Müller M G, Griebenow K, Holzwarth A R
Max-Planck-Institut für Strahlenchemie, Mülheim a.d. Ruhr, Germany.
Biochim Biophys Acta. 1993 Sep 13;1144(2):161-9. doi: 10.1016/0005-2728(93)90168-f.
The excitation energy transfer and trapping processes in intact cells of Chloroflexus aurantiacus were studied by picosecond time-resolved fluorescence spectroscopy. The fluorescence decay kinetics is investigated over the near infrared emission range between 730 nm and 920 nm using various excitation wavelengths and excitation intensities. The data were analyzed by global decay analysis and are presented as decay-associated spectra (DAS). The specific dependence of the decay kinetics on the excitation wavelength and on the photochemical redox state of the reaction center (RC) allows the identification of the energy transfer and trapping components. The DAS provide evidence for two chlorosomal energy transfer processes. The first one occurs between the chlorosomal bacteriochlorophyll (BChl)-c and the BChl-a792 complex (B792) in the chlorosomal baseplate with an equilibration time constant of 15-16 ps, while the second one occurs from the B792 pigments to the BChl-a806 pigments in the B806-866 complex with a time constant of 35-40 ps. The overall energy trapping process in whole cells is mainly determined by the kinetics of the primary charge separation process in the RCs. With open RCs (QA oxidized) the trapping time constant is 70-90 ps, while the trapping process with closed RCs (QA reduced) takes as long as 180-200 ps. The results on whole cells reported here are interpreted in conjunction with those reported earlier for the various isolated complexes, i.e., two different chlorosome preparations (Holzwarth, A.R., Müller, M.G. and Griebenow, K. (1990) J. Photochem. Photobiol. B 5, 457-465), the B806-866 complex (Griebenow, K., Müller, M.G. and Holzwarth, A.R. (1991) Biochim. Biophys. Acta 1059, 226-232) and isolated reaction centers (Müller, M.G., Griebenow, K. and Holzwarth, A.R. (1991) Biochim. Biophys. Acta 1098, 1-12). Based on these data, a unified and self-consistent scheme for the primary processes in the whole photosynthetic system of C. aurantiacus is presented. The BChl antenna pigment groups are arranged to form a linear energy transfer cascade with four energy transfer steps from shorter-wavelength- to longer-wavelength-absorbing antenna pools. The overall fluorescence decay kinetics of the photosynthetic system of C. aurantiacus turns out to be 'trap-limited' by the reaction center rather than 'diffusion-limited' by the energy transfer processes.
利用皮秒时间分辨荧光光谱研究了橙色绿屈挠菌完整细胞中的激发能量转移和捕获过程。使用各种激发波长和激发强度，在730纳米至920纳米的近红外发射范围内研究了荧光衰减动力学。通过全局衰减分析对数据进行分析，并以衰减相关光谱（DAS）的形式呈现。衰减动力学对激发波长和反应中心（RC）的光化学氧化还原状态的特定依赖性使得能够识别能量转移和捕获成分。DAS为两个叶绿体能量转移过程提供了证据。第一个过程发生在叶绿体底板中的叶绿体细菌叶绿素（BChl）-c和BChl-a792复合物（B792）之间，平衡时间常数为15 - 16皮秒，而第二个过程发生在B806 - 866复合物中从B792色素到BChl-a806色素，时间常数为35 - 40皮秒。全细胞中的整体能量捕获过程主要由RC中的初级电荷分离过程的动力学决定。对于开放的RC（QA氧化），捕获时间常数为70 - 90皮秒，而对于关闭的RC（QA还原），捕获过程长达180 - 200皮秒。这里报道的全细胞结果与先前报道的各种分离复合物的结果相结合进行解释，即两种不同的叶绿体制剂（Holzwarth，A.R.，Müller，M.G.和Griebenow，K.（1990）J. Photochem. Photobiol. B 5，457 - 465）、B806 - 866复合物（Griebenow，K.，Müller，M.G.和Holzwarth，A.R.（1991）Biochim. Biophys. Acta 1059，226 - 232）和分离的反应中心（Müller，M.G.，Griebenow，K.和Holzwarth，A.R.（1991）Biochim. Biophys. Acta 1098，1 - 12）。基于这些数据，提出了橙色绿屈挠菌整个光合系统初级过程的统一且自洽的方案。BChl天线色素基团排列形成一个线性能量转移级联，具有从较短波长吸收天线池到较长波长吸收天线池的四个能量转移步骤。橙色绿屈挠菌光合系统的整体荧光衰减动力学结果表明是由反应中心“陷阱限制”，而不是由能量转移过程“扩散限制”。
