Structural Studies on Heparan Sulphates

Abstract

Three heparan sulphate fractions were subjected to degradation by periodate oxidation and alkaline elimination. The starting materials were one low-sulphated fraction rich in glucuronic acid and N-acetylglucosamine (I), one fraction (IV) that was medium-sulphated, contained similar proportions of N-acetyl and N-sulphate as well as of glucuronic and iduronic acid and one fraction (V) that was oversulphated, contained an excess of N-sulphate and was rich in iduronic acid. Selective periodate oxidation of glucuronic acid residues within N-acetylated regions followed by scission in alkali yielded three categories of fragments that were isolated by gel and ion-exchange chromatography. (a) N-Acetylglucosamine-R compounds where R is the remnant of an oxidised and degraded glucuronic acid residue. (b) Medium-sized oligosaccharides, of the general structure glucosamine-(glycuronic acid-glucosamine)n-R where n = 1--4, contained largely glucuronic acid associated with glucosamines that were N-sulphated, N-acetylated or unsubstituted. In saccharides where n = 4 indications of an alternating arrangement of N-sulphate and N-acetyl groups as well as of iduronic and glucuronic acid residues were obtained. The glucuronic acid residues of the oligosaccharide fragments were susceptible to reoxidation with periodate. The smaller saccharides were not depolymerised by HNO2 despite the presence of N-sulphate groups. (c) Longer oligosaccharide fragments (n greater than or equal to 5) that were highly sulphated and contained heparin-like repeating units, i.e. iduronic acid--glucosamine-N-sulphate with ester-sulphate on both sugars. These oligosaccharides were susceptible to deaminative cleavage.