Glycosaminoglycan

Glycosaminoglycans ( GAGs) or mucopolysaccharides are linearly composed of repeating disaccharides, acidic polysaccharides. Each of disaccharide units consist of a uronic acid ( glucuronic acid usually, rare iduronic acid, uronic acid of idose ) which are 1- 3- glycoside bonds with amino sugars such as N- acetylglucosamine. The disaccharide units of the chains themselves are linked 1-4 - glycoside. Some of the glycosaminoglycans are esterified with sulfuric acid or acetic acid on.

Mucopolysaccharides are components of many biological macromolecules covalently bound about in large numbers to a protein in the form of proteoglycans. They form the backbone of many fiber-forming substances, and have by their ability to absorb water, a high elasticity.

Depending on the composition of the disaccharide units distinguishes different sub-groups of glycosaminoglycans:

Hyaluronic acid ( HA)

Hyaluronic acid consists of β ( 1 → 4) - glycoside- linked to each other β - glucuronyl - (1 → 3 )-N- acetylglucosamine disaccharide units, and up to 100,000 may be consecutive. The sugar units are unsulfatiert. Hyaluronic acid is present as an amphipathic helix and is not bound as a single glycosaminoglycan, a Proteinzentralfilament. A hyaluronic acid molecule can by hydration up to 10,000 times greater than the volume of space occupied possess the molecule itself, so that forms a viscous gel at low concentrations. Thus, it serves as a biological lubricant. Hyaluronic acid is found in cartilage, in the synovial fluid in the umbilical cord and in the vitreous body of the eye. In the fibroblasts, the hyaluronic acid is synthesized from D-glucose.

Heparin / heparan sulfate (HS)

Heparin consists of D -glucuronic acid, the β - ( 1 → 4) - glycoside, and L -iduronic acid, the α - ( 1 → 4) - glycoside- linked to a glucosamine. The bond between the different disaccharides α - ( 1 → 4) - glycoside. The amino function of glucosamine often carries an acetyl group or a sulfate group. In addition, O-sulfate groups are present. Heparan sulfate is structurally related to the heparin, but it has fewer N-and O - sulfate residue and more N- acetyl groups.

Chondroitin sulfate / dermatan sulfate (CS / DS)

Chondroitin sulfate or Chondritinsulfat consists of β - (1 → 4) - glycosidic linked glucuronyl β - (1 → 3 )-N- acetylgalactosamine disaccharides, with D -glucuronic acid is partially converted into L- iduronic acid. If more than 10 % of the Uronats present as iduronate, one speaks of dermatan sulfate. The degree of sulfation of chondroitin sulfate and dermatan sulfate is about one sulfate group per disaccharide. The sulfate in chondroitin sulfate is present as 4- sulfate or 6- sulfate. When dermatan sulfate may also glucuronate due to epimerization at C5.

The Molar mass is between 10 and 50 kDa.

Chondroitin sulfate occurs in the connective tissues (especially in the cartilage and in synovial fluid ), dermatan sulfate also in the connective tissue (mainly in the skin) before.

Keratan sulfate (KS )

The disaccharide of keratan sulfate is β - ( 1 → 3) -linked β - galactosyl - (1 → 4 )-N- Acetylglukosaminreste. Both sugars can have a sulfation at the C6 atom. Occur 0.8-1.5 sulfate groups per unit. Keratan sulfate is present in cartilage, cornea and intervertebral discs ( Disci ).