Hastings G, Reed L J, Lin S, Blankenship R E
Department of Chemistry and Biochemistry, Arizona State University, Tempe 85287-1604, USA.
Biophys J. 1995 Nov;69(5):2044-55. doi: 10.1016/S0006-3495(95)80074-3.
Femtosecond transient absorption spectroscopy has been used to investigate the energy transfer and trapping processes in both intact membranes and purified detergent-isolated particles from a photosystem II deletion mutant of the cyanobacterium Synechocystis sp. PCC 6803, which contains only the photosystem I reaction center. Processes with similar lifetimes and spectra are observed in both the membrane fragments and the detergent-isolated particles, suggesting little disruption of the core antenna resulting from the detergent treatment. For the detergent-isolated particles, three different excitation wavelengths were used to excite different distributions of pigments in the spectrally heterogeneous core antenna. Only two lifetimes of 2.7-4.3 ps and 24-28 ps, and a nondecaying component are required to describe all the data. The 24-28 ps component is associated with trapping. The trapping process gives rise to a nondecaying spectrum that is due to oxidation of the primary electron donor. The lifetimes and spectra associated with trapping and radical pair formation are independent of excitation wavelength, suggesting that trapping proceeds from an equilibrated excited state. The 2.7-4.3 ps component characterizes the evolution from the initially excited distribution of pigments to the equilibrated excited state distribution. The spectrum associated with the 2.7-4.3 ps component is therefore strongly excitation wavelength dependent. Comparison of the difference spectra associated with the spectrally equilibrated state and the radical pair state suggests that the pigments in the photosystem I core antenna display some degree of excitonic coupling.
飞秒瞬态吸收光谱已被用于研究来自蓝藻集胞藻6803光合系统II缺失突变体的完整膜和纯化去污剂分离颗粒中的能量转移和俘获过程，该突变体仅包含光合系统I反应中心。在膜片段和去污剂分离颗粒中观察到具有相似寿命和光谱的过程，这表明去污剂处理对核心天线的破坏很小。对于去污剂分离颗粒，使用三种不同的激发波长来激发光谱异质核心天线中不同的色素分布。仅需要2.7 - 4.3皮秒和24 - 28皮秒的两个寿命以及一个非衰减成分来描述所有数据。24 - 28皮秒的成分与俘获相关。俘获过程产生一个由于初级电子供体氧化而产生的非衰减光谱。与俘获和自由基对形成相关的寿命和光谱与激发波长无关，这表明俘获从平衡激发态开始。2.7 - 4.3皮秒的成分表征了从最初激发的色素分布到平衡激发态分布的演化。因此，与2.7 - 4.3皮秒成分相关的光谱强烈依赖于激发波长。与光谱平衡态和自由基对态相关的差分光谱的比较表明，光合系统I核心天线中的色素显示出一定程度的激子耦合。
