TPO g TPo g METABOLIC STEP INHIBITOR HOI/g DIT H202 FDI H,O or T a lodide transport CIO, SCN- lumen I B lodination PTU MMI EOI C Coupling PTU MMI D Colloid resorption Colchicine, Li2+, Cytochalasin B E Proteolysis F Deiodination of DIT MIT Dinitrotyrosine G Deiodination of T4 PTU L og apical membran p cel E MIT DIT. 5de- odinase T4 T G ECF A basement membrane Mechanism of inhibition of thyroid hormone synthesis by thioureas