Abstract
1. Hen ovotransferrin was examined by isoelectric fractionation. 2. The major component observed in starch-gel electrophoresis can be isolated from the minor component. 3. When non-saturating amounts of iron are added to ovotransferrin, isoelectric fractionation demonstrates the existence of three molecular species corresponding to the metal-free protein, the one-iron-atom-protein complex and the two-iron-atoms-protein complex. 4. Isoelectric fractionation of human serum labelled with (59)Fe suggests that the transferrin of normal human serum also exists as metal-free protein, the one-iron-atom-protein complex and the two-iron-atoms-protein complex. 5. It is concluded that the binding constants for the first and second iron atoms are similar.