Light harvesting in photosystem II core complexes is limited by the transfer to the trap: Can the core complex turn into a photoprotective mode?
Light harvesting in photosystem II core complexes is limited by the transfer to the trap: Can the core complex turn into a photoprotective mode?
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DOI：
10.1021/ja7099826
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发表时间：
2008-04-02
影响因子：
15
通讯作者：
Renger, Thomas
中科院分区：
文献类型：
--
作者：
Raszewski, Grzegorz;Renger, Thomas
提出了一种基于结构的光系统II（PS-II）核心复合物中初级光物理反应的建模和分析方法。建模是基于对CP 43、CP 47和D1-D2-cytb 559亚基和整个核心复合物的固定和时间分辨光谱的描述。它表明，在PS-Ⅱ核心复合物的功能（开放）的反应中心（RC）的激发态的衰减是有限的激发能量转移从CP 43和CP 47核心天线的RC发生在室温下的时间常数为40-50 ps。叶绿素负责低能量的吸收带中的CP 43和CP 47亚基的分配，和他们的签名在烧孔，荧光线变窄，和三重态减单重态光谱进行了解释。这些陷阱态在CP 43和CP 47天线相对于反应中心的不同位置导致在低温下的转移动力学的急剧变化。计算预测，与室温相比，在77 K下的荧光衰减应该揭示从CP 43到RC的更快的转移和从CP 47到RC的慢得多且高度分散的转移。据报道，RC关闭时发生的荧光最快衰减时间常数增加3倍（质体醌Q（A）被还原）在本模型中通过假设初级电子转移的固有速率常数从开放RC的100 fs（-1）降低到闭合RC的6 ps（-1）来理解，导致初级电子受体Pheo（D1）的还原，分别为300 fs和18 ps。该模型表明，降低Q（A）开关的光系统进入光保护模式，其中大部分的RC的激发能量返回到CP 43和CP 47的核心天线，在那里的叶绿素的生理危险的三重态能量可以淬灭的类胡萝卜素。建议用实验来检验这一假设。超快的初级电子转移推断开放RC提供了进一步的支持，辅助叶绿素Chl（D1）的初级电子供体在光系统II。
A structure-based modeling and analysis of the primary photophysical reactions in photosystem II (PS-II) core complexes is presented. The modeling is based on a description of stationary and time-resolved optical spectra of the CP43, CP47, and D1-D2-cytb559 subunits and whole core complexes. It shows that the decay of excited states in PS-II core complexes with functional (open) reaction centers (RCs) is limited by the excitation energy transfer from the CP43 and CP47 core antennae to the RC occurring with a time constant of 40-50 ps at room temperature. The chlorophylls responsible for the low energy absorbance bands in the CP43 and CP47 subunits are assigned, and their signatures in hole burning, fluorescence line narrowing, and triplet-minus-singlet spectra are explained. The different locations of these trap states in the CP43 and CP47 antennae with respect to the reaction center lead to a dramatic change of the transfer dynamics at low temperatures. The calculations predict that, compared to room temperature, the fluorescence decay at 77 K should reveal a faster transfer from CP43 and a much slower and highly dispersive transfer from CP47 to the RC. A factor of 3 increase in the fastest decay time constant of fluorescence that was reported to occur when the RC is closed (the plastoquinone Q(A) is reduced) is understood in the present model by assuming that the intrinsic rate constant for primary electron transfer decreases from 100 fs(-1) for open RCs to 6 ps(-1) for closed RCs, leading to a reduction of the primary electron acceptor Pheo(D1), in 300 fs and 18 ps, respectively. The model suggests that the reduced Q(A) switches the photosystem into a photoprotective mode in which a large part of the excitation energy of the RC returns to the CP43 and CP47 core antennae, where the physiologically dangerous triplet energy of the chlorophylls can be quenched by the carotenoids. Experiments are suggested to test this hypothesis. The ultrafast primary electron transfer inferred for open RCs provides further support for the accessory chlorophyll Chl(D1) to be the primary electron donor in photosystem II.