Figure 2.

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) As in panel A but with no MEU. (C) As in panel A but with no HRP. (D) As in panel A but with no H₂O₂. (E) As in panel A but with no H₂O₂ and 32 μM catalase added. The spectrometer operating conditions were the same as those described in Figure 1.