Cofactors Involved in Light-Driven Charge Separation in Photosystem I Identified by Subpicosecond Infrared Spectroscopy
Cofactors Involved in Light-Driven Charge Separation in Photosystem I Identified by Subpicosecond Infrared Spectroscopy
复制标题
DOI：
10.1021/bi101565w
复制
发表时间：
2011-02-01
期刊：
影响因子：
2.9
通讯作者：
Groot, Marie-Louise
中科院分区：
文献类型：
--
作者：
Di Donato, Mariangela;Stahl, Andreas D.;Groot, Marie-Louise
光系统I是将太阳能转化为化学能的关键参与者之一。虽然叶绿素二聚体P-700长期以来一直被认为是主要的电子供体，但PSI中参与初级电荷分离过程的成分仍未确定。在这里，我们用飞秒可见光泵浦/中红外探测光谱研究了700、710和715 nm激发下长聚球藻磷酸系统I三聚体的电荷分离动力学。由于红外区氧化还原状态的高度特异性和色素分子结构的微小差异，我们能够清楚地识别指示叶绿素(Chl)氧化的特定标记带。在700 nm激发和选择性红色激发下，观察到叶绿素阳离子信号的大小比实验的时间分辨率(类似于0.2ps)增加得更快。讨论了两种模型，分别涉及PSI中红色颜料的超快电荷分离和电荷转移特性，以解释这一现象。在亚皮秒时间尺度(0.8-1ps)上，阳离子信号的大小进一步增加，表明初级自由基对的形成。在时间常数为7和40ps的阳离子区域的演化揭示了二次自由基对的形成，涉及二次电子给体。通过对数据的建模，我们可以提取两个自由基对的光谱，这两个自由基对的IR特征一致：A(+)A(0)(-)和P(700)(+)A(1)(-)。我们认为，辅因子叶绿素A是PSI的主要供体。两个自由基对之间存在平衡，我们将其解释为电子给体和受体对之间的协同空穴/电子转移，直到40ps后，弛豫导致P(700)(+)A(1)自由基对的全部布居。
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 (similar to 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.