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M Dizdaroglu

Publications and source records attributed to M Dizdaroglu.

At least 91 records · Page 5Linked to original sources
PubMed1990

Modification of DNA bases in mammalian chromatin by radiation-generated free radicals.

Modification of DNA bases in mammalian chromatin in aqueous suspension by ionizing radiation generated free radicals was investigated. Argon, air, N2O, and N2O/O2 were used for saturation of the aqueous system in order to provide different radical environments. Radiation doses ranging from 20 to 200 Gy (J.kg-1) were used. Thirteen products resulting from radical interactions with pyrimidines and purines in chromatin were identified and quantitated by using the technique of gas chromatography/mass spectrometry with selected-ion monitoring after acidic hydrolysis and trimethylsilylation of chromatin. The methodology used permitted analysis of the modified bases directly in chromatin without the necessity of isolation of DNA from chromatin first. The results indicate that the radical environment provided by the presence of different gases in the system had a substantial effect on the types of products and their quantities. Some products were produced only in the presence of oxygen, whereas other products were detected only in the absence of oxygen. Products produced under all four gaseous conditions were also observed. Generally, the presence of oxygen in the system increased the yields of the products with the exception of formamidopyrimidines. Superoxide radical formed in the presence of air, and to a lesser extent in the presence of N2O/O2, had no effect on product formation. The presence of oxygen dramatically increased the yields of 8-hydroxypurines, whereas the yields of formamidopyrimidines were not affected by oxygen, although these products result from respective oxidation and reduction of the same hydroxyl-adduct radicals of purines. The yields of the products were much lower than those observed previously with DNA.

Animals↗
PubMed1990

Mechanistic studies of ionizing radiation and oxidative mutagenesis: genetic effects of a single 8-hydroxyguanine (7-hydro-8-oxoguanine) residue inserted at a unique site in a viral genome.

T4 RNA ligase was used to construct a deoxypentanucleotide containing a single 8-hydroxyguanine (7-hydro-8-oxoguanine; G8-OH) residue, which is one of the putatively mutagenic DNA adducts produced by oxidants and ionizing radiation. The pentamer d(GCTAG8-OH)p was prepared by the ligation of a chemically synthesized acceptor molecule, d(GCTA), to an adducted donor, 8-hydroxy-2'-deoxyguanosine 5',3'-bisphosphate. The acceptor was efficiently converted to the reaction product (greater than 95%), and the final product yield was 50%. Following 3'-dephosphorylation, the pentamer was characterized by UV spectroscopy, by high-pressure liquid chromatography, and by gas chromatography-mass spectrometry of the nucleosides released by enzymatic hydrolysis. Both d(GCTAG8-OH) and an unmodified control were 5'-phosphorylated by using [gamma -32P]ATP and incorporated covalently by DNA ligase into a five-base gap at a unique NheI restriction site in the otherwise duplex genome of an M13mp19 derivative. The ligation product contained G8-OH at the 3' residue of an in-frame amber codon (5'-TAG-3') (genome position 6276) of the phage lacZ alpha gene. The adduct was part of a nonsense codon in a unique restriction site in order to facilitate the identification and selection of mutants generated by the replication of the modified genome in Escherichia coli. Both control and adducted pentamers ligated into the genome at 50% of the maximum theoretical efficiency, and nearly all (approximately 90%) of the site-specifically adducted products possessed pentanucleotides that were covalently linked at both 5' and 3' termini. The G8-OH lesion in the NheI site inhibited the cleavage of the site by a 200-fold excess of NheI.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1990

Hydroxyl radical induced cross-linking of cytosine and tyrosine in nucleohistone.

Hydroxyl radical induced formation of a DNA-protein cross-link involving cytosine and tyrosine in nucleohistone in buffered aqueous solution is reported. The technique of gas chromatography-mass spectrometry was used for this investigation. A gamma-irradiated aqueous mixture of cytosine and tyrosine was first investigated in order to obtain gas chromatographic-mass spectrometric properties of possible cytosine-tyrosine cross-links. One cross-link was observed, and its structure was identified as the product from the formation of a covalent bond between carbon 6 of cytosine and carbon 3 of tyrosine. With the use of gas chromatography-mass spectrometry with selected-ion monitoring, this cytosine-tyrosine cross-link was identified in acidic hydrolysates of calf thymus nucleohistone gamma-irradiated in N2O-saturated aqueous solution. The yield of this DNA-protein cross-link in nucleohistone was found to be a linear function of the radiation dose in the range of 100-500 Gy (J.kg-1). This yield amounted to 0.05 nmol.J-1. Mechanisms underlying the formation of the cytosine-tyrosine cross-link in nucleohistone were proposed to involve radical-radical and/or radical addition reactions of hydroxyl adduct radicals of cytosine and tyrosine moieties, forming a covalent bond between carbon 6 of cytosine and carbon 3 of tyrosine. When oxygen was present in irradiated solutions, no cytosine-tyrosine cross-links were observed.

