Interaction of oxidized chicken ovotransferrin with chicken embryo red blood cells

Iron-saturated chicken ovotransferrin was chemically oxidized with NaIO4, converting 50% of its methionine residues to their sulfoxide derivatives while maintaining 95% of its iron-binding activity. The oxidized chicken ovotransferrin was able to deliver iron to the chicken embryo red blood cell for heme synthesis. From competition experiments, oxidized diferric chicken ovotransferrin was estimated to be approx. 65% as efficient as unmodified diferric chicken ovotransferrin at competing with diferric (55Fe2) chicken ovotransferrin for the iron-donating sites of the chicken embryo red blood cells. The presence of apo chicken ovotransferrin preparations (native or oxidized) in the incubation medium had little effect on the rate of iron incorporation into heme from diferric chicken ovotransferrin. The effect of modifying the periodate-susceptible methionine residues in chicken ovotransferrin was small but significant. These methionine residues do not appear critical for the interaction of chicken ovotransferrin with the chicken embryo red blood cell receptors, the incorporation of chicken ovotransferrin into the cell, or the release of iron from chicken ovotransferrin for heme synthesis.