The subcellular distribution of ${}^{238}{\rm Pu}$ and 239 Pu after incubation of primary cultures of rat hepatocytes with the citrate complex of these metals was studied, and the results were compared with data from in vivo experiments. As in vivo, the lysosomes are the principal organelles in which ${}^{238}{\rm Pu}$ and 239 Pu are accumulated. In contrast to in vivo studies, 239 Pu is also detectable on the pericellular membranes and in the cell nuclei, where it is predominantly bound to a high-molecular-weight component. The percentage of the total cellular 239 Pu which can be recovered in the cell nuclei increased with incubation time from 10% at 1 h to nearly 30% at 5 h. Plutonium-238, an isotope with 270-fold higher specific activity than 239 Pu, showed no association with the nuclei. The membrane-bound fraction of 239 Pu, as determined using the exogenous chelator diethylenetriaminepentaacetic acid decreased from 30% at shorter incubation times to 15% at longer incubation periods. After incubation with ${}^{238}{\rm Pu}$ the membrane fraction and the cytosolic fraction contained higher concentrations of the radionuclide than after incubation with 239 Pu.

The effects of plutonium-239, an α-particle emitting radionuclide which deposits mainly in the lysosomes, on the activity of various lysosomal enzymes have been studied in rat liver. The effects observed have been compared with those produced by the β + γ radiation from colloidal gold-198. Following administration of 0.5 μCi polymeric 239 Pu the specific activities of acid deoxyribonuclease and aryl sulphatase were increased by 30 days and remained elevated at 1 yr. β-Glucuronidase, acid β-glycerophosphatase, and cathepsin D showed increased specific acitivity at time intervals longer than 6 mo after injection of 239 Pu. All the enzymes studied showed decreased sedimentability at 30 days but this returned to approximately normal limits at longer time intervals. In comparison the administration of 0.5 mCi 198 Au colloid also caused increased specific activity of deoxyribonuclease II, β-glucuronidase, and acid β-glycerophosphatase, but did not decrease the enzyme sedimentabilities. It is concluded that at least some of the pathological effects known to be produced by 239 Pu and 198 Au may be explained in terms of lysosomal changes.

The subcellular distribution of 210 Po has been studied over periods of up to 47 days after intravenous, oral or intramuscular injection of the nuclide as citrate or in colloidal form. The majority, 50 to 80%, of the total tissue 210 Po was found in the cytosol of liver, kidney and testis irrespective of the time after injection, the route or form in which the nuclide was administered. Fractionation of the cytosol on Sephadex G.200 suggested that the 210 Po was bound nonspecifically to protein. Studies of the distribution of 210 Po in digests of freeze-dried liver from animals injected with 210 Po and in synthetic mixtures of amino acids after separation on Sephadex G.15 suggest that the sulphydryl group of cysteine may be an important binding site for 210 Po in proteins. Slight changes in the 210 Po distribution profile were seen when lipid was extracted from the freeze-dried liver powder before digestion suggesting that lipids may be involved in the 210 Po complex in vivo, but no direct evidence for polonium-lipid complexes was found.

By means of a gel filtration technique it has been shown that thorium (IV), plutonium (IV), americium (III) and curium (III) bind to five glycoprotein fractions isolated from bovine cortical bone and to certain other substances. The effects of pH on the binding of plutonium to poly-L-glutamic acid and to bone chondroitin sulfate and of curium to bone sialoprotein and chondroitin sulfate-protein complex are described. Plutonium, americium, and curium were found to bind to bone glycoproteins in the presence of a 30-fold greater mass of bone mineral than glycoprotein. Some experiments on the precipitation of calcium phosphate in vitro in the presence of plutonium and americium are also presented. These observations are discussed in the light of the hypothesis that certain actinide elements are localized at bone surfaces by binding to glycoproteins.