DNA alkylation and unwinding induced by benzo[a]pyrene diol epoxide: modulation by ionic strength and superhelicity.

Gamper, Howard; Straub, Kenneth; Calvin, Melvin; Bartholomew, James C.

doi:10.1073/pnas.77.4.2000

Cited by 37 publications

(14 citation statements)

References 29 publications

(26 reference statements)

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“…This is precisely what we have found not to be the case for pyrene moiety in neutral solutions. There are also reports (21)(22) which indicate an unwinding angle of 26-300 when anti-BPDE covalently bound to SV40 DNA, suggesting an intercalated chemical adduct. The fact that physically bound anti-BPDE unwinds the helix by half that reported for the covalent complex (10), however, leaves open the possibility that such large unwinding angle may have its origin in something other than intercalation.…”

Section: Discussionmentioning

confidence: 83%

Binding of pyrene to DNA, base squence specificity and its implication

Chen¹

1983

Nucl Acids Res

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Solubilization as well as spectral studies of pyrene in natural DNA and synthetic deoxypolynucleotide solutions at neutral pH reveal at least two binding modes. Sites I are predominant in native DNA and in poly(dA-dT): poly(dA-dT) whereas sites II are found with denatured DNA and other polynucleotides such as poly(dA):poly(dT) and three different types of guanine containing copolymers which solubilize pyrene to a lesser extent. Spectral comparison with the covalent adducts of trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10- tetrahydro-benzo(a)pyrene (anti-BPDE) and the physical complexes of its tetraols lead to the suggestion of a base sequence specific binding model for this carcinogenic metabolite to account for the puzzling fact that although its physical binding is predominantly intercalative, the covalent adducts appear not to be intercalated. It is speculated that in neutral solutions, intercalation may have little, if any, to do with the chemical lesion of this metabolite to the guanine base of the DNA and may, on the contrary, provide an efficient pathway for detoxification.

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Section: Discussionmentioning

confidence: 83%

Binding of pyrene to DNA, base squence specificity and its implication

Chen¹

1983

Nucl Acids Res

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“…This is a necessary but not sufficient condition for the mechanism. (ii) Alkylation targets are highly specific in DNA-e.g., guanine bases and exocyclic amino groups (9,10 (26)(27)(28)(29) and separate experiments will be needed to resolve it.…”

Section: Resultsmentioning

confidence: 99%

Hydrolysis of benzo[a]pyrene diol epoxide and its covalent binding to DNA proceed through similar rate-determining steps.

Meehan¹,

Bond²

1984

Proc. Natl. Acad. Sci. U.S.A.

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The (6,(9)(10)(11). Reaction at the guanine site is stereoselective both in vivo (6) and in vitro (9, 12) and results from asymmetries in the secondary structure of DNA (12). Minor adducts between racemic anti-BPDE [(+)anti-BPDE] and adenine (9, 10, 13), cytosine (9, 10), and the N-7 position of guanine (14) have been reported.(±)anti-BPDE is unstable in aqueous media and readily undergoes hydrolysis to form isomeric 7,8,9,10-tetrahydroxy-7,8,9,10-tetrahydrobenzo[a]pyrenes (tetrols). Hydrolysis of (+)anti-BPDE and the syn diastereomer (in which the 7-hydroxyl group is cis to the epoxide) occurs by general acid catalysis (15)(16)(17). Furthermore, product analyses and ionic strength effects have led to similar proposals for the mechanism of (±)anti-BPDE hydrolysis (16,17). This mechanism involves a rapid equilibrium between general acid catalyst and (±)anti-BPDE, followed by proton transfer and carbonium ion formation in the rate-determining step (rds).DNA catalyzes hydrolysis of (+)anti-BPDE (18,19), and in a recent study the acid dependence of this reaction was investigated at pH 6.5-7.5 (20). The results indicated that hydrolysis in the presence of DNA was also an acid-catalyzed process (20). A model has been proposed for DNAcatalyzed hydrolysis and covalent binding in which a carbonium ion formed in the rds serves as a common intermediate for both reactions (21). The rate of DNA-catalyzed hydrolysis may be important to the total level of covalent adduct obtained and, thus, to the genesis of tumors induced by chemical carcinogens. We have, therefore, investigated the mechanisms of these reactions in an in vitro model system utilizing calf thymus DNA. Our results suggest that a carbonium ion is formed in the rds for each process, but the activated intermediates for hydrolysis and covalent binding are formed in different domains. Kinetic results support our model that carbonium ion precursors to covalent adducts are derived from physically intercalated hydrocarbons, while tetrols are formed from carbonium ions generated on the outside of the DNA helix.MATERIALS AND METHODS Synthesis. (±)anti-BPDE was synthesized as previously described (10, 12). The preparation of 3H-labeled (±)anti-BPDE has also been reported (10).Chemicals. Calf thymus DNA was obtained from Sigma. All other chemicals were obtained from commercial sources and were reagent quality or higher grade purity.Hydrolysis Kinetics. Hydrolysis of (+)anti-BPDE was followed spectrophotometrically (15-17), both at an absorption band of the hydrocarbon (345.5 nm) and at the long-wavelength red-shifted transition representing the BPDE-DNA intercalation complex (centered at 353 nm) (22, 23). Firstorder plots resulted in straight lines, indicating that hydrolysis was measured under pseudo-first-order conditions. Lines were fitted by least-squares analysis and the resulting slopes were used to determine pseudo-first-order rate constants. Replicate values for rate constants were within 5%.Covalent Binding Assays. Covalent binding of (+)anti-BPDE was meas...

