Mechanism of DNA Cleavage Induced by Fe2+Autoxidation

Abstract

This work investigated the difference between <TEX>$Fe^{2+}$</TEX> autoxidation-induced and Fenton-type cleavage of pBR322 plasmid DNA. <TEX>$^{\cdot}OH$</TEX> generation reactions in the absence and presence of <TEX>$H_2O_2$</TEX> under various conditions were also investigated. Although both the <TEX>$Fe^{2+}$</TEX> autoxidation and Fenton-type reactions showed DNA cleavage and <TEX>$^{\cdot}OH$</TEX> generation, there were significant differences in their efficiencies and reaction rates. The rate and efficiency of the cleavage reaction were higher in the absence of 1.0 mM of <TEX>$H_2O_2$</TEX> than in its presence in 20 mM phosphate buffer. In contrast, the <TEX>$^{\cdot}OH$</TEX> generation reaction was more prominent in the presence of <TEX>$H_2O_2$</TEX> and showed a pH-independent, fast initial reaction rate, but the rate was decreased in the absence of <TEX>$H_2O_2$</TEX> at across the entire tested pH range. Studies using radical scavengers on DNA cleavage and <TEX>$^{\cdot}OH$</TEX> generation reactions in both the absence and presence of <TEX>$H_2O_2$</TEX> confirmed that both reactions spontaneously involved the active oxygen species <TEX>$^{\cdot}OH$</TEX>, <TEX>${O_2}^{\cdot-}$</TEX>, <TEX>$^1O_2$</TEX> and <TEX>$H_2O_2$</TEX>, indicating that a similar process may participate in both reactions. Based on the above observations, a new mechanism for the <TEX>$Fe^{2+}$</TEX> autoxidation-induced DNA cleavage reaction is proposed.