Cytochromes c3 are tetraheme cytochromes with unknown physiological function. We have been investigating the non-planar structures of the hemes contained in the proteins from four different organisms. Although there is virtually no amino acid sequence identity among these proteins (except for the heme axial ligands and the cysteine residues that covalent link the protein to the hemes), the hemes are distorted from planarity in a conserved fashion. Our studies focus on the origin of the heme distortions and how the distortions may influence biological function. The structure of a typical cytochome c3 is shown below; the hemes (without the iron atoms) are shown in magenta.

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