Animals↗
PubMed1990

Base modifications in plasmid DNA caused by potassium permanganate.

KMnO4 is a powerful oxidizing agent which has been used to modify DNA bases. In previous studies, mild KMnO4 treatment has been shown to preferentially modify Thy; Cyt and Gua are modified only under harsher conditions to as yet unidentified products. In the present study, denatured plasmid pCMV beta gal DNA was exposed to 0.015-1.5 mM KMnO4, pH 8.6, at 4 degrees C for 5 min, after which the DNA was hydrolyzed in formic acid, trimethylsilylated, and analyzed for modified base content by gas chromatography-mass spectrometry/selected ion monitoring. KMnO4 treatment, even at concentrations as low as 0.015 mM, caused a concentration-dependent increase in the Thy products Thy glycol and 5-hydroxy-5-methylhydantoin, the Cyt products Cyt glycol, 5,6-dihydroxycytosine, and 5-hydroxyhydantoin, the Ade product 8-hydroxyadenine, and the Gua product 8-hydroxyguanine. The Ade product 4,6-diamino-5-formamidopyrimidine and the Gua product 2,6-diamino-4-hydroxy-5-formamidopyrimidine were minimally (less than or equal to 2-fold) increased by treatment with greater than or equal to 0.8 mM KMnO4. These data demonstrate that, in addition to Thy, Cyt, Gua, and Ade bases in plasmid DNA may be modified by treatment with KMnO4, even under mild conditions. They represent the first identification of Cyt, Gua, and Ade products caused by KMnO4 treatment. Furthermore, these data suggest that previous studies which have used treatment with KMnO4 to study the mutagenicity of Thy glycol specifically or as a Thy-specific probe in DNA structure should be interpreted with caution.

Adenine↗
PubMed1990

Yields of radiation-induced base products in DNA: effects of DNA conformation and gassing conditions.

Gas chromatography-mass spectrometry with selected-ion monitoring was used to measure the yields of radiation-induced base products in aqueous solutions of native or heat-denatured DNA irradiated in the dose range 20-100 Gy. These DNA solutions were saturated with nitrous oxide, nitrogen, air or 20% oxygen in nitrous oxide during irradiation. The products measured were as follows: 5,6-dihydrothymine; 5-hydroxy-5,6-dihydrothymine; 5,6-dihydrothymine (thymine glycol); 5-hydroxy-5,6-dihydrocytosine; 5,6-dihydroxy-5,6- dihydrocytosine (cytosine glycol); 4,6-diamino-5-formamidopyrimidine; 7,8-dihydro-8-oxoadenine (8-hydroxyadenine); 2,6-diamino-4-hydroxy-5- formamidopyrimidine; and 7,8-dihydro-8-oxoguanine (8-hydroxyguanine). In oxygenated solutions, 5,6-dihydrothymine, 5-hydroxy-5,6-dihydrothymine and 5-hydroxy-5,6-dihydrocytosine were not formed. The yields of all products, other than 5,6-dihydrothymine, were greater in irradiated DNA samples from N2O-saturated solutions than from N2-saturated solutions. In N2-saturated solutions the yield of 8-hydroxyadenine was low and 8-hydroxyguanine was undetectable. Yields of pyrimidine products in heat-denatured DNA were greater than those in native DNA using all types of gases. However, the effects of DNA conformation on the yields of purine products were dependent on the type of gas used to saturate the irradiated DNA solutions. Yields of formamidopyrimidines were generally lower in solutions of DNA irradiated in the native than in the heat-denatured conformation. In air-saturated solutions of DNA, yields of 8-hydroxypurines were not influenced greatly by DNA conformation. In DNA solutions saturated with N2O/O2, 8-hydroxypurine formation was more favourable in the heat-denatured conformation than in the native conformation. On the other hand, in deoxygenated solutions, formation of 8-hydroxypurines was favoured in the native conformation. Data indicate that DNA conformation and the type of gas used to saturate the irradiated solutions have a profound influence on yields of base products in DNA.

