Absence of iron transfer from uteroferrin to transferrin

Transfer of iron from native porcine uteroferrin to apotransferrin was investigated using EPR spectroscopy. Purple (oxidized) or pink (reduced) forms of uteroferrin were incubated with porcine or human apotransferrin under conditions of temperature (37 degrees C) and pH (6.8) approximating those found in the allantoic fluid of the pregnant sow. Studies were also performed in the presence of mediators such as ascorbate, citrate, and ATP in concentrations previously claimed to be effective in promoting large-scale transfer of iron (Buhi, W. C., Ducsay, C. A., Bazer, F. W., and Roberts, R. M. (1982) J. Biol. Chem. 257, 1712-1723). Our experiments indicate that even in the presence of mediators, less than 20% of the iron in uteroferrin is transferred to apotransferrin at the end of 24 h and such transfer may be accompanied by denaturation of uteroferrin. We therefore conclude that the direct transfer of iron to apotransferrin is unlikely to be a physiological role of uteroferrin.