Photobleaching of chlorophyll in light-harvesting complex II

Light-induced photobleaching of chlorophylls in the major trimeric light-harvesting complex II (LHCII) from Pisum sativum is investigated in different molecular environments – protein aggregates, embedded in detergent micelles (beta-dodecyl maltoside, DDM) or in reconstituted membranes with thylakoid membrane lipids. Absorption, circular dichroism, and fluorescence spectra are recorded before and at different intervals after illumination with strong white light (2000 umol photons/m2/s). EPR spectra are recorded in the presence of spin trap (TEMPD) and spin label (5-SASL) to detect reactive oxygen species.
The rate of photobleaching depends on the molecular environment of the complex. Photobleaching is exacerbated in reconstituted lipid membranes. EPR spectroscopy using spin labels confirms the increased light-induced generation of singlet oxygen in the membranes. The increased susceptibility to photodamage of LHCII in lipid membranes is potentially of great significance considering that this is the native environment for the majority of photosynthetic pigment–protein complexes.

本研究探讨了来自豌豆（Pisum sativum）的主要三聚光捕获复合体II（LHCII）中叶绿素的强光诱导光漂白现象，在不同分子环境中进行，包括蛋白质聚集体，嵌入洗涤剂胶束（β-十二酰麦芽糖苷，DDM）或与类囊体膜脂质重构的膜中。在用强白光（2000 umol 光子/m²/s）照射前后及其不同时间间隔，记录了吸收、圆二色性和荧光光谱。在存在自旋捕获剂（TEMPD）和自旋标记（5-SASL）的情况下记录电子顺磁共振（EPR）光谱，以检测活性氧种类。光漂白的速率取决于复合体的分子环境。在重构脂质膜中，光漂白现象加剧。采用自旋标记的EPR光谱证实了在膜中光诱导单线态氧生成的增加。考虑到这是大多数光合色素-蛋白质复合物的天然环境，LHCII在脂质膜中光损伤的敏感性增加具有潜在的极大意义。