Further observations on the photooxidation of DNA in the presence of riboflavin

Abstract

Illumination of DNA in the presence of riboflavin results in an increase in buoyant density and a decrease in the temperature of the thermal helix-coil transition ( T m ). The increase in buoyant density is maintained even after thermal denaturation, which indicates that it reflects a chemical alteration of a DNA base (presumably guanine). β-Carotene, a quencher of singlet oxygen, inhibits the increase in buoyant density but it prevents only partially the decrease in T m . This is taken as an indication that the photo-induced alteration of the DNA structure is due to more than one reaction. Illumination of DNA in the presence of methylene blue also causes an increase in buoyant density, but this increase is not retained upon thermal denaturation.