Generates hydrogen peroxide which is required for the activity of thyroid peroxidase/TPO and lactoperoxidase/LPO. Plays a role in thyroid hormones synthesis and lactoperoxidase-mediated antimicrobial defense at the surface of mucosa. May have its own peroxidase activity through its N-terminal peroxidase-like domain. H(+) + NADH + O2 = H2O2 + NAD(+) H(+) + NADPH + O2 = H2O2 + NADP(+) The NADPH oxidase activity is calcium-dependent. Peroxidase activity is inhibited by aminobenzohydrazide (By similarity). Hormone biosynthesis; thyroid hormone biosynthesis. Heterodimer with DUOXA2; disulfide-linked. Interacts with TXNDC11, TPO and CYBA. Localizes to the apical membrane of epithelial cells. Localizes on internal membrane structures under resting conditions, translocates to the plasma membrane and cell-cell junctions upon challenge with enteric pathogens. Expressed in thyroid, and the digestive tract especially in stomach, cecum and sigmoidal colon (at protein level). Expressed in thyroid. By forskolin and down-regulated by iodide (at protein level). By insulin. N-glycosylated. In the N-terminal section; belongs to the peroxidase family.