Fig. 7. Enhanced recycling of ¹²⁵I-EGF in ctsl^-/- keratinocytes. After loading the cells for 30 minutes, cell-surface-bound ¹²⁵I-EGF was removed by an isotonic pH 3.5 wash and the fate of the internalized ¹²⁵I-EGF was followed during chase at 37°C. (A) Degradation of intracellular ¹²⁵I-EGF in ctsl^+/+ and ctsl^-/- keratinocytes. (B) Degraded ¹²⁵I-EGF in the medium. (C) Intact ¹²⁵I-EGF in the medium. ^*P<0.05 between ctsl^+/+ and ctsl^-/- of the corresponding time point. (D) Cell surface (receptor-bound) ¹²⁵I-EGF releasable by incubation at pH 3.5. ^*P<0.05, ^**P<0.01 between ctsl^+/+ and ctsl^-/- of the corresponding time point.