The NADPH oxidase is a multicomponent enzyme that transfers electrons from NADPH to O2 to generate superoxide (O2 -), a key part of the phagocytic or neutrophilic respiratory burst response. Flavocytochrome b558 is the catalytic component of the phagocyte NADPH oxidase. It is a transmembrane heterodimer composed of a large glycoprotein, gp91phox (PHagocyte OXidase) and a smaller protein, p22phox. Upon cell stimulation, flavocytochrome b558 assembles with p67phox, p47phox, and the GTP-binding protein Rac and becomes activated to generate O2 -. Mutations in gp91phox, p22phox, or other components of the NADPH oxidase can result in chronic granulomatous disease, which is associated with significant morbidity and mortality due to a predisposition to recurrent bacterial and fungal infections.Synonyms: CYBA, Cytochrome b(558) alpha chain, Cytochrome b558 subunit alpha, Neutrophil cytochrome b 22 kDa polypeptide, Superoxide-generating NADPH oxidase light chain subunit, p22 phagocyte B-cytochrome, p22-phox