Ferric and Cupric Ions Requirement for DNA Single-Strand Breakage by H₂O₂

Abstract

Hydrogen peroxide (H2O2), was able to nick the replicative form of the phage fd, without the addition of a reducing agent or of a metal. This DNA single-strand breakage decreased with an increase of the ionic strength, suggesting that H2O2 reacted with traces of metal bound to DNA. When cupric of ferric ions were added, the rate of DNA single-strand breakage by H2O2 greatly increased and it was 20-30 times faster with cupric than with ferric ions. The addition of EDTA at an equimolar ratio or in excess of metal prevented partially DNA single-strand cleavage by H2O2 in the presence of ferric ions and completely when cupric ions were used. Superoxide dismutase prevented DNA single-strand breakage by H2O2 and ferric ions. On the contrary, with cupric ions and H2O2, the addition of superoxide dismutase increased the rate of DNA single-strand breakage. That superoxide dismutase was acting catalytically was shown by the loss of its effects after heat inactivation of the enzyme. The results of the present study show that besides its involvement in the Fenton reaction, H2O2 is able to reduce the metal bound to DNA, generating the superoxide anion radical or/and its protonated form, the perhydroxyl radical involved in DNA nicking. On the other hand, the ability of cuprous ions unlike ferrous ions to dismutate the superoxide radical may explain some differences observed between iron and copper in the DNA single-strand breakage by H2O2.

Interactions and Reactions of Ferritin with DNA

“…Supercoil Relaxation Assay-DNA backbone breakage was detected using a superhelical DNA relaxation assay (30). Supercoiled plasmid pUC19 DNA (31) was used as substrate.…”

Hepatic iron deprivation prevents spontaneous development of fulminant hepatitis and liver cancer in Long-Evans Cinnamon rats.

“…seen in the LEC rat does not normally cause hepatoma in rats, and ferrous iron can reduce copper to the cuprous ion which is a more potent generator of hydroxy radicals than ferrous ions (35), iron may be acting synergistically with copper in the carcinogenesis. Further studies may be needed to prove a direct relationship between iron and carcinogenesis in LEC rats.…”

Characterization of an activity from the strict anaerobe Roseburia cecicola that degrades DNA when exposed to air

“…Hydroxyl radicals are thought to be generated in biological systems predominantly when H202 is reduced by transition metals (1,12,18,19,33). Although a number of transition metals can catalyze this reaction in vitro, the most abundant and therefore the most probable metal to catalyze the reaction in vivo is iron (Fenton reaction).…”

“…9) (6,15,33) and are therefore unlikely to be directly responsible for chromosomal degradation. The hydroxyl radical (OH.…”

“…For example, hydroxyl radicals, like purified extracts, degrade nucleic acids in a manner that is not inhibited by increases in temperature or moderate changes in pH (26,27,33). Moreover, the selective manner in which certain topological forms of plasmid DNA are degraded by purified extracts is identical to that observed when plasmid DNA is incubated with compounds that generate OHS via a Fenton reaction (4,28,33). We have also found that purified extracts are capable of degrading exogenous sources of RNA under aerobic conditions (unpublished data).…”