Biochemistry · Enzyme
Thyroid peroxidase (TPO) !
The thyroid's key enzyme: it oxidises iodide, attaches it to thyroglobulin and joins iodinated tyrosines to form T4 and T3.
Updated 2026-11-01
Key facts
- A haem protein of the thyrocyte apical membrane; it works at the interface with the colloid.
- It uses hydrogen peroxide made by the dual oxidase DUOX2.
- It does three things: oxidises iodide, iodinates thyroglobulin tyrosines (MIT and DIT) and couples DIT + DIT → T4 and MIT + DIT → T3.
- It is the main autoantigen of Hashimoto thyroiditis (anti-TPO antibodies).
- There is no human ligand-bound structure in the PDB, so this page shows no 3D model.
- Also called
- Iodide peroxidase
- EC number
- 1.11.1.8
- Genes
- TPO
Regulation
- TSH raises its expression and H₂O₂ production (through cAMP).
- An acute iodide excess holds organification back (Wolff–Chaikoff effect), a temporary brake.
Inhibitors and toxins
- Methimazole and carbimazole (thionamides)
- Propylthiouracil (also inhibits type 1 deiodinase)
Clinical notes
- Thionamides block TPO and are used in the hyperthyroidism of Graves disease.
- Anti-TPO antibodies are positive in most Hashimoto thyroiditis and in many cases of Graves disease.
- TPO mutations are a common cause of dyshormonogenesis: congenital hypothyroidism with goitre.
Pathways
Related conditions
Related
Test yourself
Think of the answer, then tap the question to see it.
Which three reactions does thyroid peroxidase catalyse?
It oxidises iodide, iodinates thyroglobulin tyrosines and couples the iodotyrosines to form T4 and T3.
Where does TPO get its hydrogen peroxide?
From the dual oxidase DUOX2, on the thyrocyte apical membrane.
Which antithyroid drugs inhibit TPO?
The thionamides: methimazole, carbimazole and propylthiouracil.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: TPO: Thyroid peroxidase (human) (UniProt, 2026); TPO gene: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); Congenital hypothyroidism: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).
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Representative model, for educational purposes only.