SPECTROSCOPIC STUDIES OF LIGHT-DRIVEN ELECTRON TRANSFER

本提案的总体目标是制定一个更详细的 了解生物电子转移的分子基础。 电子转移在所有生物氧化还原反应中具有中心重要性 反应和能量转换的线粒体和叶绿体，但 关于蛋白质结构和蛋白质以及 辅因子构象变化在此过程中起作用。 光谱 本文将介绍的研究将解决这些问题;模型系统 将被使用的是光合反应中心。 的因素 影响电子转移的效率和方向性， 在反应中心的光吸收可能是重要的， 氧化还原反应 此外，光合反应中心提供了一个 研究电子转移机制的独特系统，因为 反应可以由光引发。 本提案的具体目标 是使用电子顺磁共振（EPR）和差分傅立叶- 变换红外光谱（FT-IR）研究光驱动电子 在细菌反应中心和光系统II中， 水分解复合物 光系统II的EPR实验将针对 在鉴定中间电子转移组分时，Z+， 光系统II，这是光诱导的，被认为是一个氨基 酸残留物 合作实验将探索光谱 突变体的性质，其中其他氨基酸已被取代在 假定的Z+位点 这项工作将确定结构特征， 在光系统II供体侧的电子转移中起重要作用。 将对两种细菌进行不同的FT-IR实验， 反应中心和光系统II。 从a中减去a“dark” “光”谱使这种技术具体的振动变化 与电荷分离有关。 在细菌反应中心， 差FT-IR光谱将包含关于结构的信息， 蛋白质残基和伴随电荷的辅因子的变化 分居 在光系统II中，差分FT-IR将提供一个新的 用于研究锰的构象变化的技术 簇，水氧化的网站，并在蛋白质的研究 结构改变，如质子化/去质子化事件， 参与了Z+的形成。 解释生产者责任延伸报告和 FT-IR光谱是通过使用营养缺陷型的同位素标记; 细菌叶绿素11、叶绿素11、醌类和蛋白质氨基酸残基 都可以在体内标记。

The overall goal of this proposal is to develop a more detailed understanding of the molecular basis of biological electron transfer. Electron transfer is of central importance in all biological redox reactions and in energy conversion in the mitochondria and chloroplast, but little is known about the role that protein structure and protein and cofactor conformational changes play in this process. The spectroscopic studies to be described here will address these questions; the model system that will be used is the photosynthetic reaction center. The factors that influence the efficiency and directionality of electron transfer after light absorption in the reaction center are likely to be important in other redox reactions. Moreover, photosynthetic reaction centers provide a unique system for study of electron transfer mechanism, because the reactions can be initiated by light. The specific aims of this proposal are to use electron paramagnetic resonance (EPR) and difference Fourier- transform infrared (FT-IR) spectroscopy to study light-driven electron transfer events in bacterial reaction centers and in photosystem II, the water-splitting complex. EPR experiments on photosystem II will be aimed at the identification of an intermediate electron transfer component, Z+, of photosystem II, which is light-induced and is believed to be an amino acid residue. Collaborative experiments will explore the spectroscopic properties of mutants where other amino acids have been substituted at the putative Z+ site. This work will define the structural features that are important in electron transfer on the donor side of photosystem II. Difference FT-IR experiments will be performed on both the bacterial reaction center and on photosystem II. Subtraction of a "dark" from a "light" spectrum makes this technique specific for vibrational changes associated with charge separation. In the bacterial reaction center, difference FT-IR spectra will contain information about the structural changes in protein residues and in cofactors that accompany charge separation. In photosystem II, difference FT-IR will provide a new technique to use in studies of conformational changes in the manganese cluster, the site of water oxidation, and in the study of the protein structural alterations, such as protonation/deprotonation events, that are involved in the formation of Z+. The key to interpretation of both EPR and FT-IR spectra is isotopic labeling through the use of auxotrophs; bacteriochlorophy11, chlorophy11, quinones, and protein amino acid residues can all be labeled in vivo.