Air↗
PubMed1990

Hydrogen peroxide-induced base damage in deoxyribonucleic acid.

Aqueous solutions of calf thymus deoxyribonucleic acid (DNA) were exposed to hydrogen peroxide in the presence of air. Base products formed in DNA were identified and quantitated following acid hydrolysis and trimethylsilylation using gas chromatography-mass spectrometry. The yields of these products were dependent upon the hydrogen peroxide concentration, and increased in the following order: 8-hydroxyadenine, cytosine glycol, 2,6-diamino-4-hydroxy-5-formamidopyrimidine, 8-hydroxyguanine, thymine glycol, and 4,6-diamino-5-formamidopyrimidine. Previous studies have shown that these compounds are typically formed in DNA in aqueous solution by hydroxyl radicals generated by ionizing radiation. Hydrogen peroxide is thought to participate in a Fenton-like reaction with transition metals, which are readily bound to DNA in trace quantities, resulting in the production of hydroxyl radicals close to the DNA. This proposed mechanism was examined by exposing DNA to hydrogen peroxide either in the presence of a hydroxyl radical scavenger or following pretreatment of DNA with metal-ion chelators. The results indicate that trace quantities of transition metal ions can react readily with hydrogen peroxide to produce radical species. The production of radical species was monitored by determining the altered bases that resulted from the reaction between radicals and DNA. The yields of the base products were reduced by 40 to 60% with 10 mmol dm-3 of dimethyl sulfoxide. A 100-fold increase in the concentration of dimethyl sulfoxide did not result in a further reduction in hydrogen peroxide-induced base damage. DNA which was freed from bound metal ions by pretreatment with metal ion chelators followed by exhaustive dialysis was found to be an ineffective substrate for hydrogen peroxide. The yields of base products measured in this DNA were at background levels. These results support the role of metal ions bound to DNA in the site-specific formation of highly reactive radical species, most likely hydroxyl radicals, in hydrogen peroxide-induced damage to the bases in DNA.

Base Sequence↗
PubMed1989

Damage to the bases in DNA induced by hydrogen peroxide and ferric ion chelates.

Incubation of a number of ferric ion chelates with H2O2 at pH 7.4 generated a reactive species able to produce chemical modifications of the bases in DNA that are very similar to those produced in DNA by the hypoxanthine/xanthine oxidase system (Aruoma, O.I., Halliwell, B., and Dizdaroglu, M. (1989) J. Biol. Chem. 264, 13024-13028). Products were identified and quantitated by the use of gas chromatography-mass spectrometry with selected-ion monitoring. Compared with other complexes used, ferric ion-nitrilotriacetic acid produced by far the largest amount of the base products. Typical hydroxyl radical scavengers and superoxide dismutase provided significant decreases in the yields of the products. On this basis, it is proposed that ferric ion complexes react with H2O2 to produce hydroxyl radical; this was also shown using the deoxyribose assay. Inhibition of product formation by superoxide dismutase suggests the involvement of superoxide radical in this reaction. It is likely that hydroxyl radical generated by reaction of the ferric ion-nitrilotriacetic acid complex with H2O2 contributes to the carcinogenicity and nephrotoxicity associated with this chelating agent.

DNA↗
PubMed1989

Iron ion-dependent modification of bases in DNA by the superoxide radical-generating system hypoxanthine/xanthine oxidase.

Damage to the bases in DNA produced by the hypoxanthine/xanthine oxidase system in the presence of iron ions was studied. The base products in DNA were measured using gas chromatography-mass spectrometry with selected ion monitoring after acidic hydrolysis of DNA and trimethylsilylation. Products identified were cytosine glycol, thymine glycol, 5,6-dihydroxycytosine, 4,6-diamino-5-formamidopyrimidine, 8-hydroxyadenine, 2,6-diamino-4-hydroxy-5-formamidopyrimidine, and 8-hydroxyguanine. These are typical hydroxyl radical-induced products of the bases in DNA. 2,6-Diamino-4-hydroxy-5-formamidopyrimidine was the major product, followed by 8-hydroxyguanine, in DNA treated with hypoxanthine/xanthine oxidase/Fe3+-EDTA. The use of Fe3+ did not cause as much damage to the bases in DNA as did the use of Fe3+-EDTA. In both systems, the formation of the products was inhibited by superoxide dismutase, catalase, dimethyl sulfoxide, mannitol, and desferrioxamine, but inhibitions were much stronger in the systems containing EDTA. Hence formation of hydroxyl radicals by a superoxide radical-assisted Fenton reaction is proposed to account for the results obtained. 2,6-Diamino-4-hydroxy-5-formamidopyrimidine, 5,6-dihydroxycytosine, 4,6-diamino-5-formamidopyrimidine, and 8-hydroxyguanine were proposed as the products in DNA to measure if one aims to measure DNA products as indices of oxidative DNA damage involving hydroxyl radicals in vivo.

