Biomedical Engineering Reference
In-Depth Information
Table 8.1
Masses of most common monosaccharide residues found
in N-glycans
Monosaccharide residue
masses (monoisotopic)
Monosaccharide
Pentose
(xylose)
132.0423
Deoxyhexose
(fucose)
146.0579
Hexose
(mannose, galactose)
162.0528
N
-Acetylhexosamine
(
N
-acetylglucosamine)
203.0794
N
-Acetylneuraminic acid
(Sialic acid)
291.0954
Sum of terminal group masses (includ-
ing 2-AB label) for calculation of
[M + Na]
+
161.0685
4. Collect the high-energy CID spectra on selected [M + Na]
+
ions (
see
Note 27
). It is best to do this manually, stopping
the acquisition when the desired signal-to-noise ratios for
the fragments are achieved.
The high-energy CID spectra are characterized by signals for
cross-ring fragments and “elimination” ions. The fragments are
provide sequence information. However, the cross-rings (A
n
and
detailed information concerning antenna substitutions and link-
age positions. The following section describes how to identify the
most abundant and structurally informative fragments observed.
3.11. Interpretation
ofMALDI
High-EnergyCID
Spectra
1. The spectrum will contain Y
n
and C
n
ions, which occur from
cleavage of the glycosidic bond between the sugar residues.
In high-energy CID spectra, these normally occur concomi-
tantly with their Y
n
-2 and C
n
-2 counterparts. Therefore,
these ions can be easily identified in the spectra as doublets
that differ by 2 Da (
see
Fig.
8.3b
at
m/z
365 and 363 for C
2
and C
2
-2, respectively).
2. A predominant C-type cleavage always occurs between the
distal
N
-acetyl glucosamine in the chitobiose unit and core
β
-mannose (e.g.,
see
C
2
and C
2
-2 in both spectra). These
ions are accompanied by a D
n
ion, which is derived from
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