Fig. 9.

The β₂ integrin subunit of macrophages is a direct proteolytic target for autoactivating MMP-9. Medium conditioned by M9A or WT macrophages for 6 h was monitored for β₂ integrin peptides containing the non-tryptic MMP-9 cleavage site identified in the peptide substrate mapping studies (Fig. 8). A, XICs for the semitryptic peptide NIYNIHVEDSLECVKGPNVAA ([M + 3H]³⁺) in medium from M9A or WT macrophages. Similar results were observed in two independent experiments. B and C, tandem mass spectra of the [M + 3H]³⁺ ions and [M + 2H]²⁺ ions of NIYNIHVEDSLECVKGPNVAA in the medium of M9A macrophages. Note the almost complete coverage of b and y ions, confirming the identity of the peptide with high confidence.