α-Tocopherolquinone (TQ), a product of α-tocopherol oxidation, can function as an antioxidant after reduction to α-tocopherolhydroquinone (TQH2). We examined the ability of human NAD(P)H:quinone oxidoreductase (NQO1) to catalyze the reduction of TQ to TQH2 in cell-free and cellular systems. In reactions with purified human NQO1, TQ was reduced to TQH2. Kinetic parameters for the reduction of TQ by NQO1 ( K m = 370 μm; k cat = 5.6 × 103 min −1; k cat/ Km = 15 min−1 · μm −1) indicate that NQO1 can efficiently reduce TQ to TQH2. A comparison of the rate of reduction of TQ and coenzyme Q10 by NQO1 showed that TQ is reduced more efficiently than coenzyme Q10. Experiments with either Chinese hamster ovary (CHO) cells stably transfected with human NQO1 or CHO cell sonicates demonstrated a correlation between NQO1 activity and TQ reduction to TQH2. CHO cells with elevated NQO1 generated and maintained higher levels of TQH2 after treatment with TQ relative to NQO1-deficient CHO cells. TQH2generated from NQO1-mediated reduction of TQ prevented cumene hydroperoxide-induced lipid peroxidation in rat liver microsomes. In addition, cumene hydroperoxide-induced lipid peroxidation was inhibited more efficiently by TQ in CHO cell lines with elevated NQO1 activity. These data demonstrate that NQO1 can reduce TQ to TQH2 and that TQH2 can function as an efficient antioxidant. This work suggests that one of the physiological functions of NQO1 may be to regenerate antioxidant forms of α-tocopherol.
α-
生育酚醌(TQ)是α-
生育酚氧化的产物,还原为α-
生育酚氢醌(TQH2)后可起到
抗氧化剂的作用。我们检测了人
NAD(P)H:醌氧化还原酶 (NQO1) 在无细胞和
细胞系统中催化 TQ 还原为 TQH2 的能力。在与纯化的人 NQO1 反应中,TQ 被还原为 TQH2。 NQO1还原TQ的动力学参数(K m = 370 μm;k cat = 5.6 × 103 min −1;k cat/ Km = 15 min−1 · μm −1)表明NQO1可以有效地将TQ还原为TQH2。比较NQO1对TQ和
辅酶Q10的还原率表明,TQ比
辅酶Q10的还原效率更高。使用稳定转染人 NQO1 的中国仓鼠卵巢 (CHO) 细胞或 CHO 细胞超声处理进行的实验证明,NQO1 活性与 TQ 还原为 TQH2 之间存在相关性。与 NQO1 缺陷的 CHO 细胞相比,NQO1 升高的 CHO 细胞在用 TQ 处理后产生并维持更高
水平的 TQH2。由 NQO1 介导的 TQ 减少产生的 TQH2 可防止大鼠肝微粒体中氢过氧化
异丙苯诱导的脂质过氧化。此外,在 NQO1 活性升高的 CHO
细胞系中,TQ 可以更有效地抑制氢过氧化
异丙苯诱导的脂质过氧化。这些数据表明,NQO1 可以将 TQ 还原为 TQH2,并且 TQH2 可以充当有效的
抗氧化剂。这项工作表明,NQO1 的生理功能之一可能是再生抗氧化形式的 α-
生育酚。