Effect of ascorbate on radiosensitization of bacterial cells

The effect of ascorbate on the radiosensitization of Escherichia coli by 10/sup -3/ M KI was investigated over a concentration range of 0 to 10/sup -2/ M. The sensitization effect was reduced in the presence of ascorbate with increasing dose, but no additional protection was observed against radiation lethality. Irradiation of cells in the presence of NaI/sup 131/ showed a decrease in cell radioactivity with increasing concentration of ascorbate present during irradiation over a concentration range of 0 to 10/sup -3/ M. It is argued that ascorbate reduced the sensitizing effect by scavenging the iodine atoms which would have otherwise reacted with the cells. The sensitization by 10/sup -3/ M 2,2,6,6-tetramethyl-4-piperidone-N-oxyl (TAN) decreased with increasing concentration of ascorbate, but no net protective effect was noticed. It is suggested that a reaction between the two molecules took place because the optical absorption of ascorbate (10/sup -4/ M) at265nm decreased to half its value in the presence of equimolecular TAN, and also because the esr signal from 1 mM TAN decreased to a fifth of its value in 15 min after mixing with equimolecular solution of ascorbate. more » The presence of ascorbate during irradiation at concentrations from 10/sup -6/ M to 10/sup -3/ M did not affect the radiosensitization of anoxic E. coli cells by 5 x 10/sup -5/ M of N- ethylmaleimide (NEM). (UK) « less