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protein’s redox behavior, produce amyotrophic lateral sclerosis (Lou Gehrig’s disease).

These are the principal copper metalloenzymes found in humans. There is substantial documentation from animal studies that diets low in copper reduce the activities of many of these copper metalloenzymes. Activities of some copper metalloenzymes have been shown to decrease in human copper depletion (Milne, 1994; Turnlund, 1999). Physiologic consequences resulting from copper deficiency include defects in connective tissue that lead to vascular and skeletal problems, anemia associated with defective iron utilization, and possibly specific aspects of central nervous system dysfunction (Harris, 1997; Turnlund, 1999). Some evidence suggests that immune and cardiac dysfunction occurs in experimental copper deficiency and the development of such signs of deficiency has been demonstrated in infants (Graham and Cordano, 1969; Olivares and Uauy, 1996; Turnlund, 1999).

Physiology of Absorption, Metabolism, and Excretion

Metabolism of copper in humans relies on the intestine for control of homeostasis as the capacity for renal copper excretion is limited. Nearly two-thirds of the body copper content is located in skeleton and muscle, but studies with stable isotopes have shown that the liver is a key site in maintaining plasma copper concentrations (Olivares and Uauy, 1996; Turnlund et al., 1998). Copper has a higher binding affinity for proteins than all other divalent trace elements (da Silva and Williams, 1991). Consequently, precise control of intracellular copper trafficking is needed to regulate how it is donated to appropriate sites.

Copper absorption occurs primarily in the small intestine. Some absorption may occur in the stomach where the acidic environment promotes copper solubility by dissociation from copper-containing macromolecules derived from dietary sources (Harris, 1997; Turnlund, 1999). Both saturable-mediated and nonsaturable-nonmediated (possibly paracellular) transepithelial copper movements have been reported. The Menkes P-type ATPase (MNK; ATP7A) is believed to be responsible for copper trafficking to the secretory pathway for efflux from cells, including enterocytes (Harris and Gitlin, 1996). A defective MNK gene causes Menkes’ disease, which is characterized by reduced copper absorption and placental copper transport. The extent of copper absorption varies with dietary copper intake (Turnlund, 1998). It ranges from over 50 percent at an intake of less than 1 mg/day to less than 20 percent above 5 mg/day. About



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