Ihalainen Janne A, Croce Roberta, Morosinotto Tomas, van Stokkum Ivo H M, Bassi Roberto, Dekker Jan P, van Grondelle Rienk
Faculty of Sciences, Department of Physics and Astronomy, Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
J Phys Chem B. 2005 Nov 10;109(44):21150-8. doi: 10.1021/jp0519316.
Light-harvesting complex I (LHCI), which serves as a peripheral antenna for photosystem I (PSI) in green plants, consists mainly of four polypeptides, Lhca1-4. We report room temperature emission properties of individual reconstituted monomeric Lhca proteins (Lhca1, -2, -3, and -4) and dimeric Lhca1/4, performed by steady-state and time-resolved fluorescence techniques. The emission quantum yields of the samples are approximately 0.12, 0.085, 0.081, 0.041, and 0.063 for Lhca1, -2, -3, -4, and the -1/4 dimer, respectively, which is considerably lower than the value of 0.22 found for light-harvesting complex II (LHCII), the main peripheral antenna complex of photosystem II in green plants. The decay components of LHCI proteins can be divided in two categories: Lhca1 and Lhca3 have decay times of 1.1-1.6 ns and 3.3-3.6 ns, and Lhca2 and Lhca4 have decay times of 0.7-0.9 ns and 3.1-3.2 ns. These categories seem to correlate with the pigment composition of the samples. All decay times are faster than that observed previously for LHCII. When the absolute emission yields and the lifetimes of the Lhca samples are combined, the overall emission properties of the individual Lhca proteins are expressed in terms of their emitting dipole moment strength. In the samples without extreme red states, that is, Lhca1 and Lhca2, the emitting dipole moment has a value close to unity (relative to monomeric chlorophyll in acetone), which is similar to that for LHCII, whereas, in the samples with the red-most state (F-730), that is, Lhca3, -4, and the -1/4 dimer, the emitting dipole moment has a value less than unity (0.6-0.8), which can be explained by mixing the red-most (exciton) state with a dark charge-transfer state, as suggested in previous PSI red pigment studies. In addition, we find a lifetime component of approximately 50-150 ps in all red-pigment-containing samples, which cannot be due to "slow" energy transfer, but is instead assigned to an unrelaxed state of the pigment-protein, which, on this time-scale, is converted into the final emitting state.
捕光复合体I（LHCI）是绿色植物中光系统I（PSI）的外周天线，主要由四种多肽Lhca1 - 4组成。我们通过稳态和时间分辨荧光技术报告了单个重组单体Lhca蛋白（Lhca1、-2、-3和-4）以及二聚体Lhca1/4在室温下的发射特性。Lhca1、-2、-3、-4和-1/4二聚体样品的发射量子产率分别约为0.12、0.085、0.081、0.041和0.063，这显著低于绿色植物中光系统II的主要外周天线复合体捕光复合体II（LHCII）的0.22的值。LHCI蛋白的衰减成分可分为两类：Lhca1和Lhca3的衰减时间为1.1 - 1.6纳秒和3.3 - 3.6纳秒，Lhca2和Lhca4的衰减时间为0.7 - 0.9纳秒和3.1 - 3.2纳秒。这些类别似乎与样品的色素组成相关。所有衰减时间都比之前观察到的LHCII的衰减时间快。当将Lhca样品的绝对发射产率和寿命结合起来时，单个Lhca蛋白的整体发射特性通过其发射偶极矩强度来表示。在没有极端红色状态的样品中，即Lhca1和Lhca2，发射偶极矩的值接近1（相对于丙酮中的单体叶绿素），这与LHCII的情况类似，而在具有最红状态（F - 730）的样品中，即Lhca3、-4和-1/4二聚体，发射偶极矩的值小于1（0.6 - 0.8），正如之前PSI红色色素研究中所表明的，这可以通过将最红（激子）状态与暗电荷转移状态混合来解释。此外，我们在所有含红色色素的样品中发现了一个约50 - 150皮秒的寿命成分，这不可能是由于“缓慢”的能量转移，而是归因于色素 - 蛋白的未弛豫状态，在这个时间尺度上，它会转变为最终的发射状态。
