Department of Chemistry, National Tsing Hua University, 101, Sec. 2, Kuang-Fu Rd., Hsinchu 30013, Taiwan.
Department of Chemistry, National Tsing Hua University, 101, Sec. 2, Kuang-Fu Rd., Hsinchu 30013, Taiwan.
Bioelectrochemistry. 2014 Oct;99:1-7. doi: 10.1016/j.bioelechem.2014.05.003. Epub 2014 Jun 3.
The proton pump of bacteriorhodopsin in an aqueous solution at varied pH upon pulsed excitation was monitored using a solution-based electrochemical module. The photocurrent action spectrum agreed with the absorption contour at 495-645 nm. Diminishing the photocurrent amplitude by adding a protonophore, carbonyl cyanide m-chlorophenyl hydrazone, revealed that protons were the charge carriers of the photocurrent. The evolution of the conventional proton pump is proposed to occur in three elementary steps consecutively: first, the proton relay from the protonated Schiff base to the purple membrane (PM) surface (k1), then the proton exchange between PM surface and bulk (k2), and finally, the proton uptake (k3). The fitted temporal profiles of the photocurrent agreed with observations in the pH range 5.8-9.5. At pH 7.3, k1, k2, and k3 were 2098 s(-1), 412 s(-1), and 44 s(-1), respectively. The rate coefficients at pH 9.5 were smaller than those at pH 6.3 by a factor of approximately 2, consistent with the differences in the intrinsic mobilities of the charge carriers proton and hydroxide ion. The combination of the electrochemical detection module and the concomitant model provides a promising tool for quantitative and qualitative characterization of the light-driven ion pumps.
在不同 pH 值的水溶液中，通过脉冲激发监测菌紫质质子泵。光电流作用光谱与 495-645nm 的吸收轮廓一致。通过添加质子载体羰基氰化物 m-氯代苯腙来减小光电流幅度，表明质子是光电流的载流子。提出了传统质子泵的演化过程依次经历三个基本步骤：首先，质子从质子化的 Schiff 碱中继到紫膜（PM）表面（k1），然后 PM 表面与体相之间的质子交换（k2），最后是质子吸收（k3）。拟合的光电流时间曲线与 pH 值为 5.8-9.5 的观察结果一致。在 pH 7.3 时，k1、k2 和 k3 分别为 2098s(-1)、412s(-1)和 44s(-1)。pH 值为 9.5 时的速率系数比 pH 值为 6.3 时小约 2 倍，这与载流子质子和氢氧根离子的固有迁移率差异一致。电化学检测模块和伴随的模型的组合为定量和定性表征光驱动离子泵提供了有前途的工具。
