The reactions of hydrogen atoms with samples of calf and salmon deoxyribonucleic acid (DNA) have been investigated by an electron spin resonance technique. The reactions with component DNA nucleotides and deoxyribose were also investigated to aid in the interpretation of the DNA results. Analysis of the resultant ESR spectra was facilitated by use of a computer spectrum simulation technique. The results showed that hydrogen atoms react mainly by addition to purine (49%) and thymine (23%) base groups in DNA. The extent of attack on each base is roughly in proportion to the percentage of the base present in DNA. This result is in contrast to radiolysis where preferential attack on the thymine base occurs. Approximately 20% of the hydrogen atoms react with the deoxyribose groups in the backbone of the DNA molecule. The presence of histones in the samples is shown to inhibit hydrogen atom addition. It is expected that the presence of histones in vivo will protect DNA from hydrogen atom attack during radiolysis.

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Copyright 1969 Academic Press, Inc.
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