The Radiosensitivity of Bacteriophage DNA in Aqueous Solution

Abstract

The effect of soft X-rays on the biological activity of air-saturated aqueous solutions of single-stranded DNA of the bacteriophage [phi]X174 was studied. The inactivation is due to OH radicals, as follows from the large increase of the 37% survival dose if these radicals are scavenged by iodide ions. O2- radicals, produced by the reaction of hydrated electrons with oxygen, do not inactivate DNA. In dilute solutions of DNA the inactivation rate at low dose was much smaller than expected from the rate of base destruction as determined from the decrease of optical density at higher dose. This could be explained from the nonuniform nucleotide concentration in such solutions, which enhance the scavenging efficiency of impurities. At DNA concentrations above 1 mg/ml this effect diasppears gradually. The protection afforded by various concentrations of a mixture of free nucleotides in a molar ratio corresponding to the base composition of DNA indicates that free nucleotides react faster with free radicals than do nucleotides in DNA.