ABSTRACT
Metallothioneins (MTs) are small, cysteine-rich proteins that bind metal ions with high affinity. They have been conserved throughout evolution from yeast to man. Considering the extremely long half-life of cadmium in organisms, the main function of MT in this respect is protection against long-term toxicity. Cell-and tissue-specific gene expression of MTs points to differential regulation of expression that is metal related and concentration dependent. Metal-related expression is best exemplified in snails. Dallinger et al. claim the existence of specific MTs for cadmium and copper, in Helix pomatia. A possible mechanism could be the release of reduced transition metal from MT and local generation of hydroxyl radicals in a Fenton-driven reaction. Metal stress by cadmium highly depends on intracellular levels of cadmium. At noncytotoxic cadmium levels, the cell responds by inducing MT to sequester free cadmium, as well as by inducing glutathione to maintain redox state and stress proteins to prevent or repair damage.
