Keratan sulfate proteoglycans (KSPGs) are degraded in lysosomes as part of normal homeostasis of glycoproteins. Glycoproteins must be completely degraded to avoid undigested fragments building up and causing a variety of lysosomal storage diseases. KSPGs are Asn-linked glycoproteins and are acted upon by exo-glycosidases to release sugar monomers. The main steps of degradation are shown representing the types of cleavage reactions that occur so the full degradation of KS is not shown to avoid repetition. The proteolysis of the core protein of the glycoprotein is not shown here (Winchester 2005, Aronson & Kuranda 1989).