REVIEW: Primary Radical Ion Pairs in Photosystem II Core Complexes

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V. A. Nadtochenko¹, I. V. Shelaev¹, M. D. Mamedov², A. Ya. Shkuropatov³, A. Yu. Semenov^1,2*, and V. A. Shuvalov^2,3*

¹Semenov Institute of Chemical Physics, Russian Academy of Sciences, ul. Kosygina 4, 119991 Moscow, Russia

²Belozersky Institute of Physical-Chemical Biology, Lomonosov Moscow State University, 119991 Moscow, Russia; E-mail: shuvalov@gmail.com; shuvalov@issp.serpukhov.su; semenov@genebee.msu.ru

³Institute of Basic Biological Problems, Russian Academy of Sciences, ul. Institutskaya 2, 142290 Pushchino, Moscow Region, Russia

^* To whom correspondence should be addressed.

Received December 3, 2013; Revision received December 15, 2013

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Ultrafast absorption spectroscopy with 20-fs resolution was applied to study primary charge separation in spinach photosystem II (PSII) reaction center (RC) and PSII core complex (RC complex with integral antenna) upon excitation at maximum wavelength 700-710 nm at 278 K. It was found that the initial charge separation between P680* and Chl_D1 (Chl-670) takes place with a time constant of ~1 ps with the formation of the primary charge-separated state P680* with an admixture of: P680*^(1-δ) (P680^δ+Chl_D1^δ–), where δ ~ 0.5. The subsequent electron transfer from P680^δ+Chl_D1^δ– to pheophytin (Pheo) occurs within 13 ps and is accompanied by a relaxation of the absorption band at 670 nm (Chl_D1^δ–) and bleaching of the Pheo_D1 bands at 420, 545, and 680 nm with development of the Pheo^– band at 460 nm. Further electron transfer to Q_A occurs within 250 ps in accordance with earlier data. The spectra of P680⁺ and Pheo^– formation include a bleaching band at 670 nm; this indicates that Chl-670 is an intermediate between P680 and Pheo. Stimulated emission kinetics at 685 nm demonstrate the existence of two decaying components with time constants of ~1 and ~13 ps due to the formation of P680^δ+Chl_D1^δ– and P680⁺Pheo_D1^–, respectively.

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KEY WORDS: P680, chlorophyll, pheophytin, photosystem II core complex, primary charge separation, reaction center

DOI: 10.1134/S0006297914030043

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