FIG. 3.

EPR spectra of P. furiosus ADH. ADH was used at a concentration of 3.6 mg/ml. a, ADH as isolated in 50 mM Tris-HCl (pH 7.8) containing 5% (vol/vol) glycerol and 2 mM dithiothreitol. Spectrum was recorded at 4 K with 5 mW of microwave power. b, ADH treated with NO. The enzyme (3.6 mg/ml in 50 mM Tris-HCl [pH 7.8]) was gently bubbled with NO for 3 min at 25°C prior to being frozen in liquid N₂. The spectrum was recorded with 40 mW of microwave power at 4 K. The spectrometer settings were as follows: microwave frequency, 9.597 GHz; modulation frequency, 100 kHz; modulation amplitude, 5 G; time constant, 163.84 ms; gain, 2 × 10⁵; and scale, 16.