Animals↗
PubMed1989

Structure and mechanism of hydroxyl radical-induced formation of a DNA-protein cross-link involving thymine and lysine in nucleohistone.

Hydroxyl radical-induced formation of a DNA-protein cross-link involving thymine and lysine in calf thymus nucleohistone in vitro is reported. Basic amino acids such as lysine constitute a very high proportion of the amino acids of histones, and help histones to bind to DNA in chromatin. For this reason, basic amino acids are likely to participate in DNA-protein cross-linking. For identification of the thymine-lysine cross-link in nucleohistone, hydroxyl radical-induced cross-linking of thymine to lysine was investigated first using a model system, i.e., an aqueous mixture of thymine and lysine. Hydroxyl radicals were generated by exposure of this mixture to ionizing radiation after N2O saturation. The technique of gas chromatography-mass spectrometry was used to analyze the samples for possible cross-links. One thymine-lysine cross-link was found and its structure was elucidated. Using gas chromatography-mass spectrometry with selected-ion monitoring, this thymine-lysine cross-link was identified in acidic hydrolysates of calf thymus nucleohistone gamma-irradiated in N2O-saturated aqueous solution. The yield of this DNA-protein cross-link was also measured and found to be a linear function of radiation dose between 15 and 200 Gy. This yield amounted to 0.0085 mumol/J. Possible mechanisms for the formation of this DNA-protein cross-link in nucleohistone were proposed.

Animals↗
PubMed1989

Structure of a hydroxyl radical induced DNA-protein cross-link involving thymine and tyrosine in nucleohistone.

Hydroxyl radical induced formation of a DNA-protein cross-link involving thymine and tyrosine in nucleohistone is described. Hydroxyl radicals were generated in N2O-saturated aqueous solution by ionizing radiation. Samples of nucleohistone were hydrolyzed with HCl and trimethylsilylated. Analysis of irradiated samples by gas chromatography-mass spectrometry with selected-ion monitoring showed the presence of a thymine-tyrosine cross-link on the basis of typical fragment ions from the previously known mass spectrum of its trimethylsilyl derivative. The yield of this DNA-protein cross-link in nucleohistone was measured at incrementing doses of radiation and found to be a linear function of radiation dose between 14 and 300 Gy (J.kg-1). This yield amounted to 0.003 mumol.J-1. The mechanism of formation of this DNA-protein cross-link is thought to result from H atom abstraction by hydroxyl radicals from the methyl group of thymine followed by the addition of the resultant thymine radical to the carbon 3 position of the tyrosine ring and subsequent oxidation of the adduct radical.

Animals↗
PubMed1989

Damage to the bases in DNA induced by stimulated human neutrophils.

Leukocyte-induced DNA damage may partially account for the known association between chronic inflammation and malignancy. Since elucidation of the chemical nature of leukocyte-induced DNA damage may enhance our understanding of the mechanisms underlying leukocyte-induced DNA damage and the carcinogenesis associated with inflammation, the present study was undertaken to characterize the chemical modifications that occur in DNA exposed to stimulated human neutrophils. Calf thymus DNA was exposed to phorbol myristate acetate (PMA)-stimulated neutrophils in the presence or absence of exogenously added iron ions. DNA samples were subsequently hydrolyzed, derivatized and analyzed by gas chromatography-mass spectrometry with selected-ion monitoring. A variety of base modifications including cytosine glycol, thymine glycol, 4,6-diamino-5-formamidopyrimidine, 8-hydroxyadenine, 2,6-diamino-4-hydroxy-5-formamidopyrimidine, and 8-hydroxyguanine were identified. The yield of these various base products was increased by the addition of iron ions. Specifically, in the presence of physiologic quantities of iron ions, approximately 7 of every 1,000 DNA bases were modified. Addition of the superoxide anion scavenger, superoxide dismutase, the hydrogen peroxide scavenger, catalase, the hydroxyl scavenger, dimethylsulfoxide, or the iron chelator, deferoxamine, to DNA mixtures containing PMA, neutrophils, and iron ions, greatly decreased the yield of the damaged DNA base products. Our results indicate that stimulated human neutrophils can damage each of the four bases in DNA. It is likely that hydroxyl radical, generated via an iron catalyzed Haber-Weiss reaction, mediates neutrophil-induced DNA base damage, since: (a) the chemical structure of neutrophil-induced DNA base damage is consistent with a hydroxyl radical-mediated mechanism, (b) hydroxyl radical generated via ionizing radiation in aqueous solution produces DNA base modifications that are identical to neutrophil-induced DNA base modifications, (c) iron ions increase neutrophil-induced DNA base damage, and (d) iron chelators or scavengers of superoxide anion, hydrogen peroxide or hydroxyl radical decrease neutrophil-induced DNA base damage.

