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 catalytic oxidation of [14C]-formate to 14CO2 was adapted to measure H2O2 formation in cellfree system. Standard curves employing glucose-glucose oxidase and xanthine-xanthine oxidase demonstrated linearity between 14CO2 evolution and enzyme concentration. A particulate fraction from human neutrophils was capable of oxidizing [14C]-formate; this reaction was dependent upon the presence of catalase, reduced pyridine nucleotide, and cellular material. Reaction increased with time of incubation and protein concentration, although not in a strictly linear fashion. The pH optimum was approximately 5.5 NADPH was a significantly better substrate than NADH, although both were capable of generating H2O2. The particulate fraction derived from phagocytizing cells was more active than a corresponding fraction from resting cells with either substrate. H2O2 production was abnormal in particulate fractions derived from 2 patients with chronic granulomatous disease. H2O2 production was markedly inhibited by superoxide dismutase or cytochrome c (scavengers of superoxide anion) but not by scavengers of singlet oxygen or hydroxyl radical. Reaction was greatly stimulated by the addition of manganous ion. These results are consistent with the hypothesis that the respiratory burst in human neutrophils is initiated by an oxidase that can utilize either NADPH or NADH but exhibits a marked preference for the former. Further, the inhibitor studies strongly support a mechanism involving an initial enzymatic reaction followed by a self-sustaining free radical reaction involving superoxide anion.
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PMID:Pyridine nucleotide-dependent generation of hydrogen peroxide by a particulate fraction from human neutrophils. 689 95

The chemical reactivity of 8-chloroflavins and 8-mercaptoflavins has been exploited in order to examine the orientation of protein-bound flavins relative to solvent. The apoprotein form of a series of flavoproteins was prepared and the native flavin was replaced by either 8-Cl-flavin or 8-mercaptoflavin (FAD, FMN, or riboflavin form as was appropriate). The reconstituted proteins were exposed to reagents capable of reacting with the group at position 8. The 8-Cl-proteins were challenged with sodium sulfide and thiophenol, while the 8-mercaptoproteins were faced with iodoacetamide and iodoacetic acid. The kinetics of the ensuing reactions served as a measure of the solvent availability of position 8 for the protein-bound flavin. These studies indicated that position 8 of flavin bound to melilotate hydroxylase, D-amino acid oxidase, old yellow enzyme, p-OH-benzoate hydroxylase, and flavodoxin is accessible to solvent, while position 8 on L-lactate oxidase, glucose oxidase, putrescine oxidase, and riboflavin-binding protein appears to be inaccessible. For luciferase, D-lactate dehydrogenase, and xanthine oxidase, the data suggest that position 8 is exposed but the results are inconclusive. The effect of ligand binding on the accessibility of position 8 was also studied. NADPH binding to 8-mercapto old yellow enzyme and benzoate binding to 8-Cl-D-amino acid oxidase results in complete blockage of previously available position 8. On the other hand, p-OH-benzoate hydroxylase and melilotate hydroxylase bind their respective substrates (p-OH-benzoate and melilotate) without significantly altering the reactivity of position 8.
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PMID:Active site probes of flavoproteins. Determination of the solvent accessibility of the flavin position 8 for a series of flavoproteins. 689 55

The present study demonstrated the metabolism of N-hydroxyurethane by cell-free preparations, i.e., 9000 X g supernatant, cytosol and microsomes, from guinea pig livers. Under anaerobic conditions, the metabolizing activities of these preparations were enhanced markedly by addition of both an NADPH- or NADH-generating system and FAD. When the 30-45% ammonium sulfate fraction from liver cytosol was combined with liver microsomes or milk xanthine oxidase, the metabolic reaction of N-hydroxyurethane proceeded to a greater extent. Thin-layer chromatographic examination showed that urethane was only a metabolite formed from N-hydroxyurethane by these preparations.
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PMID:Metabolism of N-hydroxyurethane by guinea pig liver preparations. 716 23

