| Ferredoxins are the prototypical Fe4S4 cluster protein. They act as an electron transporters, carrying reducing equivalents between their redox partners. |  |
These very inorganic clusters are left over from the earlier stages of life on earth when there was no oxygen in the air. One of the signs, or footprints, of life found the Martian meteorite was the presence of FeS compounds comparable to those left by anaerobic life here on Earth!from a world without oxygen!
| Ferredoxins are the prototypical Fe4S4 cluster protein. They act as an electron transporters, carrying reducing equivalents between their redox partners. | |
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Often Fe4S4 clusters are used as by proteins as batteries or wires would be in manmade devices, to direct and store charges through a larger protein. In the NiFe Hydrogenases, a string of FeS clusters are found leading from the active site to the protein surface, likely to carry the charges generated from oxidizing H2 to the surface binding site of its redox partner. What is different about the protein cluster in the middle? |
| Aconitase contains an FeS cube with one corner Fe missing. It catalyzes the isomerization of citrate to isocitrate (thru intermediate formation of aconitate). The Fe3S4 cluster shown is the inactive state. The binding of an Fe ion from solution activates it, and the terminal Fe is the site of substrate binding. Thus the activity of aconitase is dependent on the Fe concentration. |  |
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Many other FeS clusters are known, like simple FeS4 rubredoxins and the Fe2S2 Rieske proteins depicted to the left. Can you identify the ligands that the protein uses to hold this Fe2S2 core? |
