Figure 1.

EPR fast-flow spectra of the MEU radical produced in a system of MEU, H₂O₂, and HRP. The concentrations of MEU, H₂O₂, and HRP in the flat cell were 1.75 mM, 13 mM, and 0.46 μM, respectively. Oxygen was removed from the reagent solutions by bubbling 99.9999% pure nitrogen gas through them. Equal volumes of a solution of MEU/H₂O₂ and a solution of HRP in 100 mM phosphate buffer, pH 7.4, were mixed milliseconds before they entered the flat cell at a total flow rate of 40 mL/min. The final solution also contained 10% v/v ethanol and 0.10 mM DTPA. (A) Complete system with MEU, H₂O₂, and HRP. (B) Simulated EPR spectrum with the coupling constants given in Table 1. (C) Residual plot produced when simulated spectrum B is subtracted from experimental spectrum A. EPR spectra were recorded at 20 mW microwave power, 0.10 mT field modulation, 5.0 mT field sweep width, 164 ms time constant, 82 ms conversion time, and 33 scans of 1024 data points.