Isolated Non-Heme Iron

Another way iron can occur in a protein is as an isolated non-heme atom. There are several possible geometries around these iron atoms. Here are a few examples, listed by geometry.

See-Saw

This iron center comes from the protein 2,3-dihydroxybiphenyl dioxygenase. Dioxygenase is important in the breakdown of widely found environmental pollutants PCBs. It catalyzes the extradiol ring cleavage of 2,3-dihydroxybiphenyl.

Trigonal Pyramidal

This iron center is found in the protein soy bean lipoxygenase L3. This enzyme plays a key role in the metabolism of unsaturated fatty acids. (It is likely that there are missing water molecules from the reported structure, which would give the iron center a different geometry.)

Trigonal Bipyramidal

Trigonal bipyramidal iron is found in Fe(II) superoxide dismutase, from E. coli.
This enzyme catalyzes the dismutation of superoxides, for example HO₂ and O₂^-.

There is also Fe(III) superoxide dismutase. From the foldable Molecular Origami
models it is possible to see the differences between a molecule containing an
Fe(II) and an Fe(III). As can be seen when the models are constructed, the Fe(III)
clearly has the surrounding atoms closer than the Fe(II). This is due
to the more positive character of the Fe(III) drawing the surrounding atoms nearer.

Tetrahedral

Aldehyde ferredoxin oxidoreductase

This interesting atom serves as a transition to the section of iron-sulfur systems. Aldehyde ferredoxin oxidoreductase is an enzyme that catalyzes the reversible oxidation of aldehydes to carboxylic acids. It is a very interesting molecule because of its extreme thermostability. This ferredoxin was discovered in the Archaebacteria P. furiosus, and first grabbed the attention of scientists because it contains the third-row transition metal tungsten. This ferredoxin has two areas of iron interest. It has the single iron in a tetrahedral geometry, and also has an Fe₄S₄ group. This second group contains four iron atoms in a structure with four sulfur atoms.

Octahedral

This trigonal pyramidal iron center comes from the molecule human calcineurin heterodimer. The phosphatase not only contains iron, but also contains several calcium atoms. Human calcineurin heterodimer is very important for several cellular processes, including the activation of T-cells. The three water molecules attached to the iron give this iron center a distorted octahedral geometry.

Iron in Heme Group
Iron-Sulfur Systems
Two Other Interesting Proteins

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This interesting atom serves as a transition to the section of iron-sulfur systems. Aldehyde ferredoxin oxidoreductase is an enzyme that catalyzes the reversible oxidation of aldehydes to carboxylic acids. It is a very interesting molecule because of its extreme thermostability. This ferredoxin was discovered in the Archaebacteria		P. furiosus, and first grabbed the attention of scientists because it contains the third-row transition metal tungsten. This ferredoxin has two areas of iron interest. It has the single iron in a tetrahedral geometry, and also has an Fe₄S₄ group. This second group contains four iron atoms in a structure with four sulfur atoms.