BINDING OF F-ELEMENTS TO THE IRON-TRANSPORT PROTEIN TRANSFERRIN

Chromatographic studies of in vivo and in vitro labelled blood serum indicate that the f-elements Th(IV), Pu(IV), Np(IV,V), Am(III), Cm(III), Eu(III), Gd(III) and Yb(III) bind to and are transported on transferrin (Tf). Spectroscopic studies indicate that 2 f-metal atoms are bound to each Tf molecule, thus implicating the N- and C-terminal iron binding sites of transferrin in f-element binding. However, the stability of the f-metal-Tf complexes, especially those with M(III), is lower than that of the Fe(III) complex. In some cells Fe(III) binding to transferrin facilitates cellular iron uptake via a receptor mechanism, but with Pu(IV) transferrin binding appears to inhibit cellular uptake.