Figure 5.

Peptide candidates for MRM based quantitation. Two peptides: (1) DSQEEKTEALTSAK and (2) EVQGFESATFLGYFK, derived from pGSN by trypsin digestion and representing N-terminal and C-terminal regions respectively, are well ionized and fragmented by ESI-MS/MS. As such they are excellent potential candidates for MRM based quantitation. Note that peptide (1) was identified in only 2 out of 8 bands and peptide (2) was identified in 7 out of 8 bands of pGSN circulating in plasma/CSF. Therefore, neither of these two peptides will reflect accurately levels of pGSN; additionally, use of these peptides in MRM may not validate pGSN as potential biomarker.