PROTECTION OF DNA AGAINST IONIZING RADIATION BY ACTINOMYCIN D IN VITRO

Highly-polymerized salmon-sperm DNA was irradiated in solution with and without Actinomycin D, Actinamine and the radiation-protective agent bis(2-guanidoethyl)disulphide (GED). The specific viscosity of these solutions was determined as a measure of DNA damage. Without the added agents, 25 kR (60Co γrays) reduced specific viscosity measured at 30° to less than 20 per cent of the unirradiated DNA solutions. Actinomycin D and GED preserved over 90 per cent of the specific viscosity. When viscosity was measured at 90° where DNA exists as single strands, 25 kR reduced specific viscosity to less than 10 per cent, GED showed some protection, and Actinomycin D still preserved 90 per cent of the viscosity. Actinamine was non-protective. Binding of the agents to DNA was measured by equilibrium dialysis and showed the following order: Actinamine > Actinomycin D > GED. The results indicated that protection of DNA in this system depends on (1) the structure of the protective agent, (2) the amount of agent bound to DNA, and (3) the nature of the binding of the agent to DNA. © 1969 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.