Dual oxidase 1 is an enzyme encoded by the DUOX1 gene. DUOX1 was first identified in the mammalian thyroid gland. In humans, two isoforms are found; hDUOX1 and hDUOX2. Human DUOX protein localization is not exclusive to thyroid tissue; hDUOX1 is prominent in airway epithelial cells and hDUOX2 in the salivary glands and gastrointestinal tract.Dual oxidases are characterized by a defining N-terminal, extracellular domain exhibiting considerable sequence identity with the mammalian peroxidases, a t