BIOSYNTHESIS OF DERMATAN SULFATE - LOSS OF C-5 HYDROGEN DURING CONVERSION OF D-GLUCURONATE TO L-IDURONATE

The formation of L-iduronic acid during biosynthesis of dermatan sulfate was studied in cultured human fibroblasts and in microsomes from the same cells. The cells were incubated with D-[14C]glucose and D-[5-3H]glucose for 72 h. The [14C,3H]dermatan sulfate was hydrolyzed and the disaccharides obtained were acetylated and separated by ion-exchange chromatography. The ratio of 3H/14C was 0.36 for N-acetyldermosine and 1.36 for N-acetylchondrosine. A microsomal preparation from the fibroblasts was incubated with UDP-D-[5-3H]glucuronic acid, UDP-D-[14C]glucuronic acid, UDP-N-acetyl-D-galactosamine and 3''-phospho-5''-adenylyl sulfate. The polymeric products were separated into nonsulfated and sulfated components which had 3H/14C ratios of 0.51 and 0.20 and contained 9 and 70% of their uronosyl residues in the L-ido-configuration, respectively. Chondroitinase-AC digestion of these polymers liberated all of the remaining 3H activity. Hydrolysis and N-acetylation followed by paper chromatography showed that the L-iduronic acid-containing products were devoid of 3H. Apparently the epimerization of D-glucuronosyl to L-iduronosyl residues during biosynthesis of dermatan sulfate involves an abstraction of the C-5 hydrogen of the uronosyl residue.