在皮秒时间尺度上重新连接光合作用
Photosynthesis re-wired on the pico-second timescale
AI总结：
本研究利用DCBQ和超快瞬态吸收光谱，证明可在皮秒尺度直接从活蓝细菌及分离的光激发PSI、PSII提取电子，为重连光合作用提供新路径。
摘要：
光系统II和光系统I（PSII和PSI）是驱动光合作用光反应的反应中心复合物。PSII执行光驱动水氧化（量子效率和催化速率分别最高可达80%和1000 e⁻s⁻¹），PSI则进一步为捕获的电子提供光能（量子效率约为100%）。光合作用捕光组件令人瞩目的性能，推动了大量生物学、人工和生物混合方法来重新连接光合作用，以实现更高效率和新的反应途径，例如H2析出或替代性CO2固定。迄今为止，这些方法都集中于从PSII的末端电子醌和PSI的末端铁硫簇提取电荷。理想情况下，应能直接从光激发反应中心提取电子，以获得最大的热力学收益。然而，这曾被认为是不可能的，因为反应中心从细胞质面算起深埋在PSII内约4 nm、PSI内约5 nm处。在此，我们利用体内超快瞬态吸收（TA）光谱证明，借助外源电子介体2,6-二氯-1,4-苯醌（DCBQ），在活蓝细菌细胞和分离的光系统中，都可以直接从光激发的PSI和PSII提取电子。我们推测，DCBQ能够氧化初始光激发后参与高度离域电荷转移（CT）态的外周叶绿素色素。我们的结果为研究和重新连接光合作用以服务于生物能源和半人工光合作用开辟了新途径。
英文摘要：
Photosystems II and I (PSII and PSI) are the reaction centre complexes that drive the light reactions of photosynthesis. PSII performs light-driven water oxidation (quantum efficiencies and catalysis rates of up to 80% and 1000 $e^{-}\text{s}^{-1}$, respectively) and PSI further photo-energises the harvested electrons (quantum efficiencies of ~100%). The impressive performance of the light harvesting components of photosynthesis has motivated extensive biological, artificial and biohybrid approaches to re-wire photosynthesis to enable higher efficiencies and new reaction pathways, such as H2 evolution or alternative CO2 fixation. To date these approaches have focussed on charge extraction at the terminal electron quinones of PSII and terminal iron-sulfur clusters of PSI. Ideally electron extraction would be possible immediately from the photoexcited reaction centres to enable the greatest thermodynamic gains. However, this was believed to be impossible because the reaction centres are buried around 4 nm within PSII and 5 nm within PSI from the cytoplasmic face. Here, we demonstrate using in vivo ultrafast transient absorption (TA) spectroscopy that it is possible to extract electrons directly from photoexcited PSI and PSII, using both live cyanobacterial cells and isolated photosystems, with the exogenous electron mediator 2,6-dichloro1,4-benzoquinone (DCBQ). We postulate that DCBQ can oxidise peripheral chlorophyll pigments participating in highly delocalised charge transfer (CT) states after initial photoexcitation. Our results open new avenues to study and re-wire photosynthesis for bioenergy and semi-artificial photosynthesis.
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