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)

1. 2,6-Dinitrotoluene (2,6-DNT) metabolism by human liver and male Fischer F344 rat liver subcellular fractions under aerobic (100% oxygen) and anaerobic (100% nitrogen) incubation conditions was examined. Under aerobic conditions the major 2,6-DNT metabolite formed by hepatic microsomes was 2,6-dinitrobenzyl alcohol (2,6-DNBalc); under anaerobic conditions 2-amino-6-nitrotoluene (2Am6NT) was the major metabolite. 2. Rates of 2,6-DNBalc formation by human and rat liver microsomes under aerobic conditions were 247 and 132 pmol/min per mg protein, respectively. Rates of 2Am6NT formation by human and rat liver microsomes under anaerobic conditions were 292 and 285 pmol/min per mg protein, respectively. Anaerobic reduction of 2,6-DNT to 2Am6NT by rat and human liver microsomes was inhibited by carbon monoxide and metyrapone, which indicates that microsomal metabolism of 2,6-DNT to 2Am6NT is mediated by cytochrome P-450. 3. Liver cytosolic fractions also metabolized 2,6-DNT to 2Am6NT under anaerobic conditions. Formation of 2Am6NT by human and rat liver cytosols was supported by hypoxanthine, NADPH and NADH. Allopurinol inhibited the hypoxanthine-supported anaerobic metabolism of 2,6-DNT by rat, but not human, liver cytosol. Dicumarol inhibited the NADPH-supported anaerobic metabolism of 2,6-DNT by human, but not rat, liver cytosol. These results indicate that xanthine oxidase contributes to the hypoxanthine-supported anaerobic metabolism of 2,6-DNT by human liver cytosol.
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PMID:Metabolism of 2,6-dinitro[3-3H]toluene by human and rat liver microsomal and cytosolic fractions. 141 78

We propose new hypotheses for the mechanisms of streptozotocin (STZ) and alloxan inducing experimental diabetes in animals. STZ is transported into pancreatic beta cells through glucose transporter in the cell membranes and attacks mitochondria. Mitochondrial ATP generation is inhibited and the resulting high concentration of intracellular ADP causes its degradation providing hypoxanthine, a substrate of xanthine oxidase (XOD) whose activity is intrinsically very high in beta cells. Then, XOD-catalyzing reaction is proceeded as proved by increased formation of uric acid and O2- radicals are produced, but beta cells are inefficient to scavenge these radicals because of their extremely low activity of superoxide dismutase. On the other hand, STZ directly activates XOD and enhances O2- generation. Consequently, pancreatic beta cells are dually suffered from O2- radicals or probably hydroxyl radicals derived from the former when exposed to STZ. Allopurinol, an inhibitor of XOD, can protect animals from the diabetogenic effect of STZ. In pancreatic beta cells, alloxan anion radicals are generated from alloxan probably mediated by the action of microsomal cytochrome P-450 system. These radicals have long half-life and directly damage DNA in vitro. The widely accepted hypothesis that the cause of alloxan-induced diabetes is attributable to O2- radicals formed from alloxan is excluded, because alloxan itself shows a very potent scavenging effect to O2- radicals. Therefore alloxan anion radicals seem to be directly related to the incidence of diabetes by alloxan.
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PMID:[New hypotheses for the mechanisms of streptozotocin and alloxan inducing diabetes mellitus]. 148 45

Superoxide anion radical and hydrogen peroxide (H2O2) are reactive oxygen metabolites which are thought to be involved in oxidant-induced lung injuries. Therefore, we studied their effects on the pulmonary metabolism of benzo[a]pyrene (BP) in rat lung microsomes. The microsomes were incubated with xanthine and xanthine oxidase to generate superoxide anion (effects verified with superoxide dismutase) or H2O2 and then the products formed during the metabolism of BP were measured. Both oxygen metabolites inhibit BP hydroxylase activity, i.e., the production of 3- and 9-hydroxybenzo[a]pyrene (phenols) in a concentration-dependent manner. The phenols account for approximately 75% of metabolite formation and are the major products of BP metabolism. Two components of the monooxygenase system responsible for BP metabolism, cytochrome P-450 and NADPH-cytochrome P-450 reductase, are also inhibited by the two oxygen metabolites in a similar manner. Superoxide anion is more effective than H2O2 in the inhibition of both BP hydroxylase and the monooxygenase components. Neither oxygen metabolite has any effect on the formation of minor metabolites of benzo[a]pyrene, i.e., BP-quinones and BP-dihydrodiols. These are the BP metabolites thought to produce toxic effects and which may lead to the formation of carcinogens and/or mutagens. The results of all these experiments suggest that exposure of lung microsomes to oxygen metabolites can lead to a slowing of overall BP metabolism and the increased accumulation of potentially toxic BP metabolites.
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PMID:Alterations of pulmonary benzo[a]pyrene metabolism by reactive oxygen metabolites. 165 2

