Splitting of Cis-syn Cyclobutane Thymine-thymine Dimers by Radiolysis and Its Relevance to Enzymatic Photoreactivation

Abstract

The ¹³⁷Cs-γ-irradiation of cis-syn thymine-thymine cyclobutane type dimers has been studied in aqueous solution. The mechanism of thymine dimer cleavage by e_aq⁻, 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.