Alteration of protein structure induced by low-energy (<18 eV) electrons. I. The peptide and disulfide bridges.
We present measurements of low-energy (<18 eV) electron-stimulated desorption of anions from acetamide (CH(3)CONH(2)) and dimethyl disulfide [DMDS: (CH(3)S)(2)] films. Electron irradiation of physisorbed CH(3)CONH(2) produces H(-), CH(3)(-) and O(-) anions, whereas the H(-), CH(2)(-), CH(3)(-), S(-), SH(-) and SCH(3)(-) anions are observed to desorb from the DMDS film. Below 12 eV, the dependence of the anion yields on the incident electron energy exhibits structures that indicate that a resonant process (i.e. dissociative electron attachment) is responsible for molecular fragmentation. Within the range of 1-18 eV, it is found that (1.7 and 1.4) x 10(7) H(-) ions/incident electron and (7.8 x 10(-11) and 4.3 x 10(-8)) of the other ions/incident electron are desorbed from acetamide and DMDS films, respectively. These results suggest that, within proteins, the disulfide bond is more sensitive to low-energy electron attack than the peptide bond. In biological cells, some proteins interact closely with nucleic acid. Therefore, the observed fragments, when produced from secondary low-energy electrons generated by high-energy radiation, not only may denature proteins, but may also induce reactions with the nearby nucleic acid and damage DNA.
Abdoul-Carime
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Group of the Canadian Institutes of Health Research in the Radiation Sciences, Faculté de Médecine, Université de Sherbrooke, Sherbrooke, Québec, Canada, J1H 5N4.
Cecchini
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Sanche
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D000081:Acetamides / Q000528:radiation effects; D004249:DNA Damage; D004220:Disulfides / Q000528:radiation effects*; D004583:Electrons; D013058:Mass Spectrometry; D008956:Models, Chemical; D010455:Peptides / Q000528:radiation effects*; D011487:Protein Conformation / Q000528:radiation effects*
D000081:Acetamides; D004220:Disulfides; D010455:Peptides; C021181:dimethyl disulfide; C030686:acetamide