Summary
E. coli 15 T - cells were cultured in the presence of cysteine, then removed and subjected to X-ray irradiation in cysteine-free buffer. The radiation-sensitivity was then found to decrease in inverse ratio to the concentration of cysteine used. This phenomenon occurred only with log-phase cells, while the radiosensitivity of stat-phase bacteria remained unchanged.
The biochemical background of this phenomenon was also studied by means of 35S-Cysteine. The extent and distribution of cysteine incorporation into the fractions of log-phase cells were found to differ from those occurring in the fractions of statphase cells.
The biochemical radioprotective effect of cysteine described above suggests two different explanations: a) the radioresistance induced by cysteine presupposes an active metabolic state of the cells, which may correlate with the induction of the repair systems; b) the cysteine incorporated by the cells provides a radio-protective effect; hence only the radiosensitivity of log-phase cells decreases, while that of the stationary phase cells remains unchanged owing to their inability to incorporate cysteine in an amount rendering them effective radioprotectors.
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Nagy, Z., Hernádi, F., Kovács, P. et al. Correlation between the physiological state of bacteria and the radioprotective effectiveness of cysteine. Archiv. Mikrobiol. 61, 327–334 (1968). https://doi.org/10.1007/BF00409669
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DOI: https://doi.org/10.1007/BF00409669