Flash-induced H+ binding by bacterial photosynthetic reaction centers: Comparison of spectrophotometric and conductimetric methods

Péter Maróti, Colin A. Wraight

Research output: Contribution to journalArticle

88 Citations (Scopus)

Abstract

H+ binding following flash excitation of isolated reaction centers from Rhodobacter sphaeroides was measured using a conductimetric method. A procedure is described for calibrating the H+ change and the method is compared to the more widely used spectrophotometric assay of pH-indicator dyes. The two methods agree extremely well and confirm a severe paradox in the pH dependence of the H+ binding stoichiometry - that reaction centers in the light-activated, charge-separation state, P+(QAQB)-, fail to bind net protons at pH values near neutral or lower, although proton binding is seen at higher pH. This is in contrast to expectations arising from the equilibrium redox behavior of the acceptor quinones, QA and QB, and with the pH dependence of the one-electron equilibrium between Q-AQB and QAQ-B. The observed proton binding is discussed in terms of multiple protonation equilibria linked to the redox states of the acceptor quinones and of the primary donor.

Original languageEnglish
Pages (from-to)314-328
Number of pages15
JournalBBA - Bioenergetics
Volume934
Issue number3
DOIs
Publication statusPublished - Jul 27 1988

Keywords

  • (Rb sphaeroides)
  • Bacterial photosynthesis
  • Electric conductance change
  • Proton binding
  • Reaction center
  • pH indicator dye

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

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