title: Substrate-water exchange in photosystem II is arrested before dioxygen formation.
abstract: Light-driven oxidation of water into dioxygen, catalysed by the oxygen-evolving complex (OEC) in photosystem II, is essential for life on Earth and provides the blueprint for devices for producing fuel from sunlight. Although the structure of the OEC is known at atomic level for its dark-stable state, the mechanism by which water is oxidized remains unsettled. Important mechanistic information was gained in the past two decades by mass spectrometric studies of the H2(18)O/H2(16)O substrate-water exchange in the four (semi) stable redox states of the OEC. However, until now such data were not attainable in the transient states formed immediately before the O-O bond formation. Using modified photosystem II complexes displaying up to 40-fold slower O2 production rates, we show here that in the transient S3YZ state the substrate-water exchange is dramatically slowed as compared with the earlier S states. This further constrains the possible sites for substrate-water binding in photosystem II.
authors.affiliation: Department of Chemistry, Kemiskt Biologiskt Centrum (KBC), Umeå University, Linnaeus väg 6, 901 87 Umeå, Sweden.
authors.forename: Håkan
authors.initials: H
authors.lastname: Nilsson
authors.affiliation: Institut de Biologie Physico-Chimique, UMR 7141 CNRS and Université Pierre et Marie Curie, 13 rue Pierre et Marie Curie, 75005 Paris, France.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Rappaport
authors.affiliation: iBiTec-S, CNRS UMR 8221, CEA Saclay, 91191 Gif-sur-Yvette, France.
authors.forename: Alain
authors.initials: A
authors.lastname: Boussac
authors.affiliation: Department of Chemistry, Kemiskt Biologiskt Centrum (KBC), Umeå University, Linnaeus väg 6, 901 87 Umeå, Sweden.
authors.forename: Johannes
authors.initials: J
authors.lastname: Messinger
mesh_terms: D000458:Cyanobacteria / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D014867:Water / Q000378:metabolism*
chemical_list: D045332:Photosystem II Protein Complex; D014867:Water; D010100:Oxygen