Change in DNA after Exposure to Hydrogen Atoms.

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The action of hydrogen atoms — generated in an electrodeless high frequency gas discharge — on calf thymus DNA in aqueous solution was investigated. The loss of priming activity was compared with the appearance of single strand breaks in native and denatured DNA, double strand breaks, denatured zones, base damage and rupture of hydrogen bonds. The primary lesions after exposure to H atoms and gamma radiation, respectively, are single strand breaks and base damage. Double strand breaks originating from accumulation of single breaks, and rupture of hydrogen bonds caused by single breaks and base damage, were identified as secondary lesions. In relation to strand breaks arising from radical attack on the sugar-phosphate backbone of the DNA molecule, base damage is about 12.5 times more frequent after Η-exposure than after γ-irradiation. It is concluded from this observation, that single strand breaks are the predominant critical lesions responsible for the loss of the functional activity of DNA.