Chondroitin 4-sulfate, also known as chondroitin sulfate A, is a derivative of chondroitin which has a sulfate moiety esterified to carbon 4 of the N-acetylgalactosamine (GalNAc) sugar. Chondroitin sulfate (CS) is a linear heteropolysaccharide consisting of repeating disaccharide units of glucuronic acid and galactosamine, which is commonly sulfated at C-4 and/or C-6 of galactosamine. Chondroitin sulfate is a glycosaminoglycan (GAG) covalently linked to proteins forming proteoglycans (PGs). GAGs are all anionic linear heteropolysaccharide chains of repeating disaccharide units. According to the monosaccharide types and the glycosidic bonds between them, GAGs are divided into (1) hyaluronan, (2) CS and dermatan sulfate (DS), (3) heparan sulfate and heparin, and (4) keratan sulfate. CS was isolated from cartilage in 1884, but the nature of its monosaccharides and structure was first described in 1925. On the basis of the structure of chondroitin sulfate, at least five enzyme activities could be predicted, including three transferases (EC 2.4.1.79, the initiating GalNAc transferase; EC 2.4.1.175, polymerizing GalNAc; and EC 2.4.1.17, GlcA transferase) and two sulfotransferases (EC 2.8.2.5, GalNAc 4-sulfotransferase and EC 2.8.2.17, GalNAc 6-sulfotransferase). Additional enzymes exist for the epimerization of GlcA, sulfation of the uronic acids, and other patterns of sulfation found in unusual species of chondroitin. Chondroitin sulfate assembly can occur on virtually all proteoglycans, depending on the cell in which the core protein is expressed. Chondroitin sulfates from different sources vary in the location of sulfate groups. Separation of the products reveals that many types of chondroitin sulfate exist in nature but many chains are hybrid structures containing more than one type of disaccharide. Animal cells also degrade chondroitin sulfate in lysosomes using a series of exoglycolytic activities (PMID: 8993162). Chondroiton sulfate is a polymer that can contain up to 100 individual sugars.