Temperature dependence of biphasic forward electron transfer from the phylloquinone(s) A1 in photosystem I: only the slower phase is activated.
The temperature dependence of the biphasic electron transfer (ET) from the secondary acceptor A1 (phylloquinone) to iron-sulfur cluster F(X) was investigated by flash absorption spectroscopy in photosystem I (PS I) isolated from Synechocystis sp. PCC 6803. While the slower phase (tau=340 ns at 295 K) slowed upon cooling according to an activation energy of 110 meV, the time constant of the faster phase (tau=11 ns at 295 K) was virtually independent of temperature. Following a suggestion in the literature that the two phases arise from bidirectional ET involving two symmetrically arranged phylloquinones, Q(K)-A and Q(K)-B, it is concluded that energetic parameters (most likely the driving forces) rather than the electronic couplings are different for ET from Q(K)-A to F(X) and from Q(K)-B to F(X). Two alternative schemes of ET in PS I are presented and discussed.
Agalarov
Rufat
R
Service de Bioénergétique, CEA, and URA 2096 CNRS, CEA Saclay, Gif-sur-Yvette, France.
Brettel
Klaus
K
D000458:Cyanobacteria / Q000378:metabolism; D004579:Electron Transport; D007700:Kinetics; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D013696:Temperature; D010837:Vitamin K 1 / Q000378:metabolism*
D045322:Photosynthetic Reaction Center Complex Proteins; D010837:Vitamin K 1