BASE RELEASE FROM DNA AND POLYNUCLEOTIDES UPON 193 nm LASER EXCITATION

Gurzadyan, Gagik G.; Görner, Helmut

doi:10.1111/j.1751-1097.1992.tb02173.x

Cited by 19 publications

(8 citation statements)

References 27 publications

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“…Formation of the dRib(C 1' -H) • radical in solid state DNA has been reported 22,23,. Evidence that the Cyt radical cation deprotonates at C 1' has been obtained for deoxycytidine in dilute aqueous solution24 and deprotonation at C 1' may explain some fraction of the Cyt release measured in DNA ionized by 194 nm laser excitation 25. We propose that a predominate reaction stemming from Cyt •+ is 9 whenever Gua is not adjacent to Cyt; i.e., k CG (adj) > k CdRib > k CG (op).…”

Section: Discussionmentioning

confidence: 74%

One-Electron Oxidation of DNA by Ionizing Radiation: Competition between Base-to-Base Hole-Transfer and Hole-Trapping

et al. 2010

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The distance of hole migration through DNA determines the degree to which radiation induced lesions are clustered. It is the degree of clustering that confers to ionizing radiation its high toxicity. The migration distance is governed by a competition between hole transfer and irreversible trapping reactions. An important type of trapping is reactions that lead to formation of deoxyribose radicals, which are precursors to free base release (fbr). Using HPLC, fbr was measured in X-irradiated films of d(CGCGCGCGCG) 2 and d(CGCGAATTCGCG) 2 as well as three genomic DNAs: M. luteus, calf thymus, and C. perfringens. The level of DNA hydration was varied from Γ = 2.5 to 22 mol waters/ mol nucleotide. The chemical yields of each base, G(base), were measured and used to calculate the modification factor, M(base). This factor compensates for differences in the GC/AT ratio, providing a measure of the degree to which a given base influences its own release. In the DNA oligomers, M (Gua) > M(Cyt), a result ascribed to the previously observed end effect in short oligomers. In the highly polymerized genomic DNA, we found that M(Cyt) > M(Gua) and that M(Thy) is consistently the smallest of the M factors. For these same DNA films, the yields of total DNA trapped radicals, G tot (fr), were measured using EPR spectroscopy. The yield of deoxyribose radicals was calculated using G dRib (fr) = ∼0.11 × G tot (fr). Comparing G dRib (fr) with total free base release, we found that only about half of the fbr is accounted for by deoxyribose radical intermediates. We conclude that for a hole on cytosine, Cyt •+ , base-to-base hole transfer competes with irreversible trapping by the deoxyribose. In the case of a hole on thymine, Thy •+ , base-to-base hole transfer competes with irreversible trapping by methyl deprotonation. Close proximity of Gua protects the deoxyribose of Cyt but sensitizes the deoxyribose of Thy.

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Section: Discussionmentioning

confidence: 74%

One-Electron Oxidation of DNA by Ionizing Radiation: Competition between Base-to-Base Hole-Transfer and Hole-Trapping

et al. 2010

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“…The @br and fbr values have been reported for double-stranded DNA. 19 Concerning adenine and thymine release from poly(d[A-TI) and double-stranded DNA, the difference is a factor of 2.6 or less. only by a factor of 1.7 or less ( Table 4).…”

Section: Poly(a) § 33mentioning

confidence: 99%

Damage to Uracil‐ and Adenine‐containing Bases, Nucleosides, Nucleotides and Polynucleotides: Quantum Yields on Irradiation at 193 and 254 Nm