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 antioxidant activity of nimesulide and its main metabolites, 4'-hydroxynimesulide (M1) and 2-(4'-hydroxyphenoxy)-4-N-acetylamino-methansulfonanilide (M2), was investigated using 2 in vitro models: NADPH-supported lipid peroxidation in rat liver microsomes (marker MDA formation) and xanthine/xanthine oxidase, iron-promoted depolymerisation of hyaluronic acid, determined by gel permeation chromatographic analysis (marker molecular weight distribution). In the lipid peroxidation model, all the compounds inhibited MDA formation in a concentration-dependent manner, although with different potencies; the maximum scavenging effect was observed for M1 [50% inhibitory concentration (IC50) = 30 mumol/L; M2 IC50 = 0.5 mmol/L; nimesulide = 0.8 mmol/L]. Nimesulide was more active than its metabolites in preventing OH-induced depolymerisation of hyaluronic acid, with a 50% effective concentration of approximately 230 mumol/L, which was fairly comparable to that of tenoxicam. This protective effect was due to the OH.-entrapping capacity of the drug, which, in the Fenton-driven model, is easily converted, via OH. attack, to M1 and putatively to 2-hydroxy-4-nitro-methansulfonanilide.
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PMID:Antioxidant activity of nimesulide and its main metabolites. 750 57

The dynamics and mechanisms of extracellular release of hydrogen peroxide (H2O2) from bovine pulmonary artery endothelial cells (EC) subjected to anoxia, hypoxia, and hypoxia followed by reoxygenation were examined using various inhibitors of enzymatic systems in intact cells and by direct measurement of H2O2 production from isolated EC plasma membranes. Extracellular H2O2 was measured with a fluorometric assay. EC exposed to hypoxia (3% O2) and anoxia (0% O2) released less H2O2 (29.6 +/- 1.3% and 4.2 +/- 0.7%, respectively) compared with EC exposed to normoxia (20% O2). The extracellular release of H2O2 from EC previously exposed to hypoxia for 24 h increased immediately after reoxygenation (20% O2) to 272 +/- 48%, as compared with EC exposed continuously to normoxia (100% release). Inhibition of xanthine oxidase (XO) by allopurinol did not reduce the release of H2O2 from cells exposed to normoxia or hypoxia followed by reoxygenation. Furthermore, inhibitors of cyclooxygenase (indomethacin), phospholipase A2 (quinacrine and chlorpromazine), nitric oxide synthase (L-arginine analogs), the mitochondrial electron transport chain (rotenone and cyanide), and cytochrome P-450 (methoxypsoralen) had no or minimal effect on this release. On the other hand, inhibitors of protein kinase C (calphostin and staurosporine) and NADPH oxidase (diphenyliodonium) reduced the release of H2O2 from EC in a dose-dependent manner in both exposure groups. In separate experiments, plasma membranes isolated from EC were found to produce H2O2 in the presence of NADH or NADPH as electron donors. This was inhibited by diphenyliodonium but not by allopurinol.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Release of hydrogen peroxide in response to hypoxia-reoxygenation: role of an NAD(P)H oxidase-like enzyme in endothelial cell plasma membrane. 752 30

Liver cytosolic fractions are known to catalyze the reduction of certain C-nitroso compounds to their corresponding hydroxylamines and amines. Alcohol dehydrogenase (ADH), NAD(P)H:quinone oxidoreductase, and xanthine and aldehyde oxidases have been implicated as C-nitroso reductases. To probe the role of these cytosolic enzymes in the reduction of C-nitroso compounds we have studied the effects of classical inhibitors of these enzymes on the ability of liver cytosolic fractions from ADH+ and ADH- deermice to reduce p-nitrosophenol to p-aminophenol. Pyrazole, a potent inhibitor of ADH, inhibited NADH-p-nitrosophenol reduction by ADH+ cytosol by > 85%. Thus, ADH contributes substantially to NADH-C-nitroso reduction by cytosol from ADH+ deermice. The NAD(P)H:quinone oxidoreductase inhibitor, dicumarol, inhibited NADH-dependent p-aminophenol formation by about 25%; however, dicumarol potently inhibited the NADPH-dependent formation (90-95%). As expected, cytosol from ADH- deermice did not catalyze pyrazole-sensitive (ADH-dependent) C-nitroso reduction with NADH as the cofactor. Both NADPH- and NADH-p-nitrosophenol reduction by ADH- cytosol were inhibited > 90% by dicumarol. The xanthine oxidase/aldehyde oxidase inhibitor, allopurinol, was without effect on NAD(P)H cytosolic p-nitrosophenol reduction from ADH- and ADH+ deermice under either aerobic or anaerobic conditions. Our findings suggest that in the ADH+ animal, ADH contributes significantly to NADH-dependent C-nitroso reduction by cytosol relative to NAD(P)H:quinone oxidoreductase. NADPH-dependent p-nitrosophenol reduction by liver cytosol of ADH+ animals is mostly dicumarol-sensitive, which implicates NAD(P)H:quinone oxidoreductase as the major NADPH-dependent activity. In ADH- deermice, both NADH- and NADPH-dependent p-nitrosophenol reduction are essentially dicumarol-sensitive (NAD(P)H:quinone oxidoreductase-dependent). Because the toxic expression of C-nitroso compounds is mediated by hydroxylamine intermediates, the present data indicate the importance of considering the role of ADH in the toxic sequelae of nitro and nitroso arenes.
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PMID:p-nitrosophenol reduction by liver cytosol from ADH-positive and -negative deermice (Peromyscus maniculatus). 753 87

