Reaction of A1-menaquinone in type I reaction center of heliobacterium modesticaldum at cryogenic temperature

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

Research output: Chapter in Book/Report/Conference proceedingChapter


Temperature dependence of electron transfer reaction via A1-menaquinone in type I homodimeric reaction center of Heliobacterium modesticaldum (hRC) was observed by time-resolved electron paramagnetic resonance (EPR) spectroscopy. Flash excitation induced an electron spin polarization (ESP) signal due to P800+FX radical pair at 14 K, exhibiting an E/A (E, emission; A, absorption) spectral pattern. After the hRC core complex was pre-illuminated at 210 K for 1 hour and subsequently cooled to 5 K during illumination, another ESP signal due to P800+ A1, exhibiting an A/E pattern, was flash-induced at 14 K. The decay time was estimated to be 90 μs at 5 K and 25 μs at 20 K, respectively. The recombination of P800+A1 in hRC is significantly faster at all the temperatures, compared to that of P700+A1 in PS I, which occurs in around 100 μs with little temperature dependence. The recombination time of P800+FX was a 4–11 ms at 5 K in contrast to the longer time than 100 ms in PSI. These results indicate that A1 menaquinone is involved in the rapid electron transfer between P700 and FX in hRC, as phylloquinone in PSI, probably with unique energy gap or geometry.

Original languageEnglish
Title of host publicationAdvanced Topics in Science and Technology in China
PublisherSpringer Science and Business Media Deutschland GmbH
Number of pages4
Publication statusPublished - 2013
Externally publishedYes

Publication series

NameAdvanced Topics in Science and Technology in China
ISSN (Print)1995-6819
ISSN (Electronic)1995-6827


  • EPR
  • Electron spin polarization
  • Heliobacteria
  • Homodimer RC
  • Quinone
  • Type I RC

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Engineering(all)
  • General


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