Acts as a substrate for the production of iodinated thyroid hormones thyroxine (T4) and triiodothyronine (T3) (By similarity). The synthesis of T3 and T4 involves iodination of selected tyrosine residues of TG/thyroglobulin followed by their oxidative coupling (By similarity). Following TG re-internalization and lysosomal-mediated proteolysis, T3 and T4 are released from the polypeptide backbone leading to their secretion into the bloodstream (Probable). One dimer produces 7 thyroid hormone molecules (By similarity). Monomer (PubMed:12782676). Homodimer (via ChEL region); occurs in the endoplasmic reticulum and is required for export to the Golgi apparatus (PubMed:19276074, PubMed:12782676). Homooligomer; disulfide-linked; stored in this form in the thyroid follicle lumen (By similarity). Secreted into the thyroid follicle lumen (PubMed:12782676). Localizes to colloid globules, a structure formed in the thyroid follicle lumen consisting of cross-linked TG arranged in concentric layers (PubMed:12782676). Specifically expressed in the thyroid gland. The cholinesterase-like (ChEL) region is required for dimerization and export from the endoplasmic reticulum. Iodinated on tyrosine residues by TPO (By similarity). There are 4 pairs of iodinated tyrosines used for coupling: acceptor Tyr-25 is coupled to donor Tyr-150 or Tyr-235, acceptor Tyr-2572 is coupled to donor Tyr-2539, acceptor Tyr-2764 in monomer 1 is coupled to donor Tyr-2764 in monomer 2 and acceptor Tyr-1310 in monomer 1 is coupled to donor Tyr-109 in monomer 2 (By similarity). Sulfated tyrosines are desulfated during iodination. Undergoes sequential proteolysis by cathepsins to release thyroxine (T4) and triiodothyronine (T3) hormones (PubMed:12782676). In the thyroid follicle lumen, cross-linked TG (storage form) is solubilized by limited proteolysis mediated by cathepsins CTSB and/or CTSL (PubMed:12782676). Partially cleaved TG is further processed by CTSK/cathepsin K and/or CTSL resulting in the release of T4 (PubMed:12782676). Following endocytosis, further processing occurs leading to the release of T3 and more T4 hormones (Probable). Congenital goiter (cog) is caused by a hypertrophy of the thyroid gland (goiter). Mice have reduced growth rate, hypothyroidism due to reduced production of the thyroid hormones thyroxine (T4) and triiodothyronine (T3), and lack colloid globules, a structure in the thyroid follicle lumen that is enriched in Tg/thyroglobulin. Belongs to the type-B carboxylesterase/lipase family. The cholinesterase-like (ChEL) region lacks the Ser residue of the catalytic triad suggesting that it has no esterase activity.