Chemistry Reference
In-Depth Information
Figure 30.2
Structures of the fi ve major gan-
gliosides of mammalian brain. GM1, R
1
= R
2
= H; GD1a, R
1
= Neu5Ac, R
2
= H; GD1b, R
1
= H,
R
2
= Neu5Ac; GT1b, R
1
= R
2
= Neu5Ac; GQ1b,
R
1
= Neu5Ac(2 - 8)Neu5Ac,
zig-zag lines of ceramide represent hydrocar-
bon chains. [Reproduced with permission from
R. Ledeen. Gangliosides of the neuron.
Trends
Neurosci
, 1985;
8
, 169 - 174.]
R
2
= Neu5Ac.
The
a quarter occur as major or minor gangliosides of the nervous system. An approxi-
mately equal number of neutral GSLs have been characterized in vertebrate
tissues, although these are relatively sparse in the nervous system. These numeri-
cal counts would expand considerably with inclusion of invertebrates. It seems
likely that more GSLs await discovery, in keeping with improved methodologies
such as high - performance liquid chromatography, two - dimensional thin - layer
chromatography and mass spectrometry (for glycan analysis using these methods,
please see Chapter 5). GSLs can be designated according to International Union
of Pure and Applied Chemistry-International Union of Biochemistry systematic
nomenclature, although many investigators have found it convenient for the most
common gangliosides to use the system proposed by Svennerholm following his
landmark resolution of these substances by thin- layer chromatography [4] . Both
systems were therefore listed in Table 10.3 .
The fi ve structures shown in Figure 30.2 comprise the major gangliosides of the
mammalian nervous system, with neurons as their principal locus. These are
based on GM1 as the monosialo prototype, the di-, tri- and tetrasialo analogs
(GD1a, GD1b, GT1b and GQ1b) containing additional
N
- acetylneuraminic acid
(Neu5Ac) (for abbreviations and structures of monosaccharides, please see Chapter
1) attached to the hydroxyls indicated. The much larger number of quantitatively
