Fig. 1.

Schematic representation of the active NAPDH–oxidase complex. The flavocytochrome b₅₅₈ consists of two components, gp91^phox and p22^phox, which reside in the membrane as a heterodimer. On activation of the cell, a complex of cytosolic components (see text) assembles at the membrane and induces electron transport from NADPH to molecular oxygen via flavin adenine dinucleotide (FAD) and haem groups. gp91^phox has also recently been shown to act as a voltage-gated H + channel which could participate in charge compensation. Termination of activity may be regulated by the GTPase, p21rac.