Primary Electron Transfer Processes in Photosynthetic Bacterial Reaction Centers

9723008霍尔滕细菌反应中心(RC)是结合在膜上的色素-蛋白质复合体，光能在这里被转化为化学势能。这种转化是通过一系列快速和高度特异的电子转移反应实现的，这些反应通过膜分离电荷，量子产率为100%。这项工作的最终目的是在分子水平上对初级电荷分离过程有一个全面的了解。为此，将使用跨越飞秒到秒时间尺度的瞬时吸收光谱测量以及其他光谱技术来直接探测电荷分离的中间态及其形成和衰变的速率。这项研究将集中在辅因子附近含有一个或多个突变的定点突变。许多悬而未决的问题将被解决，包括特定发色团参与电子转移的途径，电子通过两条平行传输链之一(L和M)转移的方向性的起源，以及确保电荷分离速率和竞争电荷复合过程速率之间的良好平衡的因素。本研究的总体目标是了解细菌光合作用中初级电荷分离过程的分子机制。这项研究揭示的原理也应该适用于其他生物反应中心的初级光化学，包括植物中的PSII。最后，这项研究应该对生物物理学中更广泛的主题产生积极影响，包括生物电子传递和蛋白质在调节其辅助因子的功能特性中的作用，无论是静态的还是动态的。***

9723008 Holten The bacterial reaction center (RC) is the membrane-bound pigment-protein complex where light energy is converted into chemical potential energy. This conversion occurs via a series of fast and highly specific electron transfer reactions that separate charge across the membrane with a quantum yield of (100%. The ultimate goal of this work is to arrive at a comprehensive understanding of the primary charge separation process at the molecular level. To this end, transient absorption spectroscopic measurements spanning the femtosecond to seconds time scales as well as other spectroscopic techniques will be used to directly probe the intermediate states of charge separation and the rates of their formation and decay. The research will focus on site-directed mutants containing one or more mutations near the cofactors. Numerous unresolved issues will be addressed, including the involvement of specific chromophores in the pathway of electron transfer, the origin of the directionality of electron transfer via one of two parellel transport chains (L and M), and the factors that ensure the favorable balance between the rates of charge separation and the rates of competing charge recombination processes. The overall goal of this research is to understand the molecular mechanisms of the primary charge separation process in bacterial photosynthesis. The principles uncovered by this research should also apply to the primary photochemistry in reaction centers from other organisms, including PSII in plants. Finally, the research should positively impact broader topics in biophysics including biological electron transfers and the role of a protein, both static and dynamic, in modulating the functional properties of its cofactors. ***