Detoxification of polycyclic aromatic hydrocarbon diol epoxides by human glutathione transferases:: Efficiency of conjugation in intact cells relative to purified enzymes

V79MZ cells expressing human glutathione transferases (hGST) have been constructed and used to study glutathione (GSH) conjugation of anti-diol epoxides (DEs) of dibenzo[a,1]pyrene (DBPDE), and benzo[a]pyrene (BPDE). Cells expressing hGSTM1-1 were more effective with (-)-anfi-DBPDE than hGSTP1-1. The opposite was observed with (+)-anfi-BPDE. Rates of cellular DE uptake and solvolysis in conjunction with oil/water partition coefficients were used to calculate the amount of DEs available for GST-catalyzed conjugation in the cells. Using this information and the known values of k(cat)/K-M for (+)-anfi-BPDE and (-)-anfi-DBPDE with purified hGSTs, it was calculated that up to 3% of available (+)-anfi-BPDE forms GSH conjugates whereas the corresponding figure with the less reactive and more lipophilic (-)-anfi-DBPDE was about 19%. In part, the lower fraction of (+)-anti-BPDE conjugated in cells is probably due to rapid and competing reactions with cellular constituents.