A sialoglycopeptide from bovine cerebral cortex cells was purified to apparent homogeneity by a procedure that included chloroform/methanol extraction, diethylaminoethyl ion exchange chromatography, wheat germ agglutinin affinity chromatography, size-exclusion HPLC, and hydrophobic interaction chromatography. The cell surface inhibitor had a molecular weight of approximately 18,000, no subunit composition was detectable on reduction and polyacrylamide gel electrophoresis analysis, and the glycopeptide apparently contained sialic acid, as illustrated by its ability to bind to Limulus polyhemus lectin. Deglycosylation of the molecule, however, did not reduce its protein synthesis inhibitory activity. As little as 20 ng of the sialoglycopeptide was capable of inhibiting protein synthesis in a wide variety of fibroblast cell lines but not in transformed cells. Mice immunized with the sialoglycopeptide produced antibodies that, when bound to protein A-agarose gel, removed the inhibitory activity from solution. The antibodies were used to identify a single isoelectric focused band and to establish the pI of 3.0 for the molecule.

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