英国剑桥大学Jenny Z. Zhang等研究人员合作发现，光合作用在皮秒级的时间尺度上重连。这一研究成果于2023年3月22日在线发表在国际学术期刊《自然》上。

研究人员表示，光系统II和I（PSII、PSI）是驱动光合作用光反应的含有反应中心的复合体；PSII进行光驱动的水氧化，PSI进一步使收获的电子产生光能。光系统令人印象深刻的效率促使人们采取广泛的生物、人工和生物杂交的方法来“重连”光合作用，以提高生物质转化效率和新的反应途径，如H₂演变或CO₂固定。以前的方法集中在光系统终端电子受体的电荷提取上。在较早的步骤中提取电子，也许是立即从光激发的反应中心提取，将使热力学收益更大；然而，这被认为是不可能的，因为反应中心至少埋在光系统内4纳米。

研究人员使用体内超快速瞬时吸收（TA）光谱，证明了在早期（光激发后几皮秒）直接从光激发的PSI和PSII中提取电子，用活的蓝藻细胞或分离的光系统和外源电子介质，如2,6-二氯-1,4-苯醌（DCBQ）和甲基紫精。研究人员推测，这些媒介物在最初的光激发后，会氧化外围的叶绿素色素，并参与高度脱域的电荷转移状态。这些研究结果对以前的模型提出了挑战，即光激发的反应中心在光系统蛋白支架内是绝缘的，也为研究和重连光合作用的生物技术和半人工光合作用开辟了新途径。

附：英文原文

Title: Photosynthesis re-wired on the pico-second timescale

Author: Baikie, Tomi K., Wey, Laura T., Lawrence, Joshua M., Medipally, Hitesh, Reisner, Erwin, Nowaczyk, Marc M., Friend, Richard H., Howe, Christopher J., Schnedermann, Christoph, Rao, Akshay, Zhang, Jenny Z.

Issue&Volume: 2023-03-22

Abstract: Photosystems II and I (PSII, PSI) are the reaction centre-containing complexes driving the light reactions of photosynthesis; PSII performs light-driven water oxidation and PSI further photo-energizes harvested electrons. The impressive efficiencies of the photosystems have motivated extensive biological, artificial and biohybrid approaches to ‘re-wire’ photosynthesis for higher biomass-conversion efficiencies and new reaction pathways, such as H2 evolution or CO2 fixation1,2. Previous approaches focused on charge extraction at terminal electron acceptors of the photosystems3. Electron extraction at earlier steps, perhaps immediately from photoexcited reaction centres, would enable greater thermodynamic gains; however, this was believed impossible with reaction centres buried at least 4nm within the photosystems4,5. Here, we demonstrate, using in vivo ultrafast transient absorption (TA) spectroscopy, extraction of electrons directly from photoexcited PSI and PSII at early points (several picoseconds post-photo-excitation) with live cyanobacterial cells or isolated photosystems, and exogenous electron mediators such as 2,6-dichloro-1,4-benzoquinone (DCBQ) and methyl viologen. We postulate that these mediators oxidize peripheral chlorophyll pigments participating in highly delocalized charge-transfer states after initial photo-excitation. Our results challenge previous models that the photoexcited reaction centres are insulated within the photosystem protein scaffold, opening new avenues to study and re-wire photosynthesis for biotechnologies and semi-artificial photosynthesis.

DOI: 10.1038/s41586-023-05763-9

Source: https://www.nature.com/articles/s41586-023-05763-9