Semiquinone-iron complex of Photosystem II: EPR signals assigned to the low-field edge of the ground state doublet of QA •-Fe2+ and QB•-Fe 2+

Arezki Sedoud, Nicholas Cox, Miwa Sugiura, Wolfgang Lubitz, Alain Boussac, A. William Rutherford*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

20 Citations (Scopus)

Abstract

The quinone-iron complex of the electron acceptor complex of Photosystem II was studied by EPR spectroscopy in Thermosynechococcus elongatus. New g ∼ 2 features belonging to the EPR signal of the semiquinone forms of the primary and secondary quinone, i.e., QA•-Fe2+ and QB•-Fe2+, respectively, are reported. In previous studies, these signals were missed because they were obscured by the EPR signal arising from the stable tyrosyl radical, TyrD. When the TyrD signal was removed, either by chemical reduction or by the use of a mutant lacking TyrD, the new signals dominated the spectrum. For QA•-Fe2+, the signal was formed by illumination at 77 K or by sodium dithionite reduction in the dark. For Q B•-Fe2+, the signal showed the characteristic period-of-two variations in its intensity when generated by a series of laser flashes. The new features showed relaxation characteristics comparable to those of the well-known features of the semiquinone-iron complexes and showed a temperature dependence consistent with an assignment to the low-field edge of the ground state doublet of the spin system. Spectral simulations are consistent with this assignment and with the current model of the spin system. The signal was also present in QB •-Fe2+ in plant Photosystem II, but in plants, the signal was not detected in the QA•-Fe2+ state.

Original languageEnglish
Pages (from-to)6012-6021
Number of pages10
JournalBiochemistry
Volume50
Issue number27
DOIs
Publication statusPublished - 12 Jul 2011
Externally publishedYes

Fingerprint

Dive into the research topics of 'Semiquinone-iron complex of Photosystem II: EPR signals assigned to the low-field edge of the ground state doublet of QA •-Fe2+ and QB•-Fe 2+'. Together they form a unique fingerprint.

Cite this