Heparan sulphate 2-O-sulphotransferase (Hs2st) acts at an intermediate stage in the pathway of biosynthesis of heparan sulphate (HS), catalysing the transfer of sulphate from 3'-phosphoadenosine-5'-phosphosulfate (PAPS) to the C2-position of selected hexuronic acid residues within the maturing HS chain.