Glutathione Transferase Catalyzed Conjugation of Diol Epoxides Derived from Polycyclic Aromatic Hydrocarbons with Glutathione

Abstract

Abstract Human glutathione transferase isoenzymes (GST) Al-1, Ml-1 and Pl-1 have been incubated with each of the four stereoisomers of trans-3,4-dihydroxy 1,2-epoxy l,2,3,4-tetrahydrobenzo[c]phenanthrene [(+)- and anti- and (+)-and (-)-syn-BPhDE] and glutathione (GSH). The results demonstrate that all BPhDE isomers were substrates for all the GST isoenzymes studied. However, a marked variation in catalytic efficiencies (> 10-fold) was noted. The enantiomers with 1R,2S-absolute configuration [(+)-syn- and (-)-anti-BPhDE] were in general better substrates than the corresponding 1S,2R-epoxides. Overall, GSTA1-1 was the most active isoenzyme. In preliminary experiments, a number of racemic bay- and fjord-region diol epoxides (derived from chrysene, benzo[c]- and [g]chrysene, dibenzo[a,h]anthracene and picene) have been incubated with GSTP1-1 and the formation of GSH-conjugates estimated. The results show that the syn-diastereomers in general were better substrates than the anti diastereomers. Furthermore, the enantiomers with R,S-epoxide absolute configuration were preferentially conjugated, thus demonstrating a high degree of selectivity.