Characterization of human iodothyronine sulfotransferases

Sulfation is an important pathway of thyroid hormone metabolism that facilitates the degradation of the hormone by the type I iodo-thyronine deiodinase, but little is known about which human sulfo-transferase isoenzymes are involved. We have investigated the sul-fation of the prohormone T4, the active hormone T3, and the metabolites rT3 and 3,39-diiodothyronine (3,39-T2) by human liver and kidney cytosol as well as by recombinant human SULT1A1 and SULT1A3, previously known as phenol-preferring and monoamine-preferring phenol sulfotransferase, respectively. In all cases, the sub-strate preference was 3,39-T2.. rT3. T3. T4. The apparent Km values of 3,39-T2 and T3 [at 50 mmol/L 39-phosphoadenosine-59-phos-phosulfate (PAPS)] were 1.02 and 54.9 mmol/L for liver cytosol, 0.64 and 27.8 mmol/L for kidney cytosol, 0.14 and 29.1 mmol/L for SULT1A1, and 33 and 112 mmol/L for SULT1A3, respectively. Th