The Nature of Uranium Occurrence in the Leaves of Coprosma Australis (A. Rich) Robinson

Abstract

The distribution and chemical form of uranium was investigated in leaves collected from plants of C. australis (Rubiaceae) growing in a mineralized soil in the Buller Gorge, N.Z. Only small amounts of uranium « 10%) were found in a low molecular weight form. The predominant occurrence of uranium (65%) was as a uranium-RNA complex, which was isolated by high-voltage electrophoresis from an aqueous, extract of the freeze-dried leaves. Uranium (25%) was released from the solvent-extracted leaf residue by pepsin, thus revealing the presence of a uranium-protein complex. However, in view of the known dissociation constants for these two complexes, and other tests, it is clear that the majority of the uranium in vivo is in the form of a uranium-protein complex. This finding is confirmed by a differential centrifugation experiment, in which it was shown that at least 50% of the total uranium was bound to cell wall proteins.