The role of high ionic concentrations in protection against X-irradiation

Various levels of protection against x-irradiation damage in bacteriophage T1 may be obtained by the addition of inorganic salts to the aqueous virus suspensions during irradiation. The highest survival values are obtained with the nitrite salts, and their protective power is attributed primarily to their function as reducing agents. The nitrate ion shows greater protection than the corresponding sulfate or chloride ions. This may be due in part to the lower energy level of the nitrate ion, by reason of resonance. Since greater expenditure of incident energy is required to raise the ion from the ground state, the energy thus dissipated may be ineffective in the inactivation of virus particles. The ammonium salts exhibit protection of a different order of magnitude from that of the metallic salts. It is postulated that NH₄⁺ protects in a threefold way: (a) dehydration, (b) reduction, in which the ammonia is oxidized to nitrite and the nitrite to nitrate, and (c) stabilization of the virus protein. Metallic salts likewise protect, but a point of maximum protection is reached in lower concentrations than in the case of the ammonium salts. After this maximum protection is reached, there is a rapid decline in survival with increased concentration. This prevents protection of the order of magnitude that can be obtained with the ammonium salts. It is postulated that a specific cationic interaction with the phage may be responsible for the decreased protection. Bacteriophage is protected during x-irradiation by an alkaline pH, in the case of NH₄OH. This protection could not be produced with NaOH, presumably because of the greater hydrolysis of the protein components of the virus particle in solutions of NaOH, whereas NH₄OH stabilizes the protein.