Metallothionein

Abstract

Metallothioneins are nonenzymic low molecular weight proteins of extremely high sulphur and metal content which have recently become the object of intensive interest in many branches of the life sciences (Kägi and Nordberg, 1979; Webb, 1979). They are chiefly found in parenchymatous tissues of vertebrates and invertebrates but have also been isolated from some microorganisms and plants. They were initially discovered by Margoshes and Vallee (1957) in equine kidney in their search for the biological role of cadmium, and they are still the only biological compound known to contain this metal. It has already been shown in the earliest studies that cadmium is only one of several optional metallic constituents of the metallothioneins, the others being most commonly zinc and copper (Kägi and Vallee, 1960, 1961). Hence, it is believed that these proteins play a general role in the metabolism and the detoxification of a number of essential and nonessential trace metals. In mammals, their principal physiological purpose appears to be exerting a homeostatic function for zinc and copper, both by dispensing these metal ions when they are needed for the synthesis of metal-dependent cellular components such as metalloenzymes, nucleic acids and supramolecular structures and by sequestering them in a chemically innocuous form when they exceed a critical intracellular concentration (Richards and Cousins, 1976; Brady, 1982; Bremner, 1982; Webb and Cain, 1982; Whanger and Ridlington, 1982).