Characterization of some low spin complexes of ferric hemeoctapeptide from cytochrome- c

Abstract

Complexes of hemeoctapeptide, derived from bovine cytochrome c, show similar magnetic properties to those of low spin complexes of cytochrome c and hemoglobin. The electronic properties of hemeoctapeptide and cytochrome complexes are also similar while the Soret and beta bands of these analogs are generally blue shifted from those of corresponding complexes of hemoglobin due largely to the differences in the type of heme. Electron spin resonance calculations were carried out using Taylor's method to elucidate d orbital splittings and structural differences in hemeoctapeptide, hemoglobin, and cytochrome c. A correlation between V, the rhombicity, and the position of the beta band was found to exist and was dependent on protein type. However, neither the electronic not magnetic data