title: Intermediates in assembly by photoactivation after thermally accelerated disassembly of the manganese complex of photosynthetic water oxidation.
abstract: The Mn4Ca complex bound to photosystem II (PSII) is the active site of photosynthetic water oxidation. Its assembly involves binding and light-driven oxidation of manganese, a process denoted as photoactivation. The disassembly of the Mn complex is a thermally activated process involving distinct intermediates. Starting from intermediate states of the disassembly, which was initiated by a temperature jump to 47 degrees C, we photoactivated PSII membrane particles and monitored the activity recovery by O2 polarography and delayed chlorophyll fluorescence measurements. Oxidation state and structural features of the formed intermediates of the Mn complex were assayed by X-ray absorption spectroscopy at the Mn K-edge. The photoactivation time courses, which exhibit a lag phase characteristic of intermediate formation only when starting with the apo-PSII, suggest that within approximately 5 min of photoactivation of apo-PSII, a binuclear Mn complex is formed. It is proposed that a MnIII2(di-mu-oxo) complex is a key intermediate both in the disassembly and in the assembly reaction paths.
authors.affiliation: Freie Universität Berlin, FB Physik, Arnimallee 14, D-14195 Berlin, Germany.
authors.forename: Marcos
authors.initials: M
authors.lastname: Barra
authors.forename: Michael
authors.initials: M
authors.lastname: Haumann
authors.forename: Paola
authors.initials: P
authors.lastname: Loja
authors.forename: Roland
authors.initials: R
authors.lastname: Krivanek
authors.forename: Alexander
authors.initials: A
authors.lastname: Grundmeier
authors.forename: Holger
authors.initials: H
authors.lastname: Dau
mesh_terms: D007700:Kinetics; D008345:Manganese / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism; D013057:Spectrum Analysis; D018724:Spinacia oleracea / Q000737:chemistry / Q000378:metabolism; D013696:Temperature; D014867:Water / Q000737:chemistry* / Q000378:metabolism
chemical_list: D045332:Photosystem II Protein Complex; D014867:Water; D008345:Manganese