Domain Structure of Heparan Sulfates from Bovine Organs

Samples of heparan sulfate, isolated from bovine aorta, lung, intestine, and kidney, were degraded by digestion with a mixture of heparitinases or by treatment with nitrous acid, with or without previous N-deacetylation. Analysis of the resulting oligosaccharides showed that the various heparan sulfate samples all contained regions of up to 8 or 9 consecutive N-acetylated glucosamine residues, as well as contiguous N-sulfated sequences. L-Iduronic acid accounted for a remarkably constant proportion, 50-60%, of the total hexuronic acid units within the latter structures. Of the total iduronic acid units, 36-55% were located outside the contiguous N-sulfated regions, presumably in sequences composed of alternating N-acetylated and N-sulfated disaccharide residues. While most of the iduronic acid units within the N-sulfated blocks were 2-O-sulfated, those located outside were almost exclusively nonsulfated. The heparan sulfate preparations differed markedly with regard to the content of 6-O-sulfated glucosamine units, more than half of which were located outside the N-sulfated block regions. These findings suggest that the formation of iduronic acid residues and their subsequent 2-O-sulfation are coupled within but not outside the contiguous N-sulfated regions of the heparan sulfate chains and, furthermore, that the 2-O- and 6-O-sulfotransferase reactions are differentially regulated during heparan sulfate biosynthesis.