Fe-O2 bonding and oxyheme structure in myoglobin.

In the polarized electronic absorption spectrum of oxymyoglobin in single crystals, charge-transfer states involving orbitals of the iron and dioxygen ligand are defined as probes of oxyheme orbital structure and coordination geometry. The spectrum of sperm whale oxymyoglobin is diagnostic of a bent (formula: see text) oxheme coordination geometry with totally spin-paired, ground-state electronic configurations of the iron and of the dioxygen ligand. In contrast, Aplysia myoglobin is distinguishably different in oxyheme structure, indicating that the geometry of Fe-O2 bonding in heme proteins can be altered by the protein environment.