Glycosaminoglycans(GAGs) are linear polysaccharides made up of negatively charged disaccharide repeating units. Based on the structures of the repeating unit, GAGs can be classified into hyaluronan, the chondroitins, the keratins and the heparans. In tissues, the GAGs are covalently linked to the core proteins of proteoglycans. Metabolic turnover results in internal cleavage of core proteins or component GAG chains and thus ...