Sugioka K, Nakano M, Totsune-Nakano H, Minakami H, Tero-Kubota S, Ikegami Y
College of Medical Care and Technology, School of Medicine, Gunma University, Maebashi, Japan.
Biochim Biophys Acta. 1988 Dec 7;936(3):377-85. doi: 10.1016/0005-2728(88)90014-x.
O2- generation in mitochondrial electron transport systems, especially the NADPH-coenzyme Q10 oxidoreductase system, was examined using a model system, NADPH-coenzyme Q1-NADPH-dependent cytochrome P-450 reductase. One electron reduction of coenzyme Q1 produces coenzyme Q1-. and O2- during enzyme-catalyzed reduction and O2+ coenzyme Q1-. are in equilibrium with O2- + coenzyme Q1 in the presence of enough O2. The coenzyme Q1-. produced can be completely eliminated by superoxide dismutase, identical to bound coenzyme Q10 radical produced in a succinate/fumarate couple-KCN-submitochondrial system in the presence of O2. Superoxide dismutase promotes electron transfer from reduced enzyme to coenzyme Q1 by the rapid dismutation of O2- generated, thereby preventing the reduction of coenzyme Q1 by O2-. The enzymatic reduction of coenzyme Q1 to coenzyme Q1H2 via coenzyme Q1-. is smoothly achieved under anaerobic conditions. The rate of coenzyme Q1H2 autoxidation is extremely slow, i.e., second-order constant for [O2][coenzyme Q1H2] = 1.5 M-1.s-1 at 258 microM O2, pH 7.5 and 25 degrees C.
使用模型系统NADPH-辅酶Q1- NADPH依赖性细胞色素P-450还原酶，研究了线粒体电子传递系统中O2-的生成，特别是NADPH-辅酶Q10氧化还原酶系统。辅酶Q1的单电子还原在酶催化还原过程中产生辅酶Q1-和O2-，在有足够O2的情况下，O2与辅酶Q1-处于O2-与辅酶Q1的平衡状态。产生的辅酶Q1-可以被超氧化物歧化酶完全消除，这与在有O2存在的琥珀酸/延胡索酸偶联-KCN-亚线粒体系统中产生的结合辅酶Q10自由基相同。超氧化物歧化酶通过快速歧化产生的O2-促进电子从还原酶转移到辅酶Q1，从而防止O2-还原辅酶Q1。在厌氧条件下，辅酶Q1通过辅酶Q1-顺利地酶促还原为辅酶Q1H2。辅酶Q1H2的自氧化速率极慢，即在258 microM O2、pH 7.5和25℃下，[O2][辅酶Q1H2]的二级常数为1.5 M-1·s-1。
