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Article Dans Une Revue Proceedings of the National Academy of Sciences of the United States of America Année : 2016

Bicarbonate-induced redox tuning in Photosystem II for regulation and protection.

Résumé

The midpoint potential (Em) of [Formula: see text], the one-electron acceptor quinone of Photosystem II (PSII), provides the thermodynamic reference for calibrating PSII bioenergetics. Uncertainty exists in the literature, with two values differing by ∼80 mV. Here, we have resolved this discrepancy by using spectroelectrochemistry on plant PSII-enriched membranes. Removal of bicarbonate (HCO3(-)) shifts the Em from ∼-145 mV to -70 mV. The higher values reported earlier are attributed to the loss of HCO3(-) during the titrations (pH 6.5, stirred under argon gassing). These findings mean that HCO3(-) binds less strongly when QA(-•) is present. Light-induced QA(-•) formation triggered HCO3(-) loss as manifest by the slowed electron transfer and the upshift in the Em of QA HCO3(-)-depleted PSII also showed diminished light-induced (1)O2 formation. This finding is consistent with a model in which the increase in the Em of [Formula: see text] promotes safe, direct [Formula: see text] charge recombination at the expense of the damaging back-reaction route that involves chlorophyll triplet-mediated (1)O2 formation [Johnson GN, et al. (1995) Biochim Biophys Acta 1229:202-207]. These findings provide a redox tuning mechanism, in which the interdependence of the redox state of QA and the binding by HCO3(-) regulates and protects PSII. The potential for a sink (CO2) to source (PSII) feedback mechanism is discussed.

Dates et versions

hal-01451581 , version 1 (01-02-2017)

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Citer

Katharina Brinkert, Sven de Causmaecker, Anja Krieger-Liszkay, Andrea Fantuzzi, a William Rutherford. Bicarbonate-induced redox tuning in Photosystem II for regulation and protection.. Proceedings of the National Academy of Sciences of the United States of America, 2016, 113 (43), pp.12144-12149. ⟨10.1073/pnas.1608862113⟩. ⟨hal-01451581⟩
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