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)

A new class of purine antimetabolites, directed toward xanthine oxidase, was designed by employing some of the features found in the bioreductive alkylator mitomycin C. The design involved functionalizing the purine-like imidazo[4,5-g]quinazoline ring system as a quinone (4,9-dione) bearing a 2 alpha leaving group. Due to the presence of the electron-deficient quinone ring, the leaving group cannot participate in alkylation reactions. Reduction to the hydroquinone (4,9-dihydroxy) derivative, however, permits elimination of the leaving group to afford an alkylating quinone methide. In spite of the electronic differences, both quinone and hydroquinone derivatives of the imidazo[4,5-g]quinazoline system are able to enter the purine-utilizing active site of the enzyme. Thus, the hypoxanthine-like quinone derivative [2-(bromomethyl)-3-methylimidazo[4,5-g]quinazoline-4,8, 9(3H, 7H)-trione] and its hydroquinone derivative can act as reducing substrates for the enzyme, resulting in conversion to the xanthane-like 6-oxo derivatives. Hydrolysis studies described herein indicate that the hypoxanthine-like hydroquinone derivative eliminates HBr to afford an extended quinone methide species. The observed alkylation of the enzyme by this derivative may thus pertain to quinone methide generation and nucleophile trapping during enzymatic oxidation at the 6-position. Enzymatic studies indicate that the hypoxanthine-like quinone is an oxidizing suicide substrate for the enzyme. Thus, the reduced enzyme transfers electrons to this quinone, and the resulting hydroquinone inactivates the enzyme. As with mitomycin C, reduction and quinone methide formation are necessary for alkylation by the title quinone. This system is therefore an example of a purine active-site-directed reductive alkylator.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Active-site-directed reductive alkylation of xanthine oxidase by imidazo[4,5-g]quinazoline-4,9-diones functionalized with a leaving group. 342 77

CO dehydrogenase from the aerobic bacterium Oligotropha carboxidovorans catalyzes the oxidation of CO with H(2)O, yielding CO(2), two electrons, and two H(+). Its crystal structure in the air-oxidized form has been determined to 2.2 A. The active site of the enzyme, which contains molybdenum with three oxygen ligands, molybdopterin-cytosine dinucleotide and S-selanylcysteine, delivers the electrons to an intramolecular electron transport chain composed of two types of [2Fe-2S] clusters and flavin-adenine dinucleotide. CO dehydrogenase is composed of an 88.7-kDa molybdoprotein (L), a 30. 2-kDa flavoprotein (M), and a 17.8-kDa iron-sulfur protein (S). It is organized as a dimer of LMS heterotrimers and resembles xanthine dehydrogenase/oxidase in many, but not all, aspects. A mechanism based on a structure with the bound suicide-substrate cyanide is suggested and displays the necessity of S-selanylcysteine for the catalyzed reaction.
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PMID:Crystal structure and mechanism of CO dehydrogenase, a molybdo iron-sulfur flavoprotein containing S-selanylcysteine. 1043 Aug 65

Recent work indicates that respiratory muscles generate superoxide radicals during contraction (M. B. Reid, K. E. Haack, K. M. Francik, P. A. Volberg, L. Kabzik, and M. S. West. J. Appl. Physiol. 73: 1797-1804, 1992). The intracellular pathways involved in this process are, however, unknown. The purpose of the present study was to test the hypothesis that contraction-related formation of reactive oxygen species (ROS) by skeletal muscle is linked to activation of the 14-kDa isoform of phospholipase A(2) (PLA(2)). Studies were performed by using an in vitro hemidiaphragm preparation submerged in an organ bath, and formation of ROS in muscles was assessed by using a recently described fluorescent indicator technique. We examined ROS formation in resting and contracting muscle preparations and then determined whether contraction-related ROS generation could be altered by administration of various PLA(2) inhibitors: manoalide and aristolochic acid, both inhibitors of 14-kDa PLA(2); arachidonyltrifluoromethyl ketone (AACOCF(3)), an inhibitor of 85-kDa PLA(2); and haloenol lactone suicide substrate (HELSS), an inhibitor of calcium-independent PLA(2). We found 1) little ROS formation [2.0 +/- 0.8 (SE) ng/mg] in noncontracting control diaphragms, 2) a high level of ROS (20.0 +/- 2.0 ng/mg) in electrically stimulated contracting diaphragms (trains of 20-Hz stimuli for 10 min, train rate 0.25 s(-1)), 3) near-complete suppression of ROS generation in manoalide (3.0 +/- 0.5 ng/mg, P < 0. 001)- and aristolochic acid-treated contracting diaphragms (4.0 +/- 1.0 ng/mg, P < 0.001), and 4) no effect of AACOCF(3) or HELSS on ROS formation in contracting diaphragm. During in vitro studies examining fluorescent measurement of ROS formation in response to a hypoxanthine/xanthine oxidase superoxide-generating solution, manoalide, aristolochic acid, AACOCF(3), and HELSS had no effect on signal intensity. These data indicate that ROS formation by contracting diaphragm muscle can be suppressed by the administration of inhibitors of the 14-kDa isoform of PLA(2) and suggest that this enzyme plays a critical role in modulating ROS formation during muscle contraction.
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PMID:Formation of reactive oxygen species by the contracting diaphragm is PLA(2) dependent. 1044 41

