Molecule of the Month, October 1998
Authors: Regina F. Frey, Maureen J. Donlin,
and James K. Bashkin
Department of Chemistry, Washington University
St. Louis, MO
Ref: M.J. Donlin, R.F. Frey, C. Putnam,
J.K. Proctor, J.K. Bashkin, J. Chem. Edu.,75,
437, (1998).
Iron, an essential element in living organisms, is commonly
used in the Fe(II) oxidation state. But in our oxidizing
atmosphere, Fe(III) is the more prevalent oxidation state. At the
physiological pH of 7, the Fe(III) ion concentration in aqueous
solution is minimal. However, most organisms maintain an
intracellular concentration of Fe(III) several orders of
magnitude higher than simple aqueous solutions permit. This
discrepancy in concentration demonstrates the striking ability of
biochemical systems to concentrate and store iron. Conversely,
iron can be very toxic, so the ability to store and release iron
in a controlled fashion is essential. Cells have solved this
problem of iron storage by developing ferritins, a family of
iron-storage proteins that sequester iron inside a protein coat
as a hydrous ferric oxide-phosphate mineral similar in structure
to the mineral ferrihydrite.
This graphical tutorial is used in conjunction with a general-chemistry laboratory
experiment which explores the in vitro iron-release
process. Pdb files of the compounds used in the experiment are
available at the bottom of this tutorial for downloading and
interactively viewing using an appropriate molecular-viewing
package such as Rasmol. Below are four (4) points of emphasis
within the tutorial:
- The differences between the 3-fold and 4-fold channels
found in ferritin;
- The size and shapes of the different Fe(II) compounds and
how they relate to the channel sizes;
- The structure of the iron-mineral core and how the
mineral core binds to the walls of the protein;
- The relationship between different types of structural
representations such as two-dimensional, stick, CPK, and
ribbon.