Electron Paramagnetic Resonance Spectroscopy of Metalloenzymes

EPR spectra were acquired on a Brüker EMX X-band spectrometer at 77 K using a quartz finger dewar, at 3.6 to 20 K using an Oxford Instruments liquid helium cryostat, or at 293 K using an aqueous flat cell. All spectra were acquired at 9.3–9.9 GHz, 100 kHz modulation frequency. Other acquisition parameters for dimanganese-Y• NrdF were: 1) at 77 K, 1 mW power, 1.5 G modulation amplitude, 2.52 × 10⁴ gain, 10.24 ms time constant; 2) at 20 K, 0.2 mW power, 4 G modulation amplitude, 2.52 × 10⁴ gain, 5.12 ms time constant; and 3) at 3.6 K, 0.1 mW power, 4 G modulation amplitude, 1.26 × 10⁴ gain, 20.48 ms time constant. Other parameters for Fe^III₂-Y• NrdF at 77 K were 50 μW power, 1.5 G modulation amplitude, 2.52 × 10³ gain, 5.12 ms time constant. At 293 K, the parameters for NrdI_sq were 6.3 mW power, 1.26 × 10⁴ gain, 1.5 G modulation amplitude, 10.24 ms time constant, and for Fe^III₂-Y• NrdF, 8.0 mW power, 1.26 × 10⁴ gain, 1.5 G modulation amplitude, 10.24 ms time constant (23 (link)).