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Abstract | ||
| The trace metals zinc and cadmium are taken up from solution by the shore crab Carcinus maenas via the permeable surface of the gills. On passing through the gill cells, the two metals enter the haemolymph and bind to the respiratory pigment haemocyanin. The two metals were found to have different kinetics of accumulation in the haemolymph of Carcinus maenas. Zinc is added sequentially over time to the content of zinc already present in the haemolymph, the rate of zinc being proportional to the dissolved zinc concentration to which the crab is exposed (and hence the rate of uptake by the crab). Cadmium shows accumulation in the haemolymph at a rate proportional to the external dissolved cadmium concentration (and hence the rate of cadmium uptake into the crab), but rapidly reaches an equilibrium concentration when the rate of removal matches the rate of cadmium uptake into the haemolymph. The equilibrium concentration of new cadmium in the haemolymph increases with an increase in the external dissolved cadmium concentration. In most circumstances, the haemolymph therefore acts as a transient store for accumulated cadmium, but as a long-term store for newly accumulated zinc. Investigations using FPLC and PAGE to separate the constituent dodecamer and hexamer aggregations of haemocyanin showed a difference between the distribution of cadmium and zinc between the two aggregate states. The hexamer appeared to have a higher affinity for zinc indicating that formation of the dodecamer leads to a blocking of zinc-binding sites and/or that the hexamer consists of subunits which possess a relatively high affinity for zinc. | ||
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This research was carried out at Queen Mary, University of London, whilst in receipt of a NERC studentship. | ||
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