The six Cu(I)-binding sites at the N-terminal bind one Cu(I) each. This binding site is not specific for Cu(I) and can bind various transition metal ions. Cd(II), Au(III) and Hg(II) bind to the binding site more tightly than does Zn(II), whereas Mn(II) and Ni(II) have lower affinities relative to Zn(II). In the case of Cu(I), a possible cooperative-binding mechanism is observed. When the Cu(I) concentration is low, Cu(I) has a lower affinity for ATP7A compared to Zn(II); as the Cu(I) concentration increases, a dramatic increasing affinity of Cu(I) for the protein is observed.