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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.nWhile the chlorophyll dimer P700 has long been identified as the primary electron donor, the componentsninvolved in the primary charge separation process in PSI remain undetermined. Here, we have studied thencharge separation dynamics in Photosystem I trimers from Synechococcus elongatus by femtosecond vis-npump/mid-infrared-probe spectroscopy upon excitation at 700, 710, and 715 nm. Because of the highnspecificity of the infrared region for the redox state and small differences in the molecular structure ofnpigments, we were able to clearly identify specific marker bands indicating chlorophyll (Chl) oxidation.nMagnitudes of chlorophyll cation signals are observed to increase faster than the time resolution of thenexperiment (∼0.2 ps) upon both excitation conditions: 700 nm and selective red excitation. Two models,ninvolving either ultrafast charge separation or charge transfer character of the red pigments in PSI, arendiscussed to explain this observation. A further increase in the magnitudes of cation signals on ansubpicosecond time scale (0.8-1 ps) indicates the formation of the primary radical pair. Evolution in thencation region with time constants of 7 and 40 ps reveals the formation of the secondary radical pair, involvingna secondary electron donor. Modeling of the data allows us to extract the spectra of the two radical pairs,nwhich have IR signatures consistent with AþA0n- and P700nþA1n-.We conclude that the cofactor chlorophyll Anacts as the primary donor in PSI. The existence of an equilibrium between the two radical pairs we interpret asnconcerted hole/electron transfer between the pairs of electron donors and acceptors, until after 40 ps,nrelaxation leads to a full population of the P700nþA1 radical pair.
机译：光系统I是将太阳能转化为化学能的关键因素之一。尽管长期以来人们一直认为叶绿素二聚体P700是主要的电子给体，但PSI中涉及到主要电荷分离过程的组分仍未确定。在这里，我们研究了在700、710和715 nm激发时，通过飞秒vis-npump /中红外探针光谱法研究了细长突触球菌在Photosystem 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色素分子结构的微小差异，因此我们能够清楚地鉴定出表明叶绿素（Chl）氧化的特定标记带。n观察到叶绿素阳离子信号的幅度比时间快在两个激发条件：700 nm和选择性红色激发下，实验的分辨率（约0.2 ps）。讨论了两种模型，涉及超快电荷分离或PSI中红色颜料的电荷转移特性，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的阳离子化区域的演化揭示了次级自由基对的形成，其中涉及次级电子给体。数据建模使我们能够提取两个自由基对的光谱，其中两个自由基对具有与AþA0n-和P700nþA1n-一致的IR特征。我们得出结论，辅因子叶绿素Anacts是PSI中的主要供体。我们将两个自由基对之间存在平衡，我们认为这是电子供体和受体对之间的空穴/电子转移，直到40 ps之后，弛豫导致P700nþA1自由基对完全填充。

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