In enzymology, a thyroid-hormone transaminase (EC 2.6.1.26) is an enzyme that catalyzes the chemical reaction

L-3,5,3'-triiodothyronine + 2-oxoglutarate ${\displaystyle \rightleftharpoons }$ 3-[4-(4-hydroxy-3-iodophenoxy)-3,5-diiodophenyl]-2-oxopropanoate + L-glutamate

Thus, the two substrates of this enzyme are L-3,5,3'-triiodothyronine and 2-oxoglutarate, whereas its two products are [[3-[4-(4-hydroxy-3-iodophenoxy)-3,5-diiodophenyl]-2-oxopropanoate]] and L-glutamate.

This enzyme belongs to the family of transferases, specifically the transaminases, which transfer nitrogenous groups. The systematic name of this enzyme class is L-3,5,3'-triiodothyronine:2-oxoglutarate aminotransferase. Other names in common use include 3,5-dinitrotyrosine transaminase, and thyroid hormone aminotransferase. It employs one cofactor, pyridoxal phosphate.

• Soffer RL, Hechtman P, Savage M (1973). "L-Triiodothyronine aminotransferase". J. Biol. Chem. 248 (4): 1224–30. doi:10.1016/S0021-9258(19)44286-5. PMID 4686924.