Effect of leupeptin and chloroquine on the influence of ferritin on IRP activity. DEC were incubated for 64 hours, beginning on day 6 of phase II, with the following: medium only (lane 1), 40 nmol/L ferritin (lane 2), 20 μg/mL leupeptin (lane 3), 40 nmol/L ferritin together with 20 μg/mL leupeptin (lane 4), 15 μmol/L chloroquine (lane 5), or 40 nmol/L ferritin together with 15 μmol/L chloroquine (lane 6). Fresh cytoplasmic extracts (10 μg protein) were analyzed for IRP activity by electromobility-RNA gel retardation. A control containing 120 ng of recombinant IRP-1 was included (lane 7). Cell lysates were analyzed without 2-ME (top panel) or after incubation with 2% 2-ME for 5 minutes at room temperature (lower panel).