Detoxification of copper in the cells of the digestive gland of mussel: The role of lysosomes and thioneins

The data reported shows that copper is naturally present in the lysosomes and residual bodies of mussel digestive gland, the concentration of the metal being greatly increased for mussels exposed to Cu²⁺ (0.04 ppm) for 3 days and then detoxified for 6 days. A procedure has been devised to solubilize the copper that is present in an insoluble form in lysosomes and residual bodies. This procedure disrupts lysosomes with sonication and solubilizes Cu-protein complexes in a hypotonic solution containing 1% 2-mercapto-ethanol and a mixture of antiproteolytic agents. The solubilized copper, representing more than 80% of the total metal present in the organelles, has been found mainly bound to a protein showing characteristics similar to those of metallothioneins: it has a high metal content, a molecular weight of about 12000 as evaluated by gel filtration, a relatively low UV absorbance at 280 nm and a high -SH content, as evaluated by the Shikata orcein cytochemical technique. The lysosomal extracts from the digestive gland of controls contain low basal levels of this copper-rich thionein-like protein which increases 5-6 times when the mussels are exposed to copper (0.04 ppm) for 3 days and then detoxified for 6 days.