Is NADPH oxidase activity regulated by free radicals

NADPH oxidase is a ubiquitous enzyme that is the main producer of superoxide anions in cells. In phagocytes, it is constituted by the assembly of four cytosolic (p67phox, p47phox, p40phox and Rac) and two membrane (p22phox and Nox2) proteins. In response to pro-inflammatory mediators, the NADPH oxidase complex is activated. In cells, arachidonic acid (cis-AA), released by activated phospholipase A2, plays also a role in activation of the NADPH oxidase. We are currently investigating how the production of superoxide, precursor of all ROS and hence of oxidative stress generated by the NADPH oxidase are regulated. After having investigated the role of arachidonic acid and protein assembly, we turned to the regulation by free radicals. We used gamma and pulse radiolysis to produce O 2 •– and OH radicals. On a cell-free system, we showed that during its assembly, the system passes through sub-states of different sensitivities. The regulatory activity of each sub-unit varies with their oxidation state. We are now investigating the sensitivity of human neutrophils toward oxidation by free radicals.