Chondroitin-glucuronate 5-epimerase changes D-glucuronate residues in a chondroitin chain into L-iduronate residues in a dermatan chain. Its classification is EC 5.1.3.19. The reaction alters carbon-5 stereochemistry without adding a sugar residue or changing the residue's elemental formula.[ref]
Chondroitin-glucuronate 5-epimerase in IUBMB Enzyme Nomenclature. Reaction and accepted name
This connects polymer modification to dermatan sulfate formation. It is a different enzyme assignment from heparosan-N-sulfate-glucuronate 5-epimerase, whose substrate belongs to another polysaccharide pathway. Similar names do not make the polymer substrates interchangeable.[ref]
Chondroitin-glucuronate 5-epimerase in IUBMB Enzyme Nomenclature. Comments, distinction from EC 5.1.3.17
In 1982, A. Malmström and L. Åberg reported distinct uronosyl-epimerase activities associated with dermatan- and heparan-sulfate biosynthesis in microsomal preparations from cultured fibroblasts. The comparison made substrate context experimentally relevant rather than treating all carbon-5 epimerization as one nonspecific activity.[ref]
Biosynthesis of dermatan sulphate. Assay and properties of the uronosyl C-5 epimerase by A. Malmström and L. Åberg. Abstract, two microsomal epimerase activities
For a constructed 50-position substrate segment, conversion of ten eligible glucuronate residues yields ten iduronate residues and 40 unchanged positions. The chain still contains 50 positions. A measurement sensitive only to total sugar amount or shared molecular mass cannot establish that this stereochemical conversion occurred.
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