General Properties, Occurrence, and Preparation
1.2
81
carbon N-acetyl-amino-sugar acid, with a repeating β-(1→4)-NAG-NAM sequence of 40–150
residues, giving a polysaccharide, called murein [89].
A pentapeptide is attached to the carboxyl group of the L-lactic acid by an amino group that
forms a peptide (amide) bond [90]. Attached to this pentapeptide is a pentaglycine linked to
the ε-amino group of an L-lysine by a carboxyl group. The glycine end forms a cross-link to
another decapeptide [90]. Using slightly different amino acids in both the pentapeptide and the
cross-linking peptide gives different peptides that are genus-dependent.
The murein-peptidoglycan gives rigidity and different specific shapes, such as rods, spheres, or
spirals to bacterial cells. Because of the cross-linking of the murein chains, the peptidoglycan
is considered one giant, bag-shaped macromolecule [91]. The structures of segments of chitin,
chitosan, and murein are shown in > Fig. 6.
7.4 Properties and Occurrence of Glycosaminoglycans
Composed of Amino Sugars and Uronic Acids
Glycosaminoglycans make up a group of polysaccharides that are found in animal tissues.
They are composed of repeating disaccharides units of N-acetyl-D-glucosamine or N-acetylD-galactosamine and D-glucopyranosyluronic acid residues. The linkages are primarily β at
positions 3 and 4. They are most often attached to protein backbones, forming what is called
a proteoglycan [92].
7.4.1 Hyaluronic Acid
Hyaluronic acid consists of repeating disaccharides of β-D-glucopyranosyluronic acid-(1→3)N-acetyl-D-galactosamine linked β-(1→4) to the next disaccharide. This proteoglycan can
have between 500 and 50,000 residues per chain [92]. Hyuronic acid is found widely distributed in mammalian cells and tissues, where it is found in synovial fluid that lubricates the joints,
in the vitreous humor of the eye, and in connective tissue, such as the umbilical cord, the dermis, and the arterial wall. It also occurs as a capsular polysaccharide around certain bacteria,
such as pathogenic streptococci [92].
7.4.2 Chondroitin Sulfate
Chondroitin sulfate also consists of a repeating disaccharide of β-D-glucopyranosyluronic
acid-(1→3)-N-acetyl-D-galactosamine linked β-(1→4) to the next disaccharide unit, with
sulfate groups attached to C-4 or C-6 of the N-acetyl-D-galactosamine residue. It occurs as
a major component of cartilage found in the cornea of the eye, the aorta, the skin, and lung
tissues, where it is located between fibrous protein molecules. Chondroitin sulfate provides
a soft and pliable texture to these tissues [92].
7.4.3 Dermatan Sulfate
Dermatan sulfate is derived from chondroitin 4-sulfate by the action of a C-5 epimerase that
inverts the carboxyl group of the β-D-glucuronic acid, giving the very rare sugar, α-L-idopy-
1.2
81
carbon N-acetyl-amino-sugar acid, with a repeating β-(1→4)-NAG-NAM sequence of 40–150
residues, giving a polysaccharide, called murein [89].
A pentapeptide is attached to the carboxyl group of the L-lactic acid by an amino group that
forms a peptide (amide) bond [90]. Attached to this pentapeptide is a pentaglycine linked to
the ε-amino group of an L-lysine by a carboxyl group. The glycine end forms a cross-link to
another decapeptide [90]. Using slightly different amino acids in both the pentapeptide and the
cross-linking peptide gives different peptides that are genus-dependent.
The murein-peptidoglycan gives rigidity and different specific shapes, such as rods, spheres, or
spirals to bacterial cells. Because of the cross-linking of the murein chains, the peptidoglycan
is considered one giant, bag-shaped macromolecule [91]. The structures of segments of chitin,
chitosan, and murein are shown in > Fig. 6.
7.4 Properties and Occurrence of Glycosaminoglycans
Composed of Amino Sugars and Uronic Acids
Glycosaminoglycans make up a group of polysaccharides that are found in animal tissues.
They are composed of repeating disaccharides units of N-acetyl-D-glucosamine or N-acetylD-galactosamine and D-glucopyranosyluronic acid residues. The linkages are primarily β at
positions 3 and 4. They are most often attached to protein backbones, forming what is called
a proteoglycan [92].
7.4.1 Hyaluronic Acid
Hyaluronic acid consists of repeating disaccharides of β-D-glucopyranosyluronic acid-(1→3)N-acetyl-D-galactosamine linked β-(1→4) to the next disaccharide. This proteoglycan can
have between 500 and 50,000 residues per chain [92]. Hyuronic acid is found widely distributed in mammalian cells and tissues, where it is found in synovial fluid that lubricates the joints,
in the vitreous humor of the eye, and in connective tissue, such as the umbilical cord, the dermis, and the arterial wall. It also occurs as a capsular polysaccharide around certain bacteria,
such as pathogenic streptococci [92].
7.4.2 Chondroitin Sulfate
Chondroitin sulfate also consists of a repeating disaccharide of β-D-glucopyranosyluronic
acid-(1→3)-N-acetyl-D-galactosamine linked β-(1→4) to the next disaccharide unit, with
sulfate groups attached to C-4 or C-6 of the N-acetyl-D-galactosamine residue. It occurs as
a major component of cartilage found in the cornea of the eye, the aorta, the skin, and lung
tissues, where it is located between fibrous protein molecules. Chondroitin sulfate provides
a soft and pliable texture to these tissues [92].
7.4.3 Dermatan Sulfate
Dermatan sulfate is derived from chondroitin 4-sulfate by the action of a C-5 epimerase that
inverts the carboxyl group of the β-D-glucuronic acid, giving the very rare sugar, α-L-idopy-