Fig. 6. Internalization of 125I-EGF by wild type (closed symbols) or CTSL-knockout (open symbols) primary keratinocytes. Cells were incubated with murine 125I-EGF for 30 minutes at 4°C. During the chase at 37°C, cell-surface-bound 125I-EGF (triangles) and intracellular 125I-EGF (squares) were quantified.