UPTAKE AND DEPURATION OF COPPER AND ZINC IN RELATION TO METAL-BINDINGPROTEIN IN THE POLYCHAETE EURYTHOE-COMPLANATA

Bioassays were conducted with the polychaete Eurythoe complanata to st udy the patterns of accumulation and depuration of copper and zinc in relation to the levels of metal-binding proteins during sublethal expo sure. Acute toxicity tests indicated 96-hr LC(50) of 1.3 mg Cu+2.1(-1) and 139.6 mg Zn+2.1(-1), from which sublethal levels of 0.2 mg.1(-1) of copper or 10 mg.1(-1) of zinc were established for a 24-day exposur e. At those sublethal levels, tissue (carcass) concentrations of coppe r and zinc in E. complanata reached maximal levels of 29.6 and 319 mu g.g(-1) dry mass, respectively, at the end of the exposure period, whe reas unexposed worm levels (carcass) were estimated in 5.6 and 35.9 mu g.g(-1) dry mass of copper and zinc, respectively. After 22 days of d epuration, tissue levels were reduced to a minimum of 13.7 and 108 mu g.g(-1) dry mass, respectively. Exposure to a mixture of metals result ed in lower tissue levels of copper and zinc as compared with those fo und for each individual metal analysis. During uptake and depuration p hases, Sephadex G-75 chromatography revealed metallothionein-like prot eins of molecular weights between 10 and 20 kDa with a higher affinity for zinc than for copper, as well as heavier metalloproteins (>60 kDa ), displaying a higher affinity for copper. These data suggest differe nt biochemical mechanisms underlying the control of zinc and copper me tabolism through the activity of low- and high-molecular weight metal binding proteins.