NADPH oxidase is an enzyme that catalyzes the production of superoxide from oxygen and NADPH. It is a complex enzyme consisting of two membrane-bound components and three components in the cytosol, plus rac 1 or rac 2. Activation of the oxidase involves the phosphorylation of one of the cytosolic components. Recent crystallography data indicate that the tail of this cytosolic component lies in a groove between two Src homology 3 domains and, when phosphorylated, the tail leaves the groove and is replaced by the tail of one of the membrane-bound components. Chronic granulomatous disease is an inherited immune deficiency caused by the absence of one of the components of the oxidase.
