Thyroid Peroxidase (TPO) is a critical thyroid enzyme responsible for catalyzing the biosynthesis of thyroid hormones. TPO is a glycoprotein composed of a large extracellular domain and a transmembrane domain. It is primarily located on the apical membrane of thyroid follicular cells, where it catalyzes the iodination and coupling reactions, adding iodine atoms to tyrosine residues to form thyroid hormone precursors. The activity of TPO is regulated by Thyroid-Stimulating Hormone (TSH). The TPO gene is specifically expressed in the thyroid. Mutations in the TPO gene or the production of anti-TPO antibodies due to autoimmune responses may lead to thyroid dysfunction, such as Hashimoto's thyroiditis and Graves' disease.