proteoglycan metabolic process heparin proteoglycan metabolic process The chemical reactions and pathways involving heparin proteoglycans, which consist of a core protein linked to a heparin glycosaminoglycan. The heparin chain is composed of the repeating disaccharide unit beta-(1,4)-N-acetyl-D-glucosamine-alpha-(1,4)-hexuronic acid, the former being either sulfated or deacetylated on its amino group as well as sulfated on one of its hydroxyl groups, and the latter being e a mixture of sulfated and nonsulfated D-glucuronic and L-iduronic acids. Heparin is similar to heparan sulfate but it contains more N-sulfate and O-sulfate groups. Heparin proteoglycans are stored selectively in the secretory granules of mammalian mast cells. heparin metabolism heparan sulfate metabolic process