Experimental and simulated CW-EPR spectra. (a) nNOSOX(−BH4, −l-arg), (b) nNOSOX(−BH4, +l-arg), (c) nNOSFQ(+BH4, +l-arg), and (d) nNOSFQ(+BH4, −l-arg). The black lines are experimental spectra and the red are simulations using the parameters in Table 1. The CW-EPR spectra were measured at 10 K using: microwave frequency, 9.46 GHz; microwave power, 0.21 mW; field modulation amplitude, 2 mT at 100 kHz. The region of strong signals from BH4 radicals are blanked out in (c–d).