Metabolism of Copper Forms

Copper is absorbed by the small intestinal epithelial cells by specific copper transporters or other nonspecific metal ion transporters on the brush-border surface (120). Once copper is absorbed, it is transferred to the liver. Copper is then re-secreted into the plasma bound to ceruloplasmin. Human patients who have abnormal ceruloplasmin production still exhibit normal copper metabolism. Therefore, ceruloplasmin is not thought to play a role in copper transportation into cells, and this process remains unknown (120). A well-supported theory is that copper is transported into cells by high-affinity transmembrane proteins. Once inside cells of animals, plants, yeast, and bacteria, copper is bound by protein receptor chaperones and delivered directly to target proteins in the cytoplasm and organelle membranes for incorporation into apocuproproteins (64,120). Liver, brain, and kidney tissues contain higher amounts of copper per unit weight than muscle or other bodily tissues. Copper is not usually stored in tissues and differences in amounts may be related more to concentrations of cuproenzymes. Aside from excretion of nonabsorbed copper, daily losses of copper are minimal in healthy individuals (120).