1. The carbohydrate compositions of human, pig and cattle transferrins and duck ovotransferrin have been determined. 2. Glycopeptides have been prepared from these transferrins and their carbohydrate compositions and amino acid sequences determined. One of the glycopeptides from human transferrin carries the C-terminal residue of the protein. 3. Each tranferrrin yielded two glycopeptides that appeared to be identical in carbohydrate composition but different in amino acid sequence. The two glycopeptides have been distinguished as type A, in which the residue following Asn(CHO)(where CHO represents a carbohydrate moiety) is a basic amino acid and type B in which Asn(CHO) is followed by a neutral aliphatic amino acid. Cattle transferrin is exceptional in having two glycopeptides in which this position is occupied by serine. 4. It is suggested that each molecule of human and cattle transferrin and duck ovotransferrin carries an average of two carbohydrate prosthetic groups. Hen and pig transferrins appear to carry only one carbohydrate group per mol of protein. 5. The N-terminal sequences of hen and duck ovotransferrins and of cattle, human and pig transferrins were also determined.

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