Auckland Cancer Society Research Centre, Faculty of Medical and Health Sciences, The University of Auckland , Auckland 1142, New Zealand.
Biochemistry. 2014 Mar 18;53(10):1637-46. doi: 10.1021/bi401630m. Epub 2014 Mar 3.
Single electron transfers have been examined in complex II (succinate:ubiquinone oxidoreductase) by the method of pulse radiolysis. Electrons are introduced into the enzyme initially at the [3Fe-4S] and ubiquinone sites followed by intramolecular equilibration with the b heme of the enzyme. To define thermodynamic and other controlling parameters for the pathways of electron transfer in complex II, site-directed variants were constructed and analyzed. Variants at SdhB-His207 and SdhB-Ile209 exhibit significantly perturbed electron transfer between the [3Fe-4S] cluster and ubiquinone. Analysis of the data using Marcus theory shows that the electronic coupling constants for wild-type and variant enzyme are all small, indicating that electron transfer occurs by diabatic tunneling. The presence of the ubiquinone is necessary for efficient electron transfer to the heme, which only slowly equilibrates with the [3Fe-4S] cluster in the absence of the quinone.
通过脉冲辐射解法研究了复合物 II（琥珀酸：泛醌氧化还原酶）中的单电子转移。最初，电子被引入酶中，进入[3Fe-4S]和泛醌位点，然后与酶的 b 血红素进行分子内平衡。为了确定复合物 II 中电子转移途径的热力学和其他控制参数，构建并分析了定点变异体。在 SdhB-His207 和 SdhB-Ile209 处的变异体显示出[3Fe-4S]簇和泛醌之间的电子转移明显受到干扰。使用马库斯理论对数据进行分析表明，野生型和变异酶的电子耦合常数都很小，表明电子转移是通过非绝热隧道进行的。在没有醌的情况下，血红素与[3Fe-4S]簇的缓慢平衡需要泛醌的存在以实现有效的电子转移。
