Figure 8

Fragmentation pattern of the singly charged N-terminal peptide showing evidence for N-terminal glutamine. Fragmentation pattern of the singly charged N-terminal peptide (mass 998.42), from the B1133-WT construct showing an overlapping series of y- and b- ions for the sequence -ETSCIF (mass 755.32). The first two N-terminal residues of the parent peptide, -17+QM (mass 243.10), were not directly observed in the mass spectrometer, but were deduced from the mass of the parent peptide and the mass of the observed sequence (-ETSCIF). This differential mass was used to elucidate the composition of the N-terminus from tables of known dipeptide masses. The -17 in -17+QM represents a loss in mass as a result of rearrangement of glutamine to pyroglutamic acid.