Low field EPR spectrum of purified DmsABC and NarGHI. Samples were reduced by anaerobic incubation with 6 mm sodium dithionite for 5 min. EPR conditions were as follows: temperature, 9 K; microwave power, 100 milliwatts at 9.387 GHz; and modulation amplitude, 20 Gpp (EPR modulation amplitude intensity, peak to peak, in units of Gauss) at 100 KHz.