<prompt> Mechanism of action of prophylthiouracil -Prevents synthesis of thyroglobulinPrevents iodine trappingPrevents release of T4 T3Inhibits coupling  <response>: Ans. is d i.e., Inhibits coupling o Propylthiouracil blocks thyroxine synthesis by inhibiting thyroid peroxidase, and preventing oxidation of iodide iodotyrosyl residues, there by1 Inhibit iodination of tyrosine residue in thyroglobulin.2 Inhibit coupling of MIT and DIT to form T3 T4.o Propylthiouracil also inhibit the peripheral conversion of T4 to T3 