Transferrin of the Hen

It is well known that in the hen the egg-white protein ovotransferrin (conalbumin) and the serum protein transferrin are very similar in structure and iron-binding properties (for review see Beam & Parker, 1966). Since it is evident that for the eggwhite protein the name 'ovotransferrin' (Komatsu & Feeney, 1967; Azari & Baugh, 1967) is more informative than the classical name 'conalbumin', it is suggested that the latter should not be used. It was proposed previously (Williams, 1962) that the covalent structures of the two proteins differ only in the nature of their oligosaccharide prosthetic groups, and the object of the present work was to discover whether these dissimilar prosthetic groups are attached to the polypeptide chain at the same point or at different points. For this purpose a variety of proteolytic enzymes was used to prepare glycopeptides from transferrin and ovotransferrin. From the overlapping peptides obtained the amino acid sequence in the vicinity of the point of attachment of the carbohydrate was determined, and it is shown below that most of the carbohydrate is attached to the same position in both proteins. A brief account of part of this work has been published (Williams, 1967).