NONDIALYZABLE SULFATED SIALOGLYCOPEPTIDE FRACTIONS DERIVED FROM BOVINE HEIFER BRAIN GLYCOPROTEINS. ISOLATION, CHARACTERIZATTON AND CARBOHYDRATE‐PEPTIDE LINKAGE STUDIES1

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Abstract
—: The nondialyzable sialoglycopeptides dcrived from defatted, protease digested whole boyine heifer brain tissue were isolated and characterized. The partially purified bovine heifer brain tissue were isolated and characterized. The partially purified sialoglycopeptide mixtures contained 7‐8% ester sulfate. The amount of nonsulfated material present was of the order of 15%. The total mixture was fractionated by anion exchange chromatography on AG1‐X2(CI‐) using a sodium chloride gradient to yield twelve fractions all of which contained ester sulfate to varying degrees (5.6‐21.9%).The molecular size of the fractions ranged from molecular weights of 10,400‐12,500. The molar sulfate/galactose plus glucosamine ratios ranged from 0.3 to 1.1. Carbohydrate peptide linkage studies of the fractions by treatment with 0.2 M‐NaOH‐O.3 M‐NaBH4 led to the destruction of a portion of the threonine, serine and galactosamine and the appearance in acid hydrolysates of α‐amino‐n‐butyric acid and galactosaminitol with an increase in alanine. Partial acid hydrolysis of the most abundant sialoglycopeptide liberated detectable amounts of 2‐acetarnido‐1‐(L‐4‐aspartamido‐)‐1,2‐dideoxy‐β‐D‐ glucose. These results indicated that the GalNac at the reducing end of the alkali labile carbohydrate prosthetic groups were linked O‐glycosidically to thc hydroxyl groups of threonine and serine and the alkali‐stable region of the principal sialoglycopeptide involves N‐acetylglycosaminyl‐asparagine linkages. Mild acid hydrolysis of the alkali‐stable portion of the sulfated fractions indicated that the ester sulfate was confined to the alkali‐stable region and exists as galactose 6‐O‐sulfate and N‐acetylglucosa‐ mine 6‐O‐sulfate, structural fcatures similar to those present in rat brain glycopcptides (Markgolis & Margolis, 1970; Margoliset al.; 1972). Fucose and ester sulfate were confined to the alkali‐stable region while mannose was located in both the alkali‐labilc and alkali‐stable regions of the sialoglyco‐peptide fractions.