FIG. 5.

Alveolar macrophages produce peroxynitrite. When alveolar macrophages are stimulated to produce both superoxide and nitric oxide, peroxynitrite is quantitatively produced (611) as evidenced by the amount of nitric oxide and superoxide produced and the amount of oxygen consumed. Extracellular addition of superoxide dismutase (SOD) in high concentrations does not significantly reduce the amount of peroxynitrite formed and instead serves as a catalyst of tyrosine nitration. This suggests that superoxide produced at the membrane surface and nitric oxide diffusing through the membrane react at the membrane interface so quickly that SOD in the bulk phase cannot compete.