The Science of the Total Environment, Supplement 1993 Elsevier Science Publishers B.V., Amsterdam 607 Function of metallothioneins in terrestrial gastropods Reinhard Dallinger and Burkhard Berger Institut ftir Zollogie (Abt. Okophysiologie), Universiti~tInnsbruck, Austria ABSTRACT Terrestrial gastropods accumulate high amounts of cadmium and zinc. Large proportions of these elements are concentrated in the midgut gland, in which organ the metals can be stored over extended periods of time. In contrast to cadmium and zinc, the essential trace element copper is not strongly concentrated in this organ. It is shown that in the midgut gland of these aminals most of the accumulated cadmium as well as a certain proportion of copper is bound by metaUothioneins, whereas most of the zinc is associated with lysosomal vesicles and with a low molecular weight ligand of unknown structure. The cadmium-binding metallothioein of the terrestrial snail Helix pomatia has been purified and analysed by its amino acid sequence. The results show that the metallothionein shows considerable similarities with mammalian metallothioneins. In the light of our recent findings the question concerning the biological function of metallothioneins in terrestrial gastropods is reconsidered. There are indications supporting the hypothesis that in these animals the function of metallothioneins may have shifted from regulating essential trace element concentrations towards a more efficient detoxifiction of cadmium. Key words: Metallothioneins; Terrestrial gastropods; Biological function INTRODUCTION Metallothioneins are proteins containing high proportions of cysteine and low amounts, if any, of aromatic amino acids [1]. They have a strong affinity to some borderline metals, such as copper, cadmium and zinc. So far, metallothioneins have been found in a large number of eukaryotic species, including mammals and invertebrate animals [2]. The biological function of these proteins is still a matter of discussion. Most authors agree that metallothioneins are involved in the transport and homeostatic regulation of essential trace elements [3]. Recent findings also suggest a role of these proteins in gene regulation [4]. Apart from this, it has been assumed that in some animal species metallothioneins may play 1993 Elsevier Science Publishers B.V.