Sugar acids heparin sulfate

D-Clucuronic acid residues in heparin are linked as in disaccharide units 1 and 2, that is, either to 2-acetamido-2-deoxy-D-glucose ( Ana) or to 2-deoxy-2-sulfoamino (ANS) residues. (Although not apparent from Scheme 1, the amino sugar can be sulfated at C-6.)... 

In contrast to the neutral polysaccharides, the carbohydrate skeleton of heparin and mucopolysaccharides is based on an amino sugar uronic acid repeating unit. An important biological difference is that the neutral polysaccharides (glycogen, starch) are metabolic stores, the typical mucopolysaccharides (chondroitin sulfuric acids, keratin sulfate) are important structural materials of connective tissue, and the naturally occurring heparins and heparinoids are trace substances and appear to be associated with special cells. 

Fig. 3. Configuration of disaccharide unit in heparin. Above is disaccharide produced by flavobacterium heparinum and below the disaccharide configuration in heparin. (1 - 4)-linked 4-o-(a-L-idopyranosyluronic acid 2-sulfate)-(2-deoxy-2-sulfoamino-a-D-glucopyranosyl 6-sulfate) biose residue. U=uronic acid, A = amino sugar. (After Perlin et al. [15].)...

The GAGs contain specific sugars such as glucosamine sulfate, N-acetylglucosamine and glucosamine hydrochloride, all very able of attracting water. They form long chains of molecules that retain water, such as hyaluronic acid, keratin sulfate, heparin, dermatin, and chondroitin. 

It is important to note that the foregoing, biosynthetic-polymer modification is usually incomplete. In fact, only a fraction of the heparin precursor undergoes all of the transformations shown in Scheme 1. However, as the product of each enzymic reaction constitutes the specific substrate for the succeeding enzyme, the biosynthesis of heparin is not a random process. Thus, sulfation occurs preferentially in those regions of the chain where the amino sugar residues have been N-deacetylated and N-sulfated, and where D-glucuronic has been epimerized to L-iduronic acid.20... 

More-specific methods are available for identifying and quantitating the typical, amino sugar component of heparin (and some heparan sulfate species), namely, 2-deoxy-2-sulfoamino-D-glucose. Most of these methods are based on conversion of these residues into 2,5-anhydro-D-mannose by deamination with nitrous acid (see Section VIII,2). The 2,5-anhydro-D-mannose residues may be determined either colorimetrically,52-54 or fluorimetrically.55... 

From pig mucosa. Notations as for Scheme 1. Major products (yield 40-80% of original heparin). Major disaccharide fraction (50-80%). From heparin chains terminating with a D-glucuronic acid residue at the reducing end. Minor products (yield <3% of original heparin). From the active site for antithrombin (asterisk denotes 3-C-sulfation of the amino sugar or anhydro-D-mannose). 

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