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. Hormone biosynthesis; thyroid hormone biosynthesis. Interacts with TXNDC11, TPO and CYBA. Localizes to the apical membrane of epithelial cells. Expressed in thyrocytes and tracheal surface epithelial cells (at protein level). Expressed in thyroid, trachea, bronchium, and to a lower extent, in placenta, testis, prostate, pancreas and heart. Widely expressed in fetal tissues. By forskolin (at protein level). By thyrotropin and the Th2-specific cytokines IL-4 and IL-13. N-glycosylated. In the N-terminal section; belongs to the peroxidase family. Truncated C-terminus.