Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 121 16, Praha, Czech Republic.
Photosynth Res. 2012 Mar;111(1-2):193-204. doi: 10.1007/s11120-011-9670-0. Epub 2011 Aug 11.
Chlorosomes, the light-harvesting antennae of green photosynthetic bacteria, are based on large aggregates of bacteriochlorophyll molecules. Aggregates with similar properties to those in chlorosomes can also be prepared in vitro. Several agents were shown to induce aggregation of bacteriochlorophyll c in aqueous environments, including certain lipids, carotenes, and quinones. A key distinguishing feature of bacteriochlorophyll c aggregates, both in vitro and in chlorosomes, is a large (>60 nm) red shift of their Q(y) absorption band compared with that of the monomers. In this study, we investigate the self-assembly of bacteriochlorophyll c with the xanthophyll astaxanthin, which leads to the formation of a new type of complexes. Our results indicate that, due to its specific structure, astaxanthin molecules competes with bacteriochlorophylls for the bonds involved in the aggregation, thus preventing the formation of any significant red shift compared with pure bacteriochlorophyll c in aqueous buffer. A strong interaction between both the types of pigments in the developed assemblies, is manifested by a rather efficient (~40%) excitation energy transfer from astaxanthin to bacteriochlorophyll c, as revealed by fluorescence excitation spectroscopy. Results of transient absorption spectroscopy show that the energy transfer is very fast (<500 fs) and proceeds through the S(2) state of astaxanthin.
类囊体，是光合细菌的光收集天线，基于细菌叶绿素分子的大聚集体。在体外也可以制备具有类似特性的聚集体。已经证明几种试剂可以在水相环境中诱导细菌叶绿素 c 的聚集，包括某些脂质、类胡萝卜素和醌。细菌叶绿素 c 聚集体的一个关键区别特征，无论是在体外还是在类囊体中，与单体相比，其 Q(y)吸收带都有一个较大的（>60nm）红移。在这项研究中，我们研究了细菌叶绿素 c 与叶黄素虾青素的自组装，这导致了一种新型复合物的形成。我们的结果表明，由于其特定的结构，虾青素分子与细菌叶绿素竞争参与聚集的键，因此与纯细菌叶绿素 c 在水缓冲液中相比，防止形成任何明显的红移。在发展中的组装体中，两种类型的色素之间存在很强的相互作用，这表现为从虾青素到细菌叶绿素 c 的激发能量转移相当有效（~40%），这是通过荧光激发光谱揭示的。瞬态吸收光谱的结果表明，能量转移非常快（<500fs），并通过虾青素的 S(2)态进行。
