Destruction of the Activity of Deoxyribonucleic Acid in Irradiated Cells

Abstract

The radiosensitivity of deoxyribonucleic acid within irradiated cells of pneumpcoccus (Diplococcus pneumoniae) has been studied by extracting the deoxyribonucleic acid after irradiation and measuring its ability to transform a related strain of pneumococcus to streptomycin resistance. The inactivation curves are exponential over several orders of magnitude. The D37,s are: irradiation in the dry state, 3 MR (MR = megarads); irradiation in the wet anoxic state, 1.2 MR; wet, with oxygen, 0.4 MR; wet with oxygen and 1% cysteamine, 1.2 MR The data in the dry state are consistent with a unit of transforming activity with a molecular weight of 240,000. The increase in radiosensitivity from the dry state to the wet state can be understood on the assumption of radiation-produced radicals from water diffusing a distance of the order of 10 A. The deoxyribonucleic acid radiosensitivity varies with oxygen and with cysteamine concentrations in the same way as the ability of irradiated cells to reproduce. The significance of this similarity is discussed.