The Role of Cystamine-nucleic-acid Interactions in Protection against X-ray-induced Damage of DNA

SummaryThe ability of different disulphides to protect solutions of calf-thymus DNA against x-ray-induced damage has been compared. Degradations of the DNA were followed by determining shifts of the Tm value and by determining changes in the ability of DNA to act as primer for the enzymic synthesis of RNA.Diamino-disulphides such as cystamine, which readily interact with DNA, offered significantly better protection of the DNA than diacetyl cystamine and oxidized glutathione. The difference proved to be due, at least in part, to the cystamine-nucleic-acid interaction. These data suggest that diamino-disulphides are efficient protectors of DNA because (a) they contain a disulphide group, (b) they stabilize the DNA-helix, and (c) a substantial amount of the disulphide is localized on the DNA molecule.Radiation-damage of the priming activity of DNA was only partially prevented by the disulphides. No difference in the (weak) protective effect of cystamine and diacetyl cystamine was observed.The possible significance of the cystamine-DNA interaction for radioprotection of DNA in vivo is discussed.