Path of electron transfer in photosystem I: direct evidence of forward electron transfer from A1 to Fe-Sx

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...

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Bibliographic Details
Published in:Biochemistry (Easton) 1994-08, Vol.33 (33)
Main Authors: Moenne-Loccoz, P. (University College London, London, UK.), Heathcote, P, Maclachlan, D.J, Berry, M.C, Davis, I.H, Evans, M.C.W
Format: Article
Language:English
Subjects:
AZUFRE
CYANOPHYTA
ESPECTROMETRIA
FER
FOTOSISTEMAS
HIERRO
OXIRREDUCION
OXYDOREDUCTION
PHOTOSYSTEME
SOUFRE
SPECTROMETRIE
SPINACIA OLERACEA
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Summary: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 microseconds, 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-S(A/B)-depleted PS 1 but is lost when the iron-sulfur center Fe-S(X) is removed. In the preparations depleted of all iron-sulfur centers the out-of-phase signal decays with t1/e = 1.3 microseconds reflecting either the back reaction or the decay of polarization. These results demonstrate that the electron transfer pathway in photosystem 1 is P700 leads to A1 leads to Fe-S(X) leads to Fe-S(A/B)
ISSN:0006-2960
1520-4995