Proteins with Iron in a Heme Group

There are two common and very important proteins that contain iron in a heme group: myoglobin and hemoglobin.

Myoglobin is found in muscle tissue. It stores and transports oxygen by reversibly binding the O₂ that has been transported to the tissue by hemoglobin.

Hemoglobin is a gas transporting molecule (most importantly oxygen) found in red blood cells. These two proteins occur in various states in nature. The examples given here are of deoxymyoglobin, deoxyhemoglobin, and these proteins bound to CO, N₃, and O₂.

Myoglobin

As can be seen from the views produced by the program, the geometry of deoxymyoglobin is square pyramidal, while the geometry of myoglobin with azide is octahedral. This geometry, along with the bond angles and distances between the iron and the surrounding atoms can be seen especially well with the paper models produced by the program. These models allow us to make comparisons between the distances, and thus the strength of bond, between the iron and the surrounding molecules when the ligand is and is not present. For example, we find out from these models that overall the nitrogens in the heme group are held much more closely in the deoxymyoglobin. (The average deoxymyglobin distance is 190 pm versus 202 pm for myoglobin with the azide.) This can be explained, as the N₃ in 1swm should lead to a higher electron density around the iron, and an overall more shielded iron center, thus increasing the size of the heme pocket.

Hemoglobin

The comparison can be made again between the hemoglobin molecules with and without
ligands using the paper models. The same general conclusion can be drawn
as the one drawn for myoglobin. The heme pocket gets larger when a ligand is added.

Here are the two most important myoglobin and hemoglobin molecules. These are the oxy-proteins, where an O₂ is bound to the iron across from the histidine. It is possible to use Molecular Origami again to make comparisons between the bond angles and distances of the two proteins. For example, the average nitrogen heme bond distances are very similar (199 pm for hemoglobin and 200 pm for myoglobin).

Isolated Non-Heme Iron
Iron-Sulfur Systems
Two Other Interesting Proteins

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As can be seen from the views produced by the program, the geometry of deoxymyoglobin is square pyramidal, while the geometry of myoglobin with azide is octahedral. This geometry, along with the bond angles and distances between the iron and the surrounding atoms can be seen especially well with the paper models produced by the program. These models allow us to make comparisons between the distances, and thus the strength of bond, between the iron and the surrounding molecules when the ligand is and is not present.		For example, we find out from these models that overall the nitrogens in the heme group are held much more closely in the deoxymyoglobin. (The average deoxymyglobin distance is 190 pm versus 202 pm for myoglobin with the azide.) This can be explained, as the N₃ in 1swm should lead to a higher electron density around the iron, and an overall more shielded iron center, thus increasing the size of the heme pocket.



Here are the two most important myoglobin and hemoglobin molecules. These are the oxy-proteins, where an O₂ is bound to the iron across from the histidine. It is possible to use Molecular Origami again to make comparisons between the bond angles and distances of the two proteins.		For example, the average nitrogen heme bond distances are very similar (199 pm for hemoglobin and 200 pm for myoglobin).