Reduction of the oxidized bacteriochlorophyll dimer in reaction centers by ferrocene is dependent upon the driving force

László Kálmán, Arlene L M Haffa, Joann Williams, Neal Woodbury, James Allen

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

The rates of electron transfer from ferrocene to the oxidized bacteriochlorophyll dimer, P, in reaction centers from the purple photosynthetic bacterium Rhodobacter sphaeroides, were measured for a series of mutants in which the P/P+ midpoint potentials range from 410 to 765 mV (Lin et al. Proc. Natl. Acad. Sci. USA 1994; 91: 10265-10269). The observed rate constant for each mutant was found to be linearly dependent upon the ferrocene concentration up to 50 μM. The electron transfer is described as a second order reaction with rate constants increasing from 1.5 to 35 × 10 6 M-1.s-1 with increasing P/P+ midpoint potential. This dependence was tested for three additional mutants, each of which exhibits a pH dependence of the P/P+ midpoint potential due to an electrostatic interaction with an introduced carboxylic group (Williams et al. Biochemistry 2001; 40: 15403-15407). For these mutants, the pH dependence of the bimolecular rate constants followed a sigmoidal pattern that could be described with a Henderson-Hasselbalch equation, attributable to the change of the free energy difference for the reaction due to deprotonation of the introduced carboxylic side chains.

Original languageEnglish (US)
Pages (from-to)205-211
Number of pages7
JournalJournal of Porphyrins and Phthalocyanines
Volume11
Issue number3-4
DOIs
StatePublished - 2007

Keywords

  • Bacterial reaction center
  • Bimolecular electron transfer
  • Electrostatic interactions
  • Rhodobacter sphaeroides
  • Secondary electron donor

ASJC Scopus subject areas

  • Chemistry(all)

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