Splitting of cis-syn cyclobutane thymine-thymine dimers by radiolysis and its relevance to enzymatic photoreactivation.

The 137Cs-gamma-irradiation of cis-syn thymine-thymine cyclobutane type dimers has been studied in aqueous solution. The mechanism of thymine dimer cleavage by eaq-, CO2.-, OH.,SO4.-,Br2.- and isopropanol radicals was studied using high pressure liquid chromatography (HPLC). Evidence that the one-electron reductants studied induce dimer cleavage partially by a chain reaction is presented. Approximate values for the one-electron reduction potential of thymine-thymine are obtained and thermodynamic calculations are presented in order to predict the direction of electron transfer in the case of enzymatic photoreactivation.