ABSTRACT
Glycosaminoglycans (GAG) are linear polysaccharides found ubiquitously in extracellular matrix, on cell surfaces, and in the intracellular compartment of mast cells (heparin). GAG macromolecules are characterized by a strong polyanionic and hydrophilic charge. After synthesis onto core proteins in the Golgi apparatus within the fibroblasts and related cells, the abundant majority of GAG is released into the extracellular matrix where they are bound to structural proteins to form proteoglycans. Free GAG chains are encountered in considerable amounts in the blood from where they are eliminated in the kidney. GAG as major compounds of proteoglycans in the extracellular matrix, are essential for the structure and function of connective tissues. The strong polyanionic and hydrophilic charge of GAG components, which is fundamental for the water content and electrolyte composition of the extracellular space, is due to multiple carboxyl and sulfate residues. These linear polysaccharides are composed of repetitive disaccharides consisting of one hexosamine (d-glucosamine, d-galactosamine) and one uronic acid (d-glucuronic acid, l-iduronic acid). Different substitutions and structures of the disaccharides allow the formation of various GAG components, including hyaluronic acid (HA), chondroitin sulfate (CS), and dermatan sulfate (DS), with highly variable charge and chain lengths (1-6).
