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. Interacts with TXNDC11, TPO and CYBA. Localizes to the apical membrane of epithelial cells. Expressed in thyrocytes (at protein level). N-glycosylated. In the N-terminal section; belongs to the peroxidase family.