Catalase↗
PubMed1989

Quantitative measurement of radiation-induced base products in DNA using gas chromatography-mass spectrometry.

Gas chromatography-mass spectrometry with selected-ion monitoring was used to study radiation-induced damage to DNA. Quantitative analysis of modified purine and pyrimidine bases resulting from exposure to ionizing radiation using this technique is dependent upon the selection of appropriate internal standards and calibration of the mass spectrometer for its response to known quantities of the internal standards and the products of interest. The compounds 6-azathymine and 8-azaadenine were found to be suitable internal standards for quantitative measurement of base damage in DNA. For the purpose of calibration of the mass spectrometer. relative molar response factors for intense characteristic ions were determined for the trimethylsilyl derivatives of 5-hydroxyuracil, thymine glycol, and 5,6-dihydrothymine using 6-azathymine, and for the trimethylsilyl derivatives of 4,6-diamino-5-formamidopyrimidine, 8-hydroxyadenine, 2,6-diamino-4-hydroxy-5-formamidopyrimidine, and 8-hydroxyguanine using 8-azaadenine. Accurate measurement of the yield of radiation-induced modifications to the DNA bases is also dependent upon two chemical steps in which the purines and pyrimidines are released from the sugar-phosphate backbone and then derivatized to make them volatile for gas chromatography. The completeness of these reactions, in addition to assessing the stability of the modified DNA bases in acid and their trimethylsilylated derivatives over the time necessary to complete the experimental analysis was also examined. Application of this methodology to the measurement of radiation-induced base modification in heat-denatured, nitrous oxidesaturated aqueous solutions of DNA is presented.

DNA↗
PubMed1988

Structure of a hydroxyl radical induced cross-link of thymine and tyrosine.

DNA-protein cross-links are formed when living cells or isolated chromatin is exposed to ionizing radiation. Little is known about the actual cross-linked products of DNA and proteins. In this work, a novel hydroxyl radical induced cross-link of thymine and tyrosine has been isolated along with a tyrosine dimer by high-performance liquid chromatography of aqueous mixtures of tyrosine and thymine that had been exposed to hydroxyl radicals generated by ionizing radiation. The isolated compounds have been examined by gas chromatography-mass spectrometry, high-resolution mass spectrometry, and 1H and 13C nuclear magnetic resonance spectroscopy. The structure of the thymine-tyrosine cross-link has been identified as the product from the formation of a covalent bond between the methyl group of the thymine and carbon 3 of the tyrosine ring. In addition, the 3,3' tyrosine dimer was isolated and characterized. The mechanism of the formation of these compounds is discussed. This work presents the first complete chemical characterization of a hydroxyl radical induced DNA base-amino acid cross-link.

Chromatography, High Pressure Liquid↗
PubMed1988

Effect of DNA conformation on the hydroxyl radical-induced formation of 8,5'-cyclopurine 2'-deoxyribonucleoside residues in DNA.

