Preferential Sensitization of Anoxic Bacteria to X-Rays by Organic Nitroxide-Free Radicals

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Abstract
The influence of organic nitroxide-free radicals on the sensitivity to X-rays of E. coli B/r has been studied. Di-t-butyl nitroxide (DTBN), tetramethylpentamethylene nitroxide (TMPMN), and t-butyl-2,6-dimethoxyphenyl nitroxide (TBD-MPN) all increased lethality under anoxia. Variation in sensitivity with concentration was investigated. Maximum sensitization occurred at 20 mM DTBN, sensitivity about 75% of that in pure oxygen. Nitroxides do not sensitize aerobic cells, so that the normal oxygen effect is greatly reduced in their presence. Thus, the ratio of the 1% survival doses of anoxic and oxygenated cells is about 3.9 for untreated bacteria, but less than 1.5 in the presence of 20 mM DTBN.