Effects of ionising radiation on deoxyribonucleic acid. Part VI.—Effects of hydroxyl radical scavengers on radiation damage to DNA

Abstract

Exposure of dilute aqueous DNA to ionizing radiation at ambient temperatures results in indirect damage to the DNA, major reactions being the addition of ˙OH radicals to DNA bases and abstraction of C—H hydrogen atoms from deoxyribose units. In order to concentrate on direct damage processes, we have studied frozen aqueous solutions, but it remains possible that some damage is still caused by ˙OH radicals generated close to DNA molecules.

In order to check this, we have used two ˙OH radical scavengers, dimethyl sulphoxide (DMSO) and t-butyl alcohol (TBA). For both, in low concentrations (⩽ 1 : 1, base-pair), the damage is confined to DNA and exactly corresponds to normal damage in the absence of scavengers. In a second series of experiments, solid solutions containing hydrogen peroxide were photolysed with UV light at 77 K. This gave a poorly defined sextet assigned to sugar radicals or possibly to thymine ˙OH-radical adducts, which was not detected in the absence of hydrogen peroxide, or during γ-radiolysis. We conclude that hydroxyl radical attack is not important for fully hydrated frozen DNA.

The nature and significance of a range of other radicals detected in DNA solutions more concentrated in DMSO and TBA are also discussed, together with the identification of a species giving a broad singlet in the hydrogen peroxide studies.