EPR spectra of Co-reconstituted AtzC. (A) Co(II)-reconstituted AtzC (475 μM). (B) Simulation of A with geff values of 5.18, 3.93, and 2.24. (C) Co(II)-reconstituted AtzC (475 μM) with the addition of 1 mM 5-azacytosine. (D) Simulation of C with geff values of 5.11, 4.02, and 2.25. Extraneous Cu(II) signals for both panels A and C are evident in the g = 2 region. Buffer for the samples was 25 mM MOPS (pH 6.9). EPR parameters: temperature, 10.0 K; microwave power, 781 μW; modulation amplitude, 10 G; microwave frequency, 9.604 GHz.