Electric-Field Control of the pH-Dependent Redox Process of Cytochrome c Immobilized on a Gold Electrode
Electric-Field Control of the pH-Dependent Redox Process of Cytochrome c Immobilized on a Gold Electrode
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电场控制金电极上固定的细胞色素 c 的 pH 依赖性氧化还原过程
DOI：
10.1021/jp303740e
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发表时间：
2012-06-21
影响因子：
3.7
通讯作者：
Xia, Xing-Hua
中科院分区：
文献类型：
--
作者：
Jin, Bo;Wang, Gui-Xia;Xia, Xing-Hua
采用电化学方法结合石英晶体微天平（QCM）和表面增强红外吸收（SEIRA）光谱研究了固定在涂有巯基十一烷酸（MUA）自组装单层（SAM）的金电极上的细胞色素c（cyt c）的pH依赖性氧化还原过程。溶液 pH 值在 4.0 至 10.0 范围内的变化决定了 SAM 的表面电荷，其表观 pK(a) 为 6.0，而静电结合的细胞色素 c 的结构基本保持不变。因此，界面氧化还原过程的 pH 依赖性反映了细胞色素 c 固定的电场控制，这反过来又对电子转移过程产生显着影响。在pH 7.0和4.0之间的范围内，由于SAM的羧基头基的质子化，与阳离子蛋白质的静电相互作用减弱，使得固定化蛋白质保持高度的移动性，并且可以快速采取最有利于电子转移的方向。因此，直接电子转移的速率常数在此 pH 范围内保持不变，但当 pH 值增加到 7.0 以上时，速率常数会降低。界面电子转移的急剧减慢归因于静电结合强度的增加，静电结合将蛋白质捕获在不利于与电极进行电子交换的方向上。本研究表明，溶液 pH 值是一个重要参数，可以优化静电结合蛋白质的界面电子转移过程。
The pH-dependent redox processes of cytochrome c (cyt c) immobilized on a gold electrode that was coated with a self-assembled monolayer (SAM) of mercaptounadecanoic acid (MUA) were studied by electrochemical methods combined with quartz crystal microbalance (QCM) and surface enhanced infrared absorption (SEIRA) spectroscopy. Variation of the solution pH in the range from 4.0 to 10.0 determines the surface charge of the SAM, for which an apparent pK(a) of 6.0 was determined, whereas the structure of the electrostatically bound cyt c remains largely unchanged. Thus, the pH-dependence of the interfacial redox process reflects the electric-field control of cyt c immobilization which in turn has a pronounced impact on the electron transfer process. In the pH range between 7.0 and 4.0, the electrostatic interactions with the cationic protein are weakened due to the protonation of the carboxyl headgroups of the SAM such that the immobilized protein remains highly mobile and can rapidly adopt the orientation which is most favorable for electron transfer. Thus, the rate constant for direct electron transfer remains unchanged in this pH range, but it decreases upon increasing the pH above 7.0. The dramatic slowdown of the interfacial electron transfer is attributed to the increased strength of electrostatic binding which traps the protein in an orientation that is unfavorable for electron exchange with the electrode. The present study demonstrates that the solution pH is an important parameter that allows for optimizing interfacial electron transfer processes of electrostatically bound proteins.