Radiation-induced DNA double-strand breaks in dependence on protein concentration and under aerobic and anaerobic conditions

Double-stranded DNA alone and with serum albumin in eight different weight ratios were irradiated with X-rays in phosphate buffer in air-free and aerated media. Double-strand breaks (dsb) were determined by electrophoresis. The oxygen enhancement ratio for dsb increased with increasing protein concentration from 0.8 to 3.0, presumably caused by the reaction of protein peroxyl radicals. In air-free media, serum albumin protects against radiation-induced double-strand breaking more effectively than in the presence of air, because a part of DNA radicals does not form dsb, but DNA-protein crosslinks.