Fig. 5.

The ectodomain of APP is shed by macrophages expressing active MMP-9. Conditioned medium from M9A or WT cells was analyzed by 2D LC-MS/MS or immunoblotting. A, the number of unique peptides derived from APP that were detected by MS/MS in conditioned medium incubated with cells for 24 h. Results represent the means and S.D. of three independent experiments. B, XIC for peptide STNLHDYGMLLPCGIDK (m/z 967, [M + 2H]²⁺) of APP. Results represent three independent experiments. The peptide was detected only in one salt gradient fraction. C, peptides derived from APP identified in medium conditioned by M9A macrophages (underlined). The predicted transmembrane domain is shown in boldface type. Note that only peptides from the extracellular domain were detected.