukotriene contents. Pretreatment with famotidine or omeprazole reduced lesion index, and the protective effects were equivalent to those of 1.0 mg/kg of FK506, although FK506 did not affect gastric secretion during water-immersion stress. Water-immersion stress did not change the activities of xanthine oxidase in either stomach or serum. Polyoxyethylene-modified superoxide dismutase did not prevent gastric lesions. Water-immersion stress significantly increased myeloperoxidase activity in gastric mucosa, and FK506 reduced the increase in myeloperoxidase activity induced by stress. From our results, other factors besides gastric acid secretion and tissue eicosanoid contents, such as chemoattractant factor, might also be involved in the genesis of water-immersion stress-induced gastric lesions in rats.
 ...
PMID:Effects of FK506, an immunosuppressive agent, on genesis of water-immersion stress-induced gastric lesions in rats. 751 15

Rat abdominal skin flaps were subjected to total venous occlusion for 8 h. Five minutes before release of the vascular occlusion, mannitol, mannitol plus anisodamin, anisodamin or placebo (0.9% normal saline) was administered intravenously. Drug treated flaps showed a statistically significant increase in the proportion of area surviving (P < 0.001). The combination of mannitol and anisodamin was not more effective than either agent alone in increasing the proportion of area surviving. The results of biochemical analyses indicated that neither mannitol nor anisodamin affected xanthine oxidase activity (p > 0.05) but that both agents significantly reduced the increase of malondialdehyde (MDA) concentration caused by ischaemia-reperfusion (p < 0.01). Treatment with mannitol or anisodamin also prevented the increase of lactate and water content and the decrease in glucose content in the island skin flap tissue which occurred on reperfusion. The data indicate that mannitol and/or anisodamin have the potential to salvage anticipated flap necrosis. It is possible that the mechanism of action is inhibition of damage caused by toxic oxygen species and improvement in capillary reperfusion.
 ...
PMID:The effect of mannitol and anisodamin on the prevention of free radical injury to post-ischaemia flaps: an experimental study. 764 Aug 54

Cellular signalling by the inflammatory cytokine tumour necrosis factor alpha (TNF alpha) has been suggested to involve generation of low levels of reactive oxygen species (ROS). Certain antioxidants and metal chelators can inhibit cytotoxicity and gene expression in response to TNF alpha in numerous cell types. However, neither the source nor function of TNF alpha-induced oxidant generation is known. Using specific inhibitors, we ruled out involvement of several oxidant-generating enzymes [cyclo-oxygenase (indomethacin), cytochrome P-450 (metyrapone), nitric oxide synthase (NG-methyl-L-arginine), NADPH oxidase (iodonium diphenyl), xanthine oxidase (allopurinol), ribonucleotide reductase (hydroxyurea)] in TNF alpha-mediated apoptosis of the murine fibrosarcoma line, L929. We also demonstrated no role for mitochondrial-derived radicals/respiratory chain in the lytic pathway using specific inhibitors/uncouplers (rotenone, KCN, carboxin, fluoroacetate, antimycin, malonate, carbonyl cyanide p-trifluoromethoxyphenylhydrazone) and chloramphenicol-derived respiration-deficient cells. Significant ROS (H2O2, O2-.) generation was not observed in response to TNF alpha in L929 cells using four separate assays. Also, prevention of intracellular H2O2 removal by inhibition of catalase did not potentiate TNF alpha-mediated cell death. These data suggest that neither H2O2 nor O2-. plays a direct role in TNF alpha cytotoxicity. Finally, we suggest a central role for lipoxygenase in TNF alpha-mediated lysis. Three inhibitors of this radical-generating signalling pathway, including an arachidonate analogue (5,8,11,14-eicosatetraynoic acid), could protect cells against TNF alpha. The inhibitor nordihydroguaiaretic acid is also a radical scavenger, but it could not protect cells from ROS toxicity at concentrations that effectively prevented TNF alpha killing. Therefore protection by nordihydroguaiaretic acid cannot be due to scavenging of cytotoxic H2O or O2-.. The lipoxygenase product, (12S)-hydroxyeicosatetraenoic acid, was also significantly protective. As this analogue can act as a substrate for certain lipoxygenases, this effect may be due to prevention of generation of physiological products.
 ...
PMID:Involvement of oxidants and oxidant-generating enzyme(s) in tumour-necrosis-factor-alpha-mediated apoptosis: role for lipoxygenase pathway but not mitochondrial respiratory chain. 764 35

Neuronal viability is affected by reactive oxygen species. Lipid peroxidation is often defined as a major reason for cellular breakdown. Additionally, certain indispensable proteins are possible targets for excessively formed reactive oxygen species. Evidence is given here that protease nexin-1 (PN-1), an endogenous thrombin inhibitor and neurite outgrowth promoter, is inactivated by xanthine oxidase-derived free radicals. Varying protection by superoxide dismutase and catalase was observed, depending on the reaction conditions. The water-soluble alpha-tocopherol analogues MDL 74,406 (R(+)-3,4-dihydro-6-hydroxy-N,N,N-2,5,7,8-heptamethyl-2H-1-benzopy ran-2- ethanaminium 4-methylbenzenesulfonate), MDL 74,180DA (2,3-dihydro-2,2,4,6,7-pentamethyl-3-(4-methyl-piperazino)-1-benzo furan-5-ol dihydro-chloride) and trolox also protected PN-1. Neurodegeneration may be triggered by oxidative inactivation of protease inhibitors such as PN-1. Protection of PN-1 in Alzheimer's or Parkinson's diseases, could be a possible target for a therapeutic function of antioxidants in these diseases.
 ...
PMID:Inactivation of protease nexin-1 by xanthine oxidase-derived free radicals. 767 Mar 62

The superoxide-dismutase-like activity of a series of divalent metal saccharinates of general stoichiometry [MII(Sac)2(H2O)4].2H2O (with MII = Mn,Fe,Co,Ni,Cu,Zn) has been investigated using the nitroblue tetrazolium O2- reduction assay. The results show that all these complexes possess the capability to dismutate the superoxide anion generated in the xanthine/xanthine oxidase system. Interestingly, the greatest activity is shown by the corresponding copper complex. The results are discussed and compared with those obtained for native superoxide dismutase, which was tested under the same experimental conditions.
 ...
PMID:Determination of superoxide dismutase-like activity in some divalent metal saccharinates. 768 41


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>