Changes in intracellular radio-iron distribution during erythroid cell development. Three individual cultures were established from cells derived from different donors. Cells were labeled with ⁵⁹Fe-human–diferric-transferrin during the first 6 days of phase II (EPO-dependent phase, see Materials and Methods), then washed and reincubated in fresh nonradioactive medium. On days 6, 8, and 10, cell samples from equal culture volumes were taken, lysed, and applied to a 6% nonreducing SDS-PAGE gel. Human placental ferritin and human Hb (normal erythrocyte cell lysate) were used for markers. The markers were visible without staining. (A) Autoradiography of ⁵⁹Fe-containing proteins of one representative culture. (B) Quantitative analysis by densitometry (mean ± SD of three cultures). (C) Quantitative analysis by densitometry of each individual culture.