Structure and function of ovotransferrin. II. Iron-transferring activity of iron-binding fragments of ovotransferrin with chicken embryo red cells.

The iron-transferring activity of iron-binding fragments FeNF and FeCF, representing the NH2- and CO2H-terminal domains of iron-ovotransferrin (Fe2OT), with a chicken embryo red cell system, was investigated. Each fragment is able to deliver iron to a chicken embryo red cell system for the biosynthesis of heme, FeNF being 44% more efficient than FeCF. The Fe fragments are on an average approximately 2 times less effective in delivering iron to the chicken embryo red cell than Fe2OT. The binding of FeNF and FeCF to CERC is essentially identical in terms of apparent association constant (K = 1.5 X 10(6) M-1, with respect to fragments) and the number of binding sites per cell at equilibrium (n = 2.9 X 10(4)); however, they differ significantly in their rates of delivering iron for heme synthesis.