Biosynthesis of dermatan sulfate. I. Formation of L iduronic acid residues

L [¹⁴C]Iduronic acid containing sulfated galactosaminoglycans were formed by incubation of a fibroblast particulate fraction with UDP D [¹⁴]glucuronic acid, UDP N acetylgalactosamine, and sulfate donor (3 phosphoadenylylsulfate). The formation of L iduronic acid was strongly promoted by concomitant sulfation of the polymer. In the absence of sulfate donor 5 to 10% of the [¹⁴C]uronic acid residues were L iduronic acid. However, when 3 phosphoadenylylsulfate was included in the incubation mixture the amount of L iduronic acid in the product increased 3 to 5 fold. Furthermore, approximately the same quantity of L [¹⁴C]iduronic acid was recovered from the product formed in a pulse chase experiment where incorporation of ¹⁴C isotope preceded sulfation. It was therefore concluded that C 5 inversion of D glucuronic acid to L iduronic acid occurred on the polymer level as shown previously for the biosynthesis of heparin. This conclusion was supported by the finding that no L [¹⁴C]iduronic acid could be detected in the UDP hexuronic acid pool during this experiment. Nonsulfated and sulfated [¹⁴C]galactosaminoglycan products were degraded separately with chondroitinase AC. The nonsulfated products afforded primarily disaccharide and a small amount of tetrasaccharide, while the sulfated products yielded, in addition, a considerable amount of larger oligosaccharides. Tetrasaccharides from nonsulfated products contained L iduronic acid indicating that C 5 inversion at solitary sites can occur in the absence of sulfation of adjacent hexosamine moieties. The larger oligosaccharides obtained after chondroitinase AC digestion of sulfated products yielded L iduronic acid upon acid hydrolysis and were susceptible to chondroitinase ABC digestion. The split products were almost exclusively 4 sulfated disaccharides. These results demonstrate that formation of blocks of L iduronic acid containing repeat periods is associated with 4 sulfation of adjacent hexosamine moieties.