ACTIVATION AND INACTIVATION OF CARCINOGENIC DIHALOALKANES AND OTHER COMPOUNDS BY GLUTATHIONE-S-TRANSFERASE-5-5 IN SALMONELLA-TYPHIMURIUM TESTER STRAIN NM5004

A newly developed tester Salmonella typhimurium NM5004 strain was cons tructed by introducing a plasmid containing both rat GSH S-transferase (GST) 5-5 cDNA and the umuC''lacZ operon into the host strain Salmone lla typhimurium TA1535 and used to examine whether or not GST modified the genotoxic activities of several dihaloalkanes and other compounds . Twenty-nine chemicals that were suggested to be conjugated by GST we re compared with regard to their abilities to induce umu gene expressi on and cause cytotoxicity responses in both the NM5004 strain and the original tester strain (S. typhimurium TA1535/pSK1002, which is devoid of GST activity toward 1,2-epoxy-3-(4'-nitrophenoxy)propane). Ten che micals-1,2-dibromoethane, N-(2,3-epoxypropyl)phthalimide, 1,3-dichloro acetone, CH2I2, 1,2-epoxy-3-phenoxypropane, 2,3-epoxypropyl p-methoxyp henyl ether, 1-bromo-2-chloroethane, 1-bromo-2,3-dichloropropane, CH2B rCl, and CH2Br2-were found to enhance induction of umu gene expression in the NM5004 strain as compared with the TA1535/pSK1002 strain. 1,2- Epoxy-3-(4'-nitrophenoxy)propane and 2,3-dibromo-1-chloropropane were inactivated by GST 5-5 in the NM5004 tester strain, although these che micals were cytotoxic in both tester strains. Roles of GST 5-5 were al so examined for the inactivation of reactive metabolites of several pr ocarcinogens that were formed through oxidation by liver microsomes of polychlorinated biphenyl-treated rats. The results suggest that react ive metabolites (possibly epoxides) of aflatoxin B-1, sterigmatocystin , 1,2-dihydro-1,2-dihydroxy-6-aminochrysen and (+)- and (-)enantiomers of 7,8-dihydroxy-7,8-dihydrobenzo[alpha]pyrene could be trapped as in activated GSH conjugates in the NM5004 strain. High-performance liquid chromatographic analysis suggested that exo-aflatoxin B-1-8,9-oxide-G SH conjugate was formed during the oxidation of aflatoxin B-1 by rat a nd human liver microsomes in the presence of GSH and several GST enzym es including purified rat theta class GST Y-rs-Y-rs and rat liver GST (a mixture of alpha and mu class enzymes). Thus, the present results s upport the view that the theta class rat GST 5-5 enzyme participates i n the activation and inactivation of potential environmental carcinoge nic chemicals. This newly developed NM5004 tester strain is of use in the elucidation of roles of GST 5-5 in transformations.