Very active and specific thyroid hormone transporter. Stimulates cellular uptake of thyroxine (T4), triiodothyronine (T3), reverse triiodothyronine (rT3) and diidothyronine. Does not transport Leu, Phe, Trp or Tyr. Homodimer. Highly expressed in liver and kidney. Belongs to the major facilitator superfamily. Monocarboxylate porter (TC 2.A.1.13) family.