Asymmetric electron transfer in cyanobacterial photosystem I: Charge separation and secondary electron transfer dynamics of mutations near the primary electron acceptor A0

Naranbaatar Dashdorj, Wu Xu, Rachel O. Cohen, John H. Golbeck, Sergei Savikhin

Research output: Contribution to journalArticle

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Abstract

Point mutations were introduced near the primary electron acceptor sites assigned to A0 in both the PsaA and PsaB branches of Photosystem I in the cyanobacterium Synechocystis sp. PCC 6803. The residues Met688 PsaA and Met668PsaB, which provide the axial ligands to the Mg2+ of the eC-A3 and eC-B3 chlorophylls, were changed to leucine and asparagine (chlorophyll notation follows Jordan et al., 2001). The removal of the ligand is expected to alter the midpoint potential of the A 0/A0+ redox pair and result in a change in the intrinsic charge separation rate and secondary electron transfer kinetics from A0- to A1. The dynamics of primary charge separation and secondary electron transfer were studied at 690 nm and 390 nm in these mutants by ultrafast optical pump-probe spectroscopy. The data reveal that mutations in the PsaB branch do not alter electron transfer dynamics, whereas mutations in the PsaA branch have a distinct effect on electron transfer, slowing down both the primary charge separation and the secondary electron transfer step (the latter by a factor of 3-10). These results suggest that electron transfer in cyanobacterial Photosystem I is asymmetric and occurs primarily along the PsaA branch of cofactors.

Original languageEnglish (US)
Pages (from-to)1238-1249
Number of pages12
JournalBiophysical journal
Volume88
Issue number2
DOIs
StatePublished - Feb 2005

All Science Journal Classification (ASJC) codes

  • Biophysics

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