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Asymmetric binding of the 1‐ and 4‐C=O groups of QA in Rhodobacter sphaeroides R26 reaction centres monitored by Fourier transform infra‐red spectroscopy using site‐specific isotopically labelled ubiquinone‐10.
Author(s) -
Brudler R.,
Groot H.J.,
Liemt W.B.,
Steggerda W.F.,
Esmeijer R.,
Gast P.,
Hoff A.J.,
Lugtenburg J.,
Gerwert K.
Publication year - 1994
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1002/j.1460-2075.1994.tb06889.x
Subject(s) - rhodobacter sphaeroides , library science , physics , crystallography , chemistry , computer science , biochemistry , photosynthesis
Using 1‐, 2‐, 3‐ and 4‐13C site‐specifically labelled ubiquinone‐10, reconstituted at the QA site of Rhodobacter sphaeroides R26 reaction centres, the infra‐red bands dominated by the 1‐ and 4‐C = O vibration of QA are assigned in the QA(‐)‐QA difference spectra. The mode dominated by the 4‐C = O vibration is drastically downshifted in the reaction centres as compared with its absorption frequency in free ubiquinone‐10. In contrast, the mode dominated by the 1‐C = O vibration absorbs at similar frequencies in the free and the bound forms. The frequency shift of the 4‐C = O vibration is due to a large decrease in bond order and indicates a strong interaction with the protein microenvironment in the ground state. In the charge‐separated state the mode dominated by the semiquinone 4‐C = O vibration is characteristic of strong hydrogen bonding to the microenvironment, whereas the mode dominated by the 1‐C = O vibration indicates a weaker interaction. The asymmetric binding of the 1‐ and 4‐C = O groups to the protein might contribute to the factors governing different redox reactions of ubiquinone‐10 at the QA site as compared with its reactions at the QB site.