Structures of the asparagine-linked sugar chain of glucose transporter from human erythrocytes

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Abstract
The asparagine-linked sugar chain of glucose transporter from human erythrocytes was quantitatively released as oligosaccharides from the polypeptide backbone by hydrazinolysis. They were converted to radioactive oligosaccharides by NaB3H4 reduction after N-acetylation and fractionated by anion-exchange column chromatography and Bio-Gel P-4 column chromatography after sialidase treatment. Structural study of each oligosaccharide by exo- and endoglycosidase digestion and methylation analysis indicated that the glycoprotein contains a high-mannose-type oligosaccharide, Man9.cntdot.GlcNAc.cntdot.GlcNAc, and biantennary complex-type oligosaccharides with Man.alpha.1 .fwdarw. 6(.+-.GlcNAc.beta.1 .fwdarw. 4)(Man.alpha.1 .fwdarw. 3)Man.beta.1 .fwdarw.-4GlcNAc.beta.1 .fwdarw. 4(.+-. Fuc.alpha.1 .fwdarw. 6)GlcNAc as their cores and the poly-N-acetyllactosamine composed of about 16 N-acetyllactosaminyl units as their outer chains. These structural features of the sugar moiety of glucose transporter are quite different from those of two major intrinsic glycoproteins of human erythrocytes, glycophorin A and band 3.