Benzene, a known human myelotoxin and leukemogen is metabolized by liver cytochrome P-450 monooxygenase to phenol. Further hydroxylation of phenol by cytochrome P-450 monooxygenase results in the formation of mainly hydroquinone, which accumulates in the bone marrow. Bone marrow contains high levels of myeloperoxidase. Here we report that phenol hydroxylation to hydroquinone is also catalyzed by human myeloperoxidase in the presence of a superoxide anion radical generating system, hypoxanthine and xanthine oxidase. No hydroquinone formation was detected in the absence of myeloperoxidase. At low concentrations superoxide dismutase stimulated, but at high concentrations inhibited, the conversion of phenol to hydroquinone. The inhibitory effect at high superoxide dismutase concentrations indicates that the active hydroxylating species of myeloperoxidase is not derived from its interaction with hydrogen peroxide. Furthermore, catalase a hydrogen peroxide scavenger, was found to have no significant effect on hydroxylation of phenol to hydroquinone, supporting the lack of hydrogen peroxide involvement. Mannitol (a hydroxyl radical scavenger) was found to have no inhibitory effect, but histidine (a singlet oxygen scavenger) inhibited hydroquinone formation. Based on these results we postulate that a myeloperoxidase-superoxide complex spontaneously rearranges to generate singlet oxygen and that this singlet oxygen is responsible for phenol hydroxylation to hydroquinone. These results also suggest that myeloperoxidase dependent hydroquinone formation could play a role in the production and accumulation of hydroquinone in bone marrow, the target organ of benzene-induced myelotoxicity.
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PMID:Hydroxylation of phenol to hydroquinone catalyzed by a human myeloperoxidase-superoxide complex: possible implications in benzene-induced myelotoxicity. 166 26

The role of xanthine oxidase (XO) in the interferon (IFN)-dependent modulation of the hepatic cytochrome P-450 system was assessed in SENCAR mice. Intraperitoneal administration of 10(4)-10(5) units of IFN-gamma resulted in dose-dependent increases in hepatic XO activities. XO activity was significantly elevated within 12 h of IFN-gamma treatment, and reached a maximum between 24-48 h, and returned to basal levels within 72-96 h. Although the kinetics of increase and decline of XO activity correlated with the loss and subsequent recovery of hepatic P-450 levels, there was no quantitative correlation between hepatic XO activity and P-450 content. Comparable results were obtained in mice pretreated with the P-450 inducer Aroclor 1254 3 days prior to IFN-gamma administration. The increases in XO activity following IFN-gamma treatment were the consequence of increases in xanthine dehydrogenase (XD), and the conversion of XD to XO. The ad libitum administration of allopurinol to IFN-gamma-treated mice reduced XO specific activity to approximately 4% of the basal activity of control mice, but did not prevent reductions in cytochrome P-450 levels or the activities of two P-450 dependent monooxygenases. Collectively, these data suggest that the reductions in the hepatic P-450 system noted after IFN administration are not a consequence of elevated XO activities.
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PMID:Coordinate modulation of murine hepatic xanthine oxidase activity and the cytochrome P-450 system by interferons. 169 64

It has been suggested that the loss of cytochrome P-450, which is mediated by interferon and its inducers, can result from the generation of free radical species by the enzyme xanthine oxidase. Cytochrome P-450, aminopyrine N-demethylase, and ethoxyresorufin deethylase were depressed by 35, 36, 38%, respectively, in the livers of hamsters 24 h following the administration of a synthetic interferon (IFN-alpha-Con1) which contains the most frequent amino acid sequences of the human subtypes. Interferon increased the activities of the D and O forms of xanthine oxidase by 65 and 74%, respectively, in the same animals. The induction of the D form of xanthine oxidase, which is the precursor of the O form, preceded the loss in cytochrome P-450. The protein synthesis inhibitor, actinomycin D, prevented the interferon-induced loss of drug biotransformation and the increase in xanthine oxidase. The free radical scavenger, alpha-tocopherol, and the xanthine oxidase inhibitor, allopurinol, also prevented the loss of cytochrome P-450 mediated by the interferon inducer poly rI.rC. In chickens in which xanthine oxidase cannot be formed, poly rI.rC had no effect on cytochrome P-450 levels. These results suggest that xanthine oxidase induction may play some role in the interferon-mediated loss of cytochrome P-450.
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PMID:A role for xanthine oxidase in the loss of cytochrome P-450 evoked by interferon. 172 69

