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. 2007 Jul 19;104(31):12720–12725. doi: 10.1073/pnas.0705593104

Fig. 4.

Fig. 4.

EPR spectra of isolated E. coli complex I. Complex I was dialyzed anaerobically against 20 mM Tris·HCl pH 7.5, 0.1 mM NADH for 1 h at 0°C, then reduced further by the addition of 1 mM dithionite and frozen immediately. (Top) Spectrum at 40 K comprising two [2Fe-2S] clusters. (Middle) Spectrum at 12 K comprising, in addition, at least two [4Fe-4S] clusters. (Bottom) Spectrum at 5 K comprising at least two [4Fe-4S] clusters and one [2Fe-2S] cluster. Conditions were as follows: microwave power, 0.1 mW; conversion time, 81.92 ms; time constant, 20.48 ms; modulation amplitude 10 G; microwave frequency, ≈9.38 MHz.