Sensitization to X-rays of Transforming DNA by Ag⁺

Summary

A transforming DNA system has been used to study the effect of silver ion on the X-ray-induced inactivation of the functional ability of DNA. In N₂ transforming DNA is sensitized to radiation by Ag⁺, with the maximum sensitization occurring at a ratio of one Ag⁺ added per DNA base. This response can be partially prevented by addition of ^·OH scavengers. In O₂ the transforming DNA is only slightly sensitized by Ag⁺ except at very high Ag⁺ concentrations. These results are interpreted in terms of the e⁻_aq sequestration theory of radiation sensitization. Studies on the binding of Ag⁺ to DNA show that at the maximum sensitization in N₂, there is one Ag⁺ bound per DNA base pair and that this binding is unaffected by ^·OH scavengers, although radiation may change these binding properties. Steady-state radiation chemistry studies indicate a difference in the response of DNA-Ag⁺ complexes to irradiation in N₂ and in O₂. As with the transforming DNA studies, these can be interpreted in terms of the e⁻_aq sequestration theory of radiation sensitization.