ACETOPHENONE PHOTOSENSITIZATION OF THYMINE DIMER FORMATION IN AQUEOUS-SOLUTIONS OF CALF THYMUS DNA

The acetophenone-photosensitized formation of the cis-syn cyclobutane thymine dimer between two contiguous thymines on a strand of naked calf thymus DNA has been used to construct a preliminary model for the reaction kinetics of DNA. Eleven elementary steps have been proposed to describe the processes involved. Rate constants were initially assigned either from analogous values in the literature or by calculation for reactions that were thought to be diffusion controlled. The reaction scheme was then computer simulated and the rate constants were optimized to give agreement between the predictions of the computer model and the experimental data. The values arrived at in this manner agreed with those obtained from Stern-Volmer plots based on the mechanism. Mechanisms of the type proposed here could be used to provide a quantitative basis for the relationship between absorbed radiation and cellular events, in particular those causing cell death. Similar mechanisms could be applied to the reactions of DNA with chemicals.