Here we report a method to determine superoxide scavenging efficiency, using kinetic analysis of cytochrome c reduction and an automated UV/vis microtiter plate reader. Superoxide (O(2)(-&z. rad;)) was generated by xanthine oxidase metabolism of hypoxanthine, and quantified by following reduction of cytochrome c by O(2)(-&z. rad;) as increasing absorbance at 550 nm. Reaction conditions were established that provided a linear increase in O(2)(-&z.rad;) generation for more than 20 min, and good reproducibility over time. The majority of cytochrome c reduction was blocked by superoxide dismutase, indicating cytochrome c reduction derived predominantly from O(2)(-&z.rad;). Although EDTA is commonly included in this assay to eliminate undesirable Fenton side-reactions with H(2)O(2) (a co-product of reactions that use xanthine oxidase to produce O(2)(-&z.rad;)), we found that catalase, but not EDTA, blocked suicide elimination of cytochrome c from the reaction. Finally, we demonstrate the feasibility of evaluating superoxide scavenging abilities on small samples extracted from two types of neuronal cultures, a hypothalamic neuronal cell line (GT1 trk cells) and primary mouse cortical cell cultures. This assay allows rapid, high throughput assessments of superoxide scavenging efficacy for small molecules of interest, as well as for cell or tissue extracts.
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PMID:Rapid microplate assay for superoxide scavenging efficiency. 1078 68

Desulfovibrio gigas aldehyde oxidoreductase (DgAOR) is a mononuclear molybdenum-containing enzyme from the xanthine oxidase (XO) family, a group of enzymes capable of catalyzing the oxidative hydroxylation of aldehydes and heterocyclic compounds. The kinetic studies reported in this work showed that DgAOR catalyzes the oxidative hydroxylation of aromatic aldehydes, but not heterocyclic compounds. NMR spectroscopy studies using (13)C-labeled benzaldehyde confirmed that DgAOR catalyzes the conversion of aldehydes to the respective carboxylic acids. Steady-state kinetics in solution showed that high concentrations of the aromatic aldehydes produce substrate inhibition and in the case of 3-phenyl propionaldehyde a suicide substrate behavior. Hydroxyl-substituted aromatic aldehydes present none of these behaviors but the kinetic parameters are largely affected by the position of the OH group. High-resolution crystallographic structures obtained from single crystals of active-DgAOR soaked with benzaldehyde showed that the side chains of Phe425 and Tyr535 are important for the stabilization of the substrate in the active site. On the other hand, the X-ray data of DgAOR soaked with trans-cinnamaldehyde showed a cinnamic acid molecule in the substrate channel. The X-ray data of DgAOR soaked with 3-phenyl propionaldehyde showed clearly how high substrate concentrations inactivate the enzyme by binding covalently at the surface of the enzyme and blocking the substrate channel. The different reactivity of DgAOR versus aldehyde oxidase and XO towards aromatic aldehydes and N-heterocyclic compounds is explained on the basis of the present kinetic and structural data.
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PMID:Aromatic aldehydes at the active site of aldehyde oxidoreductase from Desulfovibrio gigas: reactivity and molecular details of the enzyme-substrate and enzyme-product interaction. 2534 44