N-sulfated heparosan

N-sulfated heparosan is a modified form of heparosan in which glucosamine nitrogen positions have undergone deacetylation and N-sulfation of glucosamine. The chain retains alternating uronic-acid and amino-sugar positions; the extent of modification must be stated for a particular preparation. N-sulfation changes a nitrogen substituent, rather than adding another sugar residue.^[ref]

The polymer is an informative substrate for heparosan-N-sulfate-glucuronate 5-epimerase. Neighboring N-sulfated sugar residues help determine which glucuronate positions can be converted into iduronate; additional oxygen-linked sulfate substitutions can restrict the reaction. The substrate is therefore a local arrangement within a chain, rather than free glucuronate considered in isolation.^[ref]

A 2019 study followed conversion of carbon13-labelled N-sulfated heparosan with nuclear magnetic resonance and compared enzyme variants. The assay connects a change in sugar configuration with a defined polymer substrate, rather than merely measuring total carbohydrate.^[ref]

For an original bookkeeping example, a segment with 30 complete two-sugar repeats contains 60 sugar residues before and after modifying ten eligible nitrogens. Epimerizing five uronic-acid positions still leaves 60 residues. Chain extension, nitrogen substitution and uronic-acid configuration are three different operations.