Effects of Monoenergetic X-rays with Resonance Energy of Bromine K-absorption Edge on Bromouracil-labelledE. ColiCells

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Abstract
In order to examine enhanced killing that might be induced by Auger cascades in the incorporated atoms in cells, bromouracil(BrU)-labelled E. coli cells were irradiated with monoenergetic X-rays at 13·49 and 12·40 keV, just above and below the K-absorption edge of bromine. In both cases BrU-labelled cells were more sensitive for killing than were normal cells. However, when the degree of BrU-sensitization was compared between the two energies of X-rays, the enhanced killing at 13·49 keV was only small, 2 ± 8 per cent based on the D0 value in saline. By the addition of DMSO, which is believed to suppress radical-mediated effects, killing of BrU-labelled cells was enhanced at 13·49 keV by 8 ± 4 per cent as compared with 12·40 keV, based on D0. These results have been examined in terms of absorbed energy in BrU-labelled cells and in terms of the number of induced Auger events.