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OBJECTIVES

OBJECTIVES

After studying this chapter, you should be able to:

  • Explain why essential transition metals are often referred to as micronutrients.

  • Understand the importance of multivalency to the ability of transition metals to participate in electron transport and oxidation–reduction reactions.

  • Understand how Lewis and Bronsted-Lowry acids differ.

  • Define the term complexation as it refers to metal ions.

  • Provide a rationale for why zinc is a common prosthetic group in enzymes that catalyze hydrolytic reactions.

  • List four benefits obtained by incorporating transition metals into organometallic complexes in vivo.

  • Cite examples of the ability of a given transition metal to function as an electron carrier in one protein, an oxygen carrier in another, and a redox catalyst in yet another.

  • Explain how the possession of multiple metal ions enables the metalloenzymes cytochrome oxidase and nitrogenase to catalyze the reduction of molecular oxygen and nitrogen, respectively.

  • Describe two mechanisms by which excess levels of transition metals can be harmful to living organisms.

  • Provide an operational definition of the term “heavy metal,” and list three strategies for treating acute heavy metal poisoning.

  • Describe the processes by which Fe, Co, Cu, and Mo are absorbed in the human gastrointestinal tract.

  • Describe the metabolic role of sulfite oxidase and the pathology of sulfite oxidase deficiency.

  • Describe the function of zinc finger motifs and provide an example of their role in metal ion metabolism.

BIOMEDICAL IMPORTANCE

Maintenance of human health and vitality requires the ingestion of trace levels of numerous inorganic elements, among them the transition metals iron (Fe), manganese (Mn), zinc (Zn), cobalt (Co), copper (Cu), nickel (Ni), molybdenum (Mo), vanadium (V), and chromium (Cr). In general, transition metals are sequestered in organometallic complexes within our bodies, enabling their properties to be controlled and directed where needed, and their propensity to promote the generation of harmful reactive oxygen species is minimized. Transition metals are key components of numerous enzymes and electron transport proteins as well as the oxygen transport proteins hemoglobin and hemocyanin. Zinc finger motifs provide the DNA-binding domains for many transcription factors, while Fe-S clusters are found in many of the enzymes that participate in DNA replication and repair. Nutritionally or genetically induced deficiencies of these metals are associated with a variety of pathologic conditions including pernicious anemia (Fe), Menkes disease (Cu), and sulfite oxidase deficiency (Mo). When ingested in large quantities, most heavy metals, including several of the nutritionally essential transition metals, are highly toxic and nearly all are potentially carcinogenic.

TRANSITION METALS ARE ESSENTIAL FOR HEALTH

Humans Require Minute Quantities of Several Inorganic Elements

The organic elements oxygen, carbon, hydrogen, nitrogen, sulfur, and phosphorous typically account for slightly more than 97% of the mass of the human body. Calcium, the majority of which is contained in bones, teeth, and cartilage, contributes a further ≈ 2%. The remaining 0.4 to 0.5% is accounted for by numerous ...

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