Comparison of the binding of 59Fe- and 239Pu-transferrin to rat liver cell membranes

Abstract

The binding of the ⁵⁹Fe and ²³⁹Pu complexes of transferrin and ¹²⁵I labelled transferrin [Tf (¹²⁵I) ] to isolated cell membranes of rat liver has been studied. Transferrin forms a complex with an integral protein of the membrane which has an apparent molecular weight of about 180 kDa and is stable only at pH 7.4. Iron-59 is eluted from Sephacryl S 300 columns together with Tf (¹²⁵I) or the Tf-membrane protein complex while ²³⁹Pu seems to be bound to different membrane protein(s).

After isolation of the Tf-binding protein from ³⁵S-labelled membranes and incubation with one of the metal-Tf complexes ⁵⁹Fe elutes from a Sephacryl S 300 column together with ³⁵S at an apparent molecular weight of ca. 250 kDa while ²³⁹Pu is found in fractions of lower molecular weight. It is concluded from these results that there are Tf-receptors in the liver cell membrane to which iron transferrin may bind. Plutonium, however, seems to be dissociated from Tf and bound directly to other membrane proteins.