Energy and Electron Transfer During Bacterial Photosynthesis

9513457伍德伯里技术意义。 尽管结构信息的可用性和基因工程和超快光谱的广泛使用，细菌光合作用中的初始光驱动电荷分离的机制仍然是一个有争议的话题。 现在很清楚的是，因素，如静态和/或动态的异质性的反应中心人口，振动热激发态，强烈的耦合之间的辅因子和参与交替的电子转移途径或中间体需要进行评估之前，一致的图片的太阳能转换反应可以出现。 为了研究异质性，我们提出了多脉冲光选择测量直接观察的荧光产率和在photoseleted的反应中心样品的亚群中的电荷分离的速率和产率的变化。 为了研究取决于初始激发态的振动热态和交替光化学的可能性，将进行除反应中心的初始电子供体以外的辅助因子的特定激发的实验。 初始激发单重态的性质和动力学以及激发态耦合到其他反应中心状态将使用来自James艾伦和JoAnn威廉姆斯的实验室的突变体进行研究，该突变体显示出缓慢的激发态演化，显然涉及随时间增加的追逐电荷分离特征。 %一般显著性。 生物化学中最有趣的问题之一是关于酶内部的蛋白质环境如何介导它所包含的辅因子和它所结合的反应物的化学性质。 化学动力学在这些相互作用中起着重要作用。 在正常的酶系统中研究动力学的问题是，反应物必须通过溶剂扩散才能找到彼此，实际上没有办法观察在比扩散更快的时间尺度上发生的过程（微秒），即使在这个时间尺度上，通常也不可能实际监测整个分子群体在彼此的相位上经历相同的动力学。 我们通过研究一种酶来解决这个问题，这种酶的反应是由光的吸收引发的。 紫色非硫细菌的光合反应中心是一种太阳能酶，它能还原醌分子。 使用飞秒分辨率光谱学，我们可以在实际参与化学反应的分子运动的时间尺度上启动和监测光吸收时发生的反应。 大部分拟议的工作涉及在各种不同的时间尺度上的太阳能转换过程中的动态的作用。 沿着这些线索，我们要问的是，如果我们向系统中注入额外的振动能，会发生什么。 这种额外的局部运动如何影响化学反应？ 最后，可以通过突变改变蛋白质环境，并测试这对蛋白质环境引导反应的能力的影响。 ***

9513457 Woodbury Technical Significance. Despite the availability of structural information and the extensive use of genetic engineering and ultrafast spectroscopy, the mechanism of the initial light driven charge separation in bacterial photosynthesis remains a topic of debate. It is now clear that factors such as static and/or dynamic heterogeneity of the reaction center population, vibrationally hot excited states, strong coupling between cofactors and the involvement of alternate electron transfer pathways or intermediates need to be evaluated before a consistent picture of the solar energy conversion reactions can emerge. To investigate heterogeneity, we propose multipulse photoselection measurements to directly observe changes in the fluorescence yield and in the rate and yield of charge separation in photoseleted subpopulations of a reaction center sample. To investigate the possibility of vibrationally hot states and alternate photochemistry depending on the initial excited state, experiments in which specific excitation of cofactors other than the initial electron donor of the reaction center will be performed. Initial excited singlet state properties and dynamics as well as excited state coupling to other reaction center states will be investigated using a mutant from James Allen and JoAnn Williams' laboratory that show a slow excited state evolution apparently involving increasing chasing charge separated character with time. %%% General Singificance. One of the most interesting questions in biochemistry concerns how the protein environment of an enzyme interior mediates the chemistry of the cofactors it contains and reactants it binds to. Chemical dynamics plays a major role in these interactions. The problem with studying dynamics in normal enzymatic systems where the reactants must diffuse through the solvent to find each other is that there is really no way to look at processes that occur on timescales faster than that diffusion (microseconds), and even on this timesca le, it is usually impossible to actually monitor a whole population of molecules undergoing the same dynamics in phase with each other. We circumvent this problem by studying an enzyme whose reaction is initiated by the absorption of light. The photosynthetic reaction center from purple nonsulfur bacteria is a solar powered enzyme that reduces a quinone molecule. Using femtosecond resolution spectroscopy, we can initiate and monitor the reactions that occur upon light absorption on the time scale of the molecular movements that are actually involved in the chemical reactions. Much of the proposed work involves looking at the role of dynamics on various different timescales in the solar energy conversion process. Along these lines, we are asking what happens if we inject additional vibrational energy into the system. How does this additional local motion affect the chemistry? Finally, one can change the protein environment by mutation and test the effects of this on the ability of the protein environment to guide the reaction. ***