CADMIUM ACCUMULATION AND CD-BINDING PROTEINS IN THE BIVALVE SCAPHARCA-INAEQUIVALVIS

In the arcid clam, Scapharca inaequivalvis, cadmium was accumulated in the kidneys, gills, viscera, mantle, foot, muscle and red blood cells , Maximum levels were reached in the kidney (725.70 mu g/g dry weight) after 4 weeks exposure to 0.5 mu g Cd/ml sea-water. The accumulation was higher during the warm rather than in the cold season and in anima ls exposed to 0.5 as compared with 0.05 mu g Cd/ml sea-water. Concentr ations of zinc and copper were unaffected by cadmium treatment, wherea s iron levels changed during cadmium exposure, When molluscs were retu rned to natural sea-water, cadmium levels fell slowly, The metal was f ound in the cytosolic fraction, bound to a low molecular weight ligand , shown by gel filtration to be a Cd-protein with an apparent molecula r weight of 10,000 Da, possibly a metallothionein. Ion exchange chroma tography of this protein isolated from the viscera revealed the presen ce of at least two Cd-binding isoforms; the -SH:Cd ratio of the main i soform was 2.8, the UV spectra presented a strong absorption band at 2 50 nm.