Figure 3.

Protein composition of TfR-positive endosomes. Endosomes containing m-hTfR were purified, with the use of cells expressing hTfR as a control, as in Figure 2, B and C. (A and B) Immunoisolated membranes bound to the beads (B) were analyzed by SDS-PAGE and Western blotting with the use of specific antibodies against the indicated proteins. For comparison, 50% of the total fraction used as starting material for immunoisolation (IN) was also analyzed. Asterisks mark the light chain of the antibody used for immunoisolation. (C) Immunoisolated membranes (B) are compared with unbound material sedimented at 150,000 × g for 30 min (UB) as in Figure 2B. Analysis was as in A and B, with the use of specific antibodies against the indicated proteins.