Photodynamic activity of acridine orange: peroxide radical induction in DNA and synthetic polynucleotides.

As shown by electron paramagnetic resonance, acridine orange induces the formation of peroxide radicals in DNA when dye-DNA mixtures frozen at 77 K are irradiated with visible light. The reaction is oxygen dependent and strongly reduced by the addition of an electron scavenger. Factors of the medium can modulate the reaction: an ionic strength increased up to 0.3 greatly enhances the dye efficiency whereas the presence of phosphate ions has an inhibiting influence. Acridine orange, which is slightly less efficient than proflavine on native DNA, induces an important peroxide radical formation in poly(dG).poly(dC) but has no action on the poly(dA).poly(dT)polymer.