The reactivity of cytochrome c with soft ligands

The spectral changes caused by binding soft ligands to the cytochrome c iron and their correlation to ligand affinities support the hypothesis that the iron—methionine sulfur bond of this heme protein is enhanced by delocalization of the metal l₂, electrons into the empty 3d orbitals of the ligand atom. These findings also explain the unique spectrum of cytochrome c in the far red.