Department of Physics, Arizona State University, Tempe, AZ 85287, USA.
Phys Chem Chem Phys. 2014 Aug 28;16(32):17133-41. doi: 10.1039/c4cp01981d.
Time-resolved fluorescence spectroscopy was used to explore the pathway and kinetics of energy transfer in photosynthetic membrane vesicles (chromatophores) isolated from Rhodobacter (Rba.) sphaeroides cells harvested 2, 4, 6 or 24 hours after a transition from growth in high to low level illumination. As previously observed, this light intensity transition initiates the remodeling of the photosynthetic apparatus and an increase in the number of light harvesting 2 (LH2) complexes relative to light harvesting 1 (LH1) and reaction center (RC) complexes. It has generally been thought that the increase in LH2 complexes served the purpose of increasing the overall energy transmission to the RC. However, fluorescence lifetime measurements and analysis in terms of energy transfer within LH2 and between LH2 and LH1 indicate that, during the remodeling time period measured, only a portion of the additional LH2 generated are well connected to LH1 and the reaction center. The majority of the additional LH2 fluorescence decays with a lifetime comparable to that of free, unconnected LH2 complexes. The presence of large LH2-only domains has been observed by atomic force microscopy in Rba. sphaeroides chromatophores (Bahatyrova et al., Nature, 2004, 430, 1058), providing structural support for the existence of pools of partially connected LH2 complexes. These LH2-only domains represent the light-responsive antenna complement formed after a switch in growth conditions from high to low illumination, while the remaining LH2 complexes occupy membrane regions containing mixtures of LH2 and LH1-RC core complexes. The current study utilized a multi-parameter approach to explore the fluorescence spectroscopic properties related to the remodeling process, shedding light on the structure-function relationship of the photosynthetic assembles. Possible reasons for the accumulation of these largely disconnected LH2-only pools are discussed.
时间分辨荧光光谱法被用于探索在从高光照强度到低光照强度的转变后 2、4、6 或 24 小时收获的球形红杆菌（Rba.）细胞中分离的光合膜囊泡（类囊体）中能量转移的途径和动力学。如前所述，这种光强转变会引发光合器官的重构，并增加相对于光收集 1（LH1）和反应中心（RC）复合物的光收集 2（LH2）复合物的数量。通常认为，LH2 复合物的增加是为了增加向 RC 的整体能量传递。然而，基于 LH2 内和 LH2 与 LH1 之间能量转移的荧光寿命测量和分析表明，在测量的重构时间段内，只有一部分额外生成的 LH2 与 LH1 和反应中心很好地连接。大部分额外的 LH2 荧光随寿命衰减，其寿命与游离的、未连接的 LH2 复合物相当。原子力显微镜已经观察到在球形红杆菌类囊体（Bahatyrova 等人，《自然》，2004 年，430 页，1058）中存在大的仅 LH2 结构域，为部分连接的 LH2 复合物池的存在提供了结构支持。这些仅 LH2 结构域代表在从高光照强度到低光照强度的生长条件转变后形成的光响应天线补充，而其余的 LH2 复合物占据含有 LH2 和 LH1-RC 核心复合物混合物的膜区域。本研究利用多参数方法探索与重构过程相关的荧光光谱性质，揭示了光合作用组件的结构-功能关系。讨论了积累这些大部分未连接的仅 LH2 池的可能原因。
