Faculty of Sciences, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.
Biophys J. 2010 Dec 15;99(12):4056-65. doi: 10.1016/j.bpj.2010.10.034.
Antenna complexes are key components of plant photosynthesis, the process that converts sunlight, CO2, and water into oxygen and sugars. We report the first (to our knowledge) femtosecond transient absorption study on the light-harvesting pigment-protein complexes CP26 (Lhcb5) and CP24 (Lhcb6) of Photosystem II. The complexes are excited at three different wavelengths in the chlorophyll (Chl) Qy region. Both complexes show a single subpicosecond Chl b to Chl a transfer process. In addition, a reduction in the population of the intermediate states (in the 660-670 nm range) as compared to light-harvesting complex II is correlated in CP26 to the absence of both Chls a604 and b605. However, Chl forms around 670 nm are still present in the Chl a Qy range, which undergoes relaxation with slow rates (10-15 ps). This reduction in intermediate-state amplitude CP24 shows a distinctive narrow band at 670 nm connected with Chls b and decaying to the low-energy Chl a states in 3-5 ps. This 670 nm band, which is fully populated in 0.6 ps together with the Chl a low-energy states, is proposed to originate from Chl 602 or 603. In this study, we monitored the energy flow within two minor complexes, and our results may help elucidate these structures in the future.
天线复合物是植物光合作用的关键组成部分，光合作用是将阳光、二氧化碳和水转化为氧气和糖的过程。我们报告了第一个（据我们所知）关于光收集色素-蛋白复合物 CP26（Lhcb5）和 CP24（Lhcb6）的飞秒瞬态吸收研究，该复合物存在于光系统 II 中。复合物在叶绿素（Chl）Qy 区域的三个不同波长处被激发。两个复合物都显示出单个亚皮秒 Chl b 到 Chl a 转移过程。此外，与光收集复合物 II 相比，在 CP26 中，中间态（在 660-670nm 范围内）的种群减少与 Chls a604 和 b605 的缺失相关。然而，在 Chl a Qy 范围内仍存在约 670nm 的 Chl 形式，其以较慢的速率（10-15ps）进行弛豫。CP24 中这种中间态幅度的减少显示出一个独特的窄带，在 670nm 处与 Chls b 相连，并在 3-5ps 内衰减到低能量的 Chl a 态。这个 670nm 带在 0.6ps 内与 Chl a 低能量态一起完全填充，据推测来自 Chl 602 或 603。在这项研究中，我们监测了两个次要复合物内的能量流动，我们的结果可能有助于未来阐明这些结构。
