glycosamino glycans

M.Prasad NaiduMSc Medical Biochemistry,

Ph.D.Research Scholar

GLYCOSAMINO GLYCANSThey differ form each other in a number of the following properties.

1. Chain length.2. Amino – Acid composition.3. Uronic – Acid composition.4. Linkages between these components.5. Presence or absence of sulfate groups.6. The attachment of sulfate to sugar

molecule.7. The nature of core protein linked to GAG.8. The tissue and sub. Cellular distribution of

GAG.

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FUNCTIONS OF GAG1. Structural component of extra

cellular matrix.2. Contribute to the turgor of various

tissues.3. Acts as sieves in EC matrix 4. Facilitate cell migration,acts as

shock absorber at joints,(HA)5. Maintenance of compressibility of

cartilage(HA&CS)6. Have a structural role in sclera & in

corneal transparency (KS1,DS)

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FUNCTIONS OF GAG CONT-----7. Acts as anticoagulant (HA)

8. Determines the charge selectiveness of renal glomerulus.(HS)

9. Formation of cell membrane and synaptic vesicles (HS)

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Glycosaminoglycans / GAGS or Mucopolysaccharides

Are large complex of –ve charged (carboxy & sulfate groups) heteropolysaccharide chain generally associated with a small amount of protein - proteoglycan.

Special ability to bind large amount of water producing gel like matrix, that forms the bodies ground substance.

Unbranched, long repeating diasaccharide Contains uronic acid & amino sugars.

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Amino sugar – D-Glucosamine or D-Galactosamine.

Uronic acid – D-Glucuronic acid or L-Iduronic acid.

Classification

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GAGS

Sulphate free Sulphate containing

Hyaluronic acid Chondrotin SulphateDermatan sulphate keratan sulphate Heparin Heparan Sulphate

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• Contains D-Glucoronic acid + Galactosamine.

• Most abundant GAG in body.

1. Chondroitin sulfate

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Widely distributed in bone, cartilage & tendons.

Function : In cartilage, it binds collagen & hold fibers in a

tight strong network.

Role in Compressibility of cartilage in weight bearing along with Hyaluronic acid.

2 types of chondroitin sulfate : Sulphated at C 4 or C 6 group.

2. Hyaluronic acid

Contains D-Glucoronic acid + Glucosamine.It is sulphate free GAG.

It is sulphate free GAG.

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Ground substance of synovial fluid of joints, vitreous humor of eyes and connective tissues, tendon.

Hyaluronidase is an enzyme that breaks β-1 – 4 linkages.

Present in high concentration in testes, seminal fluid, & in certain snake and insect venoms.

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Functions of Hyaluronic acid Serves as a lubricant and shock absorbant in joints.

Determines charge selectiveness of renal glomerulus.

Acts as seives in extracelluar matrix.

Permits cell migration during morphogenesis & wound repair.

Hyaluronidase enzyme of semen degrades the gel around ovum & allows effective penetration of sperm into ovum.

3. Dermatan sulfate

Contains L-iduronic acid + Glucosamine

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Present in skin, cardiac valves & tendon.

Function : Present in sclera of eye where it has important

function in maintaining overall shape of eye.

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4. Heparin

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• Contains D-Glucuronic acid + Glucosamine• it is the only intracellular GAG.

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It is an anticoagulant (prevents blood clotting )

Found in granules of mast cells that line the arteries of lung, liver, kidney, spleen.

Strongly acidic due to presence of more sulphate group.

Heparin helps in the release of the enzyme lipoprotein lipase.

Helps to clear the lipidemia after fatty meal – also called clearing factor.

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5. Heparan sulfate

Same as heparin except some amino groups carry acetyl group & % of Sulphate groups are smaller.

It is extracellular GAG .

Present in basement membrane & as a ubiquitous component of cell surface.

6. Keratan sulfate

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• contains D-Galactose + Glucosamine•Only GAG with no uronic acid.

Found in cornea & tendon.

2 types :

Keratan sulfate І – cornea Keratan sulfate ІІ – skeletal muscle

Function : Maintains the corneal transparency.

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Proteoglycan

Heteropolysaccharide Agar :Contains galactose , glucose & other sugars.Cannot be digested by bacteria.So used as supporting agent to culture

bacterial colonies.Also as support medium of immuno diffusion &

immuno-electrophoresis.

Agarose : galactose & 3,6 anhydro galactose unitsUsed as matrix for electrophoresis.

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