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TRANSFERRIN AND THE TRANSFERRIN RECEPTOR The structure, properties and functions of transferrin and the transferrin receptor have been reviewed in several recent papers [6-14]. For an extensive treatment the interested reader is referred to these publications. Table 1 lists some characteristics of human serum transferrin.

The amino acid residues involved in the specific binding of iron by transferrin appear to have been unequivocally identified by X-ray crystallography. At both the N-and C-terminal region of transferrin, iron is directly co-ordinated to two tyrosines, one histidine and one aspartic acid, and indirectly co-ordinated to an arginine via the (bi) carbonate anion. The last co-ordination position of iron is occupied by a water molecule or a hydroxyl ion. Identical results have been obtained with rabbit serum transferrin and human lactoferrin [15, 16]. Recent M6ssbauer studies have also confirmed the …