Biochemical characterization of a copper-thionein involved in Cu accumulation in the lysosomes of the digestive gland of mussels exposed to the metal

The Cu-rich protein present in an insoluble form in the digestive gland lysosomes of mussels (Mytilus galloprovincialis Lam.) exposed to sublethal concentrations of copper has been extracted and characterized. When solubilized, the Cu-protein has chromatographic and electrophoretic behaviour and a UV spectrum typical of cytosolic metallothioneins ofmussels. The amino acid composition is also similar to the cytosolic metallothioneins, from which it differs, for an unusually low glycine content and for a high level of aspartic and glutamic acid. Therefore, in mussel digestive gland metallothioneins and lysosomes may play an interrelated key role in copper homeostasis.