Characterization of benzo[a]pyrene anti-diol epoxide adducts to human histones

Nuclei from human lymphoblast cells grown in culture were treated with [7-14C]-(+/-)-r-7,t-8-dihydroxy-t-9,t-10-epoxy-7,8,9,10- tetrahydrobenzo[a]pyrene (anti-BPDE), and the nucleosomal core histones were isolated for adduct studies by cryogenic fluorescence line narrowing spectroscopy. The four core histones H2A, H2B, H3, and H4 were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, which yielded each histone free of contamination by the others. Further purification of histones H2A, H2B, and H4 by reversed-phase HPLC also yielded a tetrahydrotetrol of benzo[a]pyrene, indicating that these three histones had some labile adducts. No tetrol was observed upon purification of histone H3. Fluorescence emission spectra of the HPLC-purified histones recorded at 4K after vibronic excitation into the S1 state were generally similar. Fluorescence line-narrowed spectra of model compounds formed by reaction of anti-BPDE with acetic acid, ethylenediamine, cysteamine, and histidine were also recorded. Only the spectra of the ethylenediamine adduct model matched consistently, at different excitation wavelengths, the spectra of the adducted histones. From this it is concluded that the stable human histone adducts of anti-BPDE are formed by reaction with lysine residues and/or the amino groups of the N-termini.