FIGURE 5.

Detection of HO^∙ using EPR spin-trapping spectroscopy in U937 cells. PMA induced POBN (4-pyridyl-1-oxide-N-tert-butylnitrone)-CH(CH₃)OH adduct EPR spectra: Differentiated U937 cells with 50 mM POBN in the absence (A, trace a) and presence of 200 nM PMA (A, trace b). POBN-CH(CH₃)OH adduct EPR spectra were measured after 30 min of sonication performed in the presence of 200 nM PMA. The lower panel (B) shows the EPR spectra as in A (trace b) in the absence (trace a) and presence of 400 U/mL superoxide dismutase (SOD).