Facilitation of the conversion from B to Z conformation in poly(dG-dC) modified by anti-benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide.
The transition from B to Z conformation has been studied in poly(dG-dC) covalently modified with racemic anti- or syn-benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE), a strong and a weak carcinogen, respectively. Circular dichroism was used to study the kinetics of the transition after a sudden increase of the ionic strength to 2.7 M NaCl. The results show that the rate of the B to Z transition of poly(dG-dC) in high NaCl concentration is considerably enhanced by bound anti-BPDE and diminished by bound syn-BPDE. The results may be interpreted such that at the binding site of anti-BPDE the base stacking is distorted and made looser, which facilitates the B to Z transition. The partly intercalative nature of the syn-BPDE complexes apparently is effective in reducing the rate of the transition. These properties of the two BPDEs may be relevant to explain their different carcinogenic potencies.
D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide; D001580:Benzopyrenes; D001665:Binding Sites; D002942:Circular Dichroism; D007700:Kinetics; D009690:Nucleic Acid Conformation; D011089:Polydeoxyribonucleotides; D013237:Stereoisomerism
D001580:Benzopyrenes; D011089:Polydeoxyribonucleotides; C019530:poly(dC-dG); D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide