Oligosaccharides generated by an endoglucuronidase are intermediates in the intracellular degradation of heparan sulfate proteoglycans.

An intracellular heparan sulfate oligosaccharide has been identified in rat hepatocytes cultured in the presence of [35S]sulfate. Pulse-chase experiments suggest that [35S]sulfate is first incorporated into heparan sulfate proteoglycans which are subsequently converted to the low molecular weight component. The oligosaccharide (Mr 7000) contains little or no protein and is also present in rat liver homogenates. Subcellular fractionation and density gradient centrifugation in Percoll of liver homogenates demonstrated that the oligosaccharide was present in lysosomes or in particles of similar distribution and buoyant density. Structural analysis of oligosaccharides isolated from a rat liver lysosomal fraction indicate that glucuronic acid is present in the reducing end of the oligosaccharide and that this residue is preferentially linked to an N-acetylated glucosamine unit. These data suggest that the heparan sulfate oligosaccharide is generated through the action of a heparan sulfate-degrading endoglucuronidase previously found in human platelets and rat liver (Oldberg, A., Heldin, C.-H., Wasteson, A., Busch, C., and Hook, M. (1980) Biochemistry 19, 5755-5762).