For copper absorption from the gastrointestinal tract is required a specific mechanism because the copper ion (Cu2+) is practically insoluble. An unidentified low molecular weight substances from human saliva and gastric juice creates a complex with Cu2+, which is soluble in the pH of intestinal fluids. In the small intestine, copper is probably associated with the low molecular protein that binds metals, usually called metallothionein. Copper enters into the plasma where it binds to amino acids, especially histidine, and serum albumin. Copper is within an hour removed from the circulation by the liver.
Liver processes copper in two ways. The first is that copper is excreted via the bile in the gastrointestinal tract. The fact is that homeostasis of copper is maintained only this excretion in the bile. The more copper is excreted, the more is it in the feces. Normal urine has a trace quantity of copper.
Another way of copper metabolism in the liver is its implementation in ceruloplasmin, a glycoprotein which is synthesized only in the liver. Ceruloplasmin is a copper dependent protein. It contain about 95% of the total plasma copper. Ceruloplasmin is not a transport protein for Cu2+, because the copper in ceruloplasmin is not exchanged between the ions of copper and copper associated with other molecules. Ceruloplasmin contains 6-8 copper atoms, half of the cuprous (Cu+), and half of cupric (Cu2+) form.
Ceruloplasmin oxidizes Fe2+ to Fe3+ which is essential to the mechanism of absorption of iron from gastroinestinalnog tract. The other copper metalloproteins are cytochrome oxidase, tyrosinase, monoamine oxidase, superoxide dismutase and lysyl oxidase.