The structure of heparin was examined by characterizing a disaccharide and five of the more than a dozen tetrasaccharide components obtained by its depolymerization with flavobacterial heparinase. Enzymic depolymerization of porcine mucosal heparin results in a mixture of di-, tetra-, hexa- and higher oligo-saccharides. The di- and tetra-saccharide components represent 75mol/100mol of these heparin fragments. Ion-exchange chromatography indicates the presence of only one disaccharide, deltaIdu2S(1----4)-alpha-D-GlcNS6S (where Idu is iduronic acid, deltaIdu is 4-deoxy-alpha-L-threo-hex-4-enopyranosyluronic acid, GlcN is glucosamine, GlcA is glucuronic acid and S is sulphate), but results in the isolation of five major and at least seven minor tetrasaccharide components. The structures of the disaccharide and five major tetrasaccharides were determined by chemical, enzymic, electrophoretic and spectroscopic methods, including 13C, 1H n.m.r. and fast atom bombardment-m.s. The structure of these five tetrasaccharides are: delta Idu2S(1----4)-alpha-D-GlcNS6S(1---4)-alpha-L-Idu2S(1-- --4)-alpha -D-GlcNS6S; delta Idu2S(1----4)-alpha-D-GlcNS6S(1----4)-beta-D-GlcA(1--- -4)- alpha-D-GlcNS6S; delta Idu2S(1----4)-alpha-D-GlcNS(1----4)-beta-D-GlcA delta Idu2S(1----4)-alpha-D-GlcNAc(1----4)-beta-D-GlcA(1----4)- alpha-D-GlcNS6S; and delta Idu2S(1----4)-alpha- D-GlcNAc(1----4)-alpha-L-Idu(1----4)-alpha-D-GlcNS6S. Biological activity for the disaccharide and the five major tetrasaccharides was examined, and none of them were found to possess significant anticoagulant activity.
The first use of computer-simulation studies to examine heparin's structure has been reported. The product distributions obtained when porcine mucosal heparins were depolymerized with heparinase have been compared to computer-simulated distributions. The modeled distribution was relatively unaffected by the polydispersity and molecular weight of heparin. However, the percent of heparinase-cleavable glycosidic linkages and their distribution throughout the polymer resulted in a marked change in the simulated product distribution. The similarity between experimentally observed and computer-simulated product distributions is consistent with the random distribution of heparinase-cleavable sites in porcine mucosal heparin. Finally, a random distribution of N-acetyl residues with respect to heparinase-cleavable sites was experimentally observed.
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