A systematic survey of conserved histidines in the core subunits of Photosystem I by site-directed mutagenesis reveals the likely axial ligands of P700

Kevin Redding, Fraser MacMillan, Winfried Leibl, Klaus Brettel, Jonathan Hanley, A. William Rutherford, Jacques Breton, Jean David Rochaix

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78 Scopus citations


The Photosystem I complex catalyses the transfer of an electron from lumenal plastocyanin to stromal ferredoxin, using the energy of an absorbed photon. The initial photochemical event is the transfer of an electron from the excited state of P700, a pair of chlorophylls, to a monomer chlorophyll serving as the primary electron acceptor. We have performed a systematic survey of conserved histidines in the last six transmembrane segments of the related polytopic membrane proteins PsaA and PsaB in the green alga Chlamydomonas reinhardtii. These histidines, which are present in analogous positions in both proteins, were changed to glutamine or leucine by site-directed mutagenesis. Double mutants in which both histidines had been changed to glutamine were screened for changes in the characteristics of P700 using electron paramagnetic resonance, Fourier transform infrared and visible spectroscopy. Only mutations in the histidines of helix 10 (PsaA-His676 and PsaB-His656) resulted in changes in spectroscopic properties of P700, leading us to conclude that these histidines are most likely the axial ligands to the P700 chlorophylls.

Original languageEnglish (US)
Pages (from-to)50-60
Number of pages11
JournalEMBO Journal
Issue number1
StatePublished - Jan 2 1998
Externally publishedYes



  • Chlamydomonas reinhardtii
  • EPR
  • FTIR
  • Photosystem I
  • Site-directed mutagenesis

ASJC Scopus subject areas

  • Neuroscience(all)
  • Molecular Biology
  • Biochemistry, Genetics and Molecular Biology(all)
  • Immunology and Microbiology(all)

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