title: The terminal reaction cascade of water oxidation: proton and oxygen release.
abstract: In cyanobacteria, algae and plants Photosystem II produces the oxygen we breathe. Driven and clocked by light quanta, the catalytic Mn(4)Ca-tyrosine centre accumulates four oxidising equivalents before it abstracts four electrons from water, liberating dioxygen and protons. Aiming at intermediates of the terminal four-electron cascade, we previously have suppressed this reaction by elevating the oxygen pressure, thereby stabilising one redox intermediate. Here, we established a similar suppression by increasing the proton concentration. Data were analysed in terms of only one (peroxy) redox intermediate between the fourfold oxidised Mn(4)Ca-tyrosine centre and oxygen release. The surprising result was that the release into the bulk of one proton per dioxygen is linked to the first and rate-limiting electron transfer in the cascade rather than to the second which produces free oxygen. The penultimate intermediate might thus be conceived as a fully deprotonated peroxy-moiety.
authors.affiliation: Abteilung Biophysik, Fachbereich Biologie/Chemie, Universität Osnabrück, Osnabrück, Germany.
authors.forename: Juergen
authors.initials: J
authors.lastname: Clausen
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Junge
mesh_terms: D002734:Chlorophyll / Q000737:chemistry; D004579:Electron Transport; D006863:Hydrogen-Ion Concentration; D008345:Manganese / Q000737:chemistry; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D011522:Protons; D046939:Synechocystis / Q000737:chemistry; D014867:Water / Q000737:chemistry*
chemical_list: D045332:Photosystem II Protein Complex; D011522:Protons; D014867:Water; D002734:Chlorophyll; D008345:Manganese; D010100:Oxygen