Effect of anions on the binding and oxidation of divalent manganese and iron in modified bacterial reaction centers

Kai Tang, Joann Williams, James Allen, László Kálmán

Research output: Contribution to journalArticle

10 Scopus citations

Abstract

The influence of different anions on the binding and oxidation of manganous and ferrous cations was studied in four mutants of bacterial reaction centers that can bind and oxidize these metal ions. Light-minus-dark difference optical and electron paramagnetic resonance spectroscopies were applied to monitor electron transfer from bound divalent metal ions to the photo-oxidized bacteriochlorophyll dimer in the presence of five different anions. At pH 7, bicarbonate was found to be the most effective for both manganese and iron binding, with dissociation constants around 1 μM in three of the mutants. The pH dependence of the dissociation constants for manganese revealed that only bicarbonate and acetate were able to facilitate the binding and oxidation of the metal ion between pH 6 and 8 where the tight binding in their absence could not otherwise be established. The data are consistent with two molecules of bicarbonate or one molecule of acetate binding to the metal binding site. For ferrous ion, the binding and oxidation was facilitated not only by bicarbonate and acetate, but also by citrate. Electron paramagnetic resonance spectra suggest differences in the arrangement of the iron ligands in the presence of the various anions.

Original languageEnglish (US)
Pages (from-to)3295-3304
Number of pages10
JournalBiophysical journal
Volume96
Issue number8
DOIs
StatePublished - 2009

ASJC Scopus subject areas

  • Biophysics

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