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

Summary

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.