Generalized Primary Structures of Glycosaminoglycans and Proteoglycans

At this stage, it is essential to give a description of the glycosaminoglycans and proteoglycans in terms of chemical structures. 

Starting with the simplest of the glycosaminoglycan structures, hyaluronic acid has a disaccharide repeating structure (I) composed of the 

Hyaluronic acid and chondroitin are the only nonsulfated glycosamino-glycans occurring naturally and the structure of chondroitin is analogous to hyaluronic acid in that the repeating structure is isomeric with it. Chondroitin has a disaccharide repeating structure (II) composed of 

Chondroitin 4-sulfate and chondroitin 6-sulfate, as their names imply, are sulfated varieties of chondroitin. The sulfate group is located at the 4- and 6-positions, respectively, of the 2-acetamido-2-deoxy-4)-galac-tose residues, giving repeating structures of -0-/3-D-glucopyranuronosyl-(1 3)-0-(2-acetamido-2-deoxy-/3-D-galactopyranosyl 4-(or 6-)sulfate)-(l- 4)-, (III) and (IV), respectively. Variants of chondroitin sulfate 

Dermatan sulfate is an isomer of chondroitin 4-sulfate in which the D-glucuronic acid units have been replaced by L-iduronic acid units, the linkage positions and absolute orientations of the glycosidic linkages remaining the same. The repeating unit (V) is therefore 0-a-L-idopyra-nuronosyl-(l 3)-(2-acetamido-2-deoxy-0- -D-galactopyranosyl 4-sul- 

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