Path of Electron Transfer in Photosystem 1: Direct Evidence of Forward Electron Transfer from A1 to Fe-SX

Pierre Moénne-Loccoz, Dugald J. Maclachlan, Matthew C. Berry, Ian H. Davis, Michael C.W. Evans, Peter Heathcote

Research output: Contribution to journalArticlepeer-review

69 Scopus citations


Pulsed EPR spectroscopy and selective removal of the iron-sulfur centers in photosystem 1 have been used to study forward electron transfer from the secondary electron acceptor A1. At cryogenic temperatures where forward electron transfer is inhibited, we have observed a g = 2.003 electron spin-echo signal presenting a characteristic phase shift. This out-of-phase signal is attributed to the electron spin-polarized pair P700+/A1, it decays with t1/e = 23 µs, reflecting the recombination reaction. At room temperature the out-of-phase signal is also observed, but it decays with t1/e = 200 ns in untreated photosystem 1, due to forward electron transfer from A1 to one of the iron-sulfur centers. This rate is unchanged in Fe-SA/B-depleted PS1 but is lost when the iron-sulfur center Fe-SX is removed. In the preparations depleted of all iron-sulfur centers the out-of-phase signal decays with t1/e = 1.3 µs, reflecting either the back reaction or the decay of polarization. These results demonstrate that the electron transfer pathway in photosystem 1 is P700 → A1 → Fe-SX → Fe-SA/B.

Original languageEnglish (US)
Pages (from-to)10037-10042
Number of pages6
Issue number33
StatePublished - Aug 1 1994
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry


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