Sulfation of iodothyronines by human sulfotransferase 1C1 (SULT1C1)

Sulfation is an important component of human thyroid hormone metabolism. Th e role of the human sulfotransferase 1C1 (SULT1C1) known. Because SULT1C1 i s present in the adult thyroid, intra-thyroidal sulfation of thyroid hormon es and their metabolites might occur. We tested this hypothesis by determin ing the ability of recombinant human SULT1C1 to catalyze iodothyronine sulf ation. Apparent K-m values for 3,3',5-triiodothyronine (T-3), 3,3'-diiodoth yronine (3,3'-T-2), 3',5',3-triiodothyronine (rT(3)), and 3,3',5,5'-tetraio dothyronine (T-4) with SULT1C1 were 28.7, 10.3, 1.0.2, and 59.3 muM, respec tively. Thermal stability and responses to inhibitors also were tested with T-3 as the substrate. Enzyme aliquots were measured simultaneously to dete rmine SULT1C1 substrate preferences at optimal iodothyronine concentrations . SULT1C1 activity obtained with T-3 was used as 100%, and the activities w ith 3,3'-T-2, rT(3), T-4, and 3,5-diiodothyronine (3,5-T-2) were 614, 314, 25, and 4%, respectively. We report for the first time the characterization of human SULT1C1 with T-3 and the preferences of the enzyme for various io dothyronines. The presence of SULT1C1 in the adult thyroid gland raises the possibilities that the enzyme can contribute to intraglandular thyroid hor mone processing and iodide reutilization. (C) 2000 Elsevier Science Inc.