PARENT SESSION
1:30 PM to 3:30 PM
Wednesday, April 24, 2002
Poster Session 29 Radiation Chemistry
Room: Nevada Exhibition Center
(P34-332) Low-energy (< 35 eV) electron damage to protein subunits.
Abdoul-Carime, Hassan1, Sanche, Léon*,1, 1 Groupe des Instituts de Recherche en Santé du Canada, Sherbrooke, Québec, Canada
ABSTRACT-
At the microscopic level, the penetration of high-energy particles within biological tissues generates along their ionization tracks, various reactive species such as neutral and ionic radicals, as well as a large number of ballistic low-energy secondary electrons (~ 5x104/MeV. Such electrons induce single and double DNA strand breaks(1), via fragmentation of the nucleic acid components. Since in biological cells DNA interacts closely with certain proteins, low-energy electron damage induced on their sub-units must also be measured to assess adequately the effect of secondary electrons on cellular DNA. We report measurements of anions desorbed by low-energy (<35 eV) electron impact onto physisorbed thin films of acetamide, dimethyl disulfide DMDS and aromatic amino acids, which serve as a simple model for peptide and disulfide bonds in proteins. Electron irradiation of physisorbed CH3CONH2 produces H- , CH3- and O- anions, whereas the H-, CH2-, CH3-, S-, SH- and SCH3- anions are observed to desorb from film of DMDS. H-, O-, OH- and CN- desorb from Tryptophan, Histidine and Proline (Pro) but CH2- is only observed from Pro fragmentation. Within the range 1-18 eV, the yields vary from 0.1 to 18x10-6 H- ions/incident electron and 6x10-10 to 7.8x10-7 ions/incident electron for the higher mass anions. From the incident electron energy dependence of the anion yields, it is found that below the molecular ionization threshold energy, efficient molecular fragmentation for anion production is due to dissociative electron attachment (DEA). These results indicate that low-energy electrons may alter proteins by damaging their subunits, i.e., amino-acid residues, peptide and disulfide bonds. Thus, the radicals and anions produced via DEA, may not only denature proteins, but also react with nucleic acids within chromatin. 1. B. Boudaiffa, P. Cloutier, D. Hunting, M.A. Huels, L. Sanche, Science, 287, 1658-1660, 2000.
KEYWORDS: Protein damage, Low energy electrons