THE PHOTODYNAMIC EFFECT OF HEMATOPORPHYRIN ON DNA

Abstract— Breakage of DNA in vitro and inside E. colt cells has been determined after exposure to monochromatic 365 nm light in the presence of 10 µM hematoporphyrin. When measured by alkaline sucrose sedimentation, the yields of breaks were 1.4 × 10^-12 per dalton and per J/m² for Col El-DNA in vitro and 5.9 × 10^-3 per dalton and per J/m² for superinfecting phage Λ DNA inside E. coli cells made permeable by toluene. No breaks were found by neutral sucrose sedimentation, demonstrating that the lesions represent alkali-labile bonds. The majority of the alkali-labile bonds were induced by singlet oxygen, as evidenced by the several-fold higher yield obtained in D₂O-containing buffer.