Study of the Binding of Iron and Indium to Human Serum Apo-Transferrin

Indium is a heavy metal belonging to group IIIa. It is believed that indium may interfere with iron metabolism from the sites of absorption, transportation, utilization and storage in the cells. The present investigation was established to study and compare the binding of iron and indium to human apo-transferrin (apo-tf). Pure human apo-tf was used and the binding activity of iron and indium, as a complex with citric acid (1:20), to apo-tf was studied. The binding of iron and indium to apo-tf in Tris-HCl buffer, pH 7.4 showed a maximum absorbance at 465 and 255 nm, respectively. The binding of both metals to apo-tf appears to be pH dependent. Using equilibrium dialysis technique, the binding of iron to apo-tf and the effect of indium on the binding process were also studied. Addition of indium to the outside of dialysis sac reduced iron uptake by 37%. The results indicate that indium competes with iron in binding to apo-tf. Although, the binding sites for these two ions seem to be similar, the binding of iron to apo-tf is more tightly than indium