Glycosaminoglycanes

0
6739

Definition :

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

Kératane sulfaté.

  • 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.

Acid X = -D-Gîucuronique

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