Gurzadyan

Görner

1994

Photochem & Photobiology

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Photoreactions, such as base release and decomposition of the base moiety, induced by either 20 ns laser pulses at 193 nm or continuous 254 nm irradiation, were studied for a series of uracil and adenine derivatives in neutral aqueous solution. The quantum yield of chromophore loss (phi cl) depends significantly on the nature of the nucleic acid constituent and the saturating gas (Ar, N2O or O2). In the case of polynucleotides the destruction of nucleotides was measured by high-performance liquid chromatography after hydrolysis; the quantum yields (phi dn) are comparable to those of chromophore loss or larger. The phi cl and phi dn of 0.04-0.1 for poly(U) and poly(dU), obtained for both wavelengths of irradiation, are due to processes originating from the lowest excited singlet state, i.e. formation of photohydrates and photodimers, and a second part from photoionization using lambda irr = 193 nm. Irradiation at 193 nm effectively splits pyrimidine dimers and thus reverts them into monomers. The quantum yield for release of undamaged bases (phi br) from nucleosides, nucleotides and polynucleotides upon irradiation at 254 nm is typically phi br = (0.1-1) x 10(-4). Breakage of the N-glycosidic bond is significantly more efficient for lambda irr = 193 nm, e.g. phi br = 1.1 x 10(-3), 0.8 x 10(-3), 4.3 x 10(-3) and 0.5 x 10(-3) for poly(A), poly(dA), poly(U) and poly(dU) in Ar-saturated solution, respectively. Enhanced phi values for lambda irr = 193 nm, essentially for adenine and its derivatives, are caused by photoprocesses that are initiated by photoionization.

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“…Guanine formation also occurs in dG, guanosine, and 2‘-deoxyguanosine 5‘-monophosphate (5‘-dGMP - ) solutions irradiated at 254 nm . and in calf thymus DNA irradiated at 193 nm . Investigation of the mechanisms for G formation from nucleosides, 5‘-dGMP - and DNA provides evidence that photoionization of the guanine moiety is an initiating event. , At 254 nm, the quantum yield for G formation from 75 μM guanosine was reported to decrease to a value of zero at pH 11.9 26 a surprising result in view of the fact that the photoionization quantum yields of dG, guanosine and 5‘-GMP - increase with increasing pH. ,18a …”

Section: Introductionmentioning

confidence: 99%

Low-Energy, Low-Yield Photoionization, and Production of 8-Oxo-2‘-deoxyguanosine and Guanine from 2‘-Deoxyguanosine

et al. 2002

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Experiments employing electron scavenging methods and high performance liquid chromatography with mass spectrometry detection indicate that electrons, formed via one-photon ionization, guanine (G) and small amounts of 8-oxo-2′-deoxyguanosine (8-oxo-dG) are formed during 254 nm irradiation of deaerated alkaline 2′-deoxyguanosine (dG) solutions containing N 2 O. The G, 8-oxo-dG and electron yields vary in a similar way when the pH changes. At a dG concentration of 1.2 × 10 -4 M, the 254 nm photoionization quantum yield is in the range 0.01 to 0.02 at pH 11.4. The low sensitivity with which photoionization can be monitored in electron scavenging experiments does not permit the direct measurement of dG photoionization at near neutral pH. At pH 6.3, the 254 nm photoionization quantum yield for dG is no larger than 0.003. At pH 11.4, the yields of G and 8-oxo-dG formed from 254 nm irradiation of 1.2 × 10 -4 M dG for 40 min are more than 5× larger than that at pH 6.3. The similar pH dependence of the G, 8-oxo-dG and photoelectron yields, and earlier reports linking G and 8-oxo-dG formation to dG photoionization provide evidence that, under the present conditions, G and 8-oxo-dG quantum yields, which can be monitored with higher sensitivity than hydrated electrons in electron scavenging experiments, parallel the photoionization quantum yield. From this perspective, the wavelength dependence of G and 8-oxo-dG quantum yields indicates that dG ionization threshold wavelengths at pH 11.4 and 6.3 are 266 ( 16 and 260 ( 16 nm, respectively. When the 260 nm threshold of dG at pH 6.3 is adjusted to account for an approximately 0.5 eV lowering of the ionization energy associated with incorporation of dG into native B DNA sequences containing multiple stacked guanines (Sugiyama, H.; Saito, I.

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BASE RELEASE FROM DNA AND POLYNUCLEOTIDES UPON 193 nm LASER EXCITATION

Cited by 19 publications

References 27 publications

One-Electron Oxidation of DNA by Ionizing Radiation: Competition between Base-to-Base Hole-Transfer and Hole-Trapping

One-Electron Oxidation of DNA by Ionizing Radiation: Competition between Base-to-Base Hole-Transfer and Hole-Trapping

Damage to Uracil‐ and Adenine‐containing Bases, Nucleosides, Nucleotides and Polynucleotides: Quantum Yields on Irradiation at 193 and 254 Nm

Low-Energy, Low-Yield Photoionization, and Production of 8-Oxo-2‘-deoxyguanosine and Guanine from 2‘-Deoxyguanosine

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