Fig. 4.

CW X-Band EPR spectra of PhnZ recorded at 10 K. The spectrum of the l-ascorbate–reduced PhnZ (upper spectrum) shows signals characteristic of an AF-coupled Fe₂^II/III center. Addition of 3 mM (R)-OH-AEP to the l-ascorbate–reduced PhnZ (lower spectrum) perturbs the spectral features, leading to an increase in anisotropy and decrease in linewidth, suggesting that the substrate binds to the diiron site. Experimental conditions: microwave frequency = 9.48 GHz, microwave power = 2 mW, and modulation amplitude = 1 mT.