Sulfation is an intriguing pathway of thyroid hormone metabolism since
it facilitates the degradation of the hormone by the type I deiodinas
e (D1). This study reports the preliminary characterization of iodothy
ronine sulfotransferase activities of rat and human liver cytosol and
recombinant rSULT1C1 and hSULT1A1 isoenzymes. All these enzyme prepara
tions catalyzed the sulfation of-in decreasing order of efficiency-3,3
'-diiodothyronine (3,3'-T2) > 3,3',5-triiodothyronine (T3) approximate
to 3,3',5'-triiodothyronine (rT3)> thyroxine (T4). 3,3'-T2 sulfotrans
ferase activity was found to be higher in male than in female rat live
r, which has also been shown by others for the expression of rSULT1A1
and rSULT1C1. No sulfation of iodothyronines was observed with rSULT1A
1. Different phenol derivatives were found to be potent inhibitors of
the sulfation of 3,3'-T2 by native and recombinant sulfotransferases,
with pentachlorophenol and 2,4,6-tribromophenol being the most potent.
The inhibitions exerted by the different phenols on 3,3'-T2 sulfation
by rSULT1C1 correlated better with the effects observed in male than
with those in female liver. A strong correlation was also observed bet
ween the inhibition profiles of human liver cytosol and hSULT1A1. Thes
e results suggest that: (1) rSULT1C1 is an important isoenzyme for the
sulfation of thyroid hormone in male rat liver; (2) another isoenzyme
with similar properties, perhaps rSULT1B1, is responsible for thyroid
hormone sulfation in female rat liver and may also contribute to this
process in male rat liver; and (3) hSULT1A1 is an important isoenzyme
for thyroid hormone sulfation in human liver. (C) 1998 Elsevier Scien
ce Ireland Ltd. All rights reserved.