A structural model for the charge separated state P700̇+A1̇+ photosystem I from the orientation of the magnetic interaction tensors

Stephan G. Zech, Wulf Hofbauer, Andreas Kamlowski, Petra Fromme, Dietmar Stehlik, Wolfgang Lubitz, Robert Bittl

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70 Scopus citations


The charge separated state P700̇+A1̇+ (P700 = primary electron donor, A1 = phylloquinone electron acceptor) in photosystem I of oxygenic photosynthesis has been investigated by EPR spectroscopy in frozen solution and single crystals. The transient EPR spectra of P700̇+A1̇+ recorded in frozen solution of fully deuterated samples at X-, Q-, and W-band frequencies are shown to contain sufficient information to yield the orientation of the g-tensors of both A1̇+ and P700̇+ with respect to the axis connecting both spins. So far incomplete information on the orientation of A1̇+ relative to the membrane plane has been complemented by data from time-resolved EPR on single crystals measured at Q-band. The phylloquinone headgroup orientation evaluated from the EPR data in the charge-separated state P700̇+A1̇+ is compared with the presently available X-ray structural model. The g-tensor of P700̇+ has also been determined from cw-EPR experiments at W-band on single crystals, independent of the orientational data of the P700̇+ g-tensor from the time-resolved EPR experiments. The direction of the principal axes of g(P700̇+) differ from the molecular axes system of the chlorophylls comprising P700 as found previously in the case of P865 in bacterial reaction centers. The implications of the complete structural model from the A1̇+ and P700̇+ molecular magnetic interaction tensors in the active charge separated state P700̇+A1̇+ in PS I are discussed.

Original languageEnglish (US)
Pages (from-to)9728-9739
Number of pages12
JournalJournal of Physical Chemistry B
Issue number41
StatePublished - Oct 19 2000
Externally publishedYes

ASJC Scopus subject areas

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


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