A Correlation between Radiation-induced Free Radicals and Survival in Micro-organisms Exposed to β-mercaptoethylamine under Oxygen or Nitrogen

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Abstract
Both free radical and survival measurements were made on the same samples of micro-organisms irradiated at −196°c. Under these conditions, which minimized indirect effects, pronounced oxygen (radiosensitization) and MEA (radioprotection) effects were observed. MEA protected in the presence of N2 or O2. The reduction in certain types of bacterial radicals by MEA correlated with an increase in bacterial survival. Sulphur-type radicals were not found. These findings indicate: (1) A relation exists between free-radical reduction and radiation protection; (2) MEA is in contact with the protected biological molecules; (3) Transfer of unpaired electrons to the sulphur nucleus in MEA is not required for radiation protection; (4) MEA protection includes a mechanism that does not involve competition with oxygen; (5) The oxygen-effect involves direct interaction of oxygen with biological molecules.