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Copper is an important essential trace element for all living organisms needed for the activity of a variety of enzymes involved in critical areas of metabolism (Linder, 1991a; Linder and Hazegh-Azam, 1996). These include cytochrome c oxidase, the terminal enzyme of respiration; lysyl oxidase, essential for cross linking of elastin; dopamine-monooxygenase, required for synthesis of catecholamines; and several enzymes involved in anti-oxidant defense, notably ceruloplasmin, Cu/Zn Superoxide dismutase, and copperthionein. In most creatures including mammals, copper enters cells and organisms primarily or exclusively via absorption from the digestive tract. Adult humans consume in the range of 0.6–1.6 mg Cu per day, and a large proportion of this (60–70%) is absorbed. However, in considering the daily absorption, transport and metabolism of dietary copper, it is important to note that this occurs in the context of an even larger flux of copper from the body itself into the gastrointestinal tract, and back. This is surmised from the data on copper concentrations and daily volumes of GI fluids shown in Table 1. From these, it seems that almost 5 mg of Cu are secreted daily into the adult digestive tract as part of these various fluids. With the addition of dietary copper, a total of about 6 mg Cu daily thus enters the GI tract. Clearly, most of this is reabsorbed: only about 1 mg is lost in the feces; and dietary copper is only a small proportion of the total fluxing in and out of the digestive tract. Absorption and reabsorption of copper occur primarily in the small intestine, and the copper absorbed is in ionic form. |
