N-sulfation of glucosamine

N-sulfation of glucosamine attaches a sulfur-containing group at the nitrogen of an eligible glucosamine residue. In heparan sulfate biosynthesis, this changes nitrogen substitution within a polysaccharide; it does not add a new sugar residue or change which carbon atoms form the backbone.

The enzyme heparan sulfate glucosamine N-sulfotransferase transfers a group from the activated donor PAPS to polymer-associated glucosamine. Its official reaction produces the N-sulfated sugar position and adenosine3′,5′-bisphosphate. This specifies both the donor and the modified atom, rather than treating free inorganic sulfate as a complete account of the reaction.^[ref]

An N-acetylated position must first lose its acetyl group before that nitrogen can undergo the corresponding N-sulfation. Nitrogen substitution also matters downstream: heparosan-N-sulfate-glucuronate 5-epimerase recognizes particular neighboring N-sulfated arrangements when changing glucuronate into iduronate.^[ref]

For an original ideal stoichiometric example, modifying 12 eligible nitrogen positions consumes 12 PAPS donor molecules. A chain segment that initially contained 40 sugar residues still contains 40 afterward. Counting sulfur incorporation and counting chain extension therefore measure different processes; counting total sulfur also cannot locate which nitrogen or oxygen positions were modified.