Pulse EPR, ENDOR and ELDOR study of anionic flavin radicals in Na+-translocating NADH:quinone oxidoreductaseстатья
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:The Na+-translocating NADH:quinone oxidoreductase (Na+-NQR) is a component of respiratory chain of various bacteria and it generates a redox-driven transmembrane electrochemical Na+ potential. It contains four different flavin prosthetic groups including two FMN residues covalently bound to the subunits NqrB and NqrC. Na+-NQR from Vibrio harveyi was poised at different redox potentials to prepare two samples, containing either both FMNNqrB and FMNNqrC or only FMNNqrB in a paramagnetic state. These two samples were comparatively studied using pulse EPR, ENDOR, and ELDOR spectroscopy. The echo-detected EPR spectra and electron spin relaxation properties were very similar for flavin radicals in both samples. The splitting of the outer peaks in the proton ENDOR spectra, assigned to the C(8α) methyl protons allows to inentify the both radicals as anionic flavosemiquinones. The mean inter-spin distance between these radicals 20.7 Å was determined by pulse ELDOR experiment, which allows to estimate the edge to edge distance (re) between these flavin centers as: 11.7 Å < re < 20.7 Å. The direct electron transfer between FMNNqrB and FMNNqrC during the physiological turnover of Na+-NQR complex is suggested.