PARP blotting. The fraction of apoptotic cells was determined by blotting analysis of cell homogenates of 2 different stable clones with anti-p85 PARP antibody after running on 12% SDS-PAGE. The H-ferritin content in the 2 clones, ΔH1 and ΔH2, are 98 and 190 ng/mg of total proteins, respectively. Representative of 2 independent experiments with similar results.