Isolation of the respiratory burst oxidase: The role of a flavoprotein component

The article reviews the enzymatic and electron transfer properties of a low-potential FAD-dependent flavoprotein that is a component of the NADPH-dependent O₂^- · -generating respiratory burst oxidase of phagocytes. Current methods available for isolation of the respiratory burst oxidase and the flavo-protein component of the complex are also reviewed. These studies and data obtained from affinity-labeling of respiratory burst oxidase components, suggest that the flavoprotein has a molecular weight of 65-67 kD. The prevailing evidence suggests that the flavoprotein functions as a dehydrogenase/electron transferase and can directly catalyse NADPH-dependent O₂^- · formation when isolated. However, in neutrophil plasma membranes, the prevailing evidence suggests that the flavoprotein functions primarily to transfer electrons from NADPH to cytochrome b_-245 and that this latter redox component is the catalytic side of O₂^- · formation. A working model for the arrangement of the flavorprotein and cytochrome b_-245 components of the respiratory burst oxidase in neutrophil membranes is proposed.