Occurrence of cadmium in crabs (Cancer pagurus) and the isolation and properties of cadmium metallothionein.

The occurrence of high cadmium levels in the digestive gland (hepatopancreas) of the crab Cancer pagurus is reviewed and its possible significance to human health is discussed. Previous attempts to isolate this cadmium in its native form are briefly reviewed and the present method used in this laboratory to isolate crab cadmium metallothionein is described. Quantitative amino acid analysis of the purified protein suggests that it has a total of 55 residues, including 19 Cys, and a molecular weight of approximately 5800. This yields an extinction coefficient at 220 nm for the protein in HCl, pH 1.5, of 50,000 and at 250 nm for the native cadmium protein in Tris-HCl, pH 8.4, of 92,000.