If I understand it correctly:
(short version)
The Q cycle starts with PQH2 it removes the 2H(+) and gives one electron to Plastocyanin and the other to a stored Plastoquinone to charge it to Plastoquinone (-). This process is repeated and adds the electron to the stored Plastoquinone(-) to create a Plastoquinone (-2). This then gets 2H(+) to form PQH2. And the cycle begins anew.

But in a lot of pictures is shown that the excited P680 gives the electron to Pheophytin and that gives it to the Q cycle.

Please let me know when and where the Pheophytin interacts to give the electron.


1 Answer 1


Not sure if there is a definite answer. However, from structural studies, its proposed that essentially the Chlorophyll a and pheophytin(Pheo) are positioned ~10A away, and the transfer of a radical electron from the P680 center to Pheophytin does occur. The exact mechanism is possibly mediated by a tyrosine

  1. Durant J.R et al (1995). Proceedings of the National Academy of Sciences of the United States of America, 92, 4798–4802
  2. Oleg Victorovich (2006). Retrived:5/25/16. Site: http://samlib.ru/o/oleg_w_m/cdocumentsandsettingsolegmoidokumentythefunctionandthestructureofporphyrinmoleculesrtf.shtml

3.Zouni A et al (2001). Nature, 409, 739-743


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