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Dean, College of Agriculture
California State Polytechnic University, Pomona, CA
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INTRODUCTION |
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 TOP INTRODUCTION |
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Astrid and Helmut Sigel continue their outstanding series on metal ions in biological systems. Recent concerns related to iron overload and renewed interest in the mechanisms of biologic need and handling of iron make this volume a timely reference.
The sea of chemicals from which life began contained abundant ferrous iron, while the atmosphere contained no oxygen. Once blue-green algae began synthesis of chlorophyll to capture the energy of the sun, dioxygen appeared in the atmosphere and ferrous iron became oxidized to its ferric form. Although the ferrous state of iron is quite water soluble, the ferric state of iron is very insoluble in water at neutral pH. Thus, most living organisms had to develop mechanisms to solubilize and acquire this element.
The production of siderophores—low molecular weight, high affinity ferric chelators—provides a means for solubilization, transport and localization of iron in microbial systems (Chapters 1–4). Characterization of the coordination chemistry of siderophores, the thermodynamics and kinetics of iron chelation, and iron release was described in chapter 7. Methodology used to characterize siderophores and their mechanisms of action was described in chapter 8. The biomimetic approach to preparation of synthetic analogues that simulate natural compounds in vitro and in vivo was described. Characterization of bacterial outer membrane siderophore receptor proteins is described in chapter 9, while the iron responsive element family of mRNA regulators which stabilize the turnover of mRNA, proteins recognized by IREs, and regulation of iron uptake and storage in plants and microorganisms are described in chapter 10. Differences between plants and animals, such as the absence of ferritin mRNA regulation in plants, differences in ferritin gene organization, and the use of ferritin DNA as the iron target in plants but mRNA in animals provides scientific interest in evolution of genetic regulatory mechanisms.
For multicellular organisms, a more complex system evolved for transporting iron in plants (chapter 5–6) via transferrin in animals evolved. The transferrin receptor, and uptake of iron by cells is discussed in chapter 15. A fascinating comparative discussion of iron homeostasis in different species was presented.
Iron is difficult to acquire and must also be protected during storage to limit its properties of auto-oxidation and free radical generation of active oxygen species capable of attacking other biomolecules. To protect cells from this form of internal damage, iron is sequestered in ferritin structures found in plants, animals and microbes (Chapter 11–14). The protein shield covers a hydrous ferric oxide mineral core that is accessible for biologic use.
Chapters 16–18 detailed iron homeostasis, the effects of other metals on iron transport, as they affect iron homeostasis in bacteria, yeast, plants and animals are examined with an emphasis on humans.
In the latter, iron metabolism is highly conservative, controlled by dietary iron absorption. There is no excretory mechanism in humans to excrete iron. Thus homeostasis is dependent on absorption and storage regulation. Loss of homeostatic control allows accumulation of total body iron resulting in an increased total body burden and eventual tissue damage resulting in mortality. Elimination of iron using chelating agents for clinical use is discussed in the final chapter.
The book proved to be an excellent summary of the role of iron in biological systems. The international authors that contributed to this volume are recognized as major researchers in the field of iron metabolism. The text should be added to the reference library of every researcher working in areas related to iron metabolism. The biologic presentation provides a perspective for teachers and graduate students alike. Again I would complement the editors for another outstanding volume.
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