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)

A new HPLC method was set up for the simultaneous evaluation of the amount of uric acid and NADH produced by incubation of tissue fractions containing xanthine oxidase, from which the activity of both type "O" (oxidase) and type "D" (dehydrogenase) xanthine oxidase can be calculated. After incubation of the enzyme fraction and ethanol extraction, HPLC analysis is directly carried out. Sensitivity of the method is high enough for the evaluation of xanthine oxidase activity at the lowest reported tissue values. The reliability of the method was tested measuring the enzyme activity in rat heart and kidney extracts.
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PMID:Xanthine oxidase activity: simultaneous HPLC evaluation of the "D" and "O" forms. 275 84

Considerable evidence suggests that the release of iron from ferritin is a reductive process. A role in this process has been proposed for two hepatic enzymes, namely xanthine oxidoreductase and an NADH oxidoreductase. The abilities of xanthine and NADH to serve as a source of reducing power for the enzyme-mediated release of ferritin iron (ferrireductase activity) were compared with turkey liver and rat liver homogenates. The maximal velocity (Vmax.) for the reaction with NADH was 50 times greater than with xanthine; however, the substrate concentration required to achieve half-maximal velocity (Km) was 1000 times less with xanthine than with NADH. NADPH could be substituted for NADH with little loss in activity. Dicoumarol did not inhibit the reaction with NADH or NADPH, demonstrating that the ferrireductase activity with those substrates was not the result of the liver enzyme 'DT-diaphorase' [NAD(P)H dehydrogenase (quinone)]. A flavin nucleotide was required for ferrireductase activity with rat and turkey liver cytosol when xanthine, NADH or NADPH was used as the reducing substrate. FMN yielded twice the activity with NADH or NADPH, whereas FAD was twice as effective with xanthine as substrate. Kinetic comparisons, differences in lability and partial chromatographic resolution of the ferrireductase activities with the two types of reducing substrates strongly indicate that the ferrireductase activities with xanthine and NADH are catalysed by separate enzyme systems contained in liver cytosol. Complete inhibition by allopurinol of the ferrireductase activity endogenous to undialysed liver cytosol preparations and the ability of xanthine to restore equivalent activity to dialysed preparations indicate that the source of reducing power for the endogenous activity is xanthine. These studies suggest that xanthine, NADH or NADPH can serve as a source of reducing power for the enzyme-mediated reduction of ferritin iron, with a flavin nucleotide serving as the shuttle of electrons from the enzymes to the ferritin iron.
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PMID:The mobilization of ferritin iron by liver cytosol. A comparison of xanthine and NADH as reducing substrates. 277 99

In the presence of Cu2+ and Zn2+ carnosine (beta-alanyl-L-histidine) possesses a superoxide-scavenging activity. The efficiency of scavenging as measured by the inhibition of tetrazolium nitroblue reduction in superoxide anion generation systems (phenazine methasulfate/NADH and xanthine/xanthine oxidase) is concentration-dependent and shows a maximum in the presence of millimolar concentrations of carnosine and equimolar concentrations of Cu2+ and Zn2+. In the presence of Cu2+ and Zn2+ histidine also exhibits a superoxide-scavenging activity. The feasible role of the superoxide-scavenging activity of histidine-containing dipeptide complexes with bivalent metal ions in the realization of physiological function of these dipeptides in skeletal muscles is discussed.
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PMID:[Superoxide-scavenging activity of carnosine in the presence of copper and zinc ions]. 282 48

The ability of two low-molecular-weight copper complexes to influence the hemolysis of human erythrocytes caused by active oxygen species-generating systems was studied. Cu(II) (glycine)2 and Cu(II) (tyrosine)2 did not inhibit hemolysis due to O-2 and H2O2 generated by xanthine oxidase plus acetaldehyde but rather has a prooxidant effect. The same copper complexes as well as Cu(II) strongly inhibited the hemolysis caused by the 1O2-generating system (Rose Bengal + light). It was found that except for 1O2 the other active oxygen species (O-2, H2O2 and OH.) did not participate in the Rose Bengal + light-induced hemolysis. Thus we examined whether the inhibitory effect of copper complexes was due to 1O2 quenching. Cu(II) (glycine)2 inhibited the Rose Bengal + light-induced oxidation of compounds known to react chemically with 1O2 and its effects were analogous to the effects of physical 1O2 quenchers, e. g. NaN3 and NiCl2. The oxygen consumption upon NADH-photooxidation in the presence of Rose Bengal was inhibited competitively by Cu(II) (glycine)2 but when concentration of Rose Bengal or light intensity were varied the extent of Cu(II) (glycine)2-caused inhibition was not changed. It is concluded that the effects of Cu(II) (glycine)2 and possibly of Cu(II) (tyrosine)2 are due to quenching of 1O2 but quenching of the excited state of the dye could not be excluded.
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PMID:A study on the ability of copper complexes to act as active oxygen species scavengers. 282 28

