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)