Hyaluronan repeating disaccharide units

Figure 4-11 The repeating disaccharide units of hyaluronan and other glycosaminoglycans. See Fransson108 and Hardingham and Fosang.107...

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. 

Hyaluronan is an anionic (in the range of the physiological pH values the carboxy group of the D-glucuronic acid residue is practically completely deprotonated), linear polysaccharide, the molecular weight of which essentially depends on the source and the production method (see Chapter 2). Usually the value of the molecular mass is in the range lO -lO Da, which corresponds to 25000 and more repeatable disaccharide units. 

This type of enzyme is commonly obtained from bacterial sources like pneumococci, staphylococci, streptococci, Clostridia [29], Flavobacterium, and Proteus vulgaris [30], and has been demonstrated in Treponema pallidum [31]. Bacterial hyaluronidases degrade hyaluronan to a disaccharide containing a A-4,5-unsaturated uronic acid by eliminating 1 mole of water from the uronic acid portion of the repeating unit of hyaluronan [29]. The full mechanism of this type of reaction has been elucidated by Ludowieg et al. [32],... 

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

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