CHARACTERIZATION OF IODOTHYRONINE SULFOTRANSFERASE ACTIVITY IN RAT LIVER

Sulfation is an important pathway in the metabolism of thyroid hormone because it strongly facilitates the degradation of the hormone by the type I iodothyronine deiodinase. However, little is known about the properties and possible regulation of the sulfotransferase(s) involved in the sulfation of thyroid hormone. We have developed a convenient method for the analysis of iodothyronine sulfotransferase activity in tissue cytosolic fractions, using radioiodinated 3,3′-diiodothyronine (3,3′-T2) as the preferred substrate, unlabeled 3′-phosphoadenosine-5′-phosphosulfate (PAPS) as the sulfate donor, and Sephadex LH-20 minicolomns for separation of the products. We found that iodothyronine sulfotransferase activity in rat liver cytosol is 1) higher in male than in female rats; 2) optimal at pH 8.0; 3) characterized (at 50 μm PAPS and pH 7.2) by apparent Michaelis-Menton (Km) values for 3,3′-T2 of 1.77 and 4.19 μm, and Vmax values of 1.94 and 1.45 nmol/min per mg protein in male and female rats, respectively; 4...