A carbon-centered radical as a reaction species in the DNA strand-breakage by D-glucosamine

Electron spin resonance(ESR) studies using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and sodium 3,5-dibromo-4-nitrosobenzensulfonate (DBNBS) as a spin-trapping agent revealed the formation of both hydroxyl and carbon-centered radical-derived spin adducts in Cu2+-containing 50 mM Tris-HCl buffered solutions (pH 7.1) of D-glucosamine, D-mannosamine, and D-galactosamine, which were previously shown to have the ability to break the single-strand of plasmid pBR322 DNA in a nucleotide sequence-specific manner. HCl-free D-glucosamine has higher DNA breaking activity, and this activity is promoted more by the presence of Cu2+ than the original D-glucosamine hydrochloride, exhibits stronger radical signals in the ESR spectrum. It is suggested that D-glucosamine is unstable around neutral pH, being converted into certain intermediate(s) such as a dihydropyrazine compound, which generate(s) carbon-centered radicals, and that, besides the hydroxyl radical, the intermediate(s) is/are responsible for DNA strand breakage.