Fig. 2

Schematic representation of NADPH oxidases present in the intestine. NOX1 is a multi-subunit complex with a catalytic core composed of two transmembrane proteins: p22^phox and NOX1. In order to convert molecular oxygen to superoxide, NOX1 heterodimerizes with p22^phox, two cytosolic subunits termed NOXA1 and NOXO1, and activated RAC1 GTPase. The NOX2 heterodimer is composed of p22^phox and gp91^phox (also called NOX2). The NOX2 complex is typically inactive in resting cells, but when stimulated the cytosolic subunits p40^phox, p47^phox and p67^phox and activated RAC assemble with NOX2-p22^phox to reduce oxygen to superoxide by electron shuttling. DUOX2 (also known as thyroid oxidase) is an EF hand motif containing protein that forms a membrane-bound heterodimer with its maturation factor DUOXA2 and produces H₂O₂ in a Ca²⁺-dependent manner.