Generation of ion-radical chlorophyll states in the light-harvesting antenna and the reaction center of cyanobacterial photosystem I

The energy and charge-transfer processes in photosystem I (PS I) complexes isolated from cyanobacteria Thermosynechococcus elongatus and Synechocystis sp. PCC 6803 were investigated by pump-to-probe femtosecond spectroscopy. The formation of charge-transfer (CT) states in excitonically coupled chlor...

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Bibliographic Details
Published in:Photosynthesis research 2020-12, Vol.146 (1-3), p.55-73
Main Authors: Cherepanov, Dmitry A., Shelaev, Ivan V., Gostev, Fedor E., Aybush, Arseniy V., Mamedov, Mahir D., Shuvalov, Vladimir A., Semenov, Alexey Yu, Nadtochenko, Victor A.
Format: Article
Language:English
Subjects:
Antennas (Electronics)
Beta carotene
Biochemistry
Biomedical and Life Sciences
Carotenoids
Chlorophyll
Electron transfer
Energy charge
Life Sciences
Original Article
Photosystem I
Plant Genetics and Genomics
Plant Physiology
Plant Sciences
Spectroscopy
Synechocystis
β-Carotene
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Summary:The energy and charge-transfer processes in photosystem I (PS I) complexes isolated from cyanobacteria Thermosynechococcus elongatus and Synechocystis sp. PCC 6803 were investigated by pump-to-probe femtosecond spectroscopy. The formation of charge-transfer (CT) states in excitonically coupled chlorophyll a complexes (exciplexes) was monitored by measuring the electrochromic shift of β -carotene in the spectral range 500–510 nm. The excitation of high-energy chlorophyll in light-harvesting antenna of both species was not accompanied by immediate appearance of an electrochromic shift. In PS I from T. elongatus , the excitation of long-wavelength chlorophyll (LWC) caused a pronounced electrochromic effect at 502 nm assigned to the appearance of CT states of chlorophyll exciplexes. The formation of ion-radical pair P 700 + A 1 − at 40 ps was limited by energy transfer from LWC to the primary donor P 700 and accompanied by carotenoid bleach at 498 nm. In PS I from Synechocystis 6803, the excitation at 720 nm produced an immediate bidentate bleach at 690/704 nm and synchronous carotenoid response at 508 nm. The bidentate bleach was assigned to the formation of primary ion-radical state P B + Chl 2B − , where negative charge is localized predominantly at the accessory chlorophyll molecule in the branch B, Chl 2B . The following decrease of carotenoid signal at ~ 5 ps was ascribed to electron transfer to the more distant molecule Chl 3B . The reduction of phylloquinone in the sites A 1A and A 1B was accompanied by a synchronous blue-shift of the carotenoid response to 498 nm, pointing to fast redistribution of unpaired electron between two branches in favor of the state P B + A 1A − .
ISSN:0166-8595
1573-5079
DOI:10.1007/s11120-020-00731-0