Binding of radionuclides to proteins in fish

Radioisotope tracer experiments on binding of radionuclides to proteins in fish were carried out in order to gain further information on biochemical behavior of radionuclides in marine fish. The radionuclides, which were bound to proteins in fish through sea water or food, were extracted with a Tris-acetate buffer solution and separated by gel filtration on Sephadex G-75. Most of 137Cs in the fish liver were bound only to a peptide with a molecular weight of 1,100 - 1,300. The most remarkable feature of 60Co in the profiles of the gel filtration was the presence of two clear radioactivity peaks and the radioactivity appeated to transfer from a low molecular weight protein to high molecular weight protein in the uptake, and the reverse phenomenon was observed in the excretion. Therefore, this suggested that these proteins had each inherent turnover rate for 60Co. The profiles of the gel filtration of 65Zn varied widely among species of fish, tissues or organs even in the same fish and pathways of the uptake. Thus, it was considered that there existed some different rules peculiar to each radionuclide in the binding of radionuclides to proteins in fish. (author)