The electronic structure of Fe2+ in reaction centers from Rhodopseudomonas sphaeroides. II. Extended x-ray fine structure studies

Biophysical Journal
P EisenbergerG Feher

Abstract

Extended x-ray absorption fine structure (EXAFS) studies were performed on reaction centers (RC) of the photosynthetic bacterium Rhodopseudomonas sphaeroides R-26. RC containing two, one, and no quinones (2Q, 1Q, 0Q) samples were studied. The average ligand distance of the first coordination shell was determined to be 2.10 +/- 0.02 A with a more distant shell at 4.14 +/- 0.05 A. The Fe2+ site in RC was found to have a very large structural disorder parameter, from which a spread in ligand distance per iron site of approximately +/- 0.1 A was deduced. The most likely coordination number of the first shell is six, with a mixture of oxygens and nitrogens as ligands. The edge absorption results are consistent with the Fe2+ being in distorted octahedral environment. The EXAFS spectra of the 2Q and 1Q samples with and without O-phenanthroline were found to be the same. This indicates that either the secondary quinone and o-phenanthroline do not bind to Fe2+ or that they replace an equivalent ligand. The 0Q sample showed a 12% decrease in the EXAFS amplitude, which was restored upon addition of o-phenanthroline. These results can be explained by either a loss of a ligand or a severe conformational change when the primary quinone was r...Continue Reading

Citations

Apr 28, 2004·Bioelectrochemistry·Francesco FranciaGiovanni Venturoli
Dec 1, 1984·Proceedings of the National Academy of Sciences of the United States of America·J C WilliamsM I Simon
Nov 1, 1986·Proceedings of the National Academy of Sciences of the United States of America·J P AllenR Huber
Aug 1, 1987·Proceedings of the National Academy of Sciences of the United States of America·J P AllenD C Rees
Nov 1, 1988·Proceedings of the National Academy of Sciences of the United States of America·J P AllenD C Rees
Dec 1, 1989·Journal of Biomolecular Structure & Dynamics·M A Hadwiger, G E Fox
May 4, 2002·Annual Review of Biophysics and Biomolecular Structure·George Feher
Aug 31, 1988·Biochimica Et Biophysica Acta·S NavaratnamJ F Vliegenthart
Sep 1, 1982·Biochimica Et Biophysica Acta·L Powers

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