The action of γ -rays on sodium deoxyribonucleate in solution - III. Denaturation

Abstract

The displacement of the titration curves at 25°C of herring sperm sodium deoxyribonucleate ( DNA ) irradiated in solution by γ -rays has been confirmed. Values for the mean extent of denaturation (β - ) which have been deduced from such curves agree with those obtained from the reversible titration curves that DNA exhibits at -0∙7°C. One effect of γ -irradiation was to displace these reversible curves asymmetrically in a manner which suggested that the hydrogen bonds linking adenine and thymine were more susceptible to rupture by γ -irradiation than were those which link cytosine and guanine. The logarithm of the fraction of titratable groups in helical regions of the DNA was a decreasing linear function of radiation dosage and the significance of this observation is discussed. In the first stages of irradiation, the rupture of cross-linking hydrogen bonds is very efficient and has a G value of thirty-eight base-pairs severed per 100 eV.