POLYMORPHISM IN THE GLUTATHIONE CONJUGATION ACTIVITY OF HUMAN ERYTHROCYTES TOWARDS ETHYLENE DIBROMIDE AND 1,2-EPOXY-3-(P-NITROPHENOXY)-PROPANE

In this study a polymorphism in the conjugating activity of human eryt hrocyte cytosol towards the dihaloethane, ethylene dibromide (EDB; 1,2 -dibromoethane) was found. Two out of 12 human erythrocyte cytosols di d not catalyze the formation of glutathione (GSH) conjugates of [1,2-C -14]EDB. Ten cytosols formed the S,S'-ethylenebis(GSH) conjugate at a rate ranging from 0.5 to 3.2 (mean 1.76+/-0.95) pmol min(-1)(mg protei n)(-1). The activity of the cytosols towards EDB was compared with the activity towards 1,2-epoxy-3-(p-nitrophenoxy)-propane (EPNP) and 1-ch loro-2,4-dinitrobenzene (CDNB). The GSH conjugates formed from EDB, EP NP and CDNB were all quantified by HPLC. Every cytosol was active with the classical GST substrate CDNB (2.04+/-0.74 nmol min(-1) (mg protei n)(-1)). The two samples not showing any detectable activity towards E DB were also inactive towards EPNP: The activity towards EDB correlate d significantly with EPNP (r(s) = 0.90, P < 0.005; Spearman's rank cor relation), but not with CDNB (r(s) = 0.36, P > 0.10). In the incubatio ns with EPNP, the alpha-, mu-, and pi-class glutathione S-transferase (GST) inhibitor S-hexyl(GSH) was included, indicating that the class-t heta GST is the principal GST class conjugating EDB in erythrocyte cyt osol. The apparent polymorphism of GST-theta which has recently been r ecognized to be crucial for several mono- and dihalomethanes, will thu s also have considerable implications for the risk assessment of EDB.