Evidence of Electron Transfer from Peptides to DNA: Oxidation of DNA-Bound Tryptophan Using the Flash-Quench Technique

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• 作者：Hans-Achim Wagenknecht ; Eric D. A. Stemp ; and Jacqueline K. Barton
• 刊名：Journal of the American Chemical Society
• 出版年：2000
• 出版时间：January 12, 2000
• 年：2000
• 卷：122
• 期：1
• 页码：1 - 7
• 全文大小：123K
• 年卷期：v.122,no.1(January 12, 2000)
• ISSN：1520-5126

文摘

A flash-quench method has been employed to probe electron-transfer reactions from peptides toDNA. The photoexcited intercalators [Ru(phen)₂(dppz)]²⁺ (phen = 1,10-phenanthroline; dppz = dipyridophenazine) and [Ru(phen)(bpy')(dppz)]²⁺ (bpy' = 4-(4'-methyl-2,2'-bipyridyl)valerate) are quenched by anonintercalating and weakly bound electron-transfer quencher to generate the corresponding DNA-bound Ru(III)complexes in situ. Both Ru(III) complexes are powerful ground-state oxidants, capable of oxidizing guaninein DNA or DNA-bound tryptophan of the intercalating peptide, Lys-Trp-Lys. In mixed-sequence oligonucleotideduplexes containing [Ru(phen)(bpy')(dppz)]²⁺ tethered at one end, damage to distant guanines is observed bygel electrophoresis, consistent with the mobility of the electron through the DNA duplex. This damage atguanines is observed in both the presence and absence of Lys-Trp-Lys, but the presence of the peptide affectsthe distribution. In flash-quench experiments using mixed-sequence oligonucleotides or poly(dG·dC) in thepresence of Lys-Trp-Lys, transient absorption spectroscopy reveals a signal at ages/gifchars/lambda.gif" BORDER=0 > = 510 nm assigned to thetryptophan radical; it decays on the time scale of 60-250 ages/entities/mgr.gif">s. The final peptide product of this electron-transfer reaction has been described by UV/vis spectroscopy and mass spectrometry. No DNA-peptide adductswere detected. Significantly, the tryptophan radical is not observed in reactions with Ru(III) bound to poly(dA·dT), an observation that suggests the intermediacy of the guanine radical cation in generating the tryptophanradical. These results indicate that charge migration from tryptophan to [Ru(phen)(bpy')(dppz)]³⁺ occurs toproduce the tryptophan radical and that this process is DNA mediated. This work establishes methodology toprobe tryptophan intercalation in DNA by protein or peptides. Moreover, this methodology demonstrates anelectron-transfer event between peptides and DNA and suggests the consideration of such events within thecell.