General Veterinary Biochemistry

HETEROPOLYSACCHARIDES - MUCOPOLYSACCHARIDES

• They are also known as glycosaminoglycans. They are complex carbohydrates containing amino sugars and uronic acids.
• When glycosaminoglycan chains are attached to a protein molecule, the compound is known as “proteoglycans”.
• They are components of extracellular matrix (also known as “ground substances”), which holds the cells of a tissue together and provides a porous pathway for the diffusion of the nutrients and oxygen to the individual cells.
• They are linear polymers, composed of repeating disaccharide units. One of the 2 monosaccharides is N – Acetylglucosamine or N – Acetylgalactosamine and the other is mostly an uronic acid usually glucuronic acid.
• Some of the examples are hyaluronic acid, chondroitin sulfate and heparin.

Hyaluronic acid

• The repeating unit of hyaluronic acid is a disaccharide containing D – Glucuronic acid and N- Acetyl glucosamine held by β - 1,3 linkage and repeating disaccharide by β-1,4-linkage.
• They form clear, highly viscous solutions, which serve as lubricants in the synovial fluids of joints and provide a cushioning effect.

Chondroitin sulfate

• Chondroitin – 4- sulfate is a major polysaccharide of cartilage, which contains alternating units of D-Glucuronic acid and N-Acetyl –D-galactosamine.
• The linkage is similar to hyaluronic acid and the N-acetyl galactosamine is sulphated at 4th position.
• The presence of the negatively charged groups at C-6 of D-glucuronic acid carboxyl group) and the sulfate ester group at C-4 of N-Acetylgalactosamine, has two important consequences:
• The groups repel each other and cause the polysaccharides molecule to expand;
• They as well as the sugar hydroxyl groups are extensively hydrated. The net effect is that chondroitin –4- sulfate swells when placed in water and creates a gelatinous matrix that makes it as a good lubricant.

Heparin

• It is made up of D-glucuronate sulphate / L-idurunote sulphate and N-sulphoglucosamine –6-sulfate linked by α (1 → 4) glycosidic bonds.
• 90% of uronic acids are iduronic acids.
• It is present in liver, lungs, spleen, monocytes etc. Commercial preparation of heparin is mainly from animal lung tissues.
• It is an anti – coagulant widely used when taking blood in vitro for clinical studies.
• It is also used in vivo to prevent intra vascular coagulation.

 

Dermatan sulfate

• It is composed of alternating units of L- iduronic acid and N- acetyl galactosamine –4 – sulphate linked by β - 1,3 linkage and repeating disaccharide by β - 1,4 linkage .
• It is present in skin, blood vessels and heart valves .

Keratan sulphate

• It is a heterogeneous GAG with variable sulphate content.
• It is made up of alternating units of D-galactosamine and N-acetyl glucosamine linked by β - 1,4 linkage.