Conformations of Complexes Derived from the Interactions of Two Stereoisomeric Bay-Region 5-Methylchrysene Diol Epoxides with DNA

Abstract

The reaction mechanisms of two isomeric bay-region diol epoxides of 5-methylchrysene (trans-1,2-dihydroxy-anti-3,4-epoxy-1,2,3,4-tetrahydro-5-methylchrysene (DE-I) and trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydro-5-methylchrysene (DE-II) with double-stranded DNA in aqueous solutions were studied utilizing kinetic flow dichroism and fluorescence techniques. As in the case of the previously studied benzo(a)pyrene-7,8-diol-9,10-oxide isomers (BaPDE), both DE-I and DE-II rapidly form intercalation-type complexes (association constants K = 2700 and 1500 M-1 respectively in a neutral 5mM phosphate solution). The physically bound diol epoxide molecules react on time scales of minutes to form predominantly tetraols; a greater fraction (6 +/- 1%) of DE-I than of DE-II (2-3%) molecules react with the DNA to form covalent products. The DE-II isomer is characterized by a greater reactivity than DE-I, and the rates of reaction are markedly accelerated in the presence of DNA in both cases. The linear dichroism spectra of the covalent adducts reveal that the conformations of both types of adducts are similar, with the long axes of the phenanthrenyl chromophores tilted, on the average, at angles of 38-52 degrees with respect to the average orientations of the transition moments (at 260 nm) of the DNA bases. The conformations of the covalently bound DE-I and DE-II molecules resemble those observed in the case of the highly tumorigenic (+) enantiomer of anti-BaPDE.(ABSTRACT TRUNCATED AT 250 WORDS)

Reactions of Dihydrodiol Epoxides of 5-Methylchrysene and 5,6-Dimethylchrysene with DNA and Deoxyribonucleotides

“…This suggests that the effect of the 6-methyl group in 5,6-DMCDE in giving a lower extent of reaction with deoxyguanosine in DNA than 5-MCDE may be attributed to steric hindrance between the hydrocarbon dihydrodiol epoxide and DNA structure, since the most affected reactions were those with the amino group in the minor groove and this effect was more apparent in native than in denatured DNA. Separate intercalative noncovalent binding of PAH-dihydrodiol epoxides to DNA (28,29), with the proper orientation for forming adducts, is required for deoxyadenosine and deoxyguanosine adduct formation and is consistent with the present finding on 5-methyl-and 5,6-dimethylchrysene dihydrodiol epoxides in reactions with DNA in aqueous solutions. The basis for the difference in adduct distribution at deoxyguanosine and deoxyadenosine sites in DNA for 5,6-DMCDE versus 5-MCDE lies therefore probably in the greater reactivity of dihydrodiol epoxides from 5-methylchrysene for the amino group of deoxyguanosine residues, not in a greater affinity of the dihydrodiol epoxide derived from the nonplanar 5,6-dimethylchrysene for deoxyadenosine residues in DNA.…”

Unwinding and hydrodynamic flow linear dichroism characteristics of supercoiled DNA covalently modified with two isomeric methylchrysene diol epoxides of different biological activities

“…A10 X 25 cm Vydac 201TP1010 10-jtm column (Separations Group, Hesperia, CA) and a Waters Associates HPLC system (MiUipore, Waters Division, Milford, MA) were used to separate the adducts from one another using a 0-100% 5 mM phosphate buffer-methanol gradient (elution time 90 min, rate of elution 3 mL/min). The concentrations of the adducts in the HPLC elution peaks were determined by their UV absorbances at 254 nm using a molar extinction coefficient for MeCDE-nucleotide adducts of=27 000 M_1 cm-1 (40). The molar extinction coefficients of the DNA-bound residues at 304 nm were found to be equal to 3500 ft 300 for the (+)-5-MeCDE- DNA adducts and 2500 • 300 M_1 cm-1 for the (+)-6-MeCDE-DNA adducts.…”