Luo Y, Han Z, Chin S M, Linn S
Division of Biochemistry and Molecular Biology, University of California, Berkeley 94720-3202.
Proc Natl Acad Sci U S A. 1994 Dec 20;91(26):12438-42. doi: 10.1073/pnas.91.26.12438.
Exposure of Escherichia coli to H2O2 leads to two kinetically distinguishable modes of killing: mode I killing occurs maximally near 2 mM H2O2, whereas mode II killing is essentially independent of H2O2 concentrations up to 20 mM. A major portion of H2O2 toxicity is attributed to DNA damage caused by the iron-mediated Fenton reaction. By studying DNA damage during Fenton reactions in vitro, the same complex kinetics were observed and three types of oxidants were distinguished based upon their reactivities toward H2O2 and alcohols and upon iron-chelator effects. Type I oxidants are sensitive to H2O2 but moderately resistant to ethanol; type II oxidants are resistant to both H2O2 and ethanol; type III oxidants are sensitive to H2O2, ethanol, and t-butanol. To explain these results, we hypothesize that type I oxidants are generated upon Fe2+ associated with DNA only through electrostatic interactions and cause mode I killing of E. coli; type II oxidants arise upon Fe2+, which is at least partially base-associated, and cause mode II killing; type III oxidants arise on Fe2+ free in solution and probably do not cause killing. Therefore, particular interactions of DNA with transition metals should be considered to be an integral part of the chemistry and toxicity of H2O2.
模式I杀伤在过氧化氢浓度接近2 mM时达到最大，而模式II杀伤在过氧化氢浓度高达20 mM时基本与浓度无关。过氧化氢毒性的主要部分归因于铁介导的芬顿反应所导致的DNA损伤。通过研究体外芬顿反应过程中的DNA损伤，观察到了相同的复杂动力学，并根据它们对过氧化氢和醇类的反应性以及铁螯合剂效应区分出三种类型的氧化剂。I型氧化剂对过氧化氢敏感，但对乙醇有一定抗性；II型氧化剂对过氧化氢和乙醇均有抗性；III型氧化剂对过氧化氢、乙醇和叔丁醇敏感。为了解释这些结果，我们推测I型氧化剂仅通过静电相互作用在与DNA结合的Fe2+上产生，并导致大肠杆菌的模式I杀伤；II型氧化剂在至少部分与碱基结合的Fe2+上产生，并导致模式II杀伤；III型氧化剂在溶液中游离的Fe2+上产生，可能不会导致杀伤。因此，DNA与过渡金属的特定相互作用应被视为过氧化氢化学性质和毒性的一个组成部分。
