Importance of peri-interactions on the stereospecificity of rat hydroxysteroid sulfotransferase STa with 1-arylethanols.

Abstract

Hydroxysteroid (alcohol) sulfotransferases catalyze the sulfation of polycyclic aromatic hydrocarbons (PAHs) that contain benzylic hydroxyl functional groups. This metabolic reaction is often a critical step in the activation of a hydroxyalkyl-substituted PAH to form an electrophilic metabolite that is capable of forming covalent bonds at nucleophilic sites on DNA, RNA, and proteins. Since hydroxyalkyl-substituted PAHs are often metabolically formed by the stereoselective enzymatic hydroxylation of a benzylic position on an alkyl-substituted PAH, we have investigated the possibility that the sulfation of hydroxyalkyl aromatic hydrocarbons is also stereoselective. Homogeneous preparations of rat hepatic hydroxysteroid (alcohol) sulfotransferase STa were utilized to investigate the stereoselectivity of its catalytic function with the enantiomers of model 1-arylethanols. While only minimal stereoselectivity was observed for the catalytic efficiency of STa with the enantiomers of 1-(2-naphthyl)ethanol and 1-acenaphthenol, the enzyme was stereospecific for (R)-(+)-1-(1-naphthyl)ethanol, (R)-(+)-1-(1-pyrenyl)ethanol, and (R)-(+)-1-(9-phenanthryl)ethanol as substrates. Moreover, (S)-(-)-1-(1-naphthyl)ethanol, (S)-(-)-1-(1-pyrenyl)ethanol, and (S)-(-)- 1-(9-phenanthryl)ethanol were competitive inhibitors of STa. Structural and conformational analyses of these 1-arylethanols indicated that steric interactions between the substituents on the benzylic carbon and the hydrogen in the peri-position on the aromatic ring system were important determinants of the stereospecificity of the enzyme with these molecules. The findings presented here have implications for the more accurate prediction of the ability of hydroxyalkyl-substituted PAHs to be activated via metabolic formation of electrophilic sulfuric acid esters.