= Heparan sulfate glucosamine N-sulfotransferase
<Heparan sulfate glucosamine N-sulfotransferase> is an <enzyme> activity that transfers a sulfur-containing group from <PAPS> to a glucosamine nitrogen in <heparan sulfate>, producing a sulfated residue and <adenosine 3',5'-bisphosphate>. Its official classification is EC 2.8.2.8. The acceptor is a position within an existing carbohydrate chain, so this reaction modifies the chain rather than extending it with another sugar.<Heparan sulfate glucosamine N-sulfotransferase in IUBMB Enzyme Nomenclature>[EC 2.8.2.8, Accepted name and Reaction]{ref}
The nitrogen acceptor specifies the meaning of N-sulfation. Naming a sulfated polymer alone does not identify which atom received the group; <N-sulfation of glucosamine> concerns nitrogen substitution, while other modifications can involve oxygen-bearing groups. The donor-derived <adenosine 3',5'-bisphosphate> and the modified polymer are separate products of the transfer.<Heparan sulfate glucosamine N-sulfotransferase in IUBMB Enzyme Nomenclature>[EC 2.8.2.8, Reaction and Systematic name]{ref}
For a constructed stoichiometric example, suppose a <polymer> population contains 100 nanomoles of glucosamine positions. Twenty nanomoles present available <amino groups>, while eighty are unavailable for this reaction. With 12 nanomoles of <PAPS>, the stated transfer can create at most 12 nanomoles of newly N-sulfated positions. After that conversion, 8 nanomoles of the initially eligible positions remain unmodified. No new sugar residues are added by those transfers.
An assay that follows only disappearance of <PAPS> therefore needs a product check to establish the intended modification. Donor consumption, incorporation of the transferred group and its location on the polymer answer successively more specific questions. This differs from the chain-building activity of <heparosan synthase>, even when the reactions contribute to related polysaccharide pathways.
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