Figure 4

The NADPH Oxidase System. The assembly of the various subunits of NADPH oxidase is shown in the figure, while the molecular genetics, rough prevalence, inheritance pattern and chromosomal localization of CGD subtypes are shown in the bottom of the figure. There are several components of NADPH oxidase: of these the cytochrome-b₅₅₈ heterodimer is located in the membrane and consists of the gp91^phox and p22^phox units, while three cytosolic components exist- including the p67^phox , p47^phox and a p40^phox. Following cellular activation, the soluble cytosolic components, p67^phox , p47^phox , and a p40^phox , move to the membrane and bind to components of the cytochrome-b₅₅₈ heterodimer. This is also accompanied by the binding of the GTPase protein, Rac, culminating by unclear mechanisms in flavocytochrome activation. This catalyzes the transfer of electrons from NADPH to oxygen, resulting in the formation of superoxide in the extracellular compartment (phagolysosome). Subsequent reactions via superoxide dismutase (SOD), catalase or myeloperoxidase (MPO), occurring in the phagolysome, can result in formation of H₂O₂, H₂O or HOCl^- respectively.