Small copper-binding proteins from normal and copper-loaded liver.

The same three low molecular weight copper-binding proteins which have been purified from the soluble fractions of Cu2+-loaded livers (200 mug Cu2+ per g wet weight) were also found to be present in livers of normal rats (4 mug Cu2+ per g wet weight) but in much smaller quantities. Therefore, Cu2+ loading enhances the amount of preexisting proteins rather than inducing the synthesis of new proteins. Amino acid analyses of each of the three showed them to be different from the metallothioneins which are present on loading with other trace metals including Cd2+ and Zn2+.