Characterization of the O-glycosidically linked oligosaccharides of rat erythrocyte membrane sialoglycoproteins

Abstract
The carbohydrate units of the rat erythrocyte membrane sialoglycoprotein rSGP-4 [Edge, A. S. B., and Weber, P. (1981) Arch. Biochem. Biophys. 209, 697-705] have been characterized. All of the carbohydrate of this Mr 19,000 glycoprotein occurs in O-glycosidic linkage to the peptide; following alkaline borohydride treatment and chromtography on Bio-Gel P-2, sialic acid containing oligosaccharides terminating in N-acetylgalactosaminitol were obtained. Their structures were determined by compositional analysis, exoglycosidase digestions, alkaline sulfite degradation, and periodate oxidation. The oligosaccharides were characterized for molecular weight and linkage by direct chemical ionization and gas-liquid chromatography/mass spectrometry, respectively. The structures are proposed to be NeuAc.alpha.2 .fwdarw. 3Gal.beta.1 .fwdarw. 3GalNAc-ol, Gal.beta.1 .fwdarw. 3(NeuAc.alpha.2 .fwdarw. 6)GalNAc-ol, NeuAc.alpha.2 .fwdarw. 3Gal.beta.1 .fwdarw. 3(NeuAc.alpha.2 .fwdarw. 6)GalNAc-ol, and NeuAc.alpha.2.fwdarw. 3Gal.beta.1 .fwdarw. 3(NeuAc.alpha. 2 .fwdarw. 3Gal.beta.1 .fwdarw. 4GlcNAc.beta.1 .fwdarw. 6)GalNAc-ol. Two of the N-acetylglucosamine-containing hexasaccharides were present per molecule of rSGP-4 along with two trisaccharides and seven tetrasaccharides.

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