Fig. 5.

EPR signals of SQ in the steady state of complex I proteoliposomes (1.4 mg complex I/ml). EPR spectra were recorded at the sample temperature of 180 K. The black trace shows the SQ signal in the coupled state and the red trace in the uncoupled state (+30 μM CCCP). The proteoliposomes were suspended in the 15 mM solution of Na₂SO₄, 5 mM HEPES buffer (pH 7,5) and 400 μM Q₁ at 20°C. Then, 200 μM NADH was added, and 30 seconds later, the mixture was frozen at −80°C See text for the EPR conditions.