Chondroitin repeating units

The simple self-crosslinking treatment also crosslinks GAG chains to collagen [30]. The reaction kinetics are outlined in Fig. 2. The mechanism probably involves condensation of amino groups of collagen with carboxylic groups of glucuronic acid residues on the repeat unit of chondroitin 6-sulfate. Dehydra-... 

Most of the polysaccharides of interest in this text are termed glycosaminoglycans, polymers that contain an amino sugar in the repeat unit. Glycosaminoglycans that are abundant in mammalian tissues include hyaluronan, chondroitin sulfate, dermatan sulfate, keratan sulfate, and heparin-heparan sulfate (see Table 2.4). Most of these glycosaminoglycans,... 

Figure 9.13 Structures of repeating units of glycosaminoglycans (A) hyaluronic acid (B) chondroitin sulfate (C) dermatan sulfate (D) two types of keratan sulfate type I is N linked and type II is O linked (E) heparan sulfate. Sulfate residues have been omitted in all cases.

Thus, the cell-wall polymer of Methanosarcina barkeri is reminiscent of chondroitin sulfate, a common component of the connective tissue in humans and animals. In contrast with chondroitin, it is not sulfated and contains two instead of one N-acetylgalactosamine residue in the repeating unit. Because of its similarities to chondroitin sulfate (Fig. 6), the shape-maintaining cell-wall polymer of Methanosarcina has been named methanochondroitin [60]. 

Different glycosaminoglicans are not very different in structure. For example, the repeating unit in chondroitin is - 4)-0-(p-D-glucopyranosyluronic acid)-(1 3)-0-(2-acetamido-2-deoxy-p-D-galactopyranosyl)-(1 ->. The number of units varies but can be in the range of hundreds. Hyaluronic acid has a rather similar structure, - 4)-0-(p-D-glucopyranosyluronic acid)-(1 ->3)-0-(2-acetamido-2-deoxy-p-D-glucopyranosyl)-(1 as shown below ... 

Figure 4 The four possible repeating units of chondroitin sulfate.

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

Heteropolysaccharides are long-chain polymers that contain more than one type of monosaccharide, many of which are amino sugars. As a result, they are often referred to as gly-cosaminoglycans, which include chondroitm sulfate, hyaluronic acid, and heparin. Hyaluronic acid is abundant in the fluid of joints and in the vitreous humor of the eye. Chondroitin sulfate is an important component of cartilage and heparin has anticoagulant function. The structures of the repeat units of these polymers are shown below. 

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