Broess Koen, Trinkunas Gediminas, van Hoek Arie, Croce Roberta, van Amerongen Herbert
Wageningen University, Laboratory of Biophysics, PO Box 8128, 6700 ET, Wageningen, The Netherlands.
Biochim Biophys Acta. 2008 May;1777(5):404-9. doi: 10.1016/j.bbabio.2008.02.003. Epub 2008 Mar 4.
The fluorescence decay kinetics of Photosystem II (PSII) membranes from spinach with open reaction centers (RCs), were compared after exciting at 420 and 484 nm. These wavelengths lead to preferential excitation of chlorophyll (Chl) a and Chl b, respectively, which causes different initial excited-state populations in the inner and outer antenna system. The non-exponential fluorescence decay appears to be 4.3+/-1.8 ps slower upon 484 nm excitation for preparations that contain on average 2.45 LHCII (light-harvesting complex II) trimers per reaction center. Using a recently introduced coarse-grained model it can be concluded that the average migration time of an electronic excitation towards the RC contributes approximately 23% to the overall average trapping time. The migration time appears to be approximately two times faster than expected based on previous ultrafast transient absorption and fluorescence measurements. It is concluded that excitation energy transfer in PSII follows specific energy transfer pathways that require an optimized organization of the antenna complexes with respect to each other. Within the context of the coarse-grained model it can be calculated that the rate of primary charge separation of the RC is (5.5+/-0.4 ps)(-1), the rate of secondary charge separation is (137+/-5 ps)(-1) and the drop in free energy upon primary charge separation is 826+/-30 cm(-1). These parameters are in rather good agreement with recently published results on isolated core complexes [Y. Miloslavina, M. Szczepaniak, M.G. Muller, J. Sander, M. Nowaczyk, M. Rögner, A.R. Holzwarth, Charge separation kinetics in intact Photosystem II core particles is trap-limited. A picosecond fluorescence study, Biochemistry 45 (2006) 2436-2442].
在420和484nm激发后，比较了来自菠菜的具有开放反应中心（RC）的光系统II（PSII）膜的荧光衰减动力学。这些波长分别导致叶绿素（Chl）a和Chl b的优先激发，这在内外天线系统中引起不同的初始激发态种群。对于每个反应中心平均含有2.45个光捕获复合物II（LHCII）三聚体的制剂，在484nm激发时，非指数荧光衰减似乎慢4.3±1.8ps。使用最近引入的粗粒度模型可以得出结论，电子激发向RC的平均迁移时间对总平均捕获时间的贡献约为23%。迁移时间似乎比基于先前超快瞬态吸收和荧光测量预期的快约两倍。可以得出结论，PSII中的激发能量转移遵循特定的能量转移途径，这需要天线复合物彼此之间进行优化的组织。在粗粒度模型的背景下，可以计算出RC的初级电荷分离速率为（5.5±0.4ps）-1，次级电荷分离速率为（137±5ps）-1，初级电荷分离时自由能的下降为826±30cm-1。这些参数与最近发表的关于分离的核心复合物的结果相当吻合[Y.米洛斯拉维纳，M.斯切帕尼亚克，M.G.米勒，J.桑德，M.诺瓦茨基，M.罗格纳，A.R.霍尔兹瓦特，完整光系统II核心颗粒中的电荷分离动力学受陷阱限制。皮秒荧光研究，生物化学45（2006）2436-2442]。
