Structure of the linkage region 4. With the exception of hyaluronan, all glycosaminoglycans are synthesized on protein core. In one core protein, at least two different glycosaminoglycans can be bound, however, some proteoglycans can change the type of glycosaminoglycans or lack them completely, depending on the conditions. The biosynthesis of glycosaminoglycans occurs by adding one monosaccharide at a time at the end of growing polysaccharide chain. The biosynthesis of glycosaminoglycan is tightly connected to the metabolism of the cell, since the intermediate molecules required in the synthesis are derived from glucose.
Biosynthesis occurs through sugar nucleotides that are formed through a pyrophosphorylation.
Complex array of reactions, shown to be involved in the synthesis of glycosaminoglycans mainly in mammals, is needed. The pattern how different sugar nucleotides are formed is presented in Figure. In the liver, feedback inhibition has been shown for two sugar nucleotides. UDP-GlcNAc inhibits the formation of glucosamine, therefore regulating its own synthesis.