Electron Transfer between Guanosine Radicals and Amino Acids in Aqueous Solution. II. Reduction of Guanosine Radicals by Tryptophan

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• 作者：Olga B. Morozova ; Alexey S. Kiryutin ; Alexandra V. Yurkovskaya
• 刊名：Journal of Physical Chemistry B
• 出版年：2008
• 出版时间：March 6, 2008
• 年：2008
• 卷：112
• 期：9
• 页码：2747 - 2754
• 全文大小：118K
• 年卷期：v.112,no.9(March 6, 2008)
• ISSN：1520-5207

文摘

The efficiency of the chemical pathway of DNA repair is studied by time-resolved chemically induced dynamicnuclear polarization (CIDNP) using the model system containing guanosyl base radicals, and tryptophan asthe electron donor. Radicals were generated photochemically by pulsed laser irradiation of a solution containingthe photosensitizer 2,2'-dipyridyl, guanosine-5'-monophosphate, and N-acetyl tryptophan. Depending on thepH of the aqueous solution, four protonation states of the guanosyl radical are formed via electron or hydrogenatom transfer to the triplet excited dye. The rate constants of electron transfer from the amino acid to theguanosyl radical were determined by quantitative analysis of the CIDNP kinetics, which is very sensitive tothe efficiency of radical reactions in the bulk, and rate constants vary from (1.0 ± 0.3) × 10⁹ M^-1 s^-1 for thecation and dication radicals of the nucleotide to (1.2 ± 0.3) × 10⁷ M^-1 s^-1 for the radical in its anionic form.They were found to be higher than the corresponding values for electron transfer in the case of N-acetyltyrosine as the reducing agent.