Characterization of monoferric fragments obtained by tryptic cleavage of bovine transferrin.

1. The electrophoretically fast (F) and slow (S) fragments obtained by tryptic cleavage of bovine iron-saturated transferrin differed in carbohydrate content and peptide 'maps'. 2. A fragment capable of binding one Fe3+ ion per molecule was isolated after brief tryptic digestion of bovine apotransferrin and shown closely to resemble the S fragment obtained from the iron-saturated protein. 3. Fragments F and S are probably derived from the N- and C-terminal halves of the transferrin molecule respectively. 4. Bovine transferrin could donate iron to rabbit reticulocytes, but the monoferric fragments possessed little iron-donating ability.