HS3ST1 is the rate limiting enzyme for synthesis of HSact. HS3ST1 performs the crucial step modification in the biosynthesis of anticoagulant heparan sulfate (HSact) that is to complete the structure of the antithrombin pentasaccharide binding site.Heparan sulfate biosynthetic enzymes are key components in generating a myriad of distinct heparan sulfate fine structures that carry out multiple biologic activities. The enzyme encoded by this gene is a member of the heparan sulfate biosynthetic enzyme family. It possesses both heparan sulfate glucosaminyl 3-O-sulfotransferase activity, anticoagulant heparan sulfate conversion activity, and is a rate limiting enzyme for synthesis of anticoagulant heparan. This enzyme is an intraluminal Golgi resident protein.