title: Equilibrium binding of benzo[a]pyrene tetrol to synthetic polynucleotides: sequence selectivity, thermodynamic properties, and ionic strength dependence.
abstract: We have investigated the equilibrium binding of racemic 7r,8t,9t,10c-tetrahydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene to the double-stranded, synthetic polynucleotides poly[d(A-T)], poly[d(G-C)], and poly[d(G-m5C)] at low binding ratios. Difference absorption spectroscopy shows a 10-nm red shift for binding to poly[d(A-T)] and an 11-nm red shift for binding to either poly[d(G-C)] or poly[d(G-m5C)]. The value of delta epsilon for binding is approximately the same for all three hydrocarbon-polynucleotide complexes. Binding of this neutral polycyclic aromatic hydrocarbon derivative to these polynucleotides is dependent upon ionic strength and temperature. Analysis of complex formation employing polyelectrolyte theory shows a greater release of counterions associated with binding to poly[d(A-T)] than with the other two polynucleotides (0.5 and ca. 0.36, respectively). Thus, sequence-selective binding of this hydrocarbon in DNA would be expected to change depending on salt concentration. The temperature dependence of binding was studied at 100 mM Na+ where the equilibrium binding constants for poly[d(A-T)] and poly[d(G-m5C)] are roughly equivalent and 6-fold greater than the binding affinity for poly[d(G-C)]. The binding to poly[d(A-T)] and poly[d(G-C)] is characterized by a delta H omicron = -7.0 kcal/mol, and the large difference in affinity constants arises from differences in negative entropic contributions. Formation of hydrocarbon-poly[d(G-m5C)] complexes is accompanied by a delta H = -9.1 kcal/mol. However, the affinity for poly[d-(G-m5C)] is the same as that for poly[d(A-T)] due to the much more negative entropy associated with binding to poly[d(G-m5C)].
authors.affiliation: Division of Toxicology, University of California, San Francisco 94143-0446.
authors.forename: G H
authors.initials: GH
authors.lastname: Shimer
authors.forename: A R
authors.initials: AR
authors.lastname: Wolfe
authors.forename: T
authors.initials: T
authors.lastname: Meehan
mesh_terms: D001483:Base Sequence; D001580:Benzopyrenes; D001665:Binding Sites; D007700:Kinetics; D009994:Osmolar Concentration; D011067:Poly dA-dT; D011089:Polydeoxyribonucleotides; D013053:Spectrophotometry; D013816:Thermodynamics
chemical_list: D001580:Benzopyrenes; D011089:Polydeoxyribonucleotides; D011067:Poly dA-dT; C019530:poly(dC-dG); C029988:poly(dG-m(5)dC).poly(dG-m(5)dC); C032174:7,8,9,10-tetrahydroxytetrahydrobenzo(a)pyrene