Effect of pH on the ratio of substitution products in DNA after reaction with the carcinogen N-acetoxy-2-acetylaminofluorene.

The substitution reaction products of N-acetoxy-2-acetylaminofluorene (N-AcO-AAF) and the N-sulfate (potassium salt) of N-hydroxy-4-acetyl-aminobiphenyl (N-OSO3K-AABP) with DNA from calf thymus were determined after reaction in buffered solutions of 0.10 M NaCl at pH values from 4--9. In the case of N-AcO-AAF, the ratio of N-(guanin-8-yl)-2-acetylaminofluorene (N-(guanine-8-yl)-AAF) to 3-(guanin-N2-yl)-2-acetylaminofluorene (3-(guanin-N2-yl)-AAF) increased 2.2 times over the entire pH range studied, starting at pH 9. With the N-OSO3K-AABP, the total substitution of guanine was much lower (22--34 times) as compared with N-AcO-AAF, and the ratio of N-(guanin-8-yl)-4-acetylaminobiphenyl to 3-(guanin-N2-yl)-4-acetylaminobiphenyl was not affected by a change in pH of the reaction medium. As expected, heat-denatured DNA reacted more extensively with both esters, but an increase in substitution was much more pronounced for the biphenyl derivative (9 times) than for the fluorene compound (2.8 times). Degradation, denaturation or interstrand cross-linking of DNA were not observed under the reaction conditions employed.