PersPective

Heparin has been used as an anticoagulant for over 75 years since it entered clinical trials in 1935 [1]. It was first discovered in 1916 by McLean and Howell at Johns Hopkins University and is one of the oldest drugs still in clinical use. Heparin is a highly sulfated polysaccharide belonging to the family of heparin/heparan sulfate (HS) glycos-aminoglycans (GAGs), with an average MW of 12–15 kDa and a MW range of 5–40 kDa [2]. In the biosynthetic pathway for heparin [3,4], glycosyltransferases, called polysaccharide syn-thases, sequentially transfer activated monosac-charides, called uridinediphosphate-sugars, to an acceptor, polymerizing them into heparosan. Heparosan has a repeating, 1ψ4-linked, E-d-glucuronic acid (GlcA) and d-N-acetylglucos-amine (GlcNAc) disaccharide unit, and is the starting polysaccharide in heparin biosynthesis. Subsequent modifications through the action o