FIG. 2.

Electron paramagnetic resonance spectra of the tungsten center and the iron-sulfur cluster in substrate-reduced WOR5. The enzyme, 8 mg/ml, was incubated with 10 mM hexanal for 1 h at 60°C. Trace A is a low-temperature spectrum (15 K) dominated by the signal from the [4Fe-4S]¹⁺ cluster; trace B is a high-temperature spectrum (50 K) from W(V) in tungstobispterin. Electron paramagnetic resonance conditions: microwave frequency, 9,533 MHz; microwave power, 50 mW (A) and 200 mW (B); modulation frequency, 100 kHz; modulation amplitude, 6.3 Gauss (A) and 3.2 Gauss (B).