Superoxide, nitric oxide and peroxynitrite production by macrophages under different physiological oxygen tensions.

Macrophages count on two O-consuming enzymes to form reactive radical species: NAPDH oxidase 2 (Nox2) and nitric oxide synthase 2 (inducible isoform, iNOS) that produce superoxide radical (O) and nitric oxide (NO), respectively. If formed simultaneously, the diffusion-controlled reaction of O and NO yields peroxynitrite, a potent cytotoxic oxidant. In human tissues and cells, the oxygen partial pressure (pO) normally ranges within 2-14 %, with a typical average pO value for most tissues ca.