Reactions of hydroxyl radicals with DNA form a variety of base and sugar products and 8,5'-cyclopurine 2'-deoxyribonucleoside residues in DNA. Here we report the effect of DNA conformation on the yields of 8,5'-cyclopurine 2'-deoxynucleosides and the ratios of their (5'R)- and (5'S)-diastereomers. Calf thymus DNA in native (double-stranded DNA) or heat-denatured form (single-stranded DNA) was exposed to hydroxyl radicals generated by ionizing radiation in nitrous oxide-saturated phosphate buffer. Doses ranging from 10 to 40 Gy were used to ensure low levels of damage to DNA and thus to preserve its secondary structure in experiments with double-stranded DNA (ds-DNA). After irradiation, DNA was hydrolysed enzymatically to 2'-deoxyribonucleosides. The hydrolysates were dried, trimethylsilylated, and analyzed by capillary gas chromatography-mass spectrometry with selected-ion monitoring. An internal standard was used for quantitative measurements and added to DNA samples prior to enzymatic hydrolysis. The yields of 8,5'-cyclo-2'-deoxyadenosine and 8,5'-cyclo-2'-deoxyguanosine in single-stranded DNA (ss-DNA) were higher than those in ds-DNA. The (5'R)-diastereomers of both compounds were found to predominate over their (5'S)-diastereomers in ss-DNA. In contrast, the yields of the (5'S)-diastereomers in ds-DNA were slightly higher than those of the (5'R)-diastereomers. The G values of 8,5'-cyclo-2'-deoxyadenosine in ss-DNA and ds-DNA were 0.042 and 0.025, respectively. Those of 8,5'-cyclo-2'-deoxyguanosine in ss-DNA and ds-DNA were 0.038 and 0.017, respectively.

DNA↗
PubMed1988

Structure of hydroxyl radical-induced DNA-protein crosslinks in calf thymus nucleohistone in vitro.

Hydroxyl radicals are known to produce DNA-protein crosslinks in chromatin in vivo and in vitro. Here we investigated DNA-protein crosslinks formed between aliphatic amino acids and thymine in calf thymus nucleohistone exposed predominantly to hydroxyl radicals in gamma-irradiated N2O-saturated aqueous solution. Aliphatic amino acids are the predominant types of amino acids in the core histones of calf thymus, and thus are likely to form crosslinks with DNA. For identification of the crosslinks we first investigated hydroxyl radical-induced crosslinking of thymine to aliphatic amino acids in model systems, i.e. an aqueous mixture of thymine and a single amino acid. Samples were analyzed for possible thymine-amino acid crosslinks by gas chromatography-mass spectrometry. Using this approach the structure of the crosslinks was elucidated, and information on their gas chromatographic and mass spectral properties was obtained. Gas chromatography-mass spectrometry with selected-ion monitoring (GC-MS/SIM) was then used to identify DNA-protein crosslinks in acidic hydrolysates of calf thymus nucleohistone exposed to ionizing radiation in buffered aqueous solution. DNA-protein crosslinks involving thymine and the amino acids Gly, Ala, Val, Leu, Ile and Thr were identified. In some cases several isomers of the same crosslink were observed. The yield of the crosslinks was measured by GC-MS/SIM and was found to be a linear function of radiation dose in the range 49 to 436 Gy. The mechanism for the formation of these DNA-protein crosslinks is thought to involve hydrogen atom abstraction by hydroxyl radicals from the aliphatic amino acid followed by addition of the amino acid radical to the carbon(6)-position of thymine and subsequent oxidation of the adduct radical.

Amino Acids↗
PubMed1988

Intramolecular H atom abstraction from the sugar moiety by thymine radicals in oligo- and polydeoxynucleotides.

Hydroxyl radical addition to uracil (U) has been suggested to lead to strand breaks in polyuridylic acid, an occurrence attributed in part to H atom abstraction by .U-OH radicals from the ribose moiety [D.G.E. Lemaire et al., Int. J. Radiat. Biol. 45, 351-358 (1984)]. We have investigated this particular reaction by means of the hydroxyl radical-induced products of thymine (T), pT, TpT, TpTpT, polythymidylic acid (poly-T), (T + dR) poly-dA.poly-T, and a mixture of T and 2-deoxyribose (dR). The major monomeric product of .T-OH in TpT, TpTpT, poly-T, and poly-dA.poly-T was found to be 5-hydroxy-6-hydrothymine (H-T-OH), while that in T, pT, and T plus dR was thymine glycol (HO-T-OH). These results indicated that the intramolecular H atom abstraction from a nearby sugar (in this case, deoxyribose) moiety by base radicals, i.e., .T-OH, occurs in oligo- and polydeoxynucleotides of T. In poly-T, the yield of H-T-OH is not much greater than in TpT or TpTpT, indicating that the abstraction of an H atom from the sugar moiety of a nucleotide subunit further than two nucleotides along the chain may not be significant. Additionally, a corresponding decrease in the yield of HO-T-OH with an increase in the yield of H-T-OH suggests that the formations of these two types of thymine products are competitive.

Cobalt Radioisotopes↗