thyroid peroxidase

Thyroid peroxidase is the master assembler on the colloid workbench. It takes plain, unreactive iodide and activates it, then welds it onto the protein scaffold and joins the pieces into finished hormone.

Sitting at the colloid-facing surface of the follicular cell, this enzyme performs three linked jobs using hydrogen peroxide: it oxidizes iodide into a reactive form, attaches that iodine to tyrosine units on thyroglobulin (a step called organification), and then couples two iodinated tyrosines together to create thyroxine or triiodothyronine. Each of these steps is essential, and a defect in the enzyme can cause an inherited form of hypothyroidism with goiter.

Thyroid peroxidase matters clinically in two big ways. It is the main target of antithyroid drugs such as methimazole and propylthiouracil, which block hormone synthesis in overactive glands. It is also the chief antigen in autoimmune thyroid disease, so antibodies against it (anti-TPO antibodies) are a common blood test pointing to Hashimoto’s thyroiditis or autoimmune Graves’ disease.