A comparison of metal-binding proteins and cadmium metabolism in the marine molluscs Littorina littorea (gastropoda), Mytilus edulis and Macoma balthica (bivalvia) |
| |
| Authors: | WJ Langston MJ Bebianno Zhou Mingjiang |
| |
| Abstract: | Studies on the processes of Cd accumulation, turnover and storage in marine molluscs have revealed important qualitative and quantitative differences between species. In Littorina littorea collected from uncontaminated sites, Cd is predominantly bound to metallothionein (MT)-like proteins. Exposure to Cd, in the laboratory and field, results in an increase in Cd bound to these proteins, together with limited increases in Cd in the high molecular weight (HMW) pool (the latter partly a result of haemocyanin-mediated transport of Cd in the haemolymph). Polarographic determination of heat-stable MT-like compounds in L. littorea indicates there is little overall increase in the amount of protein produced in response to Cd exposure, suggesting that much of the newly incorporated metal may be bound to previously synthesised material. Relatively high levels of MT-like proteins, notably in the digestive gland (the major Cd-storage organ), appear to be an inherent feature of this species even in uncontaminated areas.MT-like proteins also sequester much of the Cd in exposed mussels Mytilus edulis, though, unlike Littorina, protein induction can be quantitatively related to exposure. In contrast, tellinid clams, Macoma balthica, fail to produce MT-like compounds, even in highly contaminated conditions, and Cd is mainly bound to HMW proteins.These variations in metal-binding behaviour probably explain the large interspecific differences in experimentally-determined Cd uptake rates and may account for differences in bioaccumulation potential observed in the field. Despite such variability, all three species studied appear to tolerate an influx of Cd provided the normal partitioning of metal is not irreversibly disturbed. Maintaining intracellular homeostasis, albeit at elevated Cd concentrations, probably compensates for the inability of these animals to regulate Cd uptake and for their extremely slow rates of Cd excretion. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
