An x-ray absorption study of the iron site in bacterial photosynthetic reaction centers

G. Bunker, E. A. Stern, R. E. Blankenship, W. W. Parson

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60 Scopus citations

Abstract

Measurements were made of the extended x-ray absorption fine structure (EXAFS) of the iron site in photosynthetic reaction centers from the bacterium Rhodopseudomonas sphaeroides. Forms with two quinones, two quinones with added o-phenanthroline, and one quinone were studied. Only the two forms containing two quinones maintained their integrity and were analyzed. The spectra show directly that the added o-phenanthroline does not chelate the iron atom. Further analysis indicates that the iron is octahedrally coordinated by nitrogen and/or oxygen atoms located at various distances, with the average value of about 2.14 A. The analysis suggests that most of the ligands are nitrogens and that three of the nitrogen ligands belong to histidine rings. This interpretation accounts for several unusual features of the EXAFS spectrum. We speculate that the quinones are bound to the histidine rings in some manner. Qualitative features of the absorption edge spectra also are discussed and are related to the Fe-ligand distance.

Original languageEnglish
Pages (from-to)539-551
Number of pages13
JournalBiophysical Journal
Volume37
Issue number2
DOIs
StatePublished - Feb 1982
Externally publishedYes

Bibliographical note

Funding Information:
The facilities at Stanford Synchrotron Radiation Laboratory are supported by National Science Foundation grant DMR77-27487. The research presented here was also supported by National Science Founda- tion grant PCM79-03674.

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