PHOTOINDUCTION OF STRAND SCISSIONS IN DNA BY KOJIC ACID - ROLE OF TRANSITION-METAL IONS AND OXYGEN FREE-RADICAL INTERMEDIATES IN THE REACTION

Kojic acid (5-hydroxy-2-hydroxymethyl-gamma-pyrone) is a bacterial metabolic product used intensively in the food industry. In the presence of visible light and molecular oxygen it was found to cause breakage of calf thymus DNA. Such degradation was considerably enhanced in the presence of the transition metal ions Fe(III), Fe(II) and Cu(II). The cleavage of DNA in the presence of Fe(III) did not appear to have any preferred site(s) or sequence(s) for strand scission. Kojic acid catalysed the reduction of transition metal which in the case of Cu(II) was found to play an essential role in the degradation of DNA. Kojic acid also reduced oxygen to superoxide and hydroxyl radicals were formed in the presence of metal ions. The involvement of these active oxygen species in the reaction was established by the inhibition of DNA breakage by superoxide dismutase, catalase, iodide, mannitol, formate and sodium azide.