Menaquinone as the Secondary Electron Acceptor in the Type I Homodimeric Photosynthetic Reaction Center of Heliobacterium modesticaldum

Toru Kondo, Shigeru Itoh, Masahiro Matsuoka, Chihiro Azai, Hirozo Oh-Oka

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

The type I photosynthetic reaction center (RC) of heliobacteria (hRC) is a homodimer containing cofactors almost analogous to those in the plant photosystem I (PS I). However, its three-dimensional structure is not yet clear. PS I uses phylloquinone (PhyQ) as a secondary electron acceptor (A1), while the available evidence has suggested that menaquinone (MQ) in hRC has no function as A1. The present study identified a new transient electron spin-polarized electron paramagnetic resonance (ESP-EPR) signal, arising from the radical pair of the oxidized electron donor and the reduced electron acceptor (P800+MQ-), in the hRC core complex and membranes from Heliobacterium modesticaldum. The ESP signal could be detected at 5-20 K upon flash excitation only after prereduction of the iron-sulfur center, FX, and was selectively lost by extraction of MQ with diethyl ether. MQ was suggested to be located closer to FX than PhyQ in PS I based on the simulation of the unique A/E (A, absorption; E, emission) ESP pattern, the reduction/oxidation rates of MQ, and the power saturation property of the static MQ- signal. The result revealed the quinone usage as the secondary electron acceptor in hRC, as in the case of PS I. (Chemical Equation Presented)

Original languageEnglish
Pages (from-to)8480-8489
Number of pages10
JournalJournal of Physical Chemistry B
Volume119
Issue number27
DOIs
Publication statusPublished - 2015 Jul 9
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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