Chondroitin sulfates (Figure 9.23) are molecules classified as glycosaminoglycans.Two common chondroitin sulfates are chondroitin-4-sulfate and chondroitin-6-sulfate. Each is a polymer of alternating units of D-glucuronate and N-acetyl-D-galactosamine-sulfate linked in a 1-3 linkage. The only differences between the polymers are that chondroitin-4-sulfate has the sulfate on position 4 of the N-acetyl-D-galactosamine molecule whereas the sulfate is on position 6 in chondroitin-6-sulfate.

Core proteins in cartilage have chondroitin sulfate and keratan sulfate chains covalently bound to them through serine side chains. In cartilage, this kind of structure binds collagen and helps hold the collagen fibers in a tight, strong network. The binding apparently involves electrostatic interactions between the sulfate and/or carboxylate groups of the proteoglycan complex and the basic side chains in collagen.