CHARACTERIZATION OF RADIATION-INDUCED THYMINE-TYROSINE CROSS-LINKS BYELECTROSPRAY-IONIZATION MASS-SPECTROMETRY

Exposure to ionizing radiation leads to formation of covalent crosslin ks between DNA and proteins. The nature, extent and site of the modifi cations are not well understood due to the difficulty in assessing fre e radical-induced damage in biopolymers. Electrospray ionization mass spectrometry (ESI-MS) permits direct analyses of intact oligopeptides, permitting characterization of the radiation-induced DNA-protein cova lently crosslinked constituents. Our first application of this methodo logy to free radical-induced damage was in a model system where angiot ensin, a small 10-amino acid peptide, is irradiated at various doses i n the presence of excess thymine. The relative yield of crosslinks, wh ich ranged from 0.1 to 15%, was linearly related to radiation dose for doses from 0.1 to 100 Gy. Detection of thymine-tyrosine moieties in t his model system was possible at doses as low as 0.1 Gy with a signal- to-noise ratio of 4 to 1. ESI-MS revealed that the site of crosslink w as located exclusively on the tyrosine residue as expected. (C) 1996 b y Radiation Research Society