| Abstract: | Heparan sulfate proteoglycans were extracted from rat brain microsomal membranes or whole forebrain with deoxycholate and purified from accompanying chondroitin sulfate proteoglycans and membrane glycoproteins by ion-exchange chromatography, affinity chromatography on lipoprotein lipase-Sepharose, and gel filtration. The proteoglycan has a molecular size of approximately 220,000, containing glycosaminoglycan chains of Mr = 14,000-15,000. In 3H]glucosamine-labeled heparan sulfate proteoglycans, approximately 22% of the radioactivity is present in glycoprotein oligosaccharides, consisting predominantly of N-glycosidically linked tri- and tetraantennary complex oligosaccharides (60%, some of which are sulfated) and O-glycosidic oligosaccharides (33%). Small amounts of chondroitin sulfate (4-6% of the total glycosaminoglycans) copurified with the heparan sulfate proteoglycan through a variety of fractionation procedures. Incubation of 35S]sulfate-labeled microsomes with heparin or 2 M NaCl released approximately 21 and 13%, respectively, of the total heparan sulfate, as compared to the 8-9% released by buffered saline or chondroitin sulfate and the 82% which is extracted by 0.2% deoxycholate. It therefore appears that there are at least two distinct types of association of heparan sulfate proteoglycans with brain membranes. |
