(A) The NADPH oxidase complex consists of two membrane bound subunits (gp91phox and p22phox) and three cytosolic subunits (p67phox, rac, and p47phox), which upon activation translocate and associate with the membrane bound subunits (B). Upon activation, the NADPH oxidase complex transfers electrons from NADPH substrate to molecular oxygen, thus producing superoxide. During this process NADPH oxidase also pumps protons across the membrane.