The Peroxidase Activity of a Hemin-DNA Oligonucleotide Complex: Free Radical Damage to Specific Guanine Bases of the DNA

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• 作者：Paola Travascio ; Paul K. Witting ; A. Grant Mauk ; and Dipankar Sen
• 刊名：Journal of the American Chemical Society
• 出版年：2001
• 出版时间：February 21, 2001
• 年：2001
• 卷：123
• 期：7
• 页码：1337 - 1348
• 全文大小：207K
• 年卷期：v.123,no.7(February 21, 2001)
• ISSN：1520-5126

文摘

A specific DNA oligonucleotide-hemin complex (PS2.M-hemin complex) that exhibits DNA-enhanced peroxidative activity was studied by EPR and UV-visible spectroscopy and by chemical probinganalysis. EPR data obtained from low-temperature experiments on the PS2.M-hemin complex showed botha low-field g ~6 and a high-field g ~2 signal. These EPR signals are typical of high-spin ferric heme withaxial symmetry as judged by the EPR spectrum of six-coordinate heme iron in acidic Fe(III)-myoglobin. Thissimilarity is consistent with the presence of two axial ligands to the heme iron within the PS2.M-hemincomplex, one of which is a water molecule. Optical analyses of the acid-base transition for the hemin complexyielded a pK_a value for the water ligand of 8.70 ± 0.03 (mean ± SD). Low-temperature EPR analysis coupledwith parallel spin-trapping investigations following the reaction of the PS2.M-hemin complex and hydrogenperoxide (H₂O₂) indicated the formation of a carbon-centered radical, most likely on the PS2.M oligonucleotide.Chemical probing analysis identified specific guanine bases within the PS2.M sequence that underwent oxidativedamage upon reaction with H₂O₂. These and other experimental findings support the hypothesis that theinteraction of specific guanines of PS2.M with the bound hemin cofactor might contribute to the superiorperoxidative activity of the PS2.M-hemin complex.