The microminerals are widely dispersed in the living body. They serve a variety of functions, as summarized in Table 7, and most of these minerals can be found in trace amounts in the skeletal system. The bones and teeth are primarily calcium phosphate salts, yet within the bone matrix other minerals can be found as well. Some of the microminerals have only one function, for example, cobalt in vitamin B12 and iodide in thyroxine, but others serve at multiple levels, from influencing gene expression to serving as cofactors in enzymatic reactions to contributing to the stability and hardness of bone.
Table 7. Microminerals and Their Functions
Iron Essential component of iron-sufur centers that function in redox reactions as well as in the cytochromes and hemoglobin; serves in the expression of the genes for the metallothioneins, ferritin and the transferrin receptor (7-9).
Zinc Cofactor in more than 100 enzymatic reactions. Essential component of the zinc fingers that characterize many of the nuclear DNA-binding proteins. Serves in the expression of genes for metallothionein; has a vital role in apoptosis (7, 10-13).
Copper Essential cofactor in several reactions concerning iron use, collagen synthesis, and free-radical suppression. Serves in the expression of the genes for metallothionein superoxide dismutase, and several mitochondrial enzymes (14-17).
Cobalt Essential to the structure of vitamin B12.
Iodine Essential for thyroid hormone synthesis (18).
Manganese Essential cofactor in many enzymatic reactions, especially those using ATP or UTP.
Molybdenum Activates adenylate cyclase; cofactor in sulfite oxidase and xanthine oxidase (19).
Selenium Essential to glutathione peroxidase and thyroxine deiodinase. Serves in the expression of the gene for glutathione peroxidase (20,21)'
"Arsenic, chromium, nickel, silicon, and vanadium appear to be essential for optimal growth and metabolism of several animal species, but their essentiality and function in humans has yet to be documented.
Figure 3. Zinc bound to cysteine and histidine residues from fingerlike projections that bind to DNA at specific regions.
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