title: Influence of the redox potential of the primary quinone electron acceptor on photoinhibition in photosystem II.
abstract: We report the characterization of the effects of the A249S mutation located within the binding pocket of the primary quinone electron acceptor, Q(A), in the D2 subunit of photosystem II in Thermosynechococcus elongatus. This mutation shifts the redox potential of Q(A) by approximately -60 mV. This mutant provides an opportunity to test the hypothesis, proposed earlier from herbicide-induced redox effects, that photoinhibition (light-induced damage of the photosynthetic apparatus) is modulated by the potential of Q(A). Thus the influence of the redox potential of Q(A) on photoinhibition was investigated in vivo and in vitro. Compared with the wild-type, the A249S mutant showed an accelerated photoinhibition and an increase in singlet oxygen production. Measurements of thermoluminescence and of the fluorescence yield decay kinetics indicated that the charge-separated state involving Q(A) was destabilized in the A249S mutant. These findings support the hypothesis that a decrease in the redox potential of Q(A) causes an increase in singlet oxygen-mediated photoinhibition by favoring the back-reaction route that involves formation of the reaction center chlorophyll triplet. The kinetics of charge recombination are interpreted in terms of a dynamic structural heterogeneity in photosystem II that results in high and low potential forms of Q(A). The effect of the A249S mutation seems to reflect a shift in the structural equilibrium favoring the low potential form.
authors.affiliation: Service de Bioénergétique, Département de Biologie, Joliot Curie, CNRS unite de recherché associé 2096, Commissariat á I'Energie Atomique Saclay, Gif-sur-Yvette 91191, France. christian@fufezan.net
authors.forename: Christian
authors.initials: C
authors.lastname: Fufezan
authors.forename: Christine M
authors.initials: CM
authors.lastname: Gross
authors.forename: Martin
authors.initials: M
authors.lastname: Sjödin
authors.forename: A William
authors.initials: AW
authors.lastname: Rutherford
authors.forename: Anja
authors.initials: A
authors.lastname: Krieger-Liszkay
authors.forename: Diana
authors.initials: D
authors.lastname: Kirilovsky
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D000458:Cyanobacteria / Q000201:enzymology* / Q000235:genetics; D004579:Electron Transport / Q000502:physiology; D004583:Electrons; D007700:Kinetics; D020125:Mutation, Missense; D010084:Oxidation-Reduction; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism*; D010971:Plastoquinone / Q000378:metabolism*; D026082:Singlet Oxygen / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D045332:Photosystem II Protein Complex; D026082:Singlet Oxygen; D010971:Plastoquinone