Dermatan is a better substrate for 4-O-sulfation than chondroitin: Implications in the generation of 4-O-sulfated, L-iduronate-rich galactosaminoglycans

The biosynthesis of dermatan sulfate is a complex process that involves, in fer alia, formation of L-iduronic acid residues by C5-epimerization of D-gl ucuronic acid residues already incorporated into the growing polymer. It ha s been shown previously that this reaction is promoted by the presence of t he sulfate donor 3' -phosphoadenosine-5'-phosphosulfate. In the present inv estigation, the role of sulfation in the biosynthesis of L-iduronic acid-ri ch galactosaminoglycans was examined more closely by a study of the substra te specificities and kinetic properties of the sulfotransferases involved i n dermatan sulfate biosynthesis. Comparison of the acceptor reactivities of oligosaccharides from chondroitin and dermatan, in an in vitro system cont aining microsomes from cultured human skin fibroblasts and 3'-phosphoadenos ine-5'-phosphosulfate, showed that K-m values for the dermatan fragments we re substantially lower than those for their chondroitin counterparts. Calcu lation of V-max values likewise showed that dermatan was the better substra te. Whereas dermatan incorporated [S-35]sulfate exclusively at the C4 posit ion of N-acetylgalactosamine residues, approximately equal amounts of radio activity were found at the C4 and C6 positions in the labelled chondroitin. Under standard assay conditions, the 4-O-sulfation of dermatan proceeded a bout six times faster than the 4-O-sulfation of chondroitin, On the basis o f these results, we propose that L-iduronic acids, formed in the course of the biosynthesis of dermatan sulfates, enhance sulfation of their adjacent N-acetylgalactosamine residues, and will thereby be locked in the L-ido con figuration. (C) 2000 Academic Press.