Cell-surface heparan sulfate. Isolation and characterization of a proteoglycan from rat liver membranes

Solubilization of heparan sulfate proteoglycans from a rat liver membrane fraction was obtained by the use of the charged detergent deoxycholate or alternatively a combination of NaCl and the nonionic detergent Triton-X 100. Subsequently, proteoglycans solubilized from microsomal and plasma membrane fractions, respectively, were purified by a procedure involving gel chromatography, anion exchange chromatography, and density gradient centrifugation. The purified heparan sulfate proteoglycan had a molecular weight of about 75,000 as determined by sedimentation equilibrium analysis or gel chromatography. Molecular weights of 17,000 to 40,000 were obtained for the 125I-labeled core protein after removal of the heparan sulfate polysaccharide chains by different enzymatic and chemical methods. An average molecular weight of 14,000 was found for the polysaccharide chains released from the core protein by alkali treatment. The data are consistent with a proteoglycan structure containing four polysaccharide chains attached to the core protein. The amino acid composition of native and alkali-treated proteoglycan support the proposed proteoglycan model.