Superoxide Dismutase Enhanced the Formation of Hydroxyl Radicals in a Reaction Mixture Containing Xanthone under UVA Irradiation

To clarify the effect of superoxide dismutase (SOD) on the formation of hydroxyl radical in a standard reaction mixture containing 15 μM of xanthone, 0.1 M of 5,5-dimethyl-1-pyrroline N-oxide (DMPO), and 45 mM of phosphate buffer (pH 7.4) under UVA irradiation, electron paramagnetic resonance (EPR) measurements were performed. SOD enhanced the formation of hydroxyl radicals. The formation of hydroxyl radicals was inhibited on the addition of catalase. The rate of hydroxyl radical formation also slowed down under a reduced oxygen concentration, whereas it was stimulated by disodium ethylenediaminetetraacetate (EDTA) and diethyleneaminepentaacetic acid (DETAPAC). Above findings suggest that O₂, H₂O₂, and iron ions participate in the reaction. SOD possibly enhances the formation of the hydroxyl radical in reaction mixtures of photosensitizers that can produce O₂ ^?·.