Photoinduction of strand scissions in DNA by kojic acid: role of transition metal ions and oxygen free radical intermediates in the reaction

Abstract

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.

Tunable DNA Photocleavage by an Acridine−Imidazole Conjugate

“…Spectrophotometric Determination of Fe(II) and V(IV). To test for photoreduction of Fe(III), we employed 1,10-phenanthroline, which forms a stable complex with Fe(II) (λ max = 510 nm) . Because vanadium(IV) reduces ferric to ferrous ions, we then used a modified version of this colorimetric assay to detect V(IV) .…”

“…To test for photoreduction of Fe(III), we employed 1,10phenanthroline, which forms a stable complex with Fe(II) (λ max ) 510 nm). 21 Because vanadium(IV) reduces ferric to ferrous ions, we then used a modified version of this colorimetric assay to detect V(IV). 22 For determination of Fe(II), individual photolysis reactions contained 20 mM sodium phosphate buffer pH 7.0 with two or more of the following reagents: 50 µM compound 7; 25 µM FeCl 3 ‚6H 2 O; 400 µΜ 1,10-phenanthroline monohydrate.…”

“…Colorimetric Detection of Fe(II). 21 A series of 500 µL reactions was prepared containing 20 mM sodium phosphate buffer pH 7.0 and two or more of the following reagents: 50 µM 7; 25 µM FeCl 3 ‚ 6H 2 O; 400 µΜ 1,10-phenanthroline monohydrate. The samples were irradiated with the 4W F4T5/D fluorescent lamp, while a parallel set of reactions was kept in the dark.…”