Copper-albumin: what is its functional role?

The small copper fraction in animal blood that is bound to albumin protein is generally considered to have a transport role for the metal. However, several studies have concluded that copper ion incorporation into copper-enzymes requires caeruloplasmin to act as the transport form. The kinetic rates of Cu(albumin) reactions are also not in keeping with a general transport function. Only in the portal bloodstream does the Cu(albumin) appear to have a well-established transport role, i.e. in delivering the metal ions from the intestine to the liver. Thereafter the evidence as to its function is less certain; it could act as a storage form of the metal or have no role at all. Similar considerations apply to other metal-albumin fractions e.g. those of zinc and nickel.