EPR characterization of ubisemiquinones and iron-sulfur cluster N2, central components of the energy coupling in the NADH-ubiquinone oxidoreductase (complex I) in situ.

The proton-translocating NADH-ubiquinone oxidoreductase (complex I) is the largest and least understood respiratory complex. The intrinsic redox components (FMN and iron-sulfur clusters) reside in the promontory part of the complex. Ubiquinone is the most possible key player in proton-pumping reactions in the membrane part.