DNA Binding Hydroxyl Radical Probes.

The hydroxyl radical is the primary mediator of DNA damage by the indirect effect of ionizing radiation. It is a powerful oxidizing agent produced by the radiolysis of water and is responsible for a significant fraction of the DNA damage associated with ionizing radiation. There is therefore an interest in the development of sensitive assays for its detection.

Free terminal amines in DNA-binding peptides alter the product distribution from guanine radicals produced by single electron oxidation.

Purpose: Electron deficient guanine radical species are major intermediates produced in DNA by the direct effect of ionizing irradiation. There is evidence that they react with amine groups in closely bound ligands to form covalent crosslinks. Crosslink formation is very poorly characterized in terms of quantitative rate and yield data.

Use of a coumarin-labeled hexa-arginine peptide as a fluorescent hydroxyl radical probe in a nanoparticulate plasmid DNA condensate.

Coumarin derivatives have found application as probes for the hydroxyl radical because one of the products of the reaction between them is a highly fluorescent umbelliferone. We have examined the interaction in aqueous solution between a cationic coumarin-labeled hexa-arginine peptide ligand and plasmid DNA, and compared after gamma irradiation the yields of products derived from both of them. At low ionic strengths, the ligand binds very tightly to the plasmid.