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)

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.
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PMID:Role of hydroxyl radicals in the iron-ethylenediaminetetraacetic acid mediated stimulation of microsomal oxidation of ethanol. 677 47

The mechanism of cytochrome P-450-dependent oxidation of ethanol has been investigated using reconstituted phospholipid vesicles containing purified preparations of rabbit liver microsomal NADPH-cytochrome P-450 reductase and cytochrome P-450 LM2. Incorporation of cytochrome b5 into the vesicles resulted in a 5-fold enhancement of cytochrome P-450-catalyzed O-dealkylation of 7-ethoxycoumarin, whereas the cytochrome P-450-dependent ethanol oxidation was slightly inhibited. Superoxide dismutase, added in increasing amounts to the vesicles, inhibited the formation of superoxide anions and, in a concomitant manner, also the production of acetaldehyde from ethanol in the system. Also horseradish peroxidase inhibited ethanol oxidation catalyzed by the vesicles; acetaldehyde formation and H2O2 formation decreased in a concomitant manner as the amount of the peroxidase was increased. Externally added hydrogen peroxide markedly stimulated cytochrome P-450-dependent ethanol oxidation, but not until the concentration of H2O2 reached 0.3 mM, whereas the hydroxyl radical scavenger mannitol completely inhibited the cytochrome P-450-dependent acetaldehyde production. Oxidation of ethanol was also accomplished using vesicles containing cytochrome b5 instead of cytochrome P-450 and in other systems regenerating superoxide anions, e.g. the xanthine-xanthine oxidase system and dihydroxyfumarate. The results are consistent with an iron-catalyzed Haber-Weiss mechanism for regeneration of hydroxyl radicals which subsequently react with ethanol, thereby giving the corresponding aldehyde.
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PMID:The mechanism of cytochrome P-450-dependent oxidation of ethanol in reconstituted membrane vesicles. 678 51

The effects of aspirin on N-[4-(5-nitro-2-furyl)-2-thiazolyl]-formamide (FANFT) -induced urinary bladder lesions, endogenous bladder prostaglandin E2 synthesis, and the metabolism of FANFT by bladder epithelial microsomes were examined. Rats were fed 0.5% aspirin and/or a diet containing 0.1% or 0.2% FANFT. Bladder lesions were observed with light and scanning electron microscopy, and the prostaglandin E2 content of rat bladder was measured by radioimmunoassay. Metabolism of FANFT was measured by decreased absorbance at 400 nm. Aspirin inhibited the appearance of hyperplastic lesions induced by feeding 0.1% or 0.2% FANFT for 6 or 12 weeks. Aspirin reduced bladder prostaglandin E2 content at 1, 2, 6, and 13 weeks compared to corresponding control values. Rat and rabbit microsomal metabolism of FANFT were dependent upon specific fatty acid substrate and prevented by specific inhibitors (including aspirin) of prostaglandin endoperoxide synthetase. Other inhibitor and substrate specificity studies suggest that FANFT was not metabolized by xanthine oxidase, lipoxygenase, lipid peroxidation, or mixed-function oxidases. These results suggest that the metabolism of FANFT by prostaglandin endoperoxide synthetase may be involved in the metabolic activation of FANFT necessary for the induction of bladder cancer in rats.
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PMID:Aspirin inhibition of N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide-induced lesions of the urinary bladder correlated with inhibition of metabolism by bladder prostaglandin endoperoxide synthetase. 679 Jan 63

Purified liver microsomal NADPH-cytochrome P-450 reductase is able to catalyze the activation of [14C]ronidazole to metabolite(s) which bind covalently to protein. Like the reaction catalyzed by microsomes, protein alkylation catalyzed by the reductase is (1) sensitive to oxygen, (2) requires reducing equivalents, (3) is inhibited by sulfhydryl-containing compounds and (4) is stimulated several fold by either flavin mononucleotide (FMN) or methytlviologen. A cytochrome P-450 dependent pathway of ronidazole activation can be demonstrated as judged by the inhibition of the reaction by carbon monoxide, metyrapone and 2,4-dichloro-6-phenylphenoxyethylamine but the involvement of specific microsomal cytochrome P-450 isozymes has not been definitively established. Milk xanthine oxidase is also capable of catalyzing ronidazole activation. Polyacrylamide sodium dodecyl sulfate (SDS)-gel electrophoresis reveals that the reactive intermediate(s) of ronidazole does not alkylate proteins selectively.
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PMID:Drug residue formation from ronidazole, a 5-nitroimidazole. II. Involvement of microsomal NADPH-cytochrome P-450 reductase in protein alkylation in vitro. 680 46

