FIGURE 5.

The Swedish type APP is not exposed to the plasma membrane, whereas wild type is. A, SHwt and SHswe cell surfaces were biotinylated for 1 h at 4 °C, conditions under which no endocytosis occurs. The biotinylated cell surface APP was precipitated with streptavidin-coated beads, and the precipitated and total APP were subjected to Western blot analysis with anti-APP antibody 6E10. Black arrowheads indicate mature APP; white arrowheads indicate immature APP. βCTF was barely detectable in the SHswe lysate lane. B, APP on the surface of SHwt and SHswe cells was labeled with antibody 6E10 for 45 min at 4 °C. After washing, the cells were immediately fixed with 4% paraformaldehyde. Scale bar, 10 μm. C, same as B, except that the washed cells were incubated for 15 min at 37 °C before fixing with 4% paraformaldehyde. Scale bar, 10 μm. IB, immunoblot.