We have characterized a chemically reactive propranolol (PL) metabolite which binds to proteins in rat liver microsomes. During incubation with rat liver microsomes (1 mg of protein) fortified with an NADPH-generating system, 4-hydroxypropranolol (4-OH-PL) quickly disappeared from the reaction medium, but none of the possible metabolite peaks was detected under the high-performance liquid chromatographic conditions used. The consumption of 4-OH-PL depended on microsomes and NADPH. The reaction was not affected by inhibitors of cytochrome P450 or FAD monooxygenase, but was markedly diminished in the presence of cytosol and ascorbic acid. The effect of cytosol was inhibited by potassium cyanide but not by sodium benzoate or dimethyl sulfoxide, and was also not affected by heating at 60 degrees C for 30 min, suggesting that superoxide (SO) ion was involved in the reaction and that it was blocked by superoxide dismutase (SOD) present in the cytosol. Cu,Zn-SOD, purified from cytosol, effectively mimicked the suppressive effect of cytosol. Incubation of 4-OH-PL in an SO-generating system of xanthine and xanthine oxidase generated 1,4-naphthoquinone (1,4-NQ), which was identified by TLC, HPLC, and GC/MS. 1,4-NQ was also formed in microsomal incubates containing NADPH and small amounts of microsomes (below 0.1 mg of protein). These results indicate that 4-OH-PL is converted by SO, or some reactive oxygen species derived from it, to 1,4-NQ which binds to proteins and is one of the reactive metabolites of PL.
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PMID:Characterization of a chemically reactive propranolol metabolite that binds to microsomal proteins of rat liver. 754 55

Superoxide anion can modulate vascular smooth muscle tone and potentially affect the growth response in vascular disease. The present studies were undertaken to characterize the source of superoxide in rabbit aorta. Rings of aorta (5 mm) were incubated in physiological salt solution (PSS) for 30 min at 37 degrees C in the presence of 10 mM diethyldithiocarbamate (DDC) with or without inhibitors of superoxide-generating systems. Rings were then placed in PSS containing 250 microM lucigenin at 37 degrees C in the presence or absence of inhibitors, and changes in amounts of superoxide were determined by measuring chemiluminescence (units). The inhibitors of xanthine oxidase, oxypurinol (300 microM), and of mitochondrial NADH dehydrogenase, rotenone (50 microM), had no significant effect on superoxide levels. An inhibitor of NADPH oxidase, iodonium thiophen, caused a concentration-dependent inhibition of superoxide anion (12.49 +/- 1.48 vs 5.27 +/- 1.81 and 2.30 +/- 0.36 units, control vs 7 microM and 70 microM iodonium thiopen, respectively). A structurally related iodonium compound, diphenyleneiodonium (20 microM), caused a 78% reduction in basal and DDC-evoked superoxide levels. In the presence or absence of DDC, exogenous administration of NADPH (10 microM-1 mM), but not NADP (1 mM), elicited a concentration-dependent rise in superoxide levels that was inhibited by iodonium thiophen. Particulate fractions of whole aortic tissue exhibited NADPH-dependent superoxide production that was inhibited by 1 microM diphenyleneiodonium.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:An NADPH oxidase superoxide-generating system in the rabbit aorta. 761 77


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