Identification of transferrin as the principal neptunium-binding protein in the blood serum of rats

Abstract

The binding of 239Np(V) to blood serum components of rats was examined in vivo and in vitro. After gel filtration of the serum using a Sephacryl S-300 column, 98% of the applied activity appeared with protein fractions representing coeluted albumins and transferrin. A separation of the albumin- and transferrinproteins by ion-exchange chromatography using DEAE-cellulose showed the 239Np being entirely bound to the iron-carrier protein transferrin. The high elution yields from the ion-exchange columns, >90%, suggest that the binding may be quite strong. The binding capacity of transferrin for neptunium in vivo was found to decline when the iron level in blood serum was increased. Precipitation experiments showed that 84 ± 2% of the 239Np was precipitated with 10% (w/v) trichloracetic acid, 77 ± 3% with 90'/ ethanol but only 6 ± l% with saturated ammonium sulphate at pH 7.4. The available data indicate that as for plutonium, thorium, americium and curium, the iron transport protein, transferrin, may be the main carrier protein for neptunium in mammalian blood serum.