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Reaction of 2-acetylaminofluorene-N-sulfate with RNA and glutathione: evidence for the generation of two reactive intermediates with different reactivities towards RNA and glutathione
Division of Toxicology, Center for Bio-Pharmaceutical Sciences, University of Leiden, Sylvius Laboratories P.O.Box 9503, 2300 RA Leiden, The Netherlands
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The sulfate ester of N-hydroxy-2-acetylaminofluorene (AAF-N-sulfate) is one of the reactive intermediates of this carcinogen. This ester breaks down spontaneously to a very reactive nitrenium ion, which reacts with nucleophilic groups in protein, DNA, RNA and glutathione (GSH). Reactions involving the nitrenium ion with several nudeophiles under various conditions were studied. The adduct formation to RNA was much higher in Tris-HCI buffer than in phosphate buffer (at pH 7.4), while adduct formation to deoxy-guanosine monomers was the same in both buffers. The presence of 150 mM KCI had the same decreasing effect in both cases. Ionic strength effects may be involved in these phenomena. GSH decreased RNA adduct formation by 2045%, while other thiols were much more effective. On the other hand, RNA did not decrease the formation of GSH conjugates from AAF-N-sulfate. The decrease in RNA adduct formation by thiols corresponded with an increase in the formation of 2-acetyl-aminofluorene (AAF) from AAF-N-sulfate, while no N-hydroxy-AAF was formed. These results suggest that two independent reactive intermediates are formed from AAF-N-sulfate, with different reactivities towards RNA and glutathione. Possibly these intermediates are the hard triplet state nitrenium ion and the soft singlet state nitrenium ion. Cysteine, cysteamine and penicillamine were most effective in the inhibition of RNA adduct formation; the extent of inhibition correlated with the extent of AAF formation. The mechanisms involved are discussed.
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