Structural studies on rabbit transferrin: isolation and characterization of the glycopeptides

Comparison of bovine serum transferrin A and D2. II. Glycopeptides

Glycopeptides are isolated from subtilisin and pronase digests of whole bovine serum transferrin A and D2. The two variants yield glycopeptides with identical amino acid composition. Hence, there is probably no amino acid substitution in this region of the peptide chain. Amino acid sequence determination of one glycopeptide (subtilisin glycopeptide 8) gives the sequence: (CHO)Asn-Ser-Ser-Leu-Cys. This sequence is identical with that of residues 491-495 of the sequence for human serum transferrin (MacGillivray et al., 1982) except that in the bovine transferrin, Asp is replaced by Asn, enabling carbohydrate attachment. A second glycopeptide sequence Arg-(CHO)Asn-Ala-Thr-Tyr is observed, and the significance discussed in relation to carbohydrate moieties of serum glycoproteins.

Evidence for a single glycan moiety in rabbit serum transferrin and location of the glycan within the polypeptide chain

The sequential removal of N-acetylneuraminic acid from rabbit serum transferrin has been followed by urea-polyacrylamide gel electrophoresis. The electrophoretic pattern is consistent with the presence of a single biantennary glycan chain. From the amino acid sequence of the carbohydrate-containing cyanogen bromide fragment we have shown that the glycan is attached to an asparaginyl side chain at a position equivalent to residue 491 in the sequence of human serum transferrin.