STRUCTURAL STUDIES ON HEPARAN SULFATES - CHARACTERIZATION OF OLIGOSACCHARIDES - OBTAINED BY PERIODATE-OXIDATION AND ALKALINE ELIMINATION

Abstract

Three heparan sulfate fractions were subjected to degradation by periodate oxidation and alkaline elimination. The starting materials were one low-sulfated fraction rich in glucuronic acid and N-acetylglucosamine (I). One fraction (IV) that was medium-sulfated contained similar proportions of N-acetyl and N-sulphate as well as of glucuronic and iduronic acid and one fraction (V) that was oversulfated, contained an excess of N-sulfate and was rich in iduronic acid. Selective periodate oxidation of glucuronic acid residues within N-acetylated regions followed by scission in alkali yielded 3 categories of fragments that were isolated by gel and ion-exchange chromatography. N-Acetylglucosamine-R compounds where R is the remnant of an oxidized and degraded glucuronic acid residue. 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-sulfated, N-acetylated or unsubstituted. In saccharides where n = 4, indications of an alternating arrangement of N-sulfate 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 depolymerized by HNO2 despite the presence of N-sulfate groups. Longer oligosaccharide fragments (n .gtoreq. 5) that were highly sulfated and contained heparin-like repeating units, i.e. iduronic acid-glucosamine-N-sulfate with ester-sulfate on both sugars. These oligosaccharides were susceptible to deaminative cleavage.