The binding of reactive metabolites of the carcinogen N-hydroxy-2-acetylaminofluorene to DNA and protein in isolated rat liver nuclei: Effects of glutathione and methionine

The covalent binding of reactive metabolites of the carcinogen N‐hydroxy‐2‐acetylaminofluorene to DNA and protein in isolated, intact rat liver nuclei was studied. The chemically synthesized 2‐acetylaminofluorene‐N‐sulfate became covalently bound to DNA and protein to form adducts, 50% to 60% of which retained the N‐acetyl group. Glutathione decreased the covalent binding of acetylated adducts to DNA by 18% and to protein by 50%. Methionine was more effective; it decreased DNA binding by 52% and protein binding by 79%. N‐Hydroxy‐2‐acetylaminofluorene was deacetylated by the nuclear preparation. Almost exclusively, deacetylated 2‐aminofluorene adducts to DNA and protein were formed. Glutathione decreased the covalent binding of deacetylated adducts to DNA by only 14%. Protein binding, however, was decreased by 57%. Methionine had no effect on the formation of these adducts to DNA and protein. Formation of 2‐aminofluorene‐glutathione conjugates was reduced by ascorbic acid by 65%. Covalent binding of deacetylated adducts to DNA and protein, however, was not decreased by ascorbic acid. These data suggest that “harder” nucleophiles like methionine can be used to protect macromolecules in vivo from damage by “hard” electrophiles such as those generated from the reactive 2‐acetylaminofluorene‐N‐sulfate. However, such nucleophiles seem not to be effective with N‐hydroxylamines, such as N‐hydroxy‐2‐aminofluorene, formed by deacetylation of N‐hydroxy‐2‐acetylaminofluorene.