Reaction Dynamics in Manybody Chemical Systems : Specificity in Biomolecular Reactions

我们研究了生物分子化学反应的机理。特别是，我们的主要目标是视紫红质（例如光驱动质子泵细菌视紫红质和视觉视紫红质）中的顺反异构化和质子转移反应。在视紫红质中，蛋白质环境中的特定反应将光转化为蛋白质结构变化，其松弛导致功能过程。在这个项目中，我们从动力学和结构两个方面来探讨这种特殊性。在动力学方面，我们利用飞秒荧光光谱技术分别研究了视觉视紫红质和pharaonis phoborhodopsin的激发态动力学。结果表明，蛋白质环境促进了视网膜发色团的顺-反光异构化。在结构方面，我们通过傅立叶变换红外光谱技术监测了蛋白质原子间振动的结构变化。特别是，高度优化的实验装置允许首次检测X-H和X-D伸缩频率区域的光谱变化。获得了关于氢键改变的直接信息。结果涉及细菌视紫红质、绿色和红色光的彩色视色素以及法老视紫红质。这些结果提供了关于反应特异性的新结构信息;关于蛋白质如何响应光，以及功能过程是如何驱动的。

We have investigated the mechanism of biomolecular chemical reactions. In particular, our main target was cis-trans isomerization and proton transfer reactions in rhodopsins, such as light-driven proton pump bacteriorhodopsin and visual rhodopsin. In rhodopsins, specific reactions in protein environments convert light into protein structural changes, whose relaxation leads to the functional processes. In this project, we approached such specificity from both dynamical and structural aspects. Following results were obtained.As the dynamical aspects, we were able to capture the excited-state dynamics of visual rhodopsin and pharaonis phoborhodopsin, acting as light sensors in our vision and bacterial phototaxis, respectively, by means of femtosecond fluorescence spectroscopy. It was revealed that the protein environment facilitates efficient cis-trans photoisomerization of the retinal chromophore.As the structural aspects, we monitored protein structural changes through inter-atomic vibrations by (Fourier-transform) infrared spectroscopy. In particular, highly optimized experimental set-up allowed to detect the spectral changes in the X-H and X-D stretching frequency regions for the first time. Direct information on the hydrogen-bonding alterations was obtained. The results involved were for bacteriorhodopsin, color visual pigments for green and red lights, and pharaonis phoborhodopsin. These results provide new structural information on the reaction specificity ; on how protein respond to light, and functional processes are driven.