CRUSTACEANS AS MODELS FOR METAL METABOLISM .2. INDUCTION AND CHARACTERIZATION OF METALLOTHIONEIN ISOFORMS FROM THE BLUE-CRAB (CALLINECTES-SAPIDUS)

To clarify the role of metallothionein (MT) in metal-regulatory processes in blue crabs (Callinectes sapidus), we have determined how many different MT isoforms are present and how these different forms respond to elevated dietary levels of copper (Cu) and cadmium (Cd). Anion-exchange HPLC showed two MT isoforms in control (CuZnMT-I, CuZnMT-II) and Cd-treated crabs (CdMT-I, CdMT-II) while three forms (CuMT-I, CuMT-II, CuMT-III) were present in Cu-treated animals. CuMT-III was induced to a much greater extent than CuMT-I or CuMT-II. In the case of Cd, however, the induction of CdMT-I was much more significant than that of CdMT-II. Purification of the metal-free MTs by reverse-phase HPLC and subsequent amino-acid analysis showed that CdMT-I, CdMT-II, CuMT-I, and CuMT-II were very similar, whereas CuMT-III was unique. After a combined exposure of Cd and Cu, five chromatographically distinct isoforms were observed that corresponded to the two Cd and three Cu isoforms. The expression of multiple isoforms after varied types of metal exposure indicated that regulation of crab metallothionein isoforms may be metal-safe specific.