Schödel R, Irrgang K D, Voigt J, Renger G
AG Molekulare Biophysik und Spektroskopie, Institut für Physik der Humboldt Universität zu Berlin, Berlin, Germany.
Biophys J. 1998 Dec;75(6):3143-53. doi: 10.1016/S0006-3495(98)77756-2.
In the present study the rate of triplet transfer from chlorophyll to carotenoids in solubilized LHCII was investigated by flash spectroscopy using laser pulses of approximately 2 ns for both pump and probe. Special attention has been paid to calibration of the experimental setup and to avoid saturation effects. Carotenoid triplets were identified by the pronounced positive peak at approximately 507 nm in the triplet-singlet difference spectra. DeltaOD (507 nm) exhibits a monoexponential relaxation kinetics with characteristic lifetimes of 2-9 micros (depending on the oxygen content) that was found to be independent of the pump pulse intensity. The rise of DeltaOD (507 nm) was resolved via a pump probe technique where an optical delay of up to 20 ns was used. A thorough analysis of these experimental data leads to the conclusion that the kinetics of carotenoid triplet formation in solubilized LHCII is almost entirely limited by the lifetime of the excited singlet state of chlorophyll but neither by the pulse width nor by the rate constant of triplet-triplet transfer. Within the experimental error the rate constant of triplet-triplet transfer from chlorophyll to carotenoids was estimated to be kTT > (0.5 ns)-1. This value exceeds all data reported so far by at least one order of magnitude. The implications of this finding are briefly discussed.
在本研究中，通过闪光光谱法，使用泵浦光和探测光均为约2 ns的激光脉冲，研究了溶解的光系统II捕光复合物（LHCII）中三线态从叶绿素向类胡萝卜素的转移速率。特别关注了实验装置的校准并避免饱和效应。在三线态 - 单线态差分光谱中，类胡萝卜素三线态通过约507 nm处明显的正峰来识别。ΔOD（507 nm）呈现单指数弛豫动力学，其特征寿命为2 - 9微秒（取决于氧气含量），且发现该寿命与泵浦脉冲强度无关。通过使用高达20 ns光程延迟的泵浦 - 探测技术解析了ΔOD（507 nm）的上升过程。对这些实验数据的深入分析得出结论，溶解的LHCII中类胡萝卜素三线态形成的动力学几乎完全受叶绿素激发单线态寿命的限制，而不受脉冲宽度或三线态 - 三线态转移速率常数的限制。在实验误差范围内，从叶绿素到类胡萝卜素的三线态 - 三线态转移速率常数估计为kTT > (0.5 ns)-1。该值比迄今报道的所有数据至少高出一个数量级。简要讨论了这一发现的意义。
