Heparan sulfate 2-O-sulfotransferase (Hs2st) and mouse development. 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-positi