Glycosaminoglycans modifications

Glycosaminoglycans are usually attached to proteins to form proteoglycans. Heparin is synthesized in a nonsulfated form, which is then deacet-ylated and sulfated. Incomplete modification leads to a mixture of variously sulfated sequences. Some of them act as anticoagulants by binding specifically to antithrombin, which accelerates its sequestration of thromhin (Section 10.5.6). Heparan sulfate is like heparin except that it has fewer TV- and O-sulfate groups and more acetyl groups. 

Besides the typical structures previously indicated, irregularities may also be present in the repeating units. Glycosaminoglycans contain numerous anionic groups (carboxyl, sulfate) and in nature they may be present as sodium, potassium, etc. forms, which is not always possible to know because of the modifications suffered during the purification process. 

Many complex polysaccharides contain modified sugars that are covalently linked to various small groups, particularly amino, sulfate, and acetyl groups. Such modifications are abundant in glycosaminoglycans, major polysaccharide components of the extracellular matrix that we describe In Chapter 6. 

Part of the mechanism of the above vitreous glycosaminoglycan transformation in retinal detachment may be explained by modification of blood components. 

---