239Pu(IV) binding by extracellular rat liver proteins

Previous studies in rats have shown that a significant amount of the 239Pu liver burden together with a quantity of protein can be removed by perfusion of the isolated liver with buffer. The possible role of the extracellular compartment and/or the cell surface as a specific intraorgan site involved in the uptake and/or loss of nuclide from the rat liver was investigated. Male rats were injected with 3.0 μCi 239Pu/kg as the citrate I.V. and sacrificed 36 hours later. The liver was rapidly removed and perfused through the portal vein with 400 ml of buffer. The perfusate was fractionated by molecular sieving and the resulting fractions were studied by a combination of analytical techniques. The perfusate contained 9.2 percent of the total liver burden of Pu, 74 percent of which was retained by a 100,000 M. W. sieve, 100K retentate (100K Ret). Chromatography of this retentate on Sepharose 4B demonstrated that more than 90 percent of the 239Pu was found with proteins having a M.W. of about 500,000. Further, ion-exchange chromatography of this and other fractions produced peaks of Pu-activity coincident with rat liver cytosol ferritin. Isoelectric focusing of the 100K Ret resolved two separate protein fractions; one containing 65 percent of the Pu was tentatively identified as ferritin, the other containing 30 percent of the Pu has not been identified