Studies on the Chemical Basis of Cellular Radiosensitization by 5-bromouracil Substitution in DNA

Abstract

Pulse- and steady-state radiolysis techniques were combined in a comparative study of the radiation chemistry of aqueous oxygen-free solutions of 5-bromouracil (BU) and thymine (T). The results show several important differences in the radiolysis of these two molecules, which may form the chemical basis of BU sensitization. The hydrated electron (e_aq⁻, ·CO₂⁻, and certain organic radicals destroy BU by reactions which yield a uracilyl radical and Br⁻. In contrast, these species are not important in T destruction. The uracilyl radical is a transient species having a weak absorption maximum at 335 nm. It is very reactive, being able to abstract H· from a variety of molecules to form uracil and to propagate a chain reaction in formate BU solutions.