Biological effects of Auger processes of bromine on yeast cells induced by monochromatic synchrotron X-rays.
The 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 inner-shell photoionization, followed by an Auger cascade of the bromine in the DNA. The quantum yield of lethality caused by the photoabsorption of bromine K-shell is not affected by the presence of cysteamine, suggesting the biological enhancement by the Auger processes may not be influenced by chemical protection.
Usami
N
N
Institute of Biological Sciences, University of Tsukuba, Ibaraki, Japan.
Kobayashi
K
K
Maezawa
H
H
Hieda
K
K
Ishizaka
S
S
D001973:Bromodeoxyuridine / Q000528:radiation effects*; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D004271:DNA, Fungal / Q000187:drug effects / Q000528:radiation effects*; D004583:Electrons; D009154:Mutation; D010315:Particle Accelerators; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000187:drug effects / Q000528:radiation effects*; D013938:Thymidine Monophosphate / Q000494:pharmacology
D004271:DNA, Fungal; D013938:Thymidine Monophosphate; D001973:Bromodeoxyuridine