Heme iron structures basic properties

Mitochondrial cytochrome c is perhaps the most widely studied of all metalloproteins with respect to its electrochemical properties. It is located in the inner-membrane space of mitochondria and transfers electrons between membrane-bound complex III and complex IV. The active site is an iron porphyrin with a redox potential (7) of -1-260 mV vs. NHE. The crystal structures of cytochrome c from tuna have been determined (8, 9) in both oxidation states at atomic resolution. It is found that the heme group is covalently linked to the protein via two thioether bridges, and part of its edge is exposed at the protein surface. Cytochrome c is a very basic protein, with an overall charge of -1-7/-l-8 at neutral pH. Furthermore, many of the excess basic lysine residues are clustered around the mouth of the heme crevice, giving rise to a pronounced charge asymmetry. 

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