CONJUGATION OF ANTI-DIHYDRODIOL EPOXIDES OF BENZO[A]PYRENE, CHRYSENE, BENZO[C]PHENANTHRENE AND DIBENZ[A,H]ANTHRACENE WITH GLUTATHIONE CATALYZED BY CYTOSOL AND BY THE MU-CLASS GLUTATHIONE TRANSFERASE HTP-II FROM RAT-LIVER

The (+/-)-anti-dihydrodiol epoxides (DE) of benzo[a]pyrene (BP), chrysene (Chr), benzo[c]phenanthrene (BcPh) and dibenz[a,h]anthracene (DBA) were incubated in the presence of glutathione (GSH) with hepatic cytosol from untreated and Aroclor 1254 pretreated rats and with the Mu-class glutathione transferase (GST) HTP II from rat liver. The diastereoisomeric GSH conjugates formed were separated, identified and quantified by HPLC employing synthetic reference compounds. All (+/-)-anti-dihydrodiol epoxides investigated in this study were proven to be substrates of the cytosolic GSTs. The highly mutagenic and carcinogenic (+)anti-DE with R,S,S,R absolute configuration was preferentially conjugated in the case of BP and Chr. Aroclor 1254 pretreatment increased the turnover 2-3-fold and changed the enantioselectivity. The previously purified GST HTP II exhibited a high degree of enantioselectivity (greater than or equal to 95%) towards the R,S,S,R-configurated enantiomer in the case of the bay-region (+/-)-anti-BPDE, (+/-)-anti-ChrDE and (+/-)-anti-DBADE, whereas in the case of the fjord-region (+/-)-anti-BcPhDE both enantiomers were good substrates. The contribution of HTP II to the enzymatic activity of the Cytosolic GST pool was estimated to be in the range of 11-32%. In agreement with previous results, the observed enantioselectivity of the purified enzyme seems to be of minor significance considering the total GST pool in the liver.