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(+) Peroxidase activity is inhibited by aminobenzohydrazide (By similarity). The NADPH oxidase activity is calcium-dependent. Hormone biosynthesis; thyroid hormone biosynthesis. Interacts with TPO and CYBA (By similarity). Interacts with TXNDC11. Localizes to the apical membrane of epithelial cells. Expressed in thyrocytes (at protein level). Specifically expressed in thyroid. By forskolin (at protein level). By thyrotropin. N-glycosylated. In the N-terminal section; belongs to the peroxidase family.