Zehetmayer P, Hellerer Th, Parbel A, Scheer H, Zumbusch A
Department Chemie, Ludwig-Maximilians Universität München, D-81377 München, Germany.
Biophys J. 2002 Jul;83(1):407-15. doi: 10.1016/S0006-3495(02)75178-3.
Phycoerythrocyanin (PEC) is part of the light harvesting system of cyanobacteria. The PEC monomer contains one phycoviolobilin chromophore, which transfers excitation energy onto two phycocyanobilin chromophores. Many spectroscopical methods have been used in the past to study the bulk properties of PEC. These methods average over many molecules. Therefore, differences in the behavior of individual molecules remain hidden. The energy transfer within photosynthetic complexes is however sensitive to changes in the spectroscopic properties of the participating subunits. Knowledge about heterogeneities is therefore important for the description of the energy transfer in photosynthetic systems. Here, the recording of the fluorescence emission of single PEC molecules is used as a tool to obtain such information. Spectrally resolved detection as well as double resonance excitation of single PEC molecules is used to investigate their bleaching behavior. The trans isomer of the phycoviolobilin chromophore is identified as a short-lived dark state of monomeric PEC. Polarization sensitive single molecule detection is used for the direct observation of the energy transfer in individual PEC molecules. The experiments reveal that more than one-half of the PEC molecules exhibit an energy transfer behavior significantly different from the bulk. These heterogeneities persist on a time scale of several seconds. Model calculations lead to the conclusion that they are caused by minor shifts in the spectra of the chromophores.
藻红藻蓝蛋白（PEC）是蓝细菌光捕获系统的一部分。PEC单体包含一个藻紫胆素发色团，它将激发能传递给两个藻蓝胆素发色团。过去已经使用了许多光谱学方法来研究PEC的整体性质。这些方法对许多分子进行平均。因此，单个分子行为的差异仍然隐藏着。然而，光合复合物中的能量转移对参与亚基的光谱性质变化很敏感。因此，关于异质性的知识对于描述光合系统中的能量转移很重要。在这里，记录单个PEC分子的荧光发射被用作获取此类信息的工具。对单个PEC分子进行光谱分辨检测以及双共振激发，以研究它们的漂白行为。藻紫胆素发色团的反式异构体被确定为单体PEC的一种短寿命暗态。偏振敏感单分子检测用于直接观察单个PEC分子中的能量转移。实验表明，超过一半的PEC分子表现出与整体明显不同的能量转移行为。这些异质性在几秒钟的时间尺度上持续存在。模型计算得出结论，它们是由发色团光谱的微小变化引起的。
