The Role of Reactive Oxygen Species in the Light-Induced Deformation of DNA

Dimerizations and reactions with water of pyrimidine bases are the primary steps held respon­ sible for the deformation o f D N A at short wavelengths in vitro and in vivo experiments. H owever the influence of oxygen in combination with water on the U V deformation at wavelengths rep­ resentative for troposphere is evident from the observed data and both together are needed to change the D N A structure. The only plausible explanation for the effect of oxygen is the forma­ tion o f reactive oxygen species during the U V irradiation of D N A . In the present work the deformation of D N A by different oxygen species like singlet oxygen ( ' 0 2), superoxideanion ( 0 2~‘), hydroxyradical ( O H ), ozone ( 0 3) and hydrogenperoxide (H 20 2) is excluded with the help o f chemical-trapping experiments. The photo-induced transformation proceeds via excited states of D N A , which react with groundstate oxygen to afford peroxide.