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[7] Reaction of superoxide with glutathioneand other thiols

1995; Academic Press; Linguagem: Inglês

10.1016/0076-6879(95)51112-1

1557-7988

Christine C. Winterbourn, Diana Metodiewa,

Redox biology and oxidative stress

This chapter discusses the reaction of superoxide with glutathione (GSH) and other thiols. To detect a reaction with superoxide, it is necessary to add GSH or the thiol of interest to a superoxide-generating system and measure either thiol oxidation or oxygen consumption. The involvement of superoxide is verified by inhibiting the reaction with superoxide dismutase. Because superoxide is regenerated, competition assays do not detect the reaction and are inappropriate. The source of superoxide can be either radiolytic or enzymatic. Because it is not possible to generate superoxide without producing other radicals (for example, OH·) or hydrogen peroxide either directly or by dismutation, these must be taken into account when interpreting the results. The existence of a reaction between the thiol and superoxide can be established using superoxide dismutase, but the complexity of the reaction sequence makes analysis difficult. The xanthine oxidase system produces superoxide as the only initial radical, but it also produces hydrogen peroxide. This is not a radical reaction and can be separated from the superoxide-dependent chain. It involves the thiolate anion, and its rate increases with increasing pH. Whether hydrogen peroxide is produced or not can be determined by measuring oxygen uptake in the presence and absence of catalase, but it is more accurate to measure peroxide production directly. This is best accomplished using a hydrogen peroxide electrode.