Croce Roberta, Chojnicka Agnieszka, Morosinotto Tomas, Ihalainen Janne A, van Mourik Frank, Dekker Jan P, Bassi Roberto, van Grondelle Rienk
Department of Biophysical Chemistry, Groningen Bimolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands.
Biophys J. 2007 Oct 1;93(7):2418-28. doi: 10.1529/biophysj.107.106955. Epub 2007 Jun 1.
In this work the spectroscopic properties of the special low-energy absorption bands of the outer antenna complexes of higher plant Photosystem I have been investigated by means of low-temperature absorption, fluorescence, and fluorescence line-narrowing experiments. It was found that the red-most absorption bands of Lhca3, Lhca4, and Lhca1-4 peak, respectively, at 704, 708, and 709 nm and are responsible for 725-, 733-, and 732-nm fluorescence emission bands. These bands are more red shifted compared to "normal" chlorophyll a (Chl a) bands present in light-harvesting complexes. The low-energy forms are characterized by a very large bandwidth (400-450 cm(-1)), which is the result of both large homogeneous and inhomogeneous broadening. The observed optical reorganization energy is untypical for Chl a and resembles more that of BChl a antenna systems. The large broadening and the changes in optical reorganization energy are explained by a mixing of an Lhca excitonic state with a charge transfer state. Such a charge transfer state can be stabilized by the polar residues around Chl 1025. It is shown that the optical reorganization energy is changing through the inhomogeneous distribution of the red-most absorption band, with the pigments contributing to the red part of the distribution showing higher values. A second red emission form in Lhca4 was detected at 705 nm and originates from a broad absorption band peaking at 690 nm. This fluorescence emission is present also in the Lhca4-N-47H mutant, which lacks the 733-nm emission band.
在这项工作中，通过低温吸收、荧光和荧光谱线窄化实验，研究了高等植物光系统I外周天线复合物特殊低能吸收带的光谱性质。结果发现，Lhca3、Lhca4以及Lhca1 - 4最红的吸收带分别在704、708和709 nm处达到峰值，并分别对应725、733和732 nm的荧光发射带。与光捕获复合物中存在的“正常”叶绿素a（Chl a）带相比，这些带发生了更大程度的红移。低能形式的特征是具有非常大的带宽（400 - 450 cm⁻¹），这是由较大的均匀展宽和非均匀展宽共同导致的。观察到的光学重组能对于Chl a来说是不典型的，更类似于细菌叶绿素a（BChl a）天线系统的光学重组能。这种大的展宽和光学重组能的变化可以通过Lhca激子态与电荷转移态的混合来解释。这样的电荷转移态可以通过Chl 1025周围的极性残基来稳定。结果表明，光学重组能通过最红吸收带的非均匀分布而发生变化，对分布红色部分有贡献的色素表现出更高的值。在Lhca4中还检测到了第二种在705 nm处的红色发射形式，它起源于一个在690 nm处达到峰值的宽吸收带。这种荧光发射在缺乏733 nm发射带的Lhca4 - N - 47H突变体中也存在。
