Figure 6.

(a) The MS/MS spectrum of the CD166 glycopeptide LNLSEN^#YTLSISNAR (AA#90-144, N^# denotes a conversion of N to D with ¹⁸O for the N-linked site Asn⁹⁵) containing two N-linked consensus sequons. The detected mass difference of 117 Da between y9 and y10 demonstrates that Asn⁹⁵ is deamidated, labeled with ¹⁸O and thus, was glycosylated. (b) The MS/MS spectrum of the zinc-α-2-glycoprotein glycopeptide DIVEYYN^#DSN *GSHVLQGR (AA#103-120, N^# denotes a conversion of N to D with ¹⁸O for the N-linked site Asn¹⁰⁹, and N* denotes a conversion of N to D for the N-linked site Asn¹¹²) that contains two N-linked consensus sequons. The detected mass difference of 117 Da between y11 and y12 demonstrates that the Asn¹⁰⁹ is deamidated and is labeled with ¹⁸O thus is glycosylated. The detected mass difference of 115 Da between y8 and y9 demonstrates that the Asn¹¹² is not glycosylated, and has undergone non-enzymatic deamidation.