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Molecular Mechanism of the Reaction and Regulation of the Quinone Electron Acceptors in Photosystem II

光系统II中醌电子受体反应与调控的分子机制

基本信息

批准号：
18570145
负责人：
NOGUCHI Takumi
金额：
$ 2.61万
依托单位：
University of Tsukuba
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2006
资助国家：
日本
起止时间：
2006 至 2007
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-18570145/
关键词：
photosystem II plastoquinone primary quinone electron acceptor Q_A secondary quinone electron acceptor Q_B Fourier transform infrared snectroscopy density functional theory 第二キノン電子受容体Q_B

项目摘要

1. To investigate the H-bond structures of the primary quinone electron acceptor Q_A and the secondary quinone acceptor Q_B, vibrational analysis using density functional theory (DFT) calculations was performed for model H-bonded complexes of plastoquinone (PQ). It was shown that the symmetry of the H-bond structures of the PQ C= O groups strongly affects the CO stretching frequencies. Comparison of these calculated results with the CO bands of PQ in the Q_A-/Q_A and Q_B-/Q_B Fourier transform infrared (FTIR) difference spectra indicated that the H-bond structure of Q_B is more asymmetric than that of Q_A.2. We have investigated the changes in the redox potential of Q_A and the H-bond structures of its CO groups upon binding of different types of herbicides at the Q_B site. From the peak temperatures of the S_2, Q_A-thermoluminescence bands, it was shown that phenolic herbicides downshifted the Q_A redox potential, whereas urea, uracil and triazine-type herbicides upshifted the potential. The CO stretching bands of Q_A-was detected at lower frequencies by about 1 cm-1 upon binding of the former hirbicides than the latter ones. This small frequency difference was shown to arise from the difference in the H-bond strength of the CO groups. In addition, detailed analysis of the FTIR bands of phenolic herbicides showed that this type of herbicide binds to DI-His215 with a deprotonated form and then changes the strength of the H-bond between D2-His214 and Q_A via His-Fe^<2+>-His bridge to affect the redox potential of Q_A.From the above results of 1. and 2., it was concluded that the redox potentials of Q_A and Q_B are finely tuned by the structures and the strengths of the H-bonds of the C=O groups to realize the smooth electron flow from Q_A to Q_B.

1.为了研究醌类电子伯受体Q_A和醌类电子仲受体Q_B的氢键结构，采用密度泛函理论（DFT）对醌类氢键复合物模型进行了振动分析.结果表明，PQ C= O基团的氢键结构的对称性强烈影响CO伸缩频率。将计算结果与PQ的Q_A-/Q_A和Q_B-/Q_B傅里叶变换红外（FTIR）差谱中的CO带进行比较，发现Q_B的氢键结构比Q_A的氢键结构更不对称.本文研究了不同类型除草剂在Q_A_B位上结合后，Q_A_B_从S_2、Q_A热释光峰的温度可以看出，酚类除草剂使Q_A氧化还原电位降低，而尿素、尿嘧啶和三嗪类除草剂使Q_A氧化还原电位升高。与前两种除草剂结合时，Q_A-的CO伸缩带的频率比后两种除草剂低约1cm ~（-1）。这种小的频率差异被证明是由CO基团的氢键强度的差异引起的。此外，对酚类除草剂FTIR谱带的详细分析表明，该类除草剂以去质子化形式与DI-His 215结合，然后通过His-Fe^2+-His桥改变D2-His 214与Q_A之间的氢键强度，从而影响Q_A的氧化还原电位。和2.，结果表明，通过调节C=O基团的结构和氢键强度，Q_A和Q_B的氧化还原电位可以实现从Q_A到Q_B的平稳电子流.