title: Bicarbonate-induced redox tuning in Photosystem II for regulation and protection.
abstract: 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 Emfrom ∼-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 Emof QAHCO3--depleted PSII also showed diminished light-induced1O2formation. This finding is consistent with a model in which the increase in the Emof [Formula: see text] promotes safe, direct [Formula: see text] charge recombination at the expense of the damaging back-reaction route that involves chlorophyll triplet-mediated1O2formation [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 QAand the binding by HCO3-regulates and protects PSII. The potential for a sink (CO2) to source (PSII) feedback mechanism is discussed.
authors: Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom.
authors: Katharina
authors: K
authors: Brinkert
authors: Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom.
authors: Sven
authors: S
authors: De Causmaecker
authors: Institute for Integrative Biology of the Cell, Commissariat à l'Énergie Atomique, CNRS, Univ Paris-Sud, Université Paris-Saclay, F-91198 Gif-sur-Yvette cedex, France.
authors: Anja
authors: A
authors: Krieger-Liszkay
authors: Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom; a.fantuzzi@imperial.ac.uk a.rutherford@imperial.ac.uk.
authors: Andrea
authors: A
authors: Fantuzzi
authors: Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom; a.fantuzzi@imperial.ac.uk a.rutherford@imperial.ac.uk.
authors: A William
authors: 0000-0002-3124-154X
authors: AW
authors: Rutherford
mesh_terms: D001639:Bicarbonates / Q000378:metabolism*; D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000737:chemistry / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D004579:Electron Transport; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008027:Light; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D018515:Plant Leaves / Q000737:chemistry / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D011809:Quinones / Q000737:chemistry / Q000378:metabolism*; D018724:Spinacia oleracea / Q000737:chemistry / Q000378:metabolism*; D013481:Superoxides / Q000737:chemistry / Q000378:metabolism; D013816:Thermodynamics
chemical_list: D001639:Bicarbonates; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D011809:Quinones; D013481:Superoxides; D002245:Carbon Dioxide; D010100:Oxygen
keywords: CO2 fixation; photoassembly; photoinhibition; photosynthesis; water oxidation