Radioprotection by superoxide dismutase of macrophage progenitor cells from mouse bone marrow.

X-ray survival of cultured macrophage progenitor cells from mouse bone marrow was represented by a two-component curve, both in the absence and presence of superoxide dismutase. Protection by the enzyme was limited to the radiosensitive fraction, for which a dose modifying factor of 2.8 +/- 0.7 was obtained. Catalase did not protect. Survival of the radiosensitive fraction, with and without exogenous superoxide dismutase, was temperature-dependent, whereas that of the radioresistant fraction was not. In the former case, the energy required for the enzyme-treated cells was approximately 13kJ/mol.