Effect of protease inhibitors on cellular radio-iron redistribution. Cells were labeled with ⁵⁹Fe-labeled human diferric Tf during the first 6 days of phase II (EPO-dependent phase, see Materials and Methods), then washed, and reincubated in fresh radioactive-free medium and treated with chymostastin (200 μg/mL) and leupeptin (20 μg/mL). At days 8 and 10, cells were harvested, lysed, and analyzed by SDS-PAGE followed by phosphor-imaging. The figure is representative of two independent experiments with cells obtained from two donors.