Cell-surface heparan sulfate: an intercalated membrane proteoglycan.

Two pools of heparan sulfate proteoglycans have been selectively solubilized from rat liver plasma membranes by successive incubations with heparin and detergent. The two populations of proteoglycans have similar polyanionic properties as indicated by identical elution positions on ion-exchange chromatography on DEAE-Sephacel but differ in buoyant density in CsCl when analyzed by density gradient centrifugation in the presence of 4 M guanidine. The detergent-extracted proteoglycan has a lower buoyant density (less than or equal to 1.40 g/ml) and is, as determined by gel chromatography, slightly larger than the heparin-released proteoglycan (buoyant density, greater than or equal to 1.55 g/ml). Furthermore, in contrast to the heparin-released proteoglycan, the detergent-extracted proteoglycan is able to bind detergent micelles, shows affinity for the hydrophobic gel octyl-Sepharose, and can be inserted into liposomes. We conclude that the detergent-extracted heparan sulfate represents a proteoglycan species that has its core protein rooted in the lipid bilayer of the plasma membrane.