ROLE OF PEROXIDE IN RADIOPROTECTIVE ACTION OF THIOLS IN E-COLI

The radioprotective action of cysteamine (MEA) and cysteine in E. coli is due partly to autoxidatively generated hydrogen peroxide (H2O2). This effect, which predominates at low concentrations of the thiols (1-2 mM in neutral solution), is regularly correlated with a metabolic block, measured as inhibition of RNA synthesis. In experiments with E. coli 15 (autotroph) under exponential growth in complete medium, the role of H2O2 was demonstrated by a decreased radioprotective action if catalase was present in the medium; a decreased protective action in the absence of catalytically active copper and oxygen being required for the radioprotective action to develop. At higher concentrations of the thiols, their radioprotective action, and the accompanying metabolic block, are less dependent on H2O2 generation and presumably due to a different mechanism. The radioprotective action of H2O2 is possibly related to the radioprotective action in mammals of catalase inhibitors.