Correlated behavior of the EPR signal of cytochrome b‐559 heme Fe(III) ligated by OH− and the multiline signal of the Mn cluster in PS‐II membrane fragments

EPR signals of Cyt b-559 heme Fe(III) ligated by OH- and the multiline signal of the Mn cluster in PS-II membrane fragments have been investigated. In 2,3-dicyano-5,6-dichloro-p-benzoquinone-oxidized PS-II membrane fragments the light-induced decrease of the EPR signal of the heme Fe(III)-OH- is accompanied by the appearance of the EPR multiline signal of the Mn cluster. Addition of F- ions, which act as a stronger ligand for heme Fe(III) than OH-, decreases to the same extent the dark- and light-induced signal of the heme Fe(III)-OH- and the light-induced multiline signal of the Mn cluster. These results are discussed in terms of the light-induced formation of a bound OH' radical shared between the Cyt b-559 heme Fe and the Mn cluster as a first step of water oxidation.