Figure 6.
MSn analyses of three Azide-DSG cross-linked peptides of cytochrome c after Staudinger ligation and affinity purification/TFA cleavage. MS/MS spectra of the selected A) inter-linked ([M+4H]4+ 542.54); B) intra-linked ([M+3H]3+ 526.96); and C) dead-end ([M+3H]3+ 745.35) modified peptides. Characteristic fragment ions (MH+ 447.2, 508.2, 520.2) were detected in all spectra. MS3 spectra of D) a fragment ion ([M+2H]2+ 824.72) observed in A), after a loss of 508.2 Da from the parent ion ([M+4H]4+ 542.54); E) a fragment ion ([M+2H]2+ 536.31) observed in B), after a loss of 508.2 Da from the parent ion ([M+3H]3+ 526.96); and F) a fragment ion ([M+2H]2+ 863.80) observed in C), after a loss of 508.2 Da from the parent ion ([M+3H]3+ 745.35). The identified cross-linked peptide sequences are displayed in D-F. dn: dead-end modification.