Induction and identification of cadmium-, zinc- and copper-metallothioneins in the shore crab Carcinus maenas (L.).

Shore crabs Carcinus maenas were injected with either Cd, Cu or Zn to determine whether different metals could induce specific metallothionein (MT) isoforms in the midgut gland. Furthermore, the relative ability of the three metals to induce MT was quantified. Accumulation of the three metals in the midgut gland caused variable and in the case of Cd and Zn significant increases in MT levels. The increase in MT levels (pmol g-1 midgut gland) per nmol of metal accumulated was determined as 90, 60 and 4 pmol for Cd, Zn, and Cu respectively. The MT isoforms were purified using a combination of acetone precipitation, FPLC and reverse phase HPLC. In contrast to Cd and Zn induced MTs, the Cu induced MT was highly susceptible to oxidation during purification. The induced MT isoforms were characterized by N-terminal amino acid sequencing and mass-spectrometry. All three metals induced the same identical isoform MTIa.