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.
Institute of Biological Sciences, University of Tsukuba, Ibaraki, Japan.
N
N
Usami
K
K
Kobayashi
H
H
Maezawa
K
K
Hieda
S
S
Ishizaka
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