Nox enzymes in immune cells.

The nicotinamide adenine dinucleotide phosphate (NADPH) oxidase of phagocytes is a multi-component electron transferase that uses cytoplasmic NADPH to convert molecular oxygen to superoxide anion, consequently delivering reactive oxygen species to the site of invading microorganisms. Together with soluble factors and other phagocyte-derived agents, the resultant toxic species kill and degrade the ingested microbe. Flavocytochrome b (558), a heterodimeric protein composed of gp91 phox and p22 phox, is the membrane component of the NADPH oxidase and was previously thought to be uniquely expressed in phagocytes. Based on structural homology with gp91 phox, recent studies have defined a family of NADPH oxidase proteins (Nox) that is widely distributed throughout the plant and animal kingdoms and in many tissues in multicellular organisms. The goals of this review are to review features of the phagocyte NADPH oxidase that serve as a paradigm for exploiting oxidants for host defense, and to discuss contributions of other Nox proteins to innate immunity.