SPECTROSCOPIC STUDIES OF LIGHT-DRIVEN ELECTRON TRANSFER

这项提案的总体目标是制定一项更详细的 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过程中起着核心作用。 线粒体和叶绿体中的反应和能量转换，但 人们对蛋白质结构和蛋白质的作用知之甚少 辅因子构象变化在这一过程中发挥作用。《光谱》 这里将要描述的研究将解决这些问题；模型系统 将使用的是光合作用反应中心。这些因素是 对电子转移效率和方向性的影响 反应中心的光吸收在其他方面可能也很重要 氧化还原反应。此外，光合作用反应中心提供了一个 研究电子转移机制的独特系统，因为 光可以引发反应。这项建议的具体目的 是使用电子顺磁共振(EPR)和差分傅立叶- 光驱电子的红外光谱研究 细菌反应中心和光系统II中的转移事件， 裂水复合体。关于光系统II的EPR实验将是目标 在识别中间电子转移分量Z时， 光系统II，它是光诱导的，被认为是一种氨基酸 酸渣。合作实验将探索光谱 其他氨基酸已被取代的突变体的性质 推定的Z点。这项工作将定义以下结构特征 在光系统II的给体侧的电子转移中起重要作用。 将对这两种细菌进行不同的FT-IR实验 反应中心和光系统II.从一个光系统中减去“暗” “光”光谱使这项技术专用于振动变化。 与电荷分离有关。在细菌反应中心， 不同的FT-IR光谱将包含有关结构的信息 蛋白质残基和伴随电荷的辅因子的变化 分离。在光系统II中，Difference FT-IR将提供新的 用于研究锰的构象变化的技术 团簇，水氧化的位置，以及在蛋白质的研究中 结构变化，如质子化/去质子化事件 参与了Z的形成。解读EPR和EPR的关键 FT-IR光谱是通过使用营养缺陷菌进行的同位素标记； 细菌叶绿素11、叶绿素11、苯二酚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.