Effect of leupeptin or chloroquine on the degradation of internalized ¹²⁵I-ferritin protein. Human DEC were incubated on day 8 of phase II for 60 minutes with either 20 μg/mL leupeptin or 15 μmol/L chloroquine. Cells were pulse labeled for 30 minutes with 4 nmol/L ¹²⁵I-ferritin then washed and chased with 400 nmol/L unlabeled ferritin. Incubation was continued for 0, 3, 8, and 24 hours (A, lanes 1, 2, 3, and 4, respectively) or for 0, 3, 24, and 48 hours (B, lanes 5, 6, 7, and 8, respectively). Inhibitors were refreshed after each wash and fresh leupeptin was added every 12 hours. Equal amounts of protein from cell lysates were analyzed on SDS-PAGE under reducing conditions.