 an aryl sulfotransferase , whose cdna was isolated from the rat liver library , was found to catalyze bioactivation of minoxidil through n - o - sulfation and n - sulfation of a carcinogenic heterocyclic amine , iq , by expression in cos-1 cells . 
 cdna of a human ortholog also was isolated and characterized as a major minoxidil - activating enzyme in human liver . 
 another group of aryl sulfotransferases catalyzing o - sulfation of carcinogenic n - hydroxyarylamines was separated from livers of rats and humans . 
 these sulfotransferases have been shown to possess similar functional properties and also to relate immunochemically with each other . 
 current understanding on the primary structure of these sulfotransferases also is discussed.imagesfigure 2 . 
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