title: Inability of chemically generated singlet oxygen to break the DNA backbone.
abstract: The capacity of a photodynamic and a chemical source of singlet molecular oxygen to cause DNA strand breakage at pH 7.8 was compared in the following systems: (1) dissolved rose bengal plus light (400-660 nm), (2) a novel water-soluble naphthalene-derived endoperoxide showing temperature-dependent singlet oxygen release, in the absence of light. Covalently closed circular DNA was efficiently converted to the open (relaxed) form upon exposure to dissolved rose bengal plus light in a time-dependent reaction, showing that this system was capable of causing DNA strand breakage at pH 7.8. The reaction was greatly reduced under hypoxic conditions (less than 5 p.p.m. O2), was stimulated when using D2O instead of H2O as a solvent and was not inhibitable by superoxide dismutase, indicating that singlet oxygen was a critical intermediate. However, comparatively large fluxes of singlet oxygen generated by the endoperoxide completely failed to produce DNA strand breaks. We conclude that, although singlet oxygen seems to play a role in DNA strand breakage by rose bengal plus light, singlet oxygen per se is very inefficient if not completely incapable of causing DNA strand breakage.
mesh_terms: D004249:DNA Damage; D004269:DNA, Bacterial; D003903:Deuterium; D004587:Electrophoresis, Agar Gel; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008027:Light; D010100:Oxygen; D010777:Photochemistry; D012395:Rose Bengal; D012995:Solubility
chemical_list: D004269:DNA, Bacterial; D012395:Rose Bengal; D003903:Deuterium; D010100:Oxygen