Proton release due to manganese binding and oxidation in modified bacterial reaction centers

L. Kálmán, M. C. Thielges, Joann Williams, James Allen

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


The pH dependence of binding and oxidation of Mn2+ in highly oxidizing reaction centers with designed metal-binding sites was characterized by light-minus-dark optical difference spectroscopy and direct measurements of proton uptake/release. These mutants bind a Mn2+ ion that can efficiently transfer an electron to the oxidized bacteriochlorophyll dimer, as described earlier [Thielges et al. (2005) Biochemistry 44, 7389-7394]. The dissociation constant, KD, significantly increased with decreasing pH. The pH dependence of KD between pH 7 and pH 8 was consistent with the binding of Mn2+ being stabilized by the electrostatic release of two protons. The strong pH dependence of proton release upon Mn2+ binding, with a maximal release of 1.4 H+ per reaction center, was interpreted as being a result of a shift in the pKa values of the coordinating residues and possibly other nearby residues. A small amount of proton release associated with Mn2+ oxidation was observed upon illumination. These results show that functional metal-binding sites can be incorporated into proteins upon consideration of both the metal coordination and protonation states of the ligands.

Original languageEnglish (US)
Pages (from-to)13266-13273
Number of pages8
Issue number40
StatePublished - Oct 11 2005

ASJC Scopus subject areas

  • Biochemistry


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