Riley Kerry J, Zazubovich Valter, Jankowiak Ryszard
Ames Laboratory-USDOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011-3111, USA.
J Phys Chem B. 2006 Nov 16;110(45):22436-46. doi: 10.1021/jp063691f.
Absorption, fluorescence excitation, emission, and hole-burning (HB) spectra were measured at liquid helium temperatures for the PS I-CP43' supercomplexes of Synechocystis PCC 6803 grown under iron stress conditions and for respective trimeric PS I cores. Results are compared with those of room temperature, time-domain experiments (Biochemistry 2003, 42, 3893) as well as with the low-temperature steady-state experiments on PS I-CP43' supercomplexes of Synechococcus PCC 7942 (Biochim. Biophys. Acta 2002, 1556, 265). In contrast to the CP43' of Synechococcus PCC 7942, CP43' of Synechocystis PCC 6803 possesses two low-energy states analogous to the quasidegenerate states A and B of CP43 of photosystem II (J. Phys. Chem. B 2000, 104, 11805). Energy transfer between the CP43' and the PS I core occurs, to a significant degree, through the state A, characterized with a broader site distribution function (SDF). It is demonstrated that the low temperature (T = 5 K) excitation energy transfer (EET) time between the state A of CP43' (IsiA) and the PS I core in PS I-CP43' supercomplexes from Synechocystis PCC 6803 is about 60 ps, which is significantly slower than the EET observed at room temperature. Our results are consistent with fast (< or =10 ps) energy transfer from state B to state A in CP43'. Energy absorbed by the CP43' manifold has, on average, a greater chance of being transferred to the reaction center (RC) and utilized for charge separation than energy absorbed by the PS I core antenna. This indicates that energy is likely transferred from the CP43' to the RC along a well-defined path and that the "red antenna states" of the PS I core are localized far away from that path, most likely on the B7-A32 and B37-B38 dimers in the vicinity of the PS I trimerization domain (near PsaL subunit). We argue that the A38-A39 dimer does not contribute to the red antenna region.
在液氦温度下，测量了在铁胁迫条件下生长的集胞藻PCC 6803的PS I - CP43'超复合物以及相应三聚体PS I核心的吸收光谱、荧光激发光谱、发射光谱和空穴烧蚀（HB）光谱。将结果与室温时域实验（《生物化学》，2003年，42卷，3893页）以及对聚球藻PCC 7942的PS I - CP43'超复合物的低温稳态实验（《生物化学与生物物理学报》，2002年，1556卷，265页）进行了比较。与聚球藻PCC 7942的CP43'不同，集胞藻PCC 6803的CP43'具有两个类似于光系统II的CP43的准简并态A和B的低能态（《物理化学杂志B》，2000年，104卷，11805页）。CP43'与PS I核心之间的能量转移在很大程度上通过态A发生，其特征是具有更宽的位点分布函数（SDF）。结果表明，集胞藻PCC 6803的PS I - CP43'超复合物中CP43'（IsiA）的态A与PS I核心之间的低温（T = 5 K）激发能量转移（EET）时间约为60皮秒，这明显慢于室温下观察到的EET。我们的结果与CP43'中从态B到态A的快速（≤10皮秒）能量转移一致。CP43'多重态吸收的能量平均而言比PS I核心天线吸收的能量更有机会转移到反应中心（RC）并用于电荷分离。这表明能量可能沿着一条明确的路径从CP43'转移到RC，并且PS I核心的“红色天线态”位于远离该路径的位置，很可能位于PS I三聚化结构域（靠近PsaL亚基）附近的B7 - A32和B37 - B38二聚体上。我们认为A38 - A39二聚体对红色天线区域没有贡献。
