Substituting Fe for two of the four Mn ions in photosystem II—effects on water-oxidation

Boris K. Semin, Michael Seibert

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13 Scopus Citations

Abstract

We have investigated the interaction of Fe(II) cations with Ca-depleted PSII membranes (PSII[-Ca,4Mn]) in the dark and found that Fe(II) incubation removes 2 of 4 Mn ions from the tetranuclear Mn cluster of the photosynthetic O2-evolving complex (OEC). The reduction of Mn ions in PSII(-Ca,4Mn) by Fe(II) and the concomitant release of two Mn(II) cations is accompanied by the binding of newly generated Fe(III) in at least one vacated Mn site. Flash-induced chlorophyll (Chl) fluorescence yield measurements of this new 2Mn/nFe cluster (PSII[-Ca,2Mn,nFe]) show that charge recombination in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) occurs between Qa - and the remaining Mn/Fe cluster (but not YZ ) in the OEC, and extraction of 2 Mn occurs uniformly in all PSII complexes. No O2 evolution is observed, but the heteronuclear metal cluster in PSII(-Ca,2Mn,nFe) samples is still able to supply electrons for reduction of the exogenous electron acceptor, 2,6-dichlorophrenolindophenol, by photooxidizing water and producing H2O2 in the absence of an exogenous donor as seen previously with PSII(-Ca,4Mn). Selective extraction of Mn or Fe cations from the 2Mn/nFe heteronuclear cluster demonstrates that the high-affinity Mn-binding site is occupied by one of the iron cations. It is notable that partial water-oxidation function still occurs when only two Mn cations are present in the PSII OEC.

Original languageAmerican English
Pages (from-to)227-240
Number of pages14
JournalJournal of Bioenergetics and Biomembranes
Volume48
Issue number3
DOIs
StatePublished - 2016

Bibliographical note

Publisher Copyright:
© 2016, Springer Science+Business Media New York.

NREL Publication Number

  • NREL/JA-2700-64010

Keywords

  • Fluorescence yield
  • Iron
  • Manganese
  • Oxygen-evolving complex
  • Photosystem II

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