▲ FIGURE 6-17 The repeating disaccharides of glycosaminoglycans (GAGs), the polysaccharide components of proteoglycans. Each of the four classes of GAGs is formed by polymerization of monomer units into repeats of a particular disaccharide and subsequent modifications, including addition of sulfate groups and inversion (epimerization) of the carboxyl group on carbon 5 of d-glucuronic acid to yield l-iduronic acid. Heparin is generated by hypersulfation of heparan sulfate, whereas hyaluronan is unsulfated. The number (n) of disaccharides typically found in each glycosaminoglycan chain is given. The squiggly lines represent covalent bonds that are oriented either above (d-glucuronic acid) or below (l-iduronic acid) the ring.
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