A previously unidentified fraction lacking xanthine:O2 activity has been isolated during affinity chromatography of bovine milk xanthine oxidase preparations on Sepharose 4B/folate gel. Unlike active, desulfo, or demolybdo forms of xanthine oxidase, this form, which typically comprises about 5% of an unfractionated enzyme solution, passes through the affinity column without binding to it, and is thus easily separated from the other species. The absorption spectrum of this fraction is very similar to that of the active form, but has a 7% lower extinction at 450 nm. Analysis of the fraction has shown that it is a dimer of normal size, but that it does not contain molybdenum or molybdopterin (MPT). The "MPT-free" xanthine oxidase contains 90-96% of the Fe found in active xanthine oxidase, and 100% of the expected sulfide. EPR and absorption difference spectroscopy indicate that the MPT-free fraction is missing approximately half of its Fe/S I centers. The presence of a new EPR signal suggests that an altered Fe/S center may account for the nearly normal Fe and sulfide content. Microwave power saturation parameters for the Fe/S II and Fe/S I centers in the MPT-free fraction are normal, with P1/2 equal to 1000 and 60 mW, respectively. The new EPR signal shows intermediate saturation behavior with a P1/2 = 200 mW. The circular dichroism spectrum of the MPT-free fraction shows distinct differences from that of active enzyme. The NADH:methylene blue activity of the MPT-free fraction is the same as that of active xanthine oxidase which exhibits xanthine:O2 activity, but NADH:cytochrome c and NADH:DCIP activities are diminished by 54 and 37%, respectively.
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PMID:A molybdopterin-free form of xanthine oxidase. 282 75

Seven flavonoids and three non-flavonoid antioxidants, i.e. butylated hydroxyanisole, chlorpromazine and BW 755 C, were studied as potential scavengers of oxygen free radicals. Superoxide anions were generated enzymatically in a xanthine-xanthine oxidase system and non-enzymatically in a phenazine methosulphate-NADH system, and assayed by reduction of nitro blue tetrazolium. The generation of malonaldehyde (MDA) by the ascorbate-stimulated air-oxidised boiled rat liver microsomes was considered as an index of the non-enzymatic formation of hydroxyl radicals. Flavonoids but not non-flavonoid antioxidants lowered the concentration of detectable superoxide anions in both enzymic and non-enzymic systems which generated these SOD-sensitive radicals. The most effective inhibitors of superoxide anions were quercetin, myricetin and rutin. Four out of seven investigated flavonoids seemed also to suppress the activity of xanthine oxidase as measured by a decrease in uric acid biosynthesis. All ten investigated compounds inhibited the MDA formation by rat liver microsomes. Non-flavonoid antioxidants were more potent MDA inhibitors than flavonoids. It is concluded that antioxidant properties of flavonoids are effected mainly via scavenging of superoxide anions whereas non-flavonoid antioxidants act on further links of free radical chain reactions, most likely by scavenging of hydroxyl radicals.
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PMID:Flavonoids are scavengers of superoxide anions. 283 Aug 82

Methylene blue competes 100 to 600 times more effectively than paraquat for reduction by three different flavo-containing enzymes; xanthine oxidase, NADH cytochrome c reductase, and NADPH cytochrome c reductase. Paraquat and methylene blue both interact with deflavo xanthine oxidase, indicating that neither electron acceptor reacted at the FAD site of the enzyme where molecular oxygen is reduced to superoxide. As the paraquat radical also directly reduced acetylated cytochrome c the hemeprotein could not be utilized for measuring superoxide production in the presence of the herbicide. In the presence of cytochrome c the methylene blue caused a sharp decrease in both paraquat-induced superoxide and hydroxyl radical production.
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PMID:Methylene blue competes with paraquat for reduction by flavo-enzymes resulting in decreased superoxide production in the presence of heme proteins. 283 6

Four calcium channel blockers were tested from the point of view of their influence on enzymic lipid oxidation and on generation of superoxide anions. All the compounds were found to be antioxidants as tested by the inhibition of NADPH-stimulated malonaldehyde formation from lipids. IC50 values were 60 microM for nifedipine; 1.1 microM for verapamil; 1.4 microM for fendiline and 20.6 microM for diltiazem. Only nifedipine scavenged superoxide anions both in an enzymic (xanthine:xanthine oxidase) and non-enzymic (phenazine methosulphate:NADH) generating system. IC50 values for this inhibition were about 2.5 times higher than for inhibition of formation of malonaldehyde. Nifedipine inhibited also xanthine oxidase-mediated formation of uric acid.
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PMID:The influence of calcium channel blockers on superoxide anions. 283 71

In the hypoxic liver an increased rate of cytosolic and peroxisomal H2O2 generation is due to the accelerated purine nucleotide degradation. The relative contribution of the oxidase type of xanthine oxidoreductase activity increases in hypoxia by less than 10%, the dehydrogenase type of this enzyme is hardly inhibited by the increased concentration of free NADH. Nevertheless, due to the high hypoxanthine supply the xanthine oxidase related H2O2 formation is increased six-fold and together with the peroxisomal uricase-mediated share it accounts for half of the oxygen consumption.
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PMID:H2O2 formation during nucleotide degradation in the hypoxic rat liver: a quantitative approach. 285 Feb 67

Methylthioketobutyric acid has been used as an indicator for the production of reactive oxygen species during incubation with xanthine oxidase or NADH diaphorase in the presence of an autooxidizable quinone. The production of OH-radical-type oxidants is enhanced in the presence of crocidolite but not by the asbestos types chrysotile or amosite. This activity of crocidolite in the diaphorase system is further stimulated by bisulfite. Crocidolite-dependent ethylene formation from methylthioketo-butyric acid is inhibited by both superoxide dismutase and catalase. In the presence of both crocidolite and bisulfite, however, the inhibition by superoxide dismutase is preserved, but the inhibition by catalase is lost. Since in some respect the NADH-diaphorase quinone system may reflect the situation in the activated macrophage, crocidolite activation may represent a biochemical model system describing potential asbestos toxicity.
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PMID:Cooperative stimulation by sulfite and crocidolite asbestos fibres of enzyme catalyzed production of reactive oxygen species. 285 63


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