The in vitro conversion of (+)-3,4-methylenedioxymethamphetamine and (-)-3,4-methylenedioxymethamphetamine to the corresponding catecholamine, 3,4-dihydroxymethamphetamine (N-methyl-alpha-methyldopamine), by rat liver microsomes was examined. Metabolite formation was monitored after short-term incubations using high-performance liquid chromatography-electrochemical detection to determine concentrations of the catecholamine. The formation of N-methyl-alpha-methyldopamine exhibited enantioselectivity and levels were significantly higher after incubation of the (+)-isomer. The reaction appears to be cytochrome P-450 dependent as it was sensitive to SKF 525A and carbon monoxide. The catecholamine was unstable and was metabolized rapidly to a compound capable of forming an adduct with glutathione (GSH) and other thiol compounds. This second oxidation did not appear to be cytochrome P-450-dependent but required NADPH and microsomal protein. Catecholamine oxidation was inhibited by superoxide dismutase and by reducing agents. The same catecholamine oxidation product, characterized as the GSH adduct, could be generated by a xanthine-xanthine oxidase mixture and by tyrosinase. Mass spectral data showed that it was a 1:1 amine GSH adduct. These results indicate that MDMA is oxidized by cytochrome P-450 to the catechol and the catecholamine oxidized by superoxide to a quinone to which GSH or other thiol functions add. The formation of this quinone and its thiol adducts may account for some of the irreversible actions of this compound on serotonergic neurons.
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PMID:Metabolism of methylenedioxymethamphetamine: formation of dihydroxymethamphetamine and a quinone identified as its glutathione adduct. 197 41

The reduction of cytochromes b5 and P-450 in mammalian hepatic microsomes by glucose oxidase and xanthine oxidase has been investigated. Under anaerobic conditions cytochrome b5 is reduced by glucose oxidase to the "dithionite" level, while cytochrome P-450 remains oxidized. Under the same conditions xanthine oxidase completely reduces both hemoproteins. Besides, neither glucose oxidase nor xanthine oxidase reduces isolated cytochromes. They can be reduced only after addition of microsomes to incubation media. Only in this case are the cytochromes, both isolated and included in microsomal membranes, reduced. The participation of microsomal flavoproteins in the reduction reaction is discussed. The method suggested makes it possible to substantially decrease the rates of reduction of microsomal hemoproteins, thus permitting the investigation of interactions between microsomal NADH- and NADPH-dependent electron-transport chains and electron carriers.
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PMID:Application of electron-donor properties of glucose oxidase and xanthine oxidase for reduction of microsomal NAD(P)H-dependent electron-transport chains. 205 5

A number of infections are capable of depressing the capacity of the liver to metabolize drugs. We have studied a number of factors which could be involved in the depression of cytochrome P-450 and related drug biotransformation enzymes during infections with Listeria monocytogenes. During the course of the infection, drug metabolism and heme content of hepatic microsomes were depressed but heme oxygenase was elevated. A free radical scavenger alpha-tocopherol did not prevent the loss and xanthine oxidase activities did not correlate with the time course of the loss. Infections in susceptible (balb/c) mice produced a larger loss in drug metabolism than in resistant (C57BL/6) mice, and an avirulent strain of the bacteria was without effect. A preparation of hemolysin isolated from Listeria monocytogenes produced a dose-dependent loss of cytochrome P-450 in isolated hepatocytes. These experiments indicate that the loss of drug metabolism during Listeria infections is most likely due to hemolysin released by the bacteria.
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PMID:Factors involved in the depression of hepatic mixed function oxidase during infections with Listeria monocytogenes. 207 Dec 96

The NADPH-dependent lipid peroxidation in human placental mitochondria has been found to be inhibited strongly by amphenone B, aminoglutethimide and carbon monoxide, inhibitors of cytochrome P-450-mediated reactions, but was hardly affected by respiratory chain inhibitors. Cytochrome c, an exogenous electron acceptor which is known to compete with cytochrome P-450 for the reducing equivalents, showed an inhibitory effect on NADPH-dependent lipid peroxidation. The observed NADPH-dependent superoxide generation was also strongly inhibited by amphenone B and aminoglutethimide. Moreover, the lipid peroxidation in placental mitochondria was demonstrated to be stimulated by xanthine/xanthine oxidase added as superoxide generating system. This peroxidation was not affected by amphenone B and aminoglutethimide. On the other hand, the superoxide dismutase was found to inhibit both the xanthine oxidase- and NADPH-dependent lipid peroxidation. These data provide evidence that cytochrome P-450 is involved in NADPH-dependent mitochondrial lipid peroxidation. It is suggested that superoxide liberated from cytochrome P-450, in combination with iron, may be responsible for initiation of NADPH-dependent lipid peroxidation in human placental mitochondria.
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PMID:Cytochrome P-450 involvement in the NADPH-dependent lipid peroxidation in human placental mitochondria. 216 Feb 83


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