Purification and characterization of a cadmium-induced metallothionein from the shore crab Carcinus maenas (L.).
Two metallothionein variants were purified from the midgut gland of crabs (Carcinus maenas) exposed to a high cadmium concentration (2 p.p.m.). One of the variants was purified from crabs exposed to a low cadmium concentration (0.5 p.p.m.). The purification method involved acetone precipitation, gel filtration and reversed-phase h.p.l.c. The complete amino acid sequences of both variants have been elucidated by m.s. and automated sequence analysis on S-methylated proteins or fragments produced by cleavage of the S-methylated proteins with Staphylococcus aureus proteinase. The two variants from crabs exposed to the high cadmium concentration differed only by a single residue of methionine at the N-terminus. The single variant isolated from crabs exposed to the low cadmium concentration was the one without the N-terminal methionine, indicating that high cadmium concentrations either inhibit the processing enzymes and/or that the processing enzymes cannot keep pace with the increased metallothionein synthesis when cadmium availability is high. Cadmium-induced metallothionein from C. maenas shows a high degree of structural similarity to metallothioneins from the decapod crustaceans Scylla serrata and Homarus americanus.[1]References
- Purification and characterization of a cadmium-induced metallothionein from the shore crab Carcinus maenas (L.). Pedersen, K.L., Pedersen, S.N., Højrup, P., Andersen, J.S., Roepstorff, P., Knudsen, J., Depledge, M.H. Biochem. J. (1994) [Pubmed]
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