Zabelin Alexey A, Neverov Konstantin V, Krasnovsky Alexander A, Shkuropatova Valentina A, Shuvalov Vladimir A, Shkuropatov Anatoly Ya
Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino, Moscow Region 142290, Russian Federation.
A.N. Bach Institute of Biochemistry, Russian Academy of Sciences, Leninskii pr., 33, Moscow 119071, Russian Federation; Biology Department, M.V. Lomonosov Moscow State University, Vorobyovy Gory, Moscow 119992, Russian Federation.
Biochim Biophys Acta. 2016 Jun;1857(6):782-8. doi: 10.1016/j.bbabio.2016.03.029. Epub 2016 Apr 27.
Phosphorescence measurements at 77 K and light-induced FTIR difference spectroscopy at 95 K were applied to study of the triplet state of chlorophyll a ((3)Chl) in photosystem II (PSII) core complexes isolated from spinach. Using both methods, (3)Chl was observed in the core preparations with doubly reduced primary quinone acceptor QA. The spectral parameters of Chl phosphorescence resemble those in the isolated PSII reaction centers (RCs). The main spectral maximum and the lifetime of the phosphorescence corresponded to 955±1 nm and of 1.65±0.05 ms respectively; in the excitation spectrum, the absorption maxima of all core complex pigments (Chl, pheophytin a (Pheo), and β-carotene) were observed. The differential signal at 1667(-)/1628(+)cm(-1) reflecting a downshift of the stretching frequency of the 13(1)-keto C=O group of Chl was found to dominate in the triplet-minus-singlet FTIR difference spectrum of core complexes. Based on FTIR results and literature data, it is proposed that (3)Chl is mostly localized on the accessory chlorophyll that is in triplet equilibrium with P680. Analysis of the data suggests that the Chl triplet state responsible for the phosphorescence and the FTIR difference spectrum is mainly generated due to charge recombination in the reaction center radical pair P680(+)PheoD1(-), and the energy and temporal parameters of this triplet state as well as the molecular environment and interactions of the triplet-bearing Chl molecule are similar in the PSII core complexes and isolated PSII RCs.
采用77K下的磷光测量和95K下的光诱导傅里叶变换红外差示光谱法，对从菠菜中分离出的光系统II（PSII）核心复合物中叶绿素a（(3)Chl）的三重态进行了研究。使用这两种方法，在初级醌受体QA双还原的核心制剂中观察到了(3)Chl。Chl磷光的光谱参数与分离的PSII反应中心（RCs）中的相似。磷光的主要光谱最大值和寿命分别对应于955±1nm和1.65±0.05ms；在激发光谱中，观察到了所有核心复合物色素（Chl、脱镁叶绿素a（Pheo）和β-胡萝卜素）的吸收最大值。在核心复合物的三重态减单重态傅里叶变换红外差示光谱中，发现反映Chl的13(1)-酮C=O基团伸缩频率下移的1667(-)/1628(+)cm(-1)处的差分信号占主导。基于傅里叶变换红外光谱结果和文献数据，提出(3)Chl主要定位于与P680处于三重态平衡的辅助叶绿素上。数据分析表明，负责磷光和傅里叶变换红外差示光谱的Chl三重态主要是由于反应中心自由基对P680(+)PheoD1(-)中的电荷复合产生的，并且该三重态的能量和时间参数以及含三重态的Chl分子的分子环境和相互作用在PSII核心复合物和分离的PSII RCs中相似。
