The Decrease of the ESEEM Frequency of P700+A1- Ion‑Radical Pair in Photosystem I Embedded in Trehalose Glassy Matrix at Room Temperature can be Explained by Acceleration of Spin–Lattice Relaxationстатья
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Дата последнего поиска статьи во внешних источниках: 7 сентября 2018 г.
Аннотация:The main observation in this work is a decrease in the modulation frequencyof the primary electron spin-echo decay (ESEEM) of the P700+ cofactor in thereaction center of Photosystem I (PS I) from cyanobacteria Synechocystis sp. PCC6803 embedded in dry trehalose matrix as the temperature rises from 150 K to roomtemperature. From the previous studies of the EPR spectrum shape of this system,it is known that, in dry trehalose matrix at room temperature, the distance betweenP700+ and A1- spins does not increase compared to the distance measured in glycerol–water solution at cryogenic temperature. From the present ESEEM study, we concludethat the decrease of modulation frequency with rising temperature in trehalosematrix can be fully attributed to the influence of accelerated spin–lattice relaxationof A1-. Our calculations show that this requires a decrease in the spin–lattice relaxationtime from 3 to 1 μs. To the best of our knowledge, this is the first time that ashift in the ESEEM frequency due to the dipole–dipole interaction between the spinsis observed that is caused by spin–lattice relaxation. Based on the above-mentionedresults, we formulate a model of the protective effect of trehalose matrix on the electrontransfer in the reaction center of PS I that is based on different hydrogen-bondnetworks between trehalose, local water, and protein.