CONTENT OF IRON AND COPPER IN THE NUCLEI AND INDUCTION OF PH 9-LABILELESIONS IN L5178Y SUBLINES INVERSELY CROSS SENSITIVE TO H2O2 AND X-RAYS

Cells from the L5178Y murine lymphoma subline LY-R are twice as resist ent to killing by ionizing radiation than the subline LY-S. In contras t, LY-R cells are more sensitive to killing by H2O2, the effect being more pronounced at 37 degrees C than 0 degrees C. Initial DNA damage a fter H2O2 treatment (both temperatures, 5 min) has been estimated by t he 'comet' assay (single-cell gel electrophoresis) and fluorescent hal o technique. According to both methods, the initial damage is signific antly higher in LY-R cells, particularly that inflicted at 0 degrees C . Differences between DNA unwinding and rewinding abilities at pH 9 an d 6.9 (estimated by the fluorescent halo technique) point to a conside rable difference in pH-9-labile damage between the sublines, as observ ed previously for x-irradiated cells (Kapiszewska et al. 1992). In con trast to findings with x-irradiated cells, however, after H2O2 treatme nt this damage is more extensive in LY-R cells than in LY-S cells. Thu s, the initial pH-9-labile damage corresponds to the pattern of sensit ivity to H2O2 and x-rays. We suggest that this is caused by different proportions of cuprous and ferric ions found in the nuclei of LY subli nes and by the different ability of these ions to react with H2O2 and water radiolysis products. The copper/iron ratio in the nucleus is 1.3 1 in LY-R cells and 4.84 in LY-S cells.