Heparin linkage region

Fig. 2.—Schematic Representation of the Heparin Proteoglycan. [The polysaccharide chains, bound to the polypeptide matrix through a linkage region," are cleaved by tissue endoglycosidases (arrows) after the transformations illustrated in Scheme 1.]...

Fig. 5. —Tentative Model for a Heparin Chain Containing the Linkage Region. [1 and 2 are sites of cleavage with 2-pyridone, affording fragments A and B A may be further cleaved by a more drastic treatment. The active site for antithrombin is proposed - 8 to be within fragment A. ...

Fic. 6.—Proposed Distribution of Disaccharide Units Along an Average Heparin Chain.151 [For simplicity, possible linkage regions and antithrombin-binding sequences are not considered. For notations, see legend and footnote to Scheme 1. Arrows indicate possible insertion of units G-Ana.]... 

Oligosaccharide Fragments Isolated from the Carbohydrate-Protein Linkage-Region of Heparan Sulfate and Heparin Proteoglycans... 

Figure 2. Structures of the glycosaminoglycans and their linkage regions to protein. Two disaccharide repeating units are shown to emphasize the microheterogeneity that exists in some cases. Heparan sulfate and heparin show many structural similarities. However, heparan sulfate contains more GlcNAc(a-1 — 4)GlcUA repeating units fewer glucosamine residues are N-sulfated, and few iduronic acid residues are sulfated at C2.

Combined incubation with the three heparin lyases eventually converts heparin and HS to disaccharides, the only sequence invariably resistant to cleavage being the linkage region. "" The HPLC profiles of the disaccharide pools thus obtained are conveniently used for compositional characterization of heparins and HS of different origin notably, however, information regarding GlcA/IdoA ratio is lost. 

The proof of this sequence, and of the nature of the carbohydrate-peptide bond, was based on enzymic erosion to a glycopeptide fragment that was then studied by adaptations of classical methods. A similar linkage-region probably occurs in heparin,86 heparitin sulfate,87 dermatan sulfate88 and chondroitin 6-sulfate.88a It is possible that the polypeptide core itself is branched.89... 

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