Morozova Olga B, Kiryutin Alexey S, Sagdeev Renad Z, Yurkovskaya Alexandra V
International Tomography Center of SB RAS, Novosibirsk, Russia.
J Phys Chem B. 2007 Jun 28;111(25):7439-48. doi: 10.1021/jp067722i. Epub 2007 May 25.
As a model of chemical DNA repair, the reductive electron transfer from the aromatic amino acid tyrosine to the radical of the purine base guanosine monophosphate (GMP) was studied by time-resolved chemically induced dynamic nuclear polarization (CIDNP). The guanosyl radicals were photochemically generated in the quenching reaction of the triplet excited dye 2,2'-dipyridyl. Depending on the pH of the aqueous solution, four different guanosyl radicals were observed. The identification of the radicals was possible because of the high sensitivity of CIDNP to distinguish them through their ability or disability of participating in the degenerate electron hopping reaction with the diamagnetic molecules of guanosine monophosphate in the ground state. The CIDNP kinetics in this three-component system containing the dye, GMP, and N-acetyl tyrosine is strongly dependent on the efficiency of the electron-transfer reaction from tyrosine to the nucleotide radical. Quantitative analysis of the CIDNP kinetics obtained at different concentrations of the amino acid, together with the comparison with the CIDNP kinetics of the two-component systems (dipyridyl/tyrosine and dipyridyl/GMP) allowed for the determination of the rate constant ke of the reductive electron-transfer reaction for five pairs of reactants, with different protonation states depending on the pH: GH++/TyrOH (pH 1.3), G+/TyrOH (pH 2.9), G(-H)/TyrOH (pH 7.5), G(-H)/TyrO- (pH 11.3), and G(-2H)-*/TyrO- (pH 13.3). The rate constant ke varies from (7.1 +/- 3.0) x 10(8) M-1 s-1 (pH 1.3, 2.9) to less than 6 x 10(6) M-1 s-1 (pH 13.3).
作为化学DNA修复的模型，通过时间分辨化学诱导动态核极化（CIDNP）研究了从芳香族氨基酸酪氨酸到嘌呤碱基鸟苷单磷酸（GMP）自由基的还原电子转移。鸟苷基自由基是在三重态激发染料2,2'-联吡啶的猝灭反应中光化学产生的。根据水溶液的pH值，观察到四种不同的鸟苷基自由基。由于CIDNP具有高灵敏度，能够通过它们参与或不参与与基态鸟苷单磷酸抗磁分子的简并电子跳跃反应的能力来区分这些自由基，因此可以对其进行鉴定。在包含染料、GMP和N-乙酰酪氨酸的三元体系中，CIDNP动力学强烈依赖于从酪氨酸到核苷酸自由基的电子转移反应效率。对不同氨基酸浓度下获得的CIDNP动力学进行定量分析，并与二元体系（联吡啶/酪氨酸和联吡啶/GMP）的CIDNP动力学进行比较，从而确定了五对反应物的还原电子转移反应速率常数ke，这五对反应物根据pH值具有不同的质子化状态：GH++/TyrOH（pH 1.3）、G+/TyrOH（pH 2.9）、G(-H)/TyrOH（pH 7.5）、G(-H)/TyrO-（pH 11.3）和G(-2H)-*/TyrO-（pH 13.3）。速率常数ke从(7.1 +/- 3.0) x 10(8) M-1 s-1（pH 1.3、2.9）变化到小于6 x 10(6) M-1 s-1（pH 13.3）。
