Propylthiouracil(6-Propyl-2-thiouracil) is a thyroperoxidase and 5'-deiodinase inhibitor. Target: Thyroperoxidase (TPO)Propylthiouracil (PTU) is a thiouracil-derived drug used to treat hyperthyroidism (including Graves' disease) by decreasing the amount of thyroid hormone produced by the thyroid gland [1]. The antithyroid drug 6-propylthiouracil (PTU) was shown to have an unexpectedly prolonged inhibitory effect on iodination in the thyroid glands of rats. Eighteen hours after injection of a relatively small dose, iodination in the thyroid remained inhibited by more than 90% [2]. PTU inhibits the enzyme thyroperoxidase, which normally acts in thyroid hormone synthesis by oxidizing the anion iodide (I-) to iodine (I0), facilitating iodine's addition to tyrosine residues on the hormone precursor thyroglobulin. This is one of the essential steps in the formation of thyroxine (T4). PTU does not inhibit the action of the sodium-dependent iodide transporter located on follicular cells' basolateral membranes. Inhibition of this step requires competitive inhibitors, such as perchlorate and thiocyanate. From Wikipedia.
References:
[1]. Nakamura, H., et al., Comparison of methimazole and propylthiouracil in patients with hyperthyroidism caused by Graves' disease. J Clin Endocrinol Metab, 2007. 92(6): p. 2157-62.
[2]. Taurog, A. and M.L. Dorris, A reexamination of the proposed inactivation of thyroid peroxidase in the rat thyroid by propylthiouracil. Endocrinology, 1989. 124(6): p. 3038-42.