Diversification of cadmium-binding proteins due to different levels of contamination in Arion lusitanicus.

Individuals of Arion lusitanicus were collected in the former mining area of Braubach (Federal Republic of Germany) which is highly polluted by various metals. The animals were transferred to the laboratory and fed contaminated litter from their original habitat. Groups of animals from a quarry near Heidelberg were reared in the laboratory and fed diets of different cadmium concentrations. Slugs fed uncontaminated food were used as controls. The concentration of cadmium in the midgut gland of cadmium-fed slugs increased in proportion with the metal concentration of the food. High amounts of zinc and copper were found in the midgut glands of slugs from Braubach. After centrifugation of homogenates, specific patterns of distribution between cytosolic components and pellets were observed for different metals. Cadmium and copper were predominantly bound to cytosolic components, whereas the main portion of zinc was associated with the pellet. In laboratory-fed slugs the increase of cadmium concentration in the food correlated with an increase of the metal content in the homogenate and in two components (supernatant, pellet) of the midgut gland. This correlation was most clearly expressed in the cytosolic components which contained 93-100% of total midgut gland cadmium. Total cadmium in control slugs was associated with components with a molecular weight of more than 15,000. In Braubach and in cadmium-loaded slugs, all the cadmium was bound to a protein with a molecular weight of 10,000, which also contained low amounts of zinc and copper. In highly contaminated individuals fed on the most concentrated cadmium diet, however, a spillover effect was observed, some cadmium being bound to an additional component with a molecular weight of more than 15,000.