Xanthine superoxide radical anion

An alternative source of the superoxide radical anion is leukocytic xanthine oxidase, acting in polymorphonuclear leukocytes of individuals with impairment of the NADPH oxidase system. Superoxide is one of the major metabolites produced in stimulated neutrophiles. Various estimations of Oj production yielded values ranging from 850 to 1350 p.mol/h/1010 cells (Bl, K16). 

The superoxide radical anion generated by reaction of xanthine and xanthene oxidase can be detected by ESR spin trapping technique. Besides being used for trapping the hydroxyl radical, DMPO is also used as a spin trapping agent to react with the superoxide radical anion, which forms the DMPO- OOH adduct for ESR spectroscopic measurement. 

The molybdoenzyme, xanthine oxidoreductase is a homodimer of 150 kDa subunits and exists in two interconvertible forms, dehydrogenase (EC 1.1.1.204) and xanthine oxidase (EC 1.1.3.22). Reduction of oxygen by either form of the enzyme yields superoxide radical anion and hydrogen peroxide with xanthine or hypoxanthine as substrates. Xanthine dehydrogenase preferentially reduces NAD whereas xanthine oxidase does not reduce NAD preferring molecular oxygen. 

Using the xanthine-xanthine oxidase system for producing superoxide radical anions Packer (1991) showed that dihydrolipoic acid, but not lipoic acid, quenched these radicals. 

The superoxide radical anion, O2, is generated especially by flavin enzymes, such as xanthine oxidase (cf. 2.3.3.2). The involvement of this enzyme in the development of milk oxidation flavor has been questioned for a long time. 

Superoxide radicals are produced by a xanthine-xanthine oxidase system. Xanthine is able to generate 02 and H2O2 by using xanthine oxidase as a substrate. The superoxide radicals are able to reduce the yellow colored nitro triazolium blue (NTE) to the blue formazan, which is used for monitoring the reaction. The superoxide anions are measured spectrophotometricaUy. This test method was developed to explore the reaction between antioxidants and 02. So the inhibition of the superoxide reductase is a mark for the ability of antioxidative activity. 

Fridovich, I. (1970). Quantitative aspects of the production of superoxide anion radical by milk xanthine oxidase. J. Biol. Chem. 245, 4053-4057. 

The production of ethylene from methional (3-thiomethylpropanal) was induced by the oxidation of xanthine by dioxygen catalysed by xanthine oxidase The second-order rate constant for the reaction of hydroxyl radicals with methional was estimated by pulse radiolysis to amount to 8.2 x lO s while the superoxide anion reacted more slowly The short lag period of the ethylene production induced by the oxidation of xanthine could be overcome by the addition of small amounts of hydrogen peroxide. The reaction was inhibited by SOD or by catalase, and by scavengers of hydroxyl radicals, so that the Haber-Weiss reaction was implicated... 

Selloum L, Reichl S, Muller M, Sebihi L, Amhold J. 2001. Effects of flavonols on the generation of superoxide anion radicals by xanthine oxidase and stimulated neutrophils. Arch Biochem Biophys 395 49-56. 

Nishikimi M (1975) Oxidation of ascorbic acid with superoxide anion generated by the xanthine-xanthine oxidase system. Biochem Biophys Res Commun 63 463-468 Niu QJ, Mendenhall GD (1992) Yields of singlet molecular oxygen from peroxyl radical termination. J Am Chem Soc 114 165-172... 

Japanese scientists believe that the anti-oketsu effects of rhubarb are brought about by the inhibition of the production of nitric oxide, inhibition of platelet aggregation, antiallergic effects, and its antiinflammatory properties. Matsuda et al. (2001) studied and reported that the methanolic extracts from five kinds of rhubarb were found to show scavenging activity for l,l-diphenyl-2-picrylhy-drazyl (DPPH) radical and superoxide anion radical (02 ) generated by the xanthine/xanthine oxidase system and/or on lipid peroxidation by terf-butyl hydroperoxide (f-BuOOH) in the erythrocyte membrane ghost system. 

Fluvastatin (Fig. 21) is a member of the drug class of statins used to treat hypercholesterolemia and to prevent cardiovascular disease. It is able to decrease ROS, such as hydroxyl radicals and superoxide anions generated by the Fenton reaction, and by the xanthine-xanthine oxidase system. The an-tioxidative effect of fluvastatin was thought to have caused not only the scav-... 

Unno, T., Sugimoto, A., and Kakuda, T. 2000. Scavenging effect of tea catechins and their epimers on superoxide anion radicals generated by a hypoxanthine and xanthine oxidase system. J. Sci. FoodAgric. 80 601-6. 

All the inhibitions reported so far indicate that there is no known specific inhibitor for the manganese superoxide dismutase. The enzyme from B. stearothermophilus was found to be inhibited by cacodylate (Thornalley et al., 1982) however, the inhibition could only be observed in the xanthine/xanthine oxidase assay and not in the pulse radiolysis assay. No evidence was obtained that cacodylate could be competing with the enzyme for because little or no inhibition was observed when the copper/zinc rather than the manganese enzyme was assayed in the presence of cacodylate. Further investigations revealed that the inhibitory effect is due to a cacodylate anion radical produced by the interaction of hydroxyl radicals (generated by the xanthine/xanthine oxidase reaction) and cacodylate anions. A radical of pamoic acid (4,4 -methylenebis-(3-... 

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