Nox2 is the catalytic, membrane-bound subunit of NADPH oxidase. It is inactive until it binds to the membrane-anchored p22"phox", forming the heterodimer known as flavocytochrome b558. After activation, the regulatory subunits p67"phox", p47"phox", p40"phox" and a GTPase, typically Rac, are recruited to the complex to form NADPH oxidase on the plasma membrane or phagosomal membrane. Nox2 itself is composed of an N-terminal transmembrane domain that binds two heme groups, and a C-terminal domain that is able to bind to FAD and NADPH.