The 2-methoxy group orientation regulates the Redox potential difference between the primary (QA) and secondary (QB) Quinones of type ii bacterial photosynthetic reaction centers

Wagner B. De Almeida, Alexander T. Taguchi, Sergei A. Dikanov, Colin A. Wraight, Patrick J. O'malley

Research output: Contribution to journalArticle

Abstract

Recent studies have shown that only quinones with a 2-methoxy group can act simultaneously as the primary (QA) and secondary (QB) electron acceptors in photosynthetic reaction centers from purple bacteria such as Rb. sphaeroides. 13C HYSCORE measurements of the 2-methoxy group in the semiquinone states, SQA and SQB, were compared with DFT calculations of the 13C hyperfine couplings as a function of the 2-methoxy dihedral angle. X-ray structure comparisons support 2-methoxy dihedral angle assignments corresponding to a redox potential gap (δE m) between QA and QB of 175-193 mV. A model having a methyl group substituted for the 2-methoxy group exhibits no electron affinity difference. This is consistent with the failure of a 2-methyl ubiquinone analogue to function as QB in mutant reaction centers with a δEm of ∼160-195 mV. The conclusion reached is that the 2-methoxy group is the principal determinant of electron transfer from Q A to QB in type II photosynthetic reaction centers with ubiquinone serving as both acceptor quinones.

Original languageEnglish (US)
Pages (from-to)2506-2509
Number of pages4
JournalJournal of Physical Chemistry Letters
Volume5
Issue number15
DOIs
StatePublished - Aug 7 2014

Keywords

  • density functional
  • electron affinity
  • electron transfer
  • isotropic hyperfine coupling
  • redox potential
  • ubisemiquinone

ASJC Scopus subject areas

  • Materials Science(all)
  • Physical and Theoretical Chemistry

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