Double‐strand break of giant DNA: protection by glucosyl‐hesperidin as evidenced through direct observation on individual DNA molecules

We have performed a real‐time observation of photo‐induced breakage on individual long DNA molecules stained by a cyanine dye, YOYO, under the intense illumination (λ=450–490 nm) in solution. It was shown that the double‐strand breakage is accelerated by Fenton's reagent (Fe2+/H2O2). In addition, it was found that the breakage reaction is protected in the presence of a water‐soluble flavonoid, glucosyl‐hesperidin. To interpret the kinetic process of the double‐strand breakage reaction, a two‐step mechanism is proposed: under light illumination on giant DNA molecules, single‐strand breaks are generated to induce nicks in a stochastic manner, and then reactive oxygen attacks these nicks causing the double‐strand break.