Primary Electron Transfer Processes in Photosynthetic Bacterial Reaction Centers

细菌反应中心（RC）是膜结合的色素-蛋白质复合物，光能在其中转化为化学能。这种光转化过程通过一系列快速和高度特异的电子转移反应发生，以单位量子产率将电荷分离出RC（从而穿过膜）。这项工作的最终目标是在分子水平上对这一过程有一个全面的了解。为此，将开展飞秒到毫秒时间尺度的瞬态吸收光谱测量以及其他光谱研究，直接识别和研究电荷分离的中间状态及其形成和衰变的速率和产率。这些研究将在野生型RCs和多种突变型RCs上进行，其中一个或多个氨基酸发生了变化。许多未解决的问题，关于特定的发色团在电子转移途径的参与，以及这些反应的选择性（或方向性）将被解决。在正向电子转移反应和失活（或反向）反应之间的竞争平衡的因素将被研究。这些研究还将在特定氨基酸水平和更广泛的水平上解决蛋白质在电荷分离过程中的作用。这项工作的结果将与各种电子转移理论模型的预测结果进行比较，实际上，这可能会成为进一步理论发展的基础。把光能转化为化学能对地球上的生命是必不可少的。详细研究这种能量转换过程的机制不仅对增加对最重要的生物过程之一的理解至关重要，而且也是设计太阳能转换仿生系统的基础。所提出的研究将为阐明反应中心发挥作用的分子机制提供多种重要信息。这些研究还将促进对控制电子转移因素的认识，电子转移是生物学和化学中最基本的过程之一。此外，该研究将为色素-蛋白质相互作用和蛋白质动力学对生物过程的能量学、速率和机制的影响提供详细的新信息。因此，本研究将对我们对光合作用的基本认识和光合能量转换的应用方面产生非常积极的影响。

The bacterial reaction center (RC) is the membrane bound pigment- protein complex within which light energy is converted into chemical energy. This photoconversion process occurs via a series of fast and highly specific electron transfer reactions that separate charge across the RC (and thus across the membrane) with unity quantum yield. The ultimate goal of this work is to arrive at a comprehensive understanding of this process at a molecular level. To this end, transient absorption spectroscopic measurements spanning the femtosecond to millisecond timescales as well as other spectroscopic studies will be carried out to directly identify and study the intermediate states of charge separation and the rates and yields of their formation and decay. These studies will be carried out on both wild-type RCs and a wide variety of mutant RCs in which one or more amino acids are changed. Numerous unresolved issues regarding the involvement of specific chromophores in the pathway of electron transfer, and the selectivity (or directionality) of these reactions will be addressed. Factors underlying the balancing of the competition between the forward electron transfer reactions and the deactivating (or back) reactions will be investigated. These studies will also address the role of the protein in the charge separation process, both at the level of specific amino acids and at a more global level. The results of this work will be compared with predictions from various theoretical models for electron transfer and, indeed, will likely form the basis for further theoretical developments. %%% The conversion of light energy into chemical energy is essential for life on earth. Detailed studies of the mechanism of this energy conversion process are essential not only for increasing the understanding of one of the most important biological processes, but also as a foundation for devising biomimetic systems for solar energy conversion. The proposed studies will provide diverse information that is critical for elucidating the molecular mechanisms by which the reaction center functions. The studies also will advance knowledge of the factors that control electron transfer, which is one of the most fundamental processes in biology and chemistry. Additionally, the research will provide detailed new information on the effects of pigment- protein interactions and protein dynamics on the energetics, rates and mechanisms of biological processes. Hence, the proposed research should have a very positive impact on our fundamental understanding of photosynthesis and on the applied aspects of photosynthetic energy conversion.