Faculty of Technical Physics, Poznan University of Technology, Piotrowo 3, 60-965, Poznan, Poland.
Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Gronostajowa 7, 30-387, Krakow, Poland.
Angew Chem Int Ed Engl. 2017 Aug 21;56(35):10457-10461. doi: 10.1002/anie.201705357. Epub 2017 Jul 25.
Photosynthetic energy conversion competes with the formation of chlorophyll triplet states and the generation of reactive oxygen species. These may, especially under high light stress, damage the photosynthetic apparatus. Many sophisticated photoprotective mechanisms have evolved to secure a harmless flow of excitation energy through the photosynthetic complexes. Time-resolved laser-induced optoacoustic spectroscopy was used to compare the properties of the T states of pheophytin a and its metallocomplexes. The lowest quantum yield of the T state is always observed in the Mg complex, which also shows the least efficient energy transfer to O . Axial coordination to the central Mg further lowers the yield of both T and singlet oxygen. These results reveal the existence of intrinsic photoprotective mechanisms in chlorophylls, embedded in their molecular design, which substantially suppress the formation of triplet states and the efficiency of energy transfer to O , each by 20-25 %. Such intrinsic photoprotective effects must have created a large evolutionary advantage for the Mg complexes during their evolution as the principal photoactive cofactors of photosynthetic proteins.
光合作用能量转换与叶绿素三重态的形成和活性氧的产生相竞争。这些物质，特别是在高光胁迫下，可能会破坏光合作用的装置。许多复杂的光保护机制已经进化出来，以确保激发能量通过光合作用复合物无害地流动。我们使用时间分辨激光诱导光声光谱来比较原叶绿素 a 及其金属配合物的 T 态的性质。在 Mg 配合物中，T 态的量子产率总是最低，该配合物向 O 转移的能量也最不有效。轴向配位到中心 Mg 进一步降低了 T 态和单线态氧的产率。这些结果表明，叶绿素分子设计中存在内在的光保护机制，可大大抑制三重态的形成和能量向 O 转移的效率，分别降低 20-25%。在作为光合作用蛋白主要光活性辅因子的 Mg 配合物的进化过程中，这种内在的光保护作用必然为其创造了巨大的进化优势。
