Chemical Study of the Radiosensitization of Micrococcus sodonensis by Iodine Compounds

IT has been shown that iodoacetamide 1 (CH 2 ICONH 2 ) and potassium iodide 2 enhance the radiation inactivation of radiation resistant bacteria. Similar results have been obtained with iodoacetic acid 3,4 . Dean and Alexander 2 found that sensitization with iodoacetamide was observed in. Micrococcus sodonensis only when the bacteria and sensitizer were irradiated together, indicating that sensitization was not caused by blocking of intracellular sulphydryl groups before irradiation or by the production of a stable toxic product. It was later demonstrated that some short lived transients of iodoacetamide were responsible for the sensitizing effect 5 . These transients would be formed by the reaction of iodoacetamide with the radiolytic products of water. The two principal species produced by irradiation of aqueous solutions are the solvated electron and the hydroxyl radical (OH). (For a comprehensive review of this subject see ref. 6.) The aim of the present investigation was to discover which of these species was involved in producing the toxic short lived transient and to determine the nature of this transient in iodoacetamide and potassium iodide. This could be done by studying the effect of scavengers for the solvated electron and the hydroxyl radical on the sensitizing ability of iodoacetamide and potassium iodide. Our results suggest that the iodine atom (I·), produced by the OH radical attack on the sensitizers, was responsible for the observed sensitization.