Zhang F G, Gillbro T, van Grondelle R, Sundström V
Department of Physical Chemistry, University of Umeå, Sweden.
Biophys J. 1992 Mar;61(3):694-703. doi: 10.1016/S0006-3495(92)81874-X.
By low intensity picosecond absorption spectroscopy it is shown that the exciton lifetime in the light-harvesting antenna of Rhodopseudomonas (Rps.) viridis membranes with photochemically active reaction centers at room temperature is 60 +/- 10 ps. This lifetime reflects the overall trapping rate of the excitation energy by the reaction center. With photochemically inactive reaction centers, in the presence of P+, the exciton lifetime increases to 150 +/- 15 ps. Prereducing the secondary electron acceptor QA does not prevent primary charge separation, but slows it down from 60 to 90 +/- 10 ps. Picosecond kinetics measured at 77 K with inactive reaction centers indicates that the light-harvesting antenna is spectrally homogeneous. Picosecond absorption anisotropy measurements show that energy transfer between identical Bchlb molecules occurs on the subpicosecond time scale. Using these experimental results as input to a random-walk model, results in strict requirements for the antenna-RC coupling. The model analysis prescribes fast trapping (approximately 1 ps) and an approximately 0.5 escape probability from the reaction center, which requires a more tightly coupled RC and antenna, as compared with the Bchla-containing bacteria Rhodospirillum (R.) rubrum and Rhodobacter (Rb.) sphaeroides.
通过低强度皮秒吸收光谱法表明，在室温下具有光化学活性反应中心的绿假单胞菌（Rps.）绿膜光捕获天线中的激子寿命为60±10皮秒。该寿命反映了反应中心对激发能的总体捕获速率。对于光化学无活性的反应中心，在存在P+的情况下，激子寿命增加到150±15皮秒。预还原次级电子受体QA不会阻止初级电荷分离，但会使其从60皮秒减慢到90±10皮秒。在77K下对无活性反应中心进行的皮秒动力学测量表明，光捕获天线在光谱上是均匀的。皮秒吸收各向异性测量表明，相同的细菌叶绿素b分子之间的能量转移发生在亚皮秒时间尺度上。将这些实验结果作为随机游走模型的输入，对天线-反应中心耦合提出了严格要求。模型分析规定快速捕获（约1皮秒）以及从反应中心约0.5的逃逸概率，与含细菌叶绿素a的红螺菌（R.）红细菌和球形红杆菌（Rb.）相比，这需要反应中心和天线之间有更紧密的耦合。
