Simulation for the primary electronic donor of photosystem IIin vitro |
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Authors: | Jie Pan Chunxi Zhang Yandao Gong Liangbi Li Nanming Zhao Tingyun Kuang |
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Institution: | (1) Photosynthesis Research Center, Institute of Botany, Chinese Academy of Sciences, 100093 Beijing, China;(2) National Laboratory of Biomembranes and Membrane Biotechnology, Department of Biological Science and Biotechnology, Tsinghua University, 100084 Beijing, China;(3) Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, 100080 Beijing, China |
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Abstract: | Histidine coordinated to Chi a is a distinct characteristic of Chl ain vivo. By using histidine analogue of 1-methylimidazole (C4H6N22) and measuring the UV/vis absorption, CD and MCD spectra of the interaction between C4H6N2 and Chl a in CCI4, we have obtained that: (i) In pure CCl4 solvent, Chl a molecule is in five-coordinate state, and two Chl a molecules form an asymmetric compact-dimer with strong
coupling interaction. We propose that the two Chl a molecules are connected by two unequally coordinated Mg-O bonds (the two
oxygen atoms come from the C=O of C131 keto and C17 ester, respectively); (ii) when the molar ratio of C4H6N2/Chl a is 0.5 or 1 (corresponding to 2Chl a · 1C4H6N2 and 2Chl a · 2C4H6N2, respectively), significant changes have been observed in the absorption, CD and MCD spectra, which indicate that the Chl
a remains in dimer form, but the coupling interaction between them reduces greatly. We postulate that C4H6N2 replaces the ligation of C=O of C17 ester and C131 keto to Mg atoms sequentially. The two Chl a molecules linked by two weakly interacted Mg…O bonds form a relaxed-dimer. The
structure of the model is essentially similar to that of the primary electronic donor, P680, of photosystem II in high plants and algae. |
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Keywords: | photosynthesis Chl a histidine coordination P680 simulation spectroscopy research |
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