Neutrophil oxygen reduction: The enzymes and the products

The human neutrophil generates a non-mitochondrial respiratory burst by the activation of a NADPH-oxidase, whose electron source, NADPH, is generated in the hexose monophosphate shunt. The reduction product, ₂⁻, is further reduced to H₂O₂, which upon the action of myeloperoxidase, oxidizes halide to form reactive chloramines and hypochlorous acid. The elusive hydroxyl radical, or kindred species, also appears as a product of the burst, but this chemistry has not been elucidated. NADPH-oxidase is a complex activity, comprised of at least two components: a low potential b cytochrome and a flavoprotein. Partial characterization and isolation of this electron transport system has been accomplished and serves as an intense focus of current research. The recent demonstration that the oxidase may be activated in a broken cell preparation should not only define mechanisms of burst activation, but this methodology should provide a powerful approach towards identifying the components of the NADPH-oxidase apparatus.