Radiation-Induced Damage in Escherichia coli B: The Effect of Superoxide Radicals and Molecular Oxygen

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Abstract
The roles of superoxide radicals and of O2 in the radiodamage of E. coli B suspended in dilute phosphate buffer were studied. The presence of high concentrations of polyethylene glycol in the .gamma.-irradiated cell suspensions had no effect on bacterial radiosensitivity. This indicates that the damage was primarily endogenous, i.e., originated intracellularly. Saturation of the cell suspensions with N2O doubles the radiosensitivity, thus indicating that OH radicals are responsible for the majority of the damage (indirect radiation effect). The presence of O2 either in the absence or presence of N2O brings about roughly a 3-fold increase in the radiosensitivity. Since in the presence of N2O all eaq- are scavenged by the N2O rather than by O2, this shows that superoxide radicals play no role in the bacterial radiodamage. These results substantiate the attribution of the O2 effect to a direct interaction of O2 with the .ovrhdot.OH-damaged sites on vital biomolecules and exclude any significant contribution of eaq- and .ovrhdot.O2- to the cellular radiodamage.