Adam W, Kurz A, Saha-Möller C R
Institute of Organic Chemistry, University of Würzburg, Germany.
Free Radic Biol Med. 1999 Mar;26(5-6):566-79. doi: 10.1016/s0891-5849(98)00229-9.
The horseradish-peroxidase(HRP)-catalyzed aerobic oxidation of aldehydes, in particular isobutanal, was used for the oxidative damage of DNA. In isolated calf-thymus DNA, the enzymatic oxidation of isobutanal led to 7,8-dihydro-8-oxoguanine (8-oxoGua) in up to 1.3% yield and appreciable single-strand breaks in supercoiled pBR 322 DNA. For the nucleoside dG, significant amounts of the guanidine-releasing products oxazolone and oxoimidazolidine have been detected, but 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxodG) was not obtained. Only enolizable aldehydes are effective, molecular oxygen is essential, and radical scavengers inhibit efficiently the oxidation. Comparative experiments with 3,3,4,4-tetramethyl-1,2-dioxetane (TMD) revealed that triplet-excited acetone does not play a significant role in this enzymatic DNA oxidation. 2-Hydroperoxy-2-methylpropanal, an intermediate in the HRP-catalyzed aerobic oxidation of isobutanal, does not contribute directly in the observed dG conversion. However, the peroxyl radical derived from the 2-hydroperoxy-2-methylpropanal appears to be active as oxidant because model studies with a structurally related peroxyl radical, produced by HRP-catalyzed one-electron oxidation of 3-hydroperoxy-3-methyl-2-butanone, causes both dG conversion and DNA strand breaks, but to a moderate extent. The active oxidant, as established by control experiments, is the peroxyisobutyric acid, that is efficiently formed through the HRP-catalyzed autoxidation of isobutanal. Still more effective is the acylperoxyl radical, conveniently generated from the peracid by one-electron oxidation by HRP.
辣根过氧化物酶（HRP）催化的醛类，特别是异丁醛的有氧氧化，被用于DNA的氧化损伤研究。在分离的小牛胸腺DNA中，异丁醛的酶促氧化导致高达1.3%产率的7,8-二氢-8-氧代鸟嘌呤（8-氧代鸟嘌呤）生成，并在超螺旋pBR 322 DNA中产生明显的单链断裂。对于核苷dG，已检测到大量释放胍的产物恶唑酮和氧代咪唑烷，但未得到7,8-二氢-8-氧代-2'-脱氧鸟苷（8-氧代脱氧鸟苷）。只有可烯醇化的醛是有效的，分子氧是必需的，自由基清除剂能有效抑制氧化。与3,3,4,4-四甲基-1,2-二氧杂环丁烷（TMD）的对比实验表明，三线态激发的丙酮在这种酶促DNA氧化中不起重要作用。2-氢过氧-2-甲基丙醛是HRP催化异丁醛有氧氧化的中间体，在观察到的dG转化中不直接起作用。然而，源自2-氢过氧-2-甲基丙醛的过氧自由基似乎作为氧化剂具有活性，因为用HRP催化3-氢过氧-3-甲基-2-丁酮的单电子氧化产生的结构相关过氧自由基进行的模型研究，会导致dG转化和DNA链断裂，但程度适中。通过对照实验确定，活性氧化剂是过氧异丁酸，它是通过HRP催化异丁醛的自氧化有效形成的。由过酸通过HRP的单电子氧化方便地生成的酰基过氧自由基更有效。
