These are heterogeneous polysaccharides resulting from the polycondensation under disaccharide units (or disaccharide) Elementary consists of :
-a carrier molecule or non-hexosamine moiety sulfated.
-a uronic acid molecule.
They are not found free in tissues, but they are united to proteins : proteoglycans.
There are according to their biological role both groups :
- Glycosaminoglycanes de structure: exp Hyaluronic Acid
- A glycosaminoglycans reserve : Heparin and its derivatives.
A/ Glycosaminoglycanes de structure :
1) Hyaluronic acid :
- it represents a barrier for foreign substances. It is present in the vitreous humor and in the joints where it has a role of lubricant.
- This is the simplest glycosaminoglycan. It is composed of units disaccharide repeated n times :
(p D glucuronic acid + N- acetyl glucosamine D)n
- connections are :
- ß (1—>3) in the pattern
- ß (1—>4) between the patterns
- Hyaluronic acid has a very high molecular weight and very many negative charges ;no sulphates.
- It is hydrolyzed by an enzyme depolymerization, hyaluronidase which acts between the links, on p bonds( 1—>4). This enzyme is found in bacteria, snake venom, semen as it facilitates the penetration of sperm into the egg at fertilization by hydrolyzing the shell of the egg.
Y = N-D-Glucosamine-AcétyI
2) Chondroitin sulfates :
- They are found in connective tissue and cartilage.
- They consist of the polycondensation disaccharide units :
(ß D glucuronic acid + N- acetyl D galactosamine) n
- Links are also beta (1->3) in the grounds and
ß ( 1->4) between the patterns.
- They therefore strongly bind cations. Sulfates are fixed C4. or C6 of
Acid X = beta-D-glucuronic
Y = N-Acetyl-D-Galactosamine
or sulfated : a sulfated moiety is attached at position 4 or 6 N-Acetyl-D-Galactosamine.
B / L secretion of glycosaminoglycans’heparin and its derivatives :
- C’is a physiological anticoagulant that is present in many tissues (foie, lung, rein, heart).
- It consists of the polycondensation :
(Acid α D glucuronique + D Glucosamine N – Sulfate) n
- The bonds are α (1->4) in the pattern and between the patterns.
- Sulfates are indispensable to’biological activity, they are fixed on the’nitrogen and’primary alcohol 6 glucosamine but some heparin may contain much more.
During the DR ZEKRI.S – Faculty of Constantine