Radiation sensitization of Escherichia coli B/r by 2'-chloro-2'-deoxythymidine under various irradiation conditions

Marked sensitization of E. coli cells by 2'-chloro-2'-deoxythymidine to x-rays was observed, when E. coli cells labelled with 2' Cl-TdR were exposed to x-rays in the absence and presence of oxygen. The sensitization factor calculated from inactivation constants from survival curves irradiated in the absence of 02 was about half that obtained in its presence. When 2'Cl-TdR was not incorporated into the DNA of E. coli cells, the presence of 2'Cl-TdR in the cell suspension fluid at the time of irradiation caused no sensitization. The sensitization factor for 2'Cl-TdR obtained under N2O was almost the same as that obtained under N2. The sensitization factor obtained in the presence of glycerol at 1 mol dm-3 under N2 was similar to that obtained in its presence. These results indicated that the radical at the C-2' position of the deoxyribose moiety in DNA produced by x-irradiation was transformed into lethal damage for E. coli cells even in the absence of O2, though more efficiently in its presence. (U.K.)