A solid-phase immunoassay was used to detect xanthine oxidase in fractions from bovine mammary glands after electrophoresis in polyacrylamide gels containing sodium dodecyl sulphate. Under these conditions the major proportion of xanthine oxidase in either mammary tissue or mild could be recovered as a protein of mol.wt. 150 000. In mammary tissue approx. 80% of the enzyme was in a soluble form and the remainder was accounted for in either 'mitochondrial' or microsomal fractions after tissue homogenization and fractionation. Affinity chromatography of either detergent-solubilized microsomal membranes or postmicrosomal supernatants on immobilized antibody to xanthine oxidase yielded a single protein that cross-reacted with antibody to the enzyme. In milk presumptive degradation products of the enzyme were detected in minor quantities with mol.wts. of 43 000 in the whey fraction and 90 000 in fat-globule membrane. Only the undegraded enzyme was present in the skim-milk membrane fraction. Xanthine oxidase is therefore synthesized and secreted as a protein with a monomeric mol.wt. of 150 000 and is not subjected to extensive proteolytic degradation during the storage of milk in mammary alveoli. The significance of the results is discussed in relation to the overall protein composition of the membranes of milk-fat globules and skim milk.
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PMID:Detection of xanthine oxidase and immunologically related proteins in fractions from bovine mammary tissue and milk after electrophoresis in polyacrylamide gels containing sodium dodecyl sulphate. 704 30

The effect of storage at - 80 degrees C for 1-28 days on the activity of 12 enzymes in intact liver tissue, liver extract and isolated hepatic microsomes was investigated. To find optimal conditions for tissue homogenization for this study the effects of three types of homogenization on the activity of 10 enzymes from different cell compartments were compared. The activities of glucokinase and phosphofructokinase decreased markedly during storage of both supernatant and liver tissue. Storage of liver tissue increased the activity of mitochondrial enzymes or isoenzymes. While this effect can be explained by additional disintegration of liver tissue caused by freezing and thawing for enzymes like glutamine dehydrogenase, other mechanisms may be involved in the prolonged increase observed in the activity of citrate synthase and xanthine oxidase during storage. The activity of a number of enzymes from the cytosol, mitochondria and microsomes decreased more markedly in the stored liver samples than in the stored supernatant or in the stored microsomal pellet. Cytochrome P 450 content remained stable throughout the whole storage period in both intact liver tissue and isolated microsomes.
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PMID:The effect of storage at - 80 degrees C on the activities of cytoplasmic, mitochondrial and microsomal enzymes in rat liver. 706 80

Plasma membranes were isolated from lactating bovine mammary gland. Two crude membrane fractions; medium/d 1.033 (light membrane) and 1.033/1.053 interfaces (heavy membrane), were obtained by Ficoll density gradient centrifugation of osmotically washed microsomal fraction. Two crude membranes were further purified separately by sucrose density gradient centrifugation. Both light and heavy membranes banded at a sucrose density of 1.14. The purified membranes appeared as heterogeneous smooth membrane vesicles on electron microscopy. The contaminating suborganelles were not detected. The yield of the purified membranes relative to the homogenate was 1.2%. The degree of purity of the membranes was shown by a great increase in the specific activity of 5'-nucleotidase over the homogenate of 20-fold for light membrane and of 16-fold for heavy membrane. The relative activities of Mg2+-ATPase, (Na+ + K+)-ATPase, gamma-glutamyl transpeptidase, phosphodiesterase I, alkaline phosphatase and xanthine oxidase were also high (12-18-times) and nearly 20% of these enzymes was recovered. The activity of marker enzyme for mitochondria, endoplasmic reticulum and Golgi apparatus was very low, while that of acid phosphatase for lysosome was relatively high (5-times). DNA and RNA contents were very low. The major polypeptides rich in other suborganelles were not detected profoundly in the membrane fraction and the polypeptide composition in both light and heavy membranes were similar upon SDS-polyacrylamide gel electorphoresis.
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PMID:Isolation and characterization of plasma membrane from lactating bovine mammary gland. 720 55

