Gale Rhodes, Department of Chemistry, University of Southern Maine rhodes@usm.maine.edu
Browse through your biochemistry text -- you will not see many metal ions pictured or mentioned. Would you guess that about one-third of all enzymes require one or more metal ions for catalytic activity? Many additional proteins contain metal ions that are involved in redox reactions. In some proteins, metal ions play structural roles, organizing a small region of a protein into its functional conformation. Metal ions also act as signals that pass between molecules, organelles, and cells. And I've mentioned only a few of the roles of metal ions in biochemistry.
Most biochemistry students are familiar with structure and bonding in organic compounds, but compounds that contain metal ions or metal-ion complexes, like the octahedral complex of iron (II) in oxyhemoglobin (shown above), are pretty mysterious. This gallery should help.
Each page in the gallery provides information on a metal ion in a specific role. In addition to a picture of the metal ion and its ligands (groups bonded to the metal ion), you will find one or more Protein Data Bank files that you can download for further study with a molecular graphics viewing program like RasMol or SwissPdbViewer. Finally, you will find brief a description of bonding and geometry in the metal-ion complex, and where possible, comments about why this particular metal is well suited to its role, or why, if various other metals could do the same job, this particular one might have landed the job by natural selection.
I hope that this gallery will eventually contain most types of metalloproteins that students encounter in beginning biochemistry courses. And I hope that studying the molecules in the gallery gives you a more coherent picture of why nature relies on metal ions for many specialized functions -- functions that amino-acid side chains and organic cofactors apparently cannot provide.
Gallery: Metal Ions in Biochemistry Explanations of Gallery Headings
· Please look at these explanations first. Then browse the gallery in any order.
Calcium Signal Carriers· Calmodulin
Copper Electron Transporters ·
Iron Oxygen Transporters
· Heme Iron (Hemoglobin)
· Non-Heme Iron
Electron Transporters
· Heme Iron (Cytochrome c)
· Non-Heme Iron (Ferredoxins)
Zinc
· In Enzymes (Lewis-Acid Catalyst)
· DNA Binding Proteins(Structural Element)
References My main sources of information for this gallery are:
1. A. Principles of Bioinorganic Chemistry by Stephen Lippard and Jeremy Berg (University Science Books, 1994), and
2. B. A series of 10 articles in J. Chem. Educ. over the past 20 years by Ei-Ichiro Ochiai of Juniata College. See J. Chem. Educ. 74, (5), pp 600-604, 1997, and the nine articles cited as the first reference therein. In directing the reader to these articles throughout this gallery, I refer to the first article in this series as reference B, #1.
I take credit for all errors and misconceptions, and I hope you will point out every one you find. Unlike text pages, these pages can (and will) be corrected!
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