Wormit Michael, Harbach Philipp H P, Mewes Jan M, Amarie Sergiu, Wachtveitl Josef, Dreuw Andreas
Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max von Laue Str.7, 60438 Frankfurt, Germany.
Biochim Biophys Acta. 2009 Jun;1787(6):738-46. doi: 10.1016/j.bbabio.2009.01.021. Epub 2009 Feb 5.
Light harvesting complexes have been identified in all chlorophyll-based photosynthetic organisms. Their major function is the absorption of light and its transport to the reaction centers, however, they are also involved in excess energy quenching, the so-called non-photochemical quenching (NPQ). In particular, electron transfer and the resulting formation of carotenoid radical cations have recently been discovered to play an important role during NPQ in green plants. Here, the results of our theoretical investigations of carotenoid radical cation formation in the major light harvesting complex LHC-II of green plants are reported. The carotenoids violaxanthin, zeaxanthin and lutein are considered as potential quenchers. In agreement with experimental results, it is shown that zeaxanthin cannot quench isolated LHC-II complexes. Furthermore, subtle structural differences in the two lutein binding pockets lead to substantial differences in the excited state properties of the two luteins. In addition, the formation mechanism of carotenoid radical cations in light harvesting complexes LH2 and LH1 of purple bacteria is studied. Here, the energetic position of the S(1) state of the involved carotenoids neurosporene, spheroidene, spheroidenone and spirilloxanthin seems to determine the occurrence of radical cations in these LHCs upon photo-excitation. An elaborate pump-deplete-probe experiment is suggested to challenge the proposed mechanism.
在所有基于叶绿素的光合生物中都已鉴定出光捕获复合物。它们的主要功能是吸收光并将其传输到反应中心，然而，它们也参与过量能量猝灭，即所谓的非光化学猝灭（NPQ）。特别是，最近发现电子转移以及由此产生的类胡萝卜素自由基阳离子的形成在绿色植物的NPQ过程中起着重要作用。在此，报告了我们对绿色植物主要光捕获复合物LHC-II中类胡萝卜素自由基阳离子形成的理论研究结果。将叶黄素、玉米黄质和叶黄素视为潜在的猝灭剂。与实验结果一致，结果表明玉米黄质不能猝灭分离的LHC-II复合物。此外，两个叶黄素结合口袋中的细微结构差异导致两种叶黄素激发态性质的显著差异。此外，还研究了紫色细菌光捕获复合物LH2和LH1中类胡萝卜素自由基阳离子的形成机制。在这里，所涉及的类胡萝卜素神经孢烯、球形烯、球形烯酮和螺旋藻黄质的S(1)态的能量位置似乎决定了这些光捕获复合物在光激发时自由基阳离子的出现。建议进行精心设计的泵浦-耗尽-探测实验来验证所提出的机制。
