Formation of hydroxyl radical in aqueous solutions containing selenite and glutathione

Abstract

The present study examined generation of hydroxyl radical (HO) in aqueous aerobic solutions (pH 7.1) containing selenite (SeO32−) and glutathione (GSH) using terephthalic acid (TA) scavenging HO to give highly fluorescent 2-hydroxyterephthalic acid (TA-OH). The highest reaction rate and yield of TA-OH were observed in a micromolar concentration range of selenite at [GSH] = 0.5 mM. Accumulation of TA-OH was substantially lower in the case of other selenium species (viz. selenomethionine, selenocystine and selenate) and their mixtures with GSH. Addition of superoxide dismutase notably increased the rate of TA-OH formation, whereas catalase inhibited the reaction. Mixture of other thiols (i.e., cysteine or cysteamine) with SeO32− hydroxylates TA as well, although the rate of the reaction is lower than in the case of GSH. The mechanism consists of the rapid reduction of SeO32− by GSH to Se(0), reversible formation of glutathione perselenide (GS-Se−) and its further reaction with hydrogen peroxide to give HO.