The significance of low molecular weight, metallothionein-like proteins in marine invertebrates: Current status

Abstract Low molecular weight, metal-binding proteins have been shown to occur in several marine invertebrate species. The molecular weights, metal contents, and induction of these proteins by metals such as cadmium, zinc, copper, and mercury suggest close similarities to metallothionein, a sulphydrl-rich, metal-binding protein of widespread occurrence in vertebrates. Metallothionein has, to date, been identified in two species of brachyuran crabs. The identity of the protein in other marine invertebrate groups such as molluscs is still to be determined. Continued study of the metal-binding proteins will undoubtedly contribute to our understanding of both the normal metabolism and toxicology of certain trace metals in marine species. It appears that these proteins may be involved in the sequestration and detoxification of metals. Organisms which have been exposed to metals such as cadmium, zinc, copper, or mercury in the laboratory or field exhibit enhanced levels of metals which are associated with the metal-binding proteins. Additional studies will be required in order to determine the biochemical and physiological significance of such bound metals.