1. The subcellular distribution of nitrobenzene reduction activity in rat liver cells indicated the existence of two different enzyme systems, one localized in microsomes and the other localized in cytosol. The activity in the cytosol was mainly attributable to xanthine oxidase, judging from its substrate specificity and the inhibition by allopurinol. 2. The participation of the microsomal electron transport system in nitrobenzene reduction was examined by using antibodies against four components of the system, NADPH-cytochrome c reductase (fpT), NADH-cytochrome b5 reductase (fpD), cytochrome b5, and cytochrome P-450. Both NADH- and NADPH-dependent nitrobenzene reduction activities were strongly inhibited by anti-fpT IG and also by anti-P450 IG, but not inhibited by anti-fpD IG or anti-b5 IG. The reduction of nitrosobenzene and phenylhydroxylamine, which are supposed to be the intermediates of nitrobenzene reduction, was also examined, and it was found that NADH- and NADPH-dependent reduction of both compounds were strongly inhibited by anti-fpT IG and anti-P450 IG, but not by anti-fpD IG or anti-b5 IG. 3. Reconstruction experiments using purified NADPH-cytochrome P-450 reductase and cytochrome P-450 were also carried out and it was confirmed that the reduction of nitrobenzene, nitrosobenzene, and phenylhydroxylamine to aniline could be effected by these two components. 4. Nitrobenzene reduction by microsomes exhibited a short initial time lag and was activated by the addition of purified NADPH-cytochrome c reductase, whereas nitrosobenzene and phenylhydroxylamine reductions did not show any initial time lag and were not activated by the reductase. These observations suggest that the reduction of nitrobenzene to an intermediate, possibly nitrosobenzene or phenylhydroxylamine, limits the rate of aniline formation, and such an initial step of nitrobenzene reduction can be catalyzed by NADPH-cytochrome c reductase alone. Cytochrome P-450 is essential at least in the final step of nitrobenzene reduction to aniline. This conclusion was further confirmed by determination of these intermediates in nitrobenzene reduction.
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PMID:Participation of cytochrome P-450 in the reduction of nitro compounds by rat liver microsomes. 739 Sep 98

Four diterpenoids, carnosic acid (1), carnosol (2), rosmanol (3), and epirosmanol (4), were isolated as antioxidative agents from the leaves of Rosmarinus officinalis by bioassay-directed fractionation. These diterpenoids inhibited superoxide anion production in the xanthine/xanthine oxidase system. Mitochondrial and microsomal lipid peroxidation induced by NADH or NADPH oxidation were also completely inhibited by these diterpenes at the concentration of 3-30 microM. Furthermore, carnosic acid protected red cells against oxidative hemolysis. These phenolic diterpenes were shown to be effective to protect biological systems against oxidative stresses.
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PMID:Inhibition of lipid peroxidation and superoxide generation by diterpenoids from Rosmarinus officinalis. 748 Jan 80

The paper deals with the mechanisms responsible for formation of active oxygen forms and with the physiological and toxic aspects of their action on the cell. The active oxygen forms are essential biological energy metabolites, such as mitochondrial respiration and microsomal oxidation. It considers the specific features of the systems of APA by various cells (neutrophils, lymphocytes, fibroblasts, endothelial cells). The results of their authors' own investigations provide evidence for the concept that there is an oxidative damage to hepatocytes in liver damage, which is associated with activation of phagocytes, conversion of xanthine oxidase, inhibition of superoxide dismutase and catalase activity and accumulation of active oxygen forms.
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PMID:[Intracellular oxygen activation and molecular mechanisms of oxidative hepatic damage]. 751 22


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