Deoxygenated RumA (0.1 mm), 5-deazariboflavin (0.0056 mm), and EDTA (0.05 mm) were irradiated briefly at room temperature and then frozen for EPR. The inset shows how two separate line shapes, both with parameters (Table I) characteristic of a [4Fe4S]1+ center, might combine to give the observed line shape. The experimental EPR spectrum was recorded at 12 K and the instrument parameters were: microwave power, 10 mW; modulation amplitude, 1.6 mT; sweep rate, 12.5 mT/min; time constant, 0.5 s.