N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 117977 Moscow, Kosygina st., 4, Russia.
N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 117977 Moscow, Kosygina st., 4, Russia.
J Photochem Photobiol B. 2021 Apr;217:112154. doi: 10.1016/j.jphotobiol.2021.112154. Epub 2021 Feb 16.
In Photosystem I (PS I), the role of the accessory chlorophyll (Chl) molecules, Chl and Chl (also termed A and A), which are directly adjacent to the special pair P and fork into the A- and B-branches of electron carriers, is incompletely understood. In this work, the Chl and Chl transient absorption ΔA(λ) at a time delay of 100 fs was identified by ultrafast pump-probe spectroscopy in three pairs of PS I complexes from Synechocystis sp. PCC 6803 with residues PsaA-N600 or PsaB-N582 (which ligate Chl or Chl through a HO molecule) substituted by Met, His, and Leu. The ΔA(λ) spectra were quantified using principal component analysis, the main component of which was interpreted as a mutation-induced shift of the equilibrium between the excited state of primary donor P and the primary charge-separated state PChl. This equilibrium is shifted to the charge-separated state in wild-type PS I and to the excited P in the PS I complexes with the substituted ligands to the Chl and Chl monomers. The results can be rationalized within the framework of an adiabatic model in which the P is electronically coupled with the symmetrically arranged monomers Chl and Chl; such a structure can be considered a symmetric tetrameric exciplex ChlPPChl, in which the excited state (ChlPPChl)* is mixed with two charge-transfer states PChl and PChl. The electron redistribution between the two branches in favor of the A-branch apparently takes place in the picosecond time scale after reduction of the Chl and Chl monomers.
在光系统 I（PS I）中，辅助叶绿素（Chl）分子和 Chl（也称为 A 和 A）的作用，它们直接与特殊对 P 相邻并分叉到电子载体的 A-和 B-分支，目前还不完全清楚。在这项工作中，通过超快泵浦探针光谱学，在来自集胞藻 6803 的三对 PS I 复合物中鉴定了 Chl 和 Chl 的瞬态吸收ΔA(λ)，延迟时间为 100 fs。这三对 PS I 复合物的 PsaA-N600 或 PsaB-N582 残基（通过 HO 分子连接 Chl 或 Chl）被 Met、His 和 Leu 取代。使用主成分分析对ΔA(λ)光谱进行了量化，其主要成分解释为突变诱导的初级供体 P 的激发态和初级电荷分离态 PChl 之间平衡的移动。在野生型 PS I 中，这种平衡向电荷分离态移动，而在与 Chl 和 Chl 单体取代配体的 PS I 复合物中，这种平衡向激发态 P 移动。在一个绝热模型的框架内，可以合理地解释这些结果，在该模型中，P 与对称排列的单体 Chl 和 Chl 电子耦合；这种结构可以被认为是一个对称的四聚体激基复合物 ChlPPChl，其中激发态（ChlPPChl）*与两个电荷转移态 PChl 和 PChl 混合。Chl 和 Chl 单体还原后，两个分支之间的电子重新分布有利于 A 分支，显然发生在皮秒时间尺度内。
