Casas-Finet J R, Toulmé J J, Santus R, Butler J, Land E J, Swallow A J
Int J Radiat Biol Relat Stud Phys Chem Med. 1984 Feb;45(2):119-32. doi: 10.1080/09553008414550141.
The rate constant of the one-electron oxidation of the tryptophan (Trp) or tyrosine (Tyr) residues by Br- X 2 radical anions is strongly decreased when the peptides are bound to DNA. Oxidation by N X 3 is much less affected by binding. These results can be explained by electrostatic repulsion between the charged polyphosphate backbone and the Br- X 2 radicals. Once oxidized, the interacting aromatic residues react with the DNA in a first order process with a rate constant of the order 10(3) s-1. These results have been extended to the single strand binding protein: the product of gene 32 of phage T4 (gp 32). The pulse radiolysis study suggests that one Trp residue of the protein oxidized by the Br- X 2 radicals reacts with the DNA in the complex while one Tyr residue is buried upon association. It is also shown that the exposure of Trp and Tyr residues to radical attack depends on whether the T4 SSB protein is bound to native or heat-denatured DNA.
当肽与DNA结合时，溴自由基阴离子对色氨酸（Trp）或酪氨酸（Tyr）残基进行单电子氧化的速率常数会大幅降低。而N₃的氧化受结合的影响则小得多。这些结果可以通过带电荷的多磷酸骨架与溴自由基之间的静电排斥来解释。一旦被氧化，相互作用的芳香族残基会以一级反应过程与DNA反应，反应速率常数约为10³ s⁻¹。这些结果已扩展到单链结合蛋白：噬菌体T4基因32的产物（gp 32）。脉冲辐解研究表明，被溴自由基氧化的该蛋白的一个Trp残基在复合物中与DNA反应，而一个Tyr残基在结合时被掩埋。研究还表明，Trp和Tyr残基受到自由基攻击的程度取决于T4单链结合蛋白是与天然DNA还是热变性DNA结合。
