Mechanism of action of prophylthiouracil -

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