Effects of sulphydryl compounds on the radiation damage in biologically active DNA

The effect of sulphydryl compounds on the induction of alkali-labile sites and on the contribution of such sites to the inactivation of single-stranded phi X174 DNA was studied. Cysteamine is capable of reacting with DNA radicals, thereby modifying the radiation damage in such a way that the induction of immediate and latent breaks is reduced. This depends on the pH of the solution. With cysteine only, a pH dependent protection, against lethal alkali-labile potential breaks could be observed. The damage other than breaks is not influenced by the presence of sulphydryl compounds.