Kishi T, Morré D M, Morré D J
Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, IN 47907, USA.
Biochim Biophys Acta. 1999 May 26;1412(1):66-77. doi: 10.1016/s0005-2728(99)00049-3.
The plasma membrane NADH oxidase activity partially purified from the surface of HeLa cells exhibited hydroquinone oxidase activity. The preparations completely lacked NADH:ubiquinone reductase activity. However, in the absence of NADH, reduced coenzyme Q10 (Q10H2=ubiquinol) was oxidized at a rate of 15+/-6 nmol min-1 mg protein-1 depending on degree of purification. The apparent Km for Q10H2 oxidation was 33 microM. Activities were inhibited competitively by the cancer cell-specific NADH oxidase inhibitors, capsaicin and the antitumor sulfonylurea N-(4-methylphenylsulfonyl)-N'-(4-chlorophenyl)urea (LY181984). With coenzyme Q0, where the preparations were unable to carry out either NADH:quinone reduction or reduced quinone oxidation, quinol oxidation was observed with an equal mixture of the Q0 and Q0H2 forms. With the mixture, a rate of Q0H2 oxidation of 8-17 nmol min-1 mg protein-1 was observed with an apparent Km of 0.22 mM. The rate of Q10H2 oxidation was not stimulated by addition of equal amounts of Q10 and Q10H2. However, addition of Q0 to the Q10H2 did stimulate. The oxidation of Q10H2 proceeded with what appeared to be a two-electron transfer. The oxidation of Q0H2 may involve Q0, but the mechanism was not clear. The findings suggest the potential participation of the plasma membrane NADH oxidase as a terminal oxidase of plasma membrane electron transport from cytosolic NAD(P)H via naturally occurring hydroquinones to acceptors at the cell surface.
从HeLa细胞表面部分纯化得到的质膜NADH氧化酶活性表现出对苯二酚氧化酶活性。这些制剂完全缺乏NADH：泛醌还原酶活性。然而，在没有NADH的情况下，还原型辅酶Q10（Q10H2 =泛醇）以15±6 nmol min-1 mg蛋白-1的速率被氧化，这取决于纯化程度。Q10H2氧化的表观Km为33 μM。活性被癌细胞特异性NADH氧化酶抑制剂辣椒素和抗肿瘤磺酰脲N-（4-甲基苯基磺酰基）-N'-（4-氯苯基）脲（LY181984）竞争性抑制。对于辅酶Q0，这些制剂既不能进行NADH：醌还原也不能进行还原醌氧化，但在Q0和Q0H2形式的等量混合物中观察到了喹醇氧化。对于该混合物，观察到Q0H2氧化速率为8 - 17 nmol min-1 mg蛋白-1，表观Km为0.22 mM。加入等量的Q10和Q10H2并不能刺激Q10H2的氧化速率。然而，向Q10H2中加入Q0确实能起到刺激作用。Q10H2的氧化似乎以双电子转移的方式进行。Q0H2的氧化可能涉及Q0，但其机制尚不清楚。这些发现表明质膜NADH氧化酶可能作为质膜电子传递的末端氧化酶参与其中，该电子传递从胞质NAD(P)H经天然存在的对苯二酚传递至细胞表面的受体。
