Regiospecific and diastereoselective inactivation of mutagenic 9,10-dihydrobenzo[a]-pyrene 7,8-oxide by hepatic cytosolic glutathione S-transferase.
Racemic, (7R,8S)-(+)-, and (7S,8R)-(-)-9,10-dihydrobenzo[a]pyrene 7,8-oxides (DBPOs) showed markedly different mutagenicity towards Salmonella typhimurium TA 98 in the order of (7R,8S)-(+)- greater than racemic greater than (7S,8R)-(-)-DBPOs. The enantiomeric epoxides were inactivated at significantly different rates by preincubating with rat liver cytosol fortified with glutathione (GSH) in the order of (7S,8R)-(-)- greater than racemic greater than (7R,8S)-(+)-DBPOs. Two non-mutagenic water-soluble metabolites were isolated from the preincubation mixture containing racemic DBPO as a substrate, separated by hplc, and identified by 13C nmr and uv absorption spectroscopy as diastereoisomers of S-(8-hydroxy-7,8,9,10-tetrahydrobenzo[a]pyren-7-yl)glutathione (conjugates I and II). Conjugates I and II were specifically yielded from (7R,8S)-(+)- and (7S,8R)-(-)-DBPOs, respectively, at different rates by rat liver cytosol; apparent values of Km were 20.1 and 15.6 microM and of Vmax 17.2 and 26.7 nmole/mg protein/min for (7R,8S)-(+)- and (7S,8R)-(-)-DBPOs, respectively. Conjugates I and II, therefore, were reasonably assigned to have (7S,8S)- and (7R,8R)-configurations, respectively. Conjugate II was yielded preferentially to conjugate I from racemic DBPO at an early stage of the enzyme reaction.
D000818:Animals; D001580:Benzopyrenes / Q000378:metabolism*; D003600:Cytosol / Q000201:enzymology*; D005978:Glutathione / Q000378:metabolism; D005982:Glutathione Transferase / Q000494:pharmacology*; D008658:Inactivation, Metabolic; D008099:Liver / Q000201:enzymology*; D008297:Male; D009153:Mutagens / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013237:Stereoisomerism
D001580:Benzopyrenes; D009153:Mutagens; C023393:benzo(a)pyrene 7,8-oxide; D005982:Glutathione Transferase; D005978:Glutathione