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.^[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.^[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.