Thyroid peroxidase is an enzyme normally found in the thyroid gland, which plays an important role in the production of thyroid hormones. Fabrication of thyroid hormones is conducted by the enzyme thyroid peroxidase, an integral membrane protein present in the apical (colloid-facing) plasma membrane of thyroid epithelial cells.

Thyroid peroxidase catalyzes two sequential reactions: Iodination of tyrosines on thyroglobulin  Synthesis of thyroxine or triiodothyronine from two iodotyrosines. Through the action of thyroid peroxidase, thyroid hormones accumulate in colloid, on the surface of thyroid epithelial cells. Remember that hormone is still tied up in molecules of thyroglobulin - the task remaining is to liberate it from the scaffold and secrete free hormone into blood.