title: Denaturation and renaturation studies of benzo[a]pyrene metabolite modified DNAs.
abstract: Evidence from absorbance, fluorescence, and circular dichroism (CD) measurements strongly suggests that adduct conformations at the binding sites are grossly different before and after thermal denaturation of (+)-trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]py ren e [(+)-anti-BPDE] modified DNAs. This conclusion is reached through the following observations: (1) upon melting and cooling, the (+)-anti-BPDE-modified DNA exhibits pronounced hypochromic effects with concomitant spectral red shifts for the pyrenyl absorbance; (2) the pyrenyl CD spectrum reverses sign upon thermal denaturation-renaturation; (3) the fluorescence emission spectra resulting from excitations at 353 nm (10 nm to the red of hydrolyzed and unbound anti-BPDE) exhibit enhanced intensities and spectral red shifts for the thermally denatured and cooled adducts; and (4) in contrast to the absence of a shoulder prior to melting, the postmelt adducts exhibit a prominent 355-nm maximum (evidence of stacking interactions) in the excitation spectrum when 384-387-nm emission is monitored. Studies with synthetic polynucleotides further reveal that (+)-anti-BPDE-modified poly(dG).poly(dC) exhibits the greatest nonreversible renaturation at the binding sites, possibly as a consequence of pyrenyl self-stacking. This, coupled with the previous findings that this polymer suffers the most extensive (+)-anti-BPDE modification, appears to suggest that (dG)n . (dC)n regions may be responsible for such observed effects in native DNA.
mesh_terms: D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide; D001564:Benzo(a)pyrene / Q000031:analogs & derivatives; D001580:Benzopyrenes; D002942:Circular Dichroism; D004247:DNA; D018736:DNA Adducts; D004101:Dihydroxydihydrobenzopyrenes; D007536:Isomerism; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D009695:Nucleic Acid Renaturation; D011089:Polydeoxyribonucleotides; D013050:Spectrometry, Fluorescence
chemical_list: D001580:Benzopyrenes; D018736:DNA Adducts; D004101:Dihydroxydihydrobenzopyrenes; D011089:Polydeoxyribonucleotides; C043931:benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide-DNA; D001564:Benzo(a)pyrene; D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide; C039385:7,8-dihydroxy-9,10-epoxy-8-methyl-7,8,9,10-tetrahydrobenzo(a)pyrene; D004247:DNA