CS/DS polysaccharides are unbranched polymers consisting of repeated alternating hexuronic acid (either glucuronic acid or iduronic acid; GlcA or IdoA) and N-acetylgalactosamime (GalNAc). DS-epi1 and 2 convert GlcA to its epimer, IdoA, to a variable degree. The presence in a chain of even a single IdoA dictates the name of DS, which is invariably composed of a mixture of the two epimers. GalNAc residues in CS/DS are almost quantitatively sulfated at the hydroxyl groups either in the C4 or C6 position (4-OS and 6-OS), or occasionally in both positions. Similarly, GlcA/IdoA can be sulfated to a certain extent at the C2 position. Four 4-O-sulfotransferases, three 6-O-sulfotransferases and a single 2-O-sulfotransferase catalyze the reactions. As a result of these modifications CS/DS contains structural microdomains endowed with biological information. For instance, less predominant structures containing GlcA/IdoA(2-OS)-GalNAC(6-OS) and IdoA(2-OS)-GalNAC(4-OS) are important for neurite outgrowth and coagulation, respectively (5, 6).
