Figure 6: An expansion of the MS/MS spectra shown in Figure 5. The fragmentation spectrum of the β-CN (60-106) peptide shows that the triply charged ion series b38, b39, and b40, corresponding to V-97, V-98, and V-99 (panel a), is missing from the spectrum of the transamidated peptide (panel b). The signals marked with an asterisk (panel b) indicate a shift in mass corresponding to that of the triply charged ion of the β-CN (116-1123) peptide minus one ammonia mass lost in the crosslinking reaction.