The Decrease of the ESEEM Frequency of \({\text{P}}_{700}^{ + } {\text{A}}_{1}^{ - }\) Ion-Radical Pair in Photosystem I Embedded in Trehalose Glassy Matrix at Room Temperature can be Explained by Acceleration of Spin–Lattice Relaxation


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Abstract

The main observation in this work is a decrease in the modulation frequency of the primary electron spin-echo decay (ESEEM) of the \({\text{P}}_{ 7 0 0}^{ + }\) cofactor in the reaction center of Photosystem I (PS I) from cyanobacteria Synechocystis sp. PCC 6803 embedded in dry trehalose matrix as the temperature rises from 150 K to room temperature. 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 between \({\text{P}}_{ 7 0 0}^{ + }\) and \({\text{A}}_{ 1}^{ - }\) spins does not increase compared to the distance measured in glycerol–water solution at cryogenic temperature. From the present ESEEM study, we conclude that the decrease of modulation frequency with rising temperature in trehalose matrix can be fully attributed to the influence of accelerated spin–lattice relaxation of \({\text{A}}_{ 1}^{ - }\). Our calculations show that this requires a decrease in the spin–lattice relaxation time from 3 to 1 μs. To the best of our knowledge, this is the first time that a shift in the ESEEM frequency due to the dipole–dipole interaction between the spins is observed that is caused by spin–lattice relaxation. Based on the above-mentioned results, we formulate a model of the protective effect of trehalose matrix on the electron transfer in the reaction center of PS I that is based on different hydrogen-bond networks between trehalose, local water, and protein.

About the authors

A. A. Sukhanov

Zavoisky Physical-Technical Institute, FRC Kazan Scientific Center of RAS

Author for correspondence.
Email: ansukhanov@mail.ru
ORCID iD: 0000-0001-8927-3715
Russian Federation, Kazan

M. D. Mamedov

A.N. Belozersky Institute of Physical–Chemical Biology

Email: ansukhanov@mail.ru
Russian Federation, Moscow

K. Möbius

Department of Physics, Free University Berlin

Email: ansukhanov@mail.ru
Germany, Berlin

A. Yu. Semenov

A.N. Belozersky Institute of Physical–Chemical Biology

Email: ansukhanov@mail.ru
Russian Federation, Moscow

K. M. Salikhov

Zavoisky Physical-Technical Institute, FRC Kazan Scientific Center of RAS

Email: ansukhanov@mail.ru
Russian Federation, Kazan

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