Mucopolysaccharides disaccharide units

The mechanism whereby the backbone chains of the mucopolysaccharides are elaborated is at present unknown. At least two possible sequences in the biosynthesis could involve stepwise addition of either (1) (alternately) amino sugar and uronic acid or (2) initially formed disaccharide units which may contain a hexuronic or hexosaminic linkage. It is, however, clear that, at this point, a tremendous gap in our knowledge of heparin and other mucopolysaccharides exists. 

D. The mucopolysaccharides of proteoglycans contain long chains of repeating disaccharide units that are covalently linked to a protein. Sulfation occurs after the monosaccharides are incorporated into the mucopolysaccharide chain. Proteoglycans are degraded by lysosomal... 

H luronic add an unbranched mucopolysaccharide, M, 200,000-400,000. The repeating subunit is a disaccharide, N-acetyl-D-glucosamine glycosidi-cally linked P-1,4 to n-glucuronic add, the latter being linked P-13 to the next disaccharide unit. H.a. occurs in various animal tissues and joint fluids. Its aqueous solution is highly viscous, which explains its biological function as a lubricant. It is synthesized from n-glu-cose in the fibroblasts. 

Like the other acid mucopolysaccharide.s, keratan sulfate contains a repeating disaccharide unit, but many of its features are more resemblant of glj coproteins. This compound, or rather group of compounds, may therefore be regarded as being on the borderline between the tw O classes of substances. 

Disaccharides of the hexuronic acid-hexosamine type constitute the fundamental repeating unit of many mucopolysaccharides, from which they are derived by hydrolytic degradation. Further hydrolytic treatment results generally in destruction of the uronic acid moiety of the disaccharide. Structural studies have been made on the disaccharides from hyaluronic acid (hyalobiouronic acid), chondroitinsulfate (chondrosine), and heparin (heparosine). 

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