Biological effects of Auger processes of bromine on yeast cells induced by monochromatic synchrotron X-rays.

SummaryThe biological effects of inner-shell ionization in bromine atoms incorporated into DNA in the form of bromodeoxyuridine monophosphate (BrdUMP), induced by monochromatized synchrotron X-rays, were studied using a deoxythymidine monophosphate (dTMP)-permeable mutant of yeast, Saccharomyces cerevisiae. The BrdUMP-incorporated yeast cells were irradiated with monochromatic X-rays of 13·51 or 13·45 keV, between which the bromine K-absorption edge (13·47 keV) is located. The cells were 1·07 times more sensitive to irradiation by 13·51 keV X-rays than at 13·45 keV, while dTMP-incorporated cells did not show any difference in sensitivity. In the presence of a radioprotector during irradiation, BrdUMP-incorporated cells showed a larger enhancement (1·20). These enhancements observed in the bromine-incorporated cells cannot be explained only by an increase of the absorbed dose due to a substitution of CH3 group of thymine by bromine. It may be concluded that a major part of the enhancement was caused by inn...