The Enzyme Database

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Accepted name: heparosan-N-sulfate-glucuronate 5-epimerase
Reaction: Epimerization of D-glucuronate in heparosan-N-sulfate to L-iduronate.
Other name(s): heparosan epimerase; heparosan-N-sulfate-D-glucuronosyl 5-epimerase; C-5 uronosyl epimerase; polyglucuronate epimerase; D-glucuronyl C-5 epimerase; poly[(1,4)-β-D-glucuronosyl-(1,4)-N-sulfo-α-D-glucosaminyl] glucurono-5-epimerase
Systematic name: poly[(1→4)-β-D-glucuronosyl-(1→4)-N-sulfo-α-D-glucosaminyl] glucurono-5-epimerase
Comments: The enzyme acts on D-glucosyluronate residues in N-sulfated heparosan polymers, converting them to L-iduronate, thus modifying the polymer to heparan-N-sulfate. The enzyme requires that at least the N-acetylglucosamine residue linked to C-4 of the substrate has been deacetylated and N-sulfated, and activity is highest with fully N-sulfated substrate. It does not act on glucuronate residues that are O-sulfated or are adjacent to N-acetylglucosamine residues that are O-sulfated at the 6 position. Thus the epimerization from D-glucuronate to L-iduronate occurs after N-sulfation of glucosamine residues but before O-sulfation. Not identical with EC chondroitin-glucuronate 5-epimerase or with EC, heparosan-glucuronate 5-epimerase.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 112567-86-9
1.  Jacobsson, I., Bäckström, G., Höök, M., Lindahl, U., Feingold, D.S., Malmström, A. and Rodén, L. Biosynthesis of heparin. Assay and properties of the microsomal uronosyl C-5 epimerase. J. Biol. Chem. 254 (1979) 2975–2982. [PMID: 107165]
2.  Jacobsson, I., Lindahl, U., Jensen, J.W., Roden, L., Prihar, H. and Feingold, D.S. Biosynthesis of heparin. Substrate specificity of heparosan N-sulfate D-glucuronosyl 5-epimerase. J. Biol. Chem. 259 (1984) 1056–1063. [PMID: 6420398]
3.  Hagner-McWhirter, A., Hannesson, H.H., Campbell, P., Westley, J., Roden, L., Lindahl, U. and Li, J.P. Biosynthesis of heparin/heparan sulfate: kinetic studies of the glucuronyl C5-epimerase with N-sulfated derivatives of the Escherichia coli K5 capsular polysaccharide as substrates. Glycobiology 10 (2000) 159–171. [DOI] [PMID: 10642607]
[EC created 1984, modified 2015]
Accepted name: chondroitin-glucuronate 5-epimerase
Reaction: chondroitin D-glucuronate = dermatan L-iduronate
For diagram of the later stages of chondroitin biosynthesis, click here
Other name(s): polyglucuronate 5-epimerase; dermatan-sulfate 5-epimerase; urunosyl C-5 epimerase; chondroitin D-glucuronosyl 5-epimerase
Systematic name: chondroitin-D-glucuronate 5-epimerase
Comments: Not identical with EC heparosan-N-sulfate-glucuronate 5-epimerase.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 70766-66-4
1.  Malmström, A. and Åberg, L. Biosynthesis of dermatan sulphate. Assay and properties of the uronosyl C-5 epimerase. Biochem. J. 201 (1982) 489–493. [PMID: 7092807]
[EC created 1986]
Accepted name: heparosan-glucuronate 5-epimerase
Reaction: [heparosan]-D-glucuronate = [acharan]-L-iduronate
Glossary: acharan = [GlcNAc-α-(1→4)-IdoA-α-(1→4)]n
heparosan = [GlcNAc-α-(1→4)-GlcA-β-(1→4)]n
Other name(s): HG-5epi
Systematic name: [heparosan]-D-glucuronate 5-epimerase
Comments: The enzyme, characterized from the giant African snail Achatina fulica, participates in the biosynthetic pathway of acharan sulfate. Unlike EC, heparosan-N-sulfate-glucuronate 5-epimerase, it shows no activity with D-glucuronate residues in heparosan-N-sulfate.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
1.  Mochizuki, H., Yamagishi, K., Suzuki, K., Kim, Y.S. and Kimata, K. Heparosan-glucuronate 5-epimerase: Molecular cloning and characterization of a novel enzyme. Glycobiology 25 (2015) 735–744. [DOI] [PMID: 25677302]
[EC created 2015]

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