Magnesium potentiation of iron-transferrin binding

The binding of iron to transferrin was studied by loading iron (III) onto apotransferrin in a chloride and a nitrilotriacetate form. When magnesium was added, a marked increase occurred in both the rate of iron binding and the maximum level of iron loaded on transferrin utilizing either iron salt. In the absence of magnesium the amount of iron required to achieve 50 percent saturation of the binding sites was 1.6 x 10(-4) M, whereas when magnesium was added, only about one-third as much iron (0.54 x 10(-4) M) was required. These data suggest an allosteric effect on transferrin by magnesium which potentiates iron (III) binding.