Copper is both a necessary micronutrient for most living things, and a potential toxicant. Cu ions are important constituents in the active sites of a number of important enzymes. These include amine oxidase, ammonia mono-oxygenase, Cu, Zn superoxide dismutase, cytochrome c oxidase, dopamine ft hydroxylase, methane mono-oxygenase, N2O reductase, nitrite reductase, tyrosinase, ubiquinone oxidase, and phytocyanin. Copper even forms the basis of a respiratory oxygen carrier protein, hemocyanin, in crustaceans, analogous to hemoglobin in vertebrates. As is apparent from this list, copper is an important mediator in a wide variety of biological functions, including energy production, protection from free radicals, and tissue building. As a consequence organisms have evolved mechanisms for accumulating and regulating copper. A protein called Ctrl (copper permease) that helps transport copper into cells has been identified in a wide variety of organisms, from single-celled yeasts to land plants and vertebrates.
As a required micronutrient, inability of cells to get required copper can lead to limitation and even death. The recommended level of Cu consumption for humans is 1.5—3.0 mgd_1. In humans (and other mammals) insufficient dietary copper can lead to anemia, impaired wound healing, and artery and heart disease. Copper is accumulated in the liver and kidneys, and circulated in the blood in the protein ceruloplasmin. Excessive zinc and iron consumption can reduce the absorption of Cu (and vice versa). One serious syndrome in infants, 'Menkes' kinky hair disease' is linked to a defect in the copper transport system. This syndrome is an X-linked recessive trait, and so occurs almost exclusively in male children. Kinky, brittle hair has also been observed in sheep from regions with copper deficient soil.
In plants, copper is important in nitrogen metabolism, protein synthesis, and chlorophyll production. Signs of copper deficiency in plants can include chlorosis (lack of chlorophyll) either in leaf tips, or mottling, and deformed new growth. Copper deficiency in plants can be caused by low copper concentrations in particular soils, or soil chemistry conditions that inhibit copper uptake (e.g., alkaline or highly organic soils). As copper is removed from soil by the successive removal of plant biomass containing the copper, soils can become copper deficient. Some crops (e.g., flax) are very susceptible to Cu deficiency, while others (e.g., canola) rarely if ever show signs of copper deficiency. Chronic Cu deficiency can reduce some grain yields up to 20% without showing visible symptoms. Copper (Cu sulfate or Cu-EDTA) treatment to the leaves or soil is used to alleviate Cu deficiency. Cu deficiency in soils, and thus plants, can be reflected in Cu deficiency in livestock (sheep, goats, and cattle) grown on local graze. Again, as with plants, Cu absorption by livestock may be suppressed by excessive concentrations of other chemicals (Zn, Fe, Mo, sulfates).
Very low concentrations of copper in many open ocean surface waters have suggested that copper may be one of several trace elements that potentially limits growth of phytoplankton in the ocean. For phytoplankton, copper has been shown to be important in the uptake of iron, which is also a limiting element.
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