Figure 12.

X-band (9.38 GHz) CW EPR (A) and Q-band (34.0 GHz) pseudo-modulated electron spin-echo detected field-swept EPR spectra (B) of dithionite-reduced wild-type PqqE. The top black trace is experimental spectrum, while the top red trace is the simulated spectrum involving the contributions from three reduced clusters, i.e., the RS cluster with g = [2.040, 1.927, 1.897], the AuxII cluster with g = [2.059, 1.940, 1.903] and the [2Fe–2S]⁺ cluster with g = [2.004, 1.958, 1.904]. The ratio of these three clusters employed for the simulation is 1 : 1 : 1. The CW EPR spectra were recorded at 10 K, with 0.02 mW microwave power (no saturation). The Q-band EPR spectra were recorded at 10 K by using a two-pulse sequence of π/2-τ-π-τ-echo, with π/2 = 12 ns and τ = 300 ns. The modulation amplitude of 3.0 mT was used to convert the absorption spectra to the pseudo-modulated spectra in (B).

The bottom three sets of spectra show the corresponding EPR signal for each cluster, with the RS cluster, the AuxII cluster and the [2Fe–2S]⁺ cluster signals obtained from dithionite-reduced samples of RS-only variant (Figure 3), AuxI/AuxII (Figure 6) and RS/AuxI (Figure S13).