Sulfated Glycoproteins, Glycolipids, and Glycosaminoglycans from Synaptic Plasma and Myelin Membranes: Isolation and Characterization of Sulfated Glycopeptides

In this report we provide biochemical evidence that a highly purified synaptic plasma membrane fraction derived from rat brain, after intraventricular injection of 35S-labeled sodium sulfate, is enriched in a number of large sulfated glycoproteins compared with a purified myelin fraction studied concurrently. A fraction of the detergent-solubilized sulfated glycoprotein bound specifically to concanavalin A-Sepharose. In addition, we have identified the ³⁵S-labeled lipid-soluble material in these membrane fractions as cerebroside sulfate. The sulfated protein in the lipid-extracted membranes was shown to consist predominantly of a class of glycoproteins containing sulfate in ester linkage to oligosaccharide chains, which are differentiated structurally from the sulfated glycosaminoglycans of brain. These two classes of sulfated macromolecules were distinguished from one another by several chemical and physical parameters. We present the chemical characterization of the sulfated glycopeptides derived from synaptic plasma and myelin membranes by extensive proteolytic digestion after quantitative removal of cerebroside sulfate. Membrane-associated glycosaminoglycans, either specifically or adventitously associated with these neuronal membranes, were quantitatively precipitated and identified.