Chemistry Reference
In-Depth Information
Figure 1.6
Illustration of the alphabet of the
sugar language. Structural representation,
name and symbol as well as the set of known
acceptor positions (arrows) in glycoconjugates
are given for each letter. Four sugars have
L
- confi guration: fucose (6 - deoxy -
L
- galactose),
rhamnose (6 - deoxy -
L
- mannose) and arabinose
are introduced during chain elongation, where-
as
L
-iduronic acid (IdoA) results from postsyn-
thetic epimerization of GlcA at C5. The
1
C
4
conformation of IdoA (a) is in equilibrium with
the
2
S
O
form (b) in glycosaminoglycan chains
where this uronic acid can be 2-sulfated (please
see Figure 1.7d). All other 'letters' are
D
- sugars.
Neu5Ac, one of the more than 50 sialic acids,
often terminates sugar chains in animal glyco-
conjugates. Kdo is a constituent of lipopolysac-
charides in the cell walls of Gram-negative
bacteria, and is also found in cell wall polysac-
charides of green algae and higher plants.
Foreign to mammalian glycobiochemistry, mi-
crobial polysaccharides contain the furanose
ring form of
D
- galactose and also
D
/
L
- arabinose
indicated by an italic '
f
' derived from the het-
erocyclus furan. The
α
- anomer is prevalent for
the pentose arabinose, for example, in myco-
bacterial cell wall arabinogalactan and lipoara-
binomannan.
β
1 - 5/6 - Linked galactofuranoside
is present in the arabinogalactan and the
β
1 - 3/6 linkage in lipopolysaccharides.
