Copper

X Xu, S Pin, J Shedlock and Z L Harris, Johns Hopkins Hospital and School of Medicine, Baltimore, MD, USA

© 2005 Elsevier Ltd. All rights reserved.

Introduction

Transition metals occupy a special niche in aerobic physiology: as facile electron donors and acceptors, they are essential participants in oxidation/ reduction reactions throughout the cell. These unique properties of transition metals are largely dependent on the electronic configuration of the electrons in the outer shell and in the penultimate outer shell. These metals can exist in different oxidation states, which is critical for their usefulness as catalysts. However, it is during these same committed reactions essential for aerobic metabolism that toxic reactive oxygen species can be generated. As such the transition metals are chaperoned as they traffic through the body and are regulated tightly. Subtle disruptions of metal homeostasis culminate in disease and death. Iron, copper, and zinc are the most abundant and well-studied transition metals. Copper is the oldest metal in use: copper artifacts dating back to 8700bc have been found. The physiology, requirements, and dietary sources of copper are described here with an emphasis on the role of copper in human health and disease.

Copper, as a trace metal, can be found in all living cells in either the oxidized Cu(II) or reduced Cu(I) state. Copper is an essential cofactor for many enzymes critical for cellular oxidation. These include: cytochrome c-oxidase, which is essential for mitochondrial respiration as the terminal enzyme in the electron transport chain; superoxide dismu-tase, a potent antioxidant defense mechanism; tyrosinase, which is critical for melanin production; dopamine B-hydroxylase, a prerequisite for catecho-lamine production; lysyl oxidase, which is responsible for collagen and elastin cross-linking; ceruloplasmin, a ferroxidase/metallo-oxidase; hephaestin, a ferroxidase/ metallo-oxidase; and peptidylglycine a-amidating monooxygenase, a peptide processor (Table 1). Mice that lack the copper transport protein Ctr1 are embryonic lethal, which confirms the importance of copper in enzyme function and normal cellular homeostasis.

Copper Homeostasis

Dietary intake of copper is approximately 5mgday-1 with an equivalent amount being excreted by bile in stool. Approximately 2 mg day-1 are directly absorbed across the gastrointestinal tract daily and incorporated into blood, serum, liver,

Table 1 Mammalian copper enzymes

Table 2 Copper content of various foods

Enzyme

Function

Cytochrome c-oxidase cu,zn-Superoxide dismutase Tyrosinase

Dopamine B-hydroxylase

Lysyl oxidase

Ceruloplasmin

Hephaestin

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