Primary Electron Transfer Processes in Photosynthetic Bacterial Reaction Centers

本研究的最终目标是实现细菌光合反应中心的光化学过程的统一分子水平的理解，光合反应中心是光合细菌中发现的色素-蛋白质复合物。植物也有类似的光合作用机制。所有这些反应中心都有两个准对称的潜在电子载流子分支。在细菌反应中心中，只有其中一个，即所谓的A-分支，用于储存（太阳）光的能量-通过A分支上的跨膜光诱导电子传递来完成。在天然反应中心，B分支是无活性的。该项目的前期工作表明，在某些独特的条件下，B分支辅因子可以被诱导以支持完全的跨膜电子转移。产率是足够高的，详细的探索电子转移沿着整个通常无活性的B-分支的反应中心辅因子现在是可能的。这些研究是这个项目的基础。这项研究将测试当前的模型，并利用从以前的研究中获得的主动分支（A-分支）过程的见解，并在这样做阐明电子转移在RC作为一个统一的整体的机械基础。从更全球的角度来看，该项目旨在使通常不活跃的B分支辅因子链以稳健的方式完全可用于各种下一代研究。这项工作将开辟新的途径，探索电子和/或构象的变化，质子运动和其他类似的过程，被认为是功能显着的QA/QB双电子门功能的两个醌（Qs）在反应中心。这些目标将通过静态和时间分辨（飞秒至秒）光谱研究RC突变体与多个氨基酸的变化，合理地操纵辅因子的性质和电荷分离和重组过程的速率和产量。这项研究不仅是中央了解主要的光化学事件在细菌RC，但也将提供路标正在进行的研究植物光系统I和II.更广泛的影响：了解光合RC的过程中的分子水平的机制奠定了基础，为太阳能收集/转换的合成系统，从而解决国家需要下一代可再生能源。本科生和研究生将参与这项研究。将研究思想融入教学和教育发展将侧重于两个项目。(1)将编制一个网上教程。它将是为本科生或高中生量身定制的，关于“为什么草是绿色而血红色？“（2）华盛顿大学的两个本科生物理化学实验室实验将得到广泛改进，以利用叶绿素和相关发色团的光谱学以及对光合作用至关重要的能量/电子转移过程，从面向应用的新角度教授分子电子光谱学和动力学。最后，将在密苏里州植物园开发一个广泛的，以科学为基础的关于光合作用的一般和基本方面的讲座，并将其与园艺兴趣联系起来，作为成人教育推广计划的一部分。尽管光合作用不可否认的相关性，该计划目前没有这样的讲座/教育组成部分。通过这些方式，我们将奋进传播光合作用的理解，它与地球的栖息地，太阳能研究到广泛的个人。

The ultimate goal of this research is to achieve a unified molecular level understanding of the photochemical processes in the bacterial photosynthetic reaction center, which is a pigment-protein complex found in photosynthetic bacteria. Plants have similar photosynthetic machinery. All these reaction centers have in common two quasi-symmetric branches of potential electron carriers. In the bacterial reaction center, only one of them, the so-called A-branch, is utilized for storing the energy of (sun)light -accomplished by trans-membrane photo-induced electron transport on the A branch. In the native reaction center, the B-branch is inactive. The previous work in this project has shown that under certain unique conditions, the B-branch cofactors can be induced to support full trans-membrane electron transfer. The yield is high enough that detailed explorations of electron transfer along the entire normally inactive B-branch of reaction center cofactors are now possible. Such studies are the basis of this project. This research will test current models and exploit insights gained from previous studies of the active-branch (A-branch) processes and in doing so elucidate mechanistic underpinnings of electron transfer in the RC as a unified whole. From a more global perspective, this project is aimed at making the normally inactive B-branch cofactor chain fully accessible in a robust manner for a variety of next-generation studies. This work will open up new avenues for exploring electronic and/or conformational changes, proton movement and other similar processes that are thought to be functionally significant in association with the QA/QB two-electron gate function of the two quinones (Qs) in the reaction center. These goals will be pursued via static and time-resolved (femtoseconds to seconds) spectroscopic studies of RC mutants with multiple amino acid changes that rationally manipulate the properties of the cofactors and the rates and yields of the charge separation and recombination processes. This research is not only central to understanding the primary photochemical events in the bacterial RC, but also will provide guideposts for research being conducted on plant photosystems I and II.Broader Impact: Understanding the molecular-level mechanisms of the processes in the photosynthetic RC lays a foundation for synthetic systems for solar-energy harvesting/conversion, thereby addressing a national need for next generation renewable energy sources. Undergraduate and graduate students will participate in this research. The integration of research ideas into teaching and educational development will focus on two projects. (1) A web-based tutorial will be developed. It will be tailored for undergraduate or high school students, on the general topic "Why is grass green and blood red?" (2) Two undergraduate physical-chemistry laboratory experiments at Washington University will be extensively upgraded to exploit the spectroscopy of chlorophyll and related chromophores, and the energy/electron transfer processes critical to photosynthesis, to teach molecular electronic spectroscopy and kinetics from new, application-oriented perspectives. Finally, a broad, science-based lecture on general and fundamental aspects of photosynthesis with links to interests in gardening will be developed as a proposed part of an adult education outreach program at the Missouri Botanical Garden. Despite the undeniable relevance of photosynthesis, the program does not have such a lecture/education component at present. In these ways we will endeavor to disseminate an understanding of photosynthesis, its relation to the earth's habitat, and to solar energy research to a broad spectrum of individuals.