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5148538 
Technical Report 
1-Alkyl Substitution Effects on the DNA Intercalation of Benzo(a)pyrene Metabolites 
Paulius, DE; Prakash, AS; Harvey, RG; Abramovich, M; Lebreton, PR 
1986 
Chemistry 
The effect of 1-alkyl substitution on DNA intercalation of benzo(a)pyrene (50328) metabolites was studied in-vitro. Trans-7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene (57404883) (BPD) and 1-isopropyl-trans-7,8-dihydroxy-7,8-dihydrobenzo(a)pyrene (isopropyl-BPD) were reacted with native or denatured calf thymus DNA at 23 degrees-C in a solvent system consisting of 85:15 double distilled water and methanol. BPD and isopropyl-BPD concentrations ranged from 10(-6) to 10(-7) molar. The solutions were analyzed by fluorescence spectrometry. Fluorescence intensity and fluorescence lifetime data were obtained from the spectra. Fluorescence quenching of BPD and isopropyl-BPD was greatly reduced by the denatured DNA, compared to native DNA. BPD was 6.5 times more effectively quenched by native DNA than isopropyl-BPD. The quenching constants for BPD and isopropyl-BPD with native DNA were 6.1x10(3) and 9.33x10(2) liters per mole, respectively. Both BPD and isopropyl-BPD exhibited fluorescence decay profiles that were not qualitatively changed in the presence of DNA. BPD and isopropyl-BPD had respective decay lifetimes of 27.0 and 16.0 nanoseconds in the absence of DNA and 27 and 15.3 nanoseconds in the presence of DNA. BPD decay also showed a small contribution from a short lived component in the presence of DNA; however, this component contributed less than 11 percent of the total observed emission intensity. Additional spectra were obtained to investigate the effect of adding spermine (71443) and varying the methanol content of the solvent from 0 to 80 percent on quenching. Fluorescence quenching of BPD was reduced when spermine was added. Fluorescence quenching of both BPD and isopropyl-BPD was reduced when the solvent methanol content was increased. The authors conclude that BPD intercalates into DNA much more efficiently than isopropyl-BPD.