DNA and 2'-deoxyguanosine damage in the horseradish-peroxidase-catalyzed autoxidation of aldehydes: the search for the oxidizing species.
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.
Adam
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Institute of Organic Chemistry, University of Würzburg, Germany. adam@chemie.uni-wuerzburg.de
Kurz
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Saha-Möller
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D000332:Aerobiosis; D000447:Aldehydes / Q000737:chemistry*; D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D003497:Cyclic N-Oxides / Q000737:chemistry; D004247:DNA / Q000737:chemistry*; D004249:DNA Damage; D004277:DNA, Single-Stranded / Q000737:chemistry; D004278:DNA, Superhelical / Q000737:chemistry; D003849:Deoxyguanosine / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D006151:Guanosine / Q000031:analogs & derivatives; D006735:Horseradish Peroxidase / Q000378:metabolism*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010957:Plasmids / Q000737:chemistry; D013113:Spin Labels
D000447:Aldehydes; D003497:Cyclic N-Oxides; D004277:DNA, Single-Stranded; D004278:DNA, Superhelical; D013113:Spin Labels; D006151:Guanosine; C046215:8-hydroxyguanosine; C017245:5,5-dimethyl-1-pyrroline-1-oxide; D004247:DNA; C017439:isobutyraldehyde; D006735:Horseradish Peroxidase; D003849:Deoxyguanosine