Light adaptation of Photosystem II is mediated by the plastoquinone pool.

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Light adaptation of Photosystem II is mediated by the plastoquinone pool. / Åhrling, Karin A; Peterson Årsköld, Sindra.

I: Biochemistry, Vol. 42, Nr. 25, 2003, s. 7655-7662.

Forskningsoutput: TidskriftsbidragArtikel i vetenskaplig tidskrift

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Åhrling, KA & Peterson Årsköld, S 2003, 'Light adaptation of Photosystem II is mediated by the plastoquinone pool.', Biochemistry, vol. 42, nr. 25, s. 7655-7662. https://doi.org/10.1021/bi034349l

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Åhrling, Karin A ; Peterson Årsköld, Sindra. / Light adaptation of Photosystem II is mediated by the plastoquinone pool. I: Biochemistry. 2003 ; Vol. 42, Nr. 25. s. 7655-7662.

RIS

TY - JOUR

T1 - Light adaptation of Photosystem II is mediated by the plastoquinone pool.

AU - Åhrling, Karin A

AU - Peterson Årsköld, Sindra

PY - 2003

Y1 - 2003

N2 - During the first few enzymatic turnovers after dark adaptation of photosystem II (PSII), the relaxation rate of the EPR signals from the Mn cluster and YD(dot) are significantly enhanced. This light-adaptation process has been suggested to involve the appearance of a new paramagnet on the PSII donor side [Peterson, Åhrling, Hogblom, and Styring, Biochemistry 2003, asap]. In the present study, a correlation is established between the observed relaxation enhancement and the redox state of the quinone pool. It is shown that the addition of quinol to dark-adapted PSII membrane fragments induces relaxation enhancement already after a single oxidation of the Mn, comparable to that observed after five oxidations in samples with quinones (PPBQ or DQ) added. The saturation behavior of YD(dot) revealed that with quinol added in the dark, a single flash was necessary for the relaxation enhancement to occur. The quinol-induced relaxation enhancement of PSII was also activated by illumination at 200 K. Whole thylakoids, with no artificial electron acceptor present but with an intact plastoquinone pool, displayed the same relaxation enhancement on the fifth flash as membrane fragments with exogenous quinones present. We conclude that (i) reduction of the quinone pool induces the relaxation enhancement of the PSII donor-side paramagnets, (ii) light is required for the quinol to effect the relaxation enhancement, and (iii) light-adaptation occurs in the intact thylakoid system, when the endogenous plastoquinone pool is gradually reduced by PSII turnover. It seems clear that a species on the PSII donor side is reduced by the quinol, to become a potent paramagnetic relaxer. On the basis of XANES reports, we suggest that this species may be the Mn ions not involved in the cyclic redox changes of the oxygen-evolving complex.

AB - During the first few enzymatic turnovers after dark adaptation of photosystem II (PSII), the relaxation rate of the EPR signals from the Mn cluster and YD(dot) are significantly enhanced. This light-adaptation process has been suggested to involve the appearance of a new paramagnet on the PSII donor side [Peterson, Åhrling, Hogblom, and Styring, Biochemistry 2003, asap]. In the present study, a correlation is established between the observed relaxation enhancement and the redox state of the quinone pool. It is shown that the addition of quinol to dark-adapted PSII membrane fragments induces relaxation enhancement already after a single oxidation of the Mn, comparable to that observed after five oxidations in samples with quinones (PPBQ or DQ) added. The saturation behavior of YD(dot) revealed that with quinol added in the dark, a single flash was necessary for the relaxation enhancement to occur. The quinol-induced relaxation enhancement of PSII was also activated by illumination at 200 K. Whole thylakoids, with no artificial electron acceptor present but with an intact plastoquinone pool, displayed the same relaxation enhancement on the fifth flash as membrane fragments with exogenous quinones present. We conclude that (i) reduction of the quinone pool induces the relaxation enhancement of the PSII donor-side paramagnets, (ii) light is required for the quinol to effect the relaxation enhancement, and (iii) light-adaptation occurs in the intact thylakoid system, when the endogenous plastoquinone pool is gradually reduced by PSII turnover. It seems clear that a species on the PSII donor side is reduced by the quinol, to become a potent paramagnetic relaxer. On the basis of XANES reports, we suggest that this species may be the Mn ions not involved in the cyclic redox changes of the oxygen-evolving complex.

KW - MN CLUSTER

KW - MANGANESE CLUSTER

KW - EPR MULTILINE SIGNAL

KW - MICROWAVE-POWER SATURATION

KW - PHOTOSYNTHETIC WATER OXIDATION

KW - OXYGEN-EVOLVING COMPLEX

KW - ELECTRON-PARAMAGNETIC-RESONANCE

KW - CRYSTAL-STRUCTURE

KW - ACCEPTOR COMPLEX

KW - S-0 STATE

U2 - 10.1021/bi034349l

DO - 10.1021/bi034349l

M3 - Article

VL - 42

SP - 7655

EP - 7662

JO - Biochemistry

JF - Biochemistry

SN - 0006-2960

IS - 25

ER -