绿色植物采光复合体
光系统II
光化学
猝灭(荧光)
叶绿素
光系统I
化学
光防护
光合作用
光系统
三重态
超快激光光谱学
700页
叶绿素a
非光化学猝灭
光谱学
物理
荧光
光学
分子
生物化学
有机化学
量子力学
作者
Jan Alster,David Bína,Kateřina Charvátová,Heiko Lokstein,Jakub Pšenčı́k
标识
DOI:10.1016/j.bbabio.2023.149016
摘要
Quenching of chlorophyll triplet states by carotenoids is an essential photoprotective process, which prevents formation of reactive singlet oxygen in photosynthetic light-harvesting complexes. The process is usually very efficient in oxygenic organisms under physiological conditions, thus preventing any observable accumulation of chlorophyll triplets. However, it subsequently prevents also the determination of the triplet transfer rate. Here we report results of nanosecond transient absorption spectroscopy on photosystem I core complexes, where a major part of chlorophyll a triplet states (~60 %) accumulates on a nanosecond time scale at ambient temperature. As a consequence, the triplet energy transfer could be resolved and the transfer time was determined to be about 24 ns. A smaller fraction of chlorophyll a triplet states (~40 %) is quenched with a faster rate, which could not be determined. Our analysis indicates that these chlorophylls are in direct contact with carotenoids. The overall chlorophyll triplet yield in the core antenna was estimated to be ~0.3 %, which is a value two orders of magnitude smaller than in most other photosynthetic light-harvesting complexes. This explains why slower quenching of chlorophyll triplet states is sufficient for photoprotection of photosystem I. Nevertheless, the core antenna of photosystem I represents one of only few photosynthetic complexes of oxygenic organisms in which the quenching rate of the majority of chlorophyll triplets can be directly monitored under physiological temperature.
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