MOLECULAR-CLONING AND FUNCTIONS OF RAT-LIVER HYDROXYSTEROID SULFOTRANSFERASES CATALYZING COVALENT BINDING OF CARCINOGENIC POLYCYCLIC ARYLMETHANOLS TO DNA

Three sulfotransferases (STs) catalysing the metabolic activation of p otent carcinogenic polycyclic arylmethanols were purified from female Sprague-Dawley (SD) rat liver cytosol without loss of their enzyme act ivities in the presence of Tween 20 used for preventing the enzymes fr om aggregation during purification and identified as hydroxysteroid su lfotransferases (HSTs). All the purified HSTs, STa, STb, and STc, with different electric charges had an apparently equal size of subunit (3 0.5 kDa) and cross-reacted with polyclonal antibody raised against STa . Our study on molecular cloning of cDNA libraries from two female SD rat livers indicated that both contained cDNA inserts coding for 5 dif ferent HST subunits, consisting of 284-285 amino acid residues (M tau, 33 084-33 535) and sharing strong amino acid sequence identity (> 83% ). Of the 5 HST subunits, two had an identical amino acid sequence exc ept for only one amino acid residue, and the other two contained only 6 amino acid substitutions in their sequences.