Brecht Marc, Studier Hauke, Elli Alexandra F, Jelezko Fedor, Bittl Robert
Fachbereich Physik, Freie Universität Berlin, Arnimalle 14, 14195 Berlin, Germany.
Biochemistry. 2007 Jan 23;46(3):799-806. doi: 10.1021/bi061975k.
Single-molecule spectroscopy at cryogenic temperatures was used to elucidate spectral properties, heterogeneities, and dynamics of the chlorophyll a (Chla) molecules responsible for the fluorescence in photosystem I (PSI) from the cyanobacteria Thermosynechococcus elongatus. Absorption and hole burning data suggest the presence of three pools absorbing at wavelengths greater than 700 nm with their absorption maxima at 708, 715, and 719 nm. The responsible Chla molecules are termed C708, C715, and C719. In the emission spectra of single PSI complexes, zero-phonon lines (ZPLs) were observed over the whole red emission range of PSI. The spectral region of the C708 pool is dominated by intense ZPLs; on the other hand, the broad emission of C715/C719 is unstructured and ZPLs are seen in this region much less frequently. Spectral jumps of ZPLs were observed. The dynamics as well as the spectral range covered by such jumps differ for C708 and C715/C719. This heterogeneity is likely caused by differences in the close environment of the chromophores. A tentative assignment of C708 and C715/C719 to Chla dimers and a Chla trimer is discussed, which is based on the remarkable structural differences in the environment of the most probable candidates for the red-most fluorescence.
利用低温下的单分子光谱来阐明来自嗜热栖热放线菌的光系统I（PSI）中负责荧光的叶绿素a（Chla）分子的光谱特性、不均匀性和动力学。吸收和烧孔数据表明存在三个吸收池，其在大于700 nm的波长处吸收，吸收最大值分别在708、715和719 nm。负责的Chla分子被称为C708、C715和C719。在单个PSI复合物的发射光谱中，在PSI的整个红色发射范围内都观察到了零声子线（ZPLs）。C708池的光谱区域以强烈的ZPLs为主；另一方面，C715/C719的宽发射是无结构的，并且在该区域中ZPLs出现的频率要低得多。观察到了ZPLs的光谱跳跃。C708和C715/C719的这种跳跃所覆盖的动力学以及光谱范围是不同的。这种不均匀性可能是由发色团紧密环境的差异引起的。讨论了将C708和C715/C719初步指定为Chla二聚体和Chla三聚体的问题，这是基于最可能的最红荧光候选物环境中的显著结构差异。
