Blum J, Fridovich I
Arch Biochem Biophys. 1985 Aug 1;240(2):500-8. doi: 10.1016/0003-9861(85)90056-6.
The selenium-containing glutathione peroxidase, when in its active reduced form, was inactivated during exposure to the xanthine oxidase reaction. Superoxide dismutase completely prevented this inactivation, whereas catalase, hydroxyl radical scavengers, or chelators did not, indicating that O2 was the responsible agent. Conversion of GSH peroxidase to its oxidized form, by exposure to hydroperoxides, rendered it insensitive toward O2. The oxidized enzyme regained susceptibility toward inactivation by O2 when reduced with GSH. The inactivation by O2 could be reversed by GSH; however, sequential exposure to O2 and then hydroperoxides caused irreversible inactivation. Reactivity toward CN- has been used as a measure of the oxidized form of GSH peroxidase, whereas reactivity toward iodoacetate has been taken as an indicator of the reduced form. By these criteria both O2 and hydroperoxides convert the reduced form to oxidized forms. A mechanism involving oxidation of the selenocysteine residue at the active site has been proposed to account for these observations.
含硒谷胱甘肽过氧化物酶在其活性还原形式下，在暴露于黄嘌呤氧化酶反应过程中会失活。超氧化物歧化酶能完全阻止这种失活，而过氧化氢酶、羟自由基清除剂或螯合剂则不能，这表明超氧阴离子是导致失活的因素。通过暴露于氢过氧化物将谷胱甘肽过氧化物酶转化为其氧化形式后，它对超氧阴离子不再敏感。当用谷胱甘肽还原时，氧化型酶又恢复了对超氧阴离子失活的敏感性。超氧阴离子导致的失活可被谷胱甘肽逆转；然而，先暴露于超氧阴离子然后再暴露于氢过氧化物会导致不可逆失活。对氰化物的反应性已被用作谷胱甘肽过氧化物酶氧化形式的一种衡量指标，而对碘乙酸的反应性则被视为还原形式的指标。根据这些标准，超氧阴离子和氢过氧化物都会将还原形式转化为氧化形式。有人提出了一种涉及活性位点硒代半胱氨酸残基氧化的机制来解释这些观察结果。
