BINDING OF ENDOGENOUS COPPER AND ZINC TO CADMIUM-INDUCED METAL-BINDING PROTEINS IN VARIOUS TISSUES OF PERNA-VIRIDIS

Green lipped mussels, Perna viridis, were exposed to cadmium chloride (CdCl2; 0.52 and 1 mu g/ml) in water for 4 days. The concentrations of cadmium (Cd), copper (Cu) and zinc (Zn) were measured in the viscera, gill, gonads, mantle, and muscle. There was a significant increase (p <0.05) in Cd concentration in all tissues studied. Results from Sephad ex G-75 chromatography indicated that most Cd was bound to a fraction of heat-stable proteins similar to the metal-binding protein (MBP) met allothionein. After exposure to Cd, there was no significant change in Cu concentration in total tissue proteins or in total cytosolic prote ins. A significant increase (p<0.05) in Cu, however, was detected in h eat-stable proteins bound to the Cd-induced MBP in both viscera and gi ll. Copper bound to MBP also occurred in the gonad, mantle, and muscle , but to a much lesser extent. These results showed that Cd-induced MB P can also bind endogenous Cu. Zinc concentration in total heat-stable protein was increased only in gill and the muscle. Unlike Cu, a small amount of Zn binding to Cd-induced MBP was detected only in these tis sues. Considering that both Cu and Zn exist intracellularly in dynamic equilibrium, the binding of Cu, but not Zn, to MBP may be explained b y the kinetic reactivity of the two different metals to protein. The r esults of this study support the thesis that induction of intracellula r MBP may also bind endogenous Cu and Zn.