Fe²⁺, Fe³⁺, and Oxygen React with DNA-Derived Radicals Formed during Iron-Mediated Fenton Reactions

Abstract

Oxidative DNA damage is decreased by the presence of O2 during Fe(2+)-mediated Fenton reactions when H2O2 is in excess. During these reactions, the presence of DNA increases H2O2 consumption relative to Fe2+ consumption under anaerobic conditions, but decreases H2O2 consumption relative to Fe2+ consumption under aerobic conditions. The pseudobimolecular rate constant of H2O2 consumption is the same under both conditions, however, indicating that the presence of DNA affects the oxidation and/or reduction of the iron pool. To understand the basis of these effects, DNA was replaced with ethanol as a model compound. Computer simulations of Fe2+ and H2O2 consumption were experimentally verified and allowed identification of the predominant reactions leading to the changes in stoichiometry. Based upon these results and upon qualitative and quantitative differences in DNA damages between aerobic and anaerobic conditions, it was concluded that, in the presence of DNA, Fe3+ is reduced by some DNA radicals. However, if O2 is present, these radicals react instead with O2 and the product of these reactions can then oxidize Fe2+. Mechanisms proposed for the alteration by O2 of products from dC- and dG-containing substrates after exposure to Fe and H2O2 fit these general schemes. These results provide another distinction between DNA damage caused by ionizing radiation and that caused by Fenton reactions.

Integrative Modeling of Oxidative Stress and C1 Metabolism Reveals Upregulation of Formaldehyde and Downregulation of Glutathione

“…Based on the systematic literature review, three major molecular systems that are involved in the oxidative stress pathway in plants are identified: These included: 1) lipid peroxidation pathway [9], 2) ascorbate-glutathione pathway [10], and 3) ROS production pathway [11].…”

“…ROS in the form of 2 O − radicals generates H 2 O 2 by the action of the anti-oxidant enzyme superoxide dismutase (SOD) [11]. The enzyme catalase decomposes H 2 O 2 into H 2 O and O 2 .…”

“…The enzyme catalase decomposes H 2 O 2 into H 2 O and O 2 . However, in stress conditions, the Fenton reaction [11] is involved in the production of ROS in the form of highly reactive hydroxyl radicals (OH·) from H 2 O 2 with the simultaneous oxidation of iron from Fe 2+ to the Fe 3+ state. Radicals in the form of HO 2 · are also produced with the reduction of Fe 2+ to the Fe 3+ .…”

Estudo Comparativo De Técnicas Fotoquímicas Aplicados Ao Tratamento De Efluentes Do Beneficiamento Da Castanha De Caju

“…Neste caso a reação passa a ser designada de foto-Fenton ou Fenton fotoassistida (Giroto, 2002), intensificando a degradação de poluentes orgânicos. Isto ocorre porque os íons férricos produzidos na Equação (4), são reduzidos, por fotólise, a íons ferrosos, de acordo com a equação (6) (Henle, Luo & Linn, 1996).…”

Annual Report 2000 Macromolecular Structure and Dynamics

“…It is possible that the small fraction of unique and unrepaired damage types resulting from exposure to ionizing radiation may lead to deleterious effects (Wallace 1998). It is important therefore to understand the real differences and similarities between DNA damage induced by normal oxidative processes versus low doses of ionizing radiation (Henle et al 1996, Dizdaroglu 1992. Recent dramatic advances in analytical methods (Smith et al 1993) 4-9 are now providing significantly more sensitive capabilities for efficiently and quantitatively detecting and characterizing the distinctive and chemically complex damage products from ionizing radiation (Hofstadler et al 1995).…”