Site, Rate, and Mechanism of Photoprotective Quenching in Cyanobacteria
Site, Rate, and Mechanism of Photoprotective Quenching in Cyanobacteria
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DOI：
10.1021/ja206414m
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发表时间：
2011-11-16
影响因子：
15
通讯作者：
van Amerongen, Herbert
中科院分区：
文献类型：
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作者：
Tian, Lijin;van Stokkum, Ivo H. M.;van Amerongen, Herbert
在蓝细菌中，强烈的蓝绿光激活橙子类胡萝卜素蛋白（OCP），引发过量吸收能量的光保护热耗散，导致捕光藻胆体的荧光减少（淬灭），同时到达反应中心的能量减少。使用光谱分辨皮秒荧光，我们研究了细胞的野生型集胞藻属PCC 6803和突变体没有和额外的OCP（三角洲OCP和OverOCP）在未淬灭和淬灭状态。使用目标分析，我们设法解决七个不同的色素池中的藻胆体和光系统I和II，并确定它们之间的激发能量转移率。此外，猝灭藻胆体的分数和电荷分离和猝灭的速率被解决。在我们的光照条件下，OverOCP中类似于72%的藻胆体似乎基本上被淬灭。对于野生型细胞，这个数字仅与19%相似。结果表明，在OCP激活后，在藻胆体的核心中的胆色素发色团，这里称为APC（660）（Q），在660 nm处具有荧光最大值，成为有效的猝灭剂，其阻止藻胆体中超过80%的激发到达光系统I和II。其激发态的猝灭速率极快，即至少（类似于140 +/- 60 fs）（-1）。可以得出结论，淬灭最有可能是由APC（660）（Q）和处于其活化形式的OCP类胡萝卜素hECN之间的电荷转移引起。
In cyanobacteria, activation of the Orange Carotenoid Protein (OCP) by intense blue-green light triggers photoprotective thermal dissipation of excess absorbed energy leading to a decrease (quenching) of fluorescence of the light harvesting phycobilisomes and, concomitantly, of the energy arriving to the reaction centers. Using spectrally resolved picosecond fluorescence, we have studied cells of wild-type Synechocystis sp. PCC 6803 and of mutants without and with extra OCP (Delta OCP and OverOCP) both in the unquenched and quenched state. With the use of target analysis, we managed to spectrally resolve seven different pigment pools in the phycobilisomes and photosystems I and II, and to determine the rates of excitation energy transfer between them. In addition, the fraction of quenched phycobilisomes and the rates of charge separation and quenching were resolved. Under our illumination conditions, similar to 72% of the phycobilisomes in OverOCP appeared to be substantially quenched. For wild-type cells, this number was only similar to 19%. It is revealed that upon OCP activation, a bilin chromophore in the core of the phycobilisome, here called APC(660)(Q), with fluorescence maximum at 660 nm becomes an effective quencher that prevents more than 80% of the excitations in the phycobilisome to reach Photosystems I and II. The quenching rate of its excited state is extremely fast, that is, at least (similar to 140 +/- 60 fs)(-1). It is concluded that the quenching is most likely caused by charge transfer between APC(660)(Q) and the OCP carotenoid hECN in its activated form.