Harold C. Box

Free radical-induced double base lesions

Evidence is presented for the formation of products in irradiated dinucleoside monophosphates in which both bases are damaged. The dinucleoside monophosphates d(GpT), d(GpC), d(TpG) and d(CpG) were X-irradiated in oxygenated aqueous solution. Product identification was by NMR spectroscopy. In products containing double base lesions, guanine is converted to 8-hydroxyguanine and the pyrimidine base is degraded to a formamido remnant.

Paramagnetic Absorption of Single Crystals of Succinic Acid Irradiated at Low Temperature

Electron spin resonance absorption was observed in single crystals of (–CH2–COOH)2, (–CH2–;COOD)2, and (–CH2–13COOH)2 irradiated at 77°K. The principal paramagnetic species observed at low temperature has an unpaired electron in a 2pπ orbital on the carbon atom of the carboxyl group. It is probably ionized succinic acid with the oxygen of the carboxyl group carrying a negative charge.

Tandem lesions and other products in X-irradiated DNA oligomers

Free radicals interact with DNA bases to produce secondary radicals. The secondary radicals are reactive species and tend to interact with neighboring bases, resulting in DNA lesions with two adjacent modified bases. In this study the DNA oligomers d(CpApTpG) and d(CpGpTpA) were exposed to free radicals generated in anoxic aqueous solution by X irradiation. Four new lesions were identified in which adjacent guanine and pyrimidine bases are covalently bonded. One of the tandem lesions formed in d(CpGpTpA) has the C5 carbon atom of cytosine covalently bonded to the C8 carbon atom of guanine. Interestingly, the same bond is formed between the terminal bases in d(CpApTpG), resulting in a cyclized molecule.

Primary radiation damage in thymidine

Several primary radiation products produced by ionizing radiation in the nucleoside thymidine have been stabilized at 4.2°K; two have been identified by ESR−ENDOR spectroscopy. One of these products is formed by reduction of the thymine ring. The other product results from the loss of a hydrogen atom from the 5′−hydroxy group.

Free radical formation in x‐irradiated histidine HCl

ENDOR spectroscopy was used to identify three primary radicals in single crystals of histidine hydrochloride x irradiated at 4.2°K. Oxidation leads to decarboxylation producing the radical R–CH2–CH–NH3+, where R stands for the protonated imidazole ring. Another oxidation product is produced by removal of an electron from the imidazole ring. The reduction process yields a carboxyl anion by addition of an electron to the carbonyl oxygen. ENDOR spectroscopy was also used to characterize more completely the final hydrogen‐adduct radical that is obtained on warming the crystals to room temperature.

ESR and ENDOR studies of DL‐serine irradiated at 4.2 °K

The primary products formed by ionizing radiation in single crystals of DL‐serine were studied by ESR and ENDOR spectroscopy. The crystals were maintained at 4.2 °K during irradiation and measurement. The primary reduction product is formed by the addition of an electron to the carbonyl oxygen of the carboxyl group. The primary oxidation product is a radical resulting from decarboxylation. A third product is a radical formed from serine by removal of hydrogen from the hydroxy group.

Radiation-Induced Formation of a Crosslink between Base Moieties of Deoxyguanosine and Thymidine in Deoxygenated Solutions of d(CpGpTpA)

A new type of tandem base lesion has been observed in d(CpGpTpA) X-irradiated in aqueous solution. The lesion is attributed to the formation of a covalent bond between the C8 carbon atom of guanine and the methyl carbon atom of thymine. This tandem base lesion is formed in the absence of oxygen. It is the main product produced by ionizing radiation under these conditions.

Double Base Lesions in DNA X-Irradiated in the Presence or Absence of Oxygen

Abstract Box, H. C., Patrzyc, H. B., Dawidzik, J. B., Wallace, J. C., Freund, H. G., Iijima, H. and Budzinski, E. E. Double Base Lesions in DNA X-Irradiated in the Presence or Absence of Oxygen. Previously, double lesions in which two adjacent bases are modified were identified in DNA oligomers exposed in solution to ionizing radiation. However, the formation of such lesions in polymer DNA had not been demonstrated. Using reference oligomer containing a specific double lesion and employing liquid chromatography-mass spectrometry (LC-MS), it was possible to show directly that double lesions are formed in irradiated calf thymus DNA. The double lesion in which a pyrimidine base is degraded to a formamido remnant and an adjacent guanine base is oxidized to 8-oxoguanine was detected in DNA X-irradiated in oxygenated aqueous solution. The double lesion in which the methyl carbon atom of a thymine base is covalently linked to carbon at the 8-position of an adjacent guanine base was detected in DNA irradiated in a deoxygenated environment.

ENDOR Study of X‐Irradiated Single Crystals of Ice

ENDOR measurements were made on x‐irradiated single crystals of hexagonal ice. The ENDOR frequencies yield the hyperfine coupling for the OH radicals produced in irradiated ice. The method is capable of distinguishing between OH radicals produced in three different environments. The principal values of the hyperfine coupling tensors in megacycles per second of the three distinct OH radicals are as follows: AxxAyyAzz(I)− 80.0− 124.4+ 9.2(II)− 81.2− 124.4+ 19.4(III)− 78.2− 126.2+ 15.6 Using ESR spectra in conjunction with ENDOR data, the g tensors were also determined with the following results: gxxgyygzz(I)2.00282.00892.0597(II)2.00312.00892.0571(III)2.00272.00882.0581

Conformations of the Free Radical in Irradiated α‐Aminoisobutyric Acid

The electron paramagnetic resonance spectrum of x‐irradiated α‐aminoisobutyric acid was studied in single crystals irradiated at 77°K and allowed to warm up gradually. Different conformations of the free‐radical (CH3)2CCOOH were observed. The g tensor and the hyperfine splitting tensor were determined for each conformation.