MECHANISM OF DIFFERENTIAL CATALYTIC EFFICIENCY OF 2 POLYMORPHIC FORMSOF HUMAN GLUTATHIONE-S-TRANSFERASE P1-1 IN THE GLUTATHIONE CONJUGATION OF CARCINOGENIC DIOL EPOXIDE OF CHRYSENE

The kinetics of the conjugation of glutathione (GSH) with i-1,2-dihydr oxy-3,4-oxy-1,2,3,4-tetrahydrochrysene (anti-CDE), the activated form of the widespread environmental pollutant chrysene, catalyzed by two n aturally occurring polymorphic forms of the pi class human GSH S-trans ferase (hGSTP1-1), has been investigated, The polymorphic forms of hGS TP1-1, which differ in their primary structure by a single amino acid in position 104, exhibited preference for the GSH conjugation of (+)-a nti-CDE, which is a far more potent carcinogen than (-)-anti-CDE. When concentration of anti-CDE was varied (5-200 mu M) and the GSH concent ration was kept constant at 2 mM, both hGSTP1-1(I104) and hGSTP1-1(V10 4) obeyed Michaelis-Menten kinetics, However, the V-max of GSH conjuga tion of anti-CDE was approximately 5.3-fold higher for the V104 varian t than for the I104 form, Calculation of catalytic efficiency (k(cat)/ K-m) thus resulted in a value for hGSTP1-1(V1O4), 28 nm(-1) s(-1), tha t was 7.0-fold higher than that for hGSTP1-1(I104), 4 mM(-1) s(-1). Th e mechanism of the differences in the kinetic properties of hGSTP1-1 i soforms toward anti-CDE was investigated by molecular modeling of the two proteins with GSH conjugation products in their active sites, Thes e studies revealed that the enantioselectivity of hGSTP1-1 for (+)-ant i-CDE and the differential catalytic efficiencies of the V104 and I104 forms of hGSTP1-1 in the GSH conjugation of (+)-anti-CDE were due to the differences in the active-site architecture of the two proteins, T he results of the present study, for the first time, provide evidence for the toxicological relevance of GSTP1-1 polymorphism in humans and suggest that the population polymorphism of hGSTP1-1 variants with dis parate enzyme activities may, at least in part, account for the differ ential susceptibility of individuals to environmental carcinogens such as anti-CDE and possibly other similar carcinogens. (C) 1997 Academic Press.