Biosynthesis of heparin. Substrate specificity of heparosan N-sulfate D-glucuronosyl 5-epimerase.

Abstract

The substrate specificity of heparosan N-sulfate D-glucuronosyl 5-epimerase from a mouse mastocytoma was examined to determine the effects of N-acetyl and O-sulfate groups on substrate recognition by the enzyme. [5-3H]Glucuronosyl-labeled heparosan N-sulfate was prepared enzymatically and was modified chemically by partial N-desulfation and N-acetylation. After enzymatic release of tritium, the location of remaining label was determined by deaminative cleavage and analysis of resulting di-, tetra-, and higher oligosaccharides. This analysis indicated that a D-glucuronosyl residue is recognized as a substrate if it is linked at C-1 to an N-acetylated glucosamine residue and at C-4 to an N-sulfated unit. However, the reverse structure, in which the D-glucuronosyl moiety is bound at C-1 to an N-sulfated residue and at C-4 to N-acetylated glucosamine, is not a substrate. Similar studies with O-sulfated heparin intermediates showed that O-sulfate groups either at C-2 of the L-iduronosyl moieties or at C-6 of vicinal D-glucosaminyl moieties prevent 5-epimerization. These findings were confirmed by studies of the reverse reaction, in which tritium was incorporated from 3H2O into partially O-desulfated heparin and the location of incorporated radioactivity was determined. These and more direct experiments corroborated the previous conclusion that the L-iduronosyl moieties are formed after N-sulfation but before O-sulfation. Assessment of the influence of substrate size on the reaction further showed that a large substrate is preferred; an octasaccharide released tritium at a rate approximately 10% of that observed for the parent polysaccharide, and some release occurred also with smaller oligosaccharides.

• Authors: I Jacobsson, U Lindahl, J W Jensen, L Rodén, H Prihar, D S Feingold
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 259 Issue 2 Pg. 1056-63 (Jan 25 1984) ISSN: 0021-9258 [Print] United States
• PMID: 6420398 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Sulfates
• Heparin
• Carbohydrate Epimerases
• heparosan N-sulfate D-glucuronosyl 5-epimerase

Topics

• Animals
• Carbohydrate Epimerases (metabolism)
• Cattle
• Chromatography, Gel
• Chromatography, Paper
• Electrophoresis, Paper
• Heparin (biosynthesis)
• Mast-Cell Sarcoma (enzymology)
• Mice
• Models, Chemical
• Substrate Specificity
• Sulfates (metabolism)