The effect of trypsin digestion on the structure and iron-donating properties of transferrins from several species.

The effect of trypsin digestion on iron-saturated and iron-free (apo) human, rabbit, bovine, pig and horse tranferrins has been studied. Iron-binding fragments were produced only from iron-saturated pig and bovine transferrins although some cleavage of the polypeptide chain occurred in all cases. The apo-transferrins were generally degraded to a greater extent than the corresponding iron-saturated proteins. The ability of the different transferrins to donate iron to rabbit reticulocytes varied in the order rabbit approximately pig greater than human approximately horse greater than bovine. Trypsin digestion considerably reduced the ability of pig and bovine transferrins to donate iron to rabbit reticulocytes, slightly reduced the iron-donating ability of rabbit transferrin, and had almost no effect on that of human or horse transferrins.