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“…In the case of (+)-5-MeCDE, the mobility of the more slowly migrating nicked DNA band increases with increasing levels of modification up to n, values near 0.06 and then decreases as the level of modification is increased still further (Figure 3A). Increases in the mobilities of BPDEmodified nicked closed circular DNA have been previously reported (30,31) and attributed to flexible hinge-like behavior at the alkylation sites (31). The diminishing mobilities at rb > 0.06 might be due to the effects of increasing masses of the modified DNA molecules at high levels of binding.…”

Section: Resultsmentioning

confidence: 71%

“…The binding of PAH diol epoxide enantiomers to DNA can cause decreases in the apparent persistence lengths due to increased flexibility, hinge joints (25)(26)(27)(28), bends, or kinks (29) at the sites of the lesions. The unwinding of supercoiled DNA (30)(31)(32)(33)(34)(35) may be another effect which produces changes in the tertiary structure of DNA which may be of biological significance. Recently, we have shown that, upon chemical binding of the (+)-BPDE enantiomer to supercoiled 0X174 DNA, the unwinding angle per bound BPDE residue is 11 ± 1.8°, while in the case of the (-)-BPDE enantiomer the unwinding angle is 6.8 ± 1.7° ( 33).…”

Section: Introductionmentioning

confidence: 99%

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

Balasta¹,

Xu²,

Geacintov³

et al. 1993

Chem. Res. Toxicol.

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Adducts derived from the covalent binding of two positional monomethyl-substituted isomers of a bay region chrysene diol epoxide to supercoiled pIBI30 DNA (2926 base pairs/genome) were prepared, and their characteristics were investigated by a combination of gel electrophoresis and flow linear dichroism techniques. The 5- and 6-methyl derivatives of trans-1,2-dihydroxy-anti-3,4-epoxy-1,2,3,4-tetrahydrochrysene [(+)-5- and (+)-6-MeCDE, respectively], both with 1R,2S,3S,4R stereochemistry, are characterized by significant differences in their biological activities [Melikian et al. (1988) Cancer Res. 48, 1781-1787]. When covalently bound to plasmid DNA, these two molecules give rise to striking differences in the gel electrophoretic and flow hydrodynamic characteristics of the modified supercoiled DNA. The hydrodynamic flow linear dichroism of linearized DNA molecules (obtained by EcoRI enzyme digestion of covalently closed supercoiled pIBI30 DNA), modified covalently with the highly tumorigenic and mutagenic (+)-5-MeCDE derivative, indicates that flexible joints, bends, or kinks are formed at the site of binding of (+)-5-MeCDE. Slab gel data, as well as ethidium bromide-titration tube agarose gel electrophoresis data, indicate that the formation of (+)-5-MeCDE-DNA lesions causes the removal of superhelical turns with an unwinding angle of 13 +/- 3 degrees per covalently bound polycyclic aromatic residue. In contrast, the biological inactive (+)-6-MeCDE does not significantly alter the characteristics of supercoiled DNA, the unwinding angle is only 2.7 +/- 1 degrees, and the changes in persistence lengths detected by the flow linear dichroism technique are significantly smaller than in the case of (+)-5-MeCDE-DNA adducts.(ABSTRACT TRUNCATED AT 250 WORDS)

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DNA alkylation and unwinding induced by benzo[a]pyrene diol epoxide: modulation by ionic strength and superhelicity.

Cited by 37 publications

References 29 publications

Binding of pyrene to DNA, base squence specificity and its implication

Binding of pyrene to DNA, base squence specificity and its implication

Hydrolysis of benzo[a]pyrene diol epoxide and its covalent binding to DNA proceed through similar rate-determining steps.

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

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