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首页> 外文期刊>Biochemistry >Cofactors Involved in Light-Driven Charge Separation in Photosystem I Identified by Subpicosecond Infrared Spectroscopy
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Cofactors Involved in Light-Driven Charge Separation in Photosystem I Identified by Subpicosecond Infrared Spectroscopy

机译：亚皮秒红外光谱法鉴定的光系统中光驱动电荷分离的辅助因子

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Photosystem I is one of the key players in the conversion of solar energy into chemical energy. While the chlorophyll dimer P_(700) has long been identified as the primary electron donor, the components involved in the primary charge separation process in PSI remain undetermined. Here, we have studied the charge separation dynamics in Phatosystem I trimers from Synechococcus elongatus by femtosecond vis-pump/mid-infrared-probe spectroscopy upon excitation at 700, 710, and 715 nm. Because of the high specificity of the infrared region for the redox state and small differences in the molecular structure of pigments, we were able to clearly identify specific marker bands indicating chlorophyll (Chl) oxidation. Magnitudes of chlorophyll cation Signals are observed to increase faster than the time resolution of the experiment (～0.2 ps) upon both excitation conditions: 700 nm and selective red excitation. Two models, involving either ultrafast charge separation or charge transfer character of the red pigments in PSI, are discussed to explain this observation. A further increase in the magnitudes of cation signals on a subpicosecond time scale (0.8-1 ps) indicates the formation of the primary radical pair. Evolution in the cation region with time constants of 7 and 40 ps reveals the formation of the secondary radical pair, involving a secondary electron donor. Modeling of the data allows us to extract the spectra of the two radical pairs, which have IR signatures consistent:with A~+A_0~- and P_(700)~+A_1~-. We conclude that the cofactor chlorophyll A acts as the primary donor in PSI. The existence of an equilibrium between the two radical pairs we interpret as concerted hole/electron transfer between the pairs of electron donors and acceptors, until after 40 Ps, relaxation leads to a full population of the P_(700)~+A_1 radical pair.
机译：光系统I是将太阳能转化为化学能的关键参与者之一。虽然长期以来人们一直将叶绿素二聚体P_（700）确定为主要电子供体，但PSI中主要电荷分离过程所涉及的成分仍未确定。在这里，我们研究了在700、710和715 nm激发时通过飞秒的可见光泵/中红外探针光谱法研究了细长突触球菌在Phatosystem I三聚体中的电荷分离动力学。由于红外区域对氧化还原状态的高度特异性以及颜料分子结构的微小差异，我们能够清楚地识别出表明叶绿素（Chl）氧化的特定标记带。在两种激发条件：700 nm和选择性红色激发下，观察到的叶绿素阳离子信号的幅度都比实验的时间分辨率（〜0.2 ps）增加得更快。讨论了两种模型，它们涉及PSI中红色颜料的超快电荷分离或电荷转移特性，以解释这一现象。阳离子信号幅度在亚皮秒级（0.8-1 ps）上的进一步增加表明形成了初级自由基对。时间常数为7和40 ps的阳离子区域中的演化揭示了涉及次级电子给体的次级自由基对的形成。数据建模使我们能够提取两个基团对的光谱，它们具有一致的IR签名：与A〜+ A_0〜-和P_（700）〜+ A_1〜-。我们得出结论，辅因子叶绿素A充当PSI中的主要供体。我们将这两个自由基对之间存在平衡，我们将其解释为电子供体和受体对之间的协调的空穴/电子转移，直到40 Ps之后，弛豫会导致P_（700）〜+ A_1自由基对的完全填充。

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