Bovine transferrin glycopeptide: the relevance of its structure to interaction with the mammalian hepatic lectin that binds asialoglycoproteins
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abstract
After proteolytic digestion of bovine transferrin (phenotype AA), a glycopeptide fraction was isolated by gel filtration and high-voltage electrophoresis. Two glycopeptide bands were recovered, each of which contained one residue of aspartic acid, two of serine, two of galactose, three of mannose, and four of N-acetyl glucosamine together with some fucose. However, the bands differed with respect to sialic acid content (two and three residues respectively). Using the same isolation procedures, a commercial sample of human transferrin yielded four glycopeptide bands (two major, two minor) on high-voltage electrophoresis. On analysis, the two major bands differed in amino-acid residues but their carbohydrate compositions were very similar. The analyses largely resembled previously published analytical data for two human transferrin glycopeptides (Jamieson, G. A., Jett, M. &DeBernardo, S. L. (1971) J. Biol. Chem. 246, 3686–3693; Spik, G., Bayard, B., Fournet, B., Strecker. G., Bouquelet, S. &Montreuil, J. (1975) FEBS Lett. 50, 296–299) and the carbohydrate analyses showed many similarities to the bovine transferrin glycopeptide. From these data and earlier observations made on bovine and human transferrins (Hatton, M. W. C, Regoeczi, E. &Wong, K.-L. (1974) Can. J. Biochem. 52, 845–853), we have concluded that, in contrast with human transferrin, bovine transferrin contains only one heterosaccharide chain per molecule.Following tritiation, bovine transferrin asialoglycopeptide was compared with asialoglycopeptides from other serum proteins for their affinity to the rat liver in vivo. Considerable differences were observed and the following order of binding was established for the asialoglycopeptide preparations: bovine transferrin < human transferrin [Formula: see text] bovine fetuin [Formula: see text] human α1-acid glycoprotein.
