Primary Electron Transfer Processes in Photosynthetic Bacterial Reaction Centers

细菌反应中心(RC)是结合在膜上的色素-蛋白质复合体，在该复合体中光能被转化为化学能。这一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，这些反应以单位量子产率在RC(从而跨膜)分离电荷。这项工作的最终目标是在分子水平上对这一过程达成全面的理解。为此，将进行跨越飞秒到毫秒时间的瞬时吸收光谱测量以及其他光谱研究，以直接识别和研究电荷分离的中间态及其形成和衰变的速率和产量。这些研究将在野生型RCS和各种突变RCS上进行，在这些RCS中，一个或多个氨基酸发生变化。关于特定发色团在电子转移途径中的参与以及这些反应的选择性(或方向性)的许多悬而未决的问题将被解决。我们将研究平衡正向电子转移反应和失活(或反向)反应之间竞争的因素。这些研究还将探讨蛋白质在电荷分离过程中的作用，既在特定氨基酸的水平上，也在更全球的水平上。这项工作的结果将与电子转移的各种理论模型的预测进行比较，实际上，可能会成为进一步理论发展的基础。将光能转化为化学能对地球上的生命是必不可少的。对这一能量转换过程机理的详细研究不仅对于加深对这一最重要的生物过程的理解是至关重要的，而且也是设计用于太阳能转换的仿生系统的基础。拟议的研究将提供各种信息，这些信息对于阐明反应中心发挥作用的分子机制至关重要。这些研究还将促进人们对控制电子转移的因素的了解，电子转移是生物和化学中最基本的过程之一。此外，这项研究将提供关于色素-蛋白质相互作用和蛋白质动力学对生物过程的能量学、速率和机制的影响的详细新信息。因此，这项拟议的研究将对我们对光合作用的基本理解和光合作用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.