Chondroitin 6-sulfate disaccharide repeating units

Figure 6 Structures of the disaccharide repeating units of chondroitin sulfate (CS), hyaluronan (HA), and keratan sulfate (KS).

Figure 5 General structure of the disaccharide repeating unit of chondroitin sulfate...

As shown in Figure 48-8, the keratan sulfates consist of repeating Gal-GlcNAc disaccharide units containing sulfate attached to the 6 position of GlcNAc or occasionally of Gal. Type 1 is abundant in cornea, and type II is found along with chondroitin sulfate attached to hyaluronic acid in loose connective tissue. Types I and II have different attachments to protein (Figure 48—8). 

The repeating disaccharide unit of the main chain of chondroitin sulfate is 50, with O-sulfo groups on the 4- or 6-hydroxyl groups of most 2-acetamido-2-deoxy-D-galactosyl residues. Fractions can be prepared... 

This structure resembles that of chondroitin sulfate, except that some of the /3-D-glucosyluronic residues of the repeating disaccharide unit are replaced by a-L-idosyluronic residues. The proportion of D-glucosyluronic residues in the polymer varies according to the source, but there can be more L-idosyluronic than D-glucosyluronic residues. 

Chondroitin sulfate also consists of a repeating disaccharide of 8-D-glucopyranosyluronic acid-(1 3)-tV-acetyl-D-galactosamine linked p- 4) to the next disaccharide unit, with sulfate groups attached to C-4 or C-6 of the A-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]. 

GAGs are classified into several major types based on the nature of the repeating disaccharide unit heparan sulfate, chondroitin sulfate, dermatan sulfate, keratan sulfate, and hyaluronan. A hypersulfated form of heparan sulfate called heparin, produced mostly by mast cells, plays a key role In allergic reactions. It is also used medically as an anticlotting drug because of its ability to activate a natural clotting inhibitor called antlthrombln III. 

At least seven types of glycosaminoglycans exist, which differ in the monosaccharides present in their repeating disaccharide units—chondroitin sulfate, dermatan sulfate, heparin, heparin sulfate, hyaluronic acid, and keratan sulfates I and II. Except for hyaluronic acid, the glycosaminoglycans are linked to proteins, usually attached covalently to serine or threonine residues (Fig. 49.9). Keratan sulfate I is attached to asparagine. 

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