Doust Alexander B, van Stokkum Ivo H M, Larsen Delmar S, Wilk Krystyna E, Curmi Paul M G, van Grondelle Rienk, Scholes Gregory D
Lash Miller Chemical Laboratories, 80 St. George Street, University of Toronto, Ontario, M5S 3H6 Canada.
J Phys Chem B. 2005 Jul 28;109(29):14219-26. doi: 10.1021/jp051173j.
We report ultrafast femtosecond transient absorption measurements of energy-transfer dynamics for the antenna protein phycoerythrin 545, PE545, isolated from a unicellular cryptophyte Rhodomonas CS24. The phycoerythrobilins are excited at both 485 and 530 nm, and the spectral response is probed between 400 and 700 nm. Room-temperature measurements are contrasted with measurements at 77 K. An evolution-associated difference spectra (EADS) analysis is combined with estimations of bilin spectral positions and energy-transfer rates to obtain a detailed kinetic model for PE545. It is found that sub pulse-width dynamics include relaxation between the exciton states of a chromophore dimer (beta 50/60) located in the core of the protein. Energy transfer from the lowest exciton state of the phycoerythrobilin (PEB) dimer to one of the periphery 15,16-dihydrobiliverdin (DBV) bilins is found to occur on a time scale of 250 fs at room temperature and 960 fs at 77 K. A host of energy-transfer dynamics involving the beta 158, beta 82, and alpha 19 bilins occur on a time scale of 2 ps at room temperature and 3 ps at 77 K. A final energy transfer occurs between the red-most DBV bilins with a time scale estimated to be approximately 30 ps. The role of the centrally located phycoerythrobilin dimer is seen as crucial-spectrally as it expands the cross-section of absorption of the protein; structurally as it sits in the middle of the protein acting as an intermediary trap; and kinetically, as the internal conversion and subsequent red-shift of the excitation is extremely fast.
我们报道了从单细胞隐藻红藻CS24中分离出的天线蛋白藻红蛋白545（PE545）能量转移动力学的超快飞秒瞬态吸收测量结果。藻胆素在485和530 nm处均被激发，并在400至700 nm之间探测光谱响应。室温测量结果与77 K下的测量结果形成对比。将与演化相关的差异光谱（EADS）分析与胆色素光谱位置和能量转移速率的估计相结合，以获得PE545的详细动力学模型。研究发现，亚脉冲宽度动力学包括位于蛋白质核心的发色团二聚体（β50/60）的激子态之间的弛豫。发现在室温下，藻胆素（PEB）二聚体的最低激子态到外周15,16-二氢胆绿素（DBV）胆色素之一的能量转移发生在250 fs的时间尺度上，在77 K下为960 fs。涉及β158、β82和α19胆色素的一系列能量转移动力学在室温下发生在2 ps的时间尺度上，在77 K下为3 ps。最终的能量转移发生在最红的DBV胆色素之间，时间尺度估计约为30 ps。位于中心的藻胆素二聚体的作用在光谱上至关重要，因为它扩大了蛋白质的吸收截面；在结构上，它位于蛋白质中间，充当中间陷阱；在动力学上，因为激发的内转换和随后的红移非常快。
