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分离的光系统II反应中心的飞秒光二色性研究。

Femtosecond photodichroism studies of isolated photosystem II reaction centers.

作者信息

Wiederrecht G P, Seibert M, Wasielewski M R

机构信息

Chemistry Division, Argonne National Laboratory, IL 60439.

出版信息

Proc Natl Acad Sci U S A. 1994 Sep 13;91(19):8999-9003. doi: 10.1073/pnas.91.19.8999.

Abstract

Photosynthetic conversion of light energy into chemical potential begins in reaction center protein complexes, where rapid charge separation occurs with nearly unit quantum efficiency. Primary charge separation was studied in isolated photosystem II reaction centers from spinach containing 6 chlorophyll a, 2 pheophytin a (Pheo), 1 cytochrome b559, and 2 beta-carotene molecules. Time-resolved pump-probe kinetic spectroscopy was carried out with 105-fs time resolution and with the pump laser polarized parallel, perpendicular, and at the magic angle (54.7 degrees) relative to the polarized probe beam. The time evolution of the transient absorption changes due to the formation of the oxidized primary electron donor P680+ and the reduced primary electron acceptor Pheo- were measured at 820 nm and 545 nm, respectively. In addition, kinetics were obtained at 680 nm, the wavelength ascribed to the Qy transition of the primary electron donor P680 in the reaction center. At each measured probe wavelength the kinetics of the transient absorption changes can be fit to two major kinetic components. The relative amplitudes of these components are strongly dependent on the polarization of the pump beam relative to that of the probe. At the magic angle, where no photoselection occurs, the amplitude of the 3-ps component, which is indicative of the charge separation, dominates. When the primary electron acceptor Pheo is reduced prior to P680 excitation, the 3-ps component is eliminated.

摘要

光能向化学势的光合转化始于反应中心蛋白复合体,在那里电荷以近乎单位量子效率快速分离。在从菠菜中分离出的含有6个叶绿素a、2个脱镁叶绿素a(Pheo)、1个细胞色素b559和2个β-胡萝卜素分子的光系统II反应中心中研究了初级电荷分离。采用105飞秒时间分辨率进行时间分辨泵浦-探测动力学光谱研究,泵浦激光相对于偏振探测光束的偏振方向为平行、垂直和魔角(54.7度)。分别在820纳米和545纳米处测量了由于氧化的初级电子供体P680+和还原的初级电子受体Pheo-的形成而导致的瞬态吸收变化的时间演化。此外,在680纳米处获得了动力学数据,该波长归因于反应中心中初级电子供体P680的Qy跃迁。在每个测量的探测波长处,瞬态吸收变化的动力学可以拟合为两个主要的动力学成分。这些成分的相对振幅强烈依赖于泵浦光束相对于探测光束的偏振。在不发生光选择的魔角处,指示电荷分离的3皮秒成分的振幅占主导。当在P680激发之前初级电子受体Pheo被还原时,3皮秒成分被消除。

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