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Orientation dependence of the EPR signal from the reduced iron‐quinone complex in a single crystal of the reaction center protein from Rhodopseudomonas viridis
Author(s) -
Gast P.,
Gottschalk A.,
Norris J.R.,
Closs G.L.
Publication year - 1989
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(89)81204-9
Subject(s) - electron paramagnetic resonance , quinone , photosynthetic reaction centre , chemistry , crystallography , crystal (programming language) , rotation (mathematics) , orientation (vector space) , perpendicular , single crystal , center (category theory) , photochemistry , stereochemistry , nuclear magnetic resonance , electron transfer , physics , geometry , mathematics , computer science , programming language
In the light‐induced charge separation that takes place in the bacterial photosynthetic reaction center protein a quinone molecule (Q) is reduced. The EPR spectrum of this reduced quinone is strongly broadened which is assumed to arise from interaction with the high spin (S=2) Fe 2+ , which is located near Q. Computer simulations of this EPR spectrum have been somewhat limited by the lack of structure in the EPR spectrum. The availability of single crystals of the reaction center protein offers the possibility to analyze the spectrum of the reduced iron‐quinone complex (FeQ − ) in much greater detail than ever before. We have therefore measured the EPR spectrum of FeQ − using single crystals from the reaction center protein from the photosynthetic bacterium Rhodopseudomonas viridis . Transitions were obtained in the g value range of 1.7–1.9 for both crystal orientations, i.e. for rotation along and rotation perpendicular to the crystal's long axis. Strong line broadening was observed at many orientations, which could indicate a heterogeneity in the zerofield parameters of Fe 2+ .