Excitation Migration, Quenching, and Regulation of Photosynthetic Light Harvesting in Photosystem II

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• 作者：Leonas Valkunas ; Jevgenij Chmeliov ; Gediminas Trinkunas ; Christopher D. P. Duffy ; Rienk van Grondelle ; Alexander V. Ruban
• 刊名：Journal of Physical Chemistry B
• 出版年：2011
• 出版时间：July 28, 2011
• 年：2011
• 卷：115
• 期：29
• 页码：9252-9260
• 全文大小：947K
• 年卷期：v.115,no.29(July 28, 2011)
• ISSN：1520-5207

文摘

Excitation energy transfer and quenching in LHCII aggregates is considered in terms of a coarse-grained model. The model assumes that the excitation energy transfer within a pigment鈥損rotein complex is much faster than the intercomplex excitation energy transfer, whereas the quenching ability is attributed to a specific pigment鈥損rotein complex responsible for the nonphotochemical quenching (NPQ). It is demonstrated that the pump鈥損robe experimental data obtained at low excitation intensities for LHCII aggregates under NPQ conditions can be equally well explained at two limiting cases, either describing the excitation kinetics in the migration-limited or in the trap-limited regime. Thus, it is concluded that low excitation conditions do not allow one to unambiguously define the relationship between the mean times of excitation migration and trapping. However, this could be achieved by using high excitation conditions when exciton鈥揺xciton annihilation is dominant. In this case it was found that in the trap-limited regime the excitation kinetics in the aggregate should be almost insensitive to the excitation density, meaning that singlet鈥搒inglet annihilation has little effect on the NPQ decay kinetics, whereas in the migration-limited case there is a clear intensity dependence. In order to account for the random distribution of the NPQ-traps within the LHCII aggregates, excitation diffusion in a continuous medium with random static traps was considered. This description demonstrates a very good correspondence to the experimental fluorescence kinetics assuming a lamellar (quasi-3D) structure of the antenna characterized by the dimension d = 2.4 and therefore justifying the diffusion-limited approach on which the model is based. Using the coarse-grained model to describe the aggregate we estimate one NPQ-trap per 100 monomeric LHCII complexes. Finally we discuss the origin of the traps responsible for excitation quenching under NPQ conditions.