Kishi T, Takahashi T, Usui A, Hashizume N, Okamoto T
Faculty of Pharmaceutical Science, Kobe Gakuin University, Japan.
Biofactors. 1999;9(2-4):189-97. doi: 10.1002/biof.5520090214.
Cellular ubiquinone (UQ) is expected to act as an endogenous antioxidant against oxidative stress. To confirm this, UQ-reductases which are necessary to regenerate ubiquinol (UQH2) were investigated in rat tissue, and a novel NADPH-dependent UQ (NADPH-UQ) reductase was found in cytosol. The cytosolic NADPH-UQ reductase activity accounted for more than 80% of UQ-10 reduction by the rat liver homogenate in the presence of NADPH. Furthermore, the NADPH-UQ reductase activities in various tissues were correlated to the redox states of UQ in the corresponding tissues. Rat liver cytosol with NADPH protected lecithin liposomes containing UQ-10, as well as UQH2-10 from AMVN (2,2'-azobis(2,4-dimethylvaleronitrile))-induced lipid peroxidation. The enzyme purified from rat liver cytosol, reduced UQ-10 in lecithin liposomes at approximately the same rate as did cytosol. These results supported that cytosolic NADPH-UQ reductase is the enzyme responsible for nonmitochondrial UQ reduction acting as an endogenous antioxidant against oxidative stress. The antioxidant role of the UQ redox cycle and NADPH-UQ reductase was discussed in relation to other cellular NADPH-dependent antioxidant enzymes.
细胞泛醌（UQ）有望作为一种内源性抗氧化剂抵抗氧化应激。为证实这一点，对大鼠组织中泛醇（UQH2）再生所必需的UQ还原酶进行了研究，并在细胞溶质中发现了一种新的依赖烟酰胺腺嘌呤二核苷酸磷酸（NADPH）的UQ（NADPH-UQ）还原酶。在存在NADPH的情况下，细胞溶质中的NADPH-UQ还原酶活性占大鼠肝脏匀浆对UQ-10还原作用的80%以上。此外，各种组织中的NADPH-UQ还原酶活性与相应组织中UQ的氧化还原状态相关。含有NADPH的大鼠肝脏细胞溶质可保护含有UQ-10以及UQH2-10的卵磷脂脂质体免受2,2'-偶氮双（2,4-二甲基戊腈）（AMVN）诱导的脂质过氧化作用。从大鼠肝脏细胞溶质中纯化得到的该酶，以与细胞溶质大致相同的速率还原卵磷脂脂质体中的UQ-10。这些结果支持细胞溶质中的NADPH-UQ还原酶是负责非线粒体UQ还原的酶，作为一种内源性抗氧化剂抵抗氧化应激。结合其他细胞依赖NADPH的抗氧化酶，讨论了UQ氧化还原循环和NADPH-UQ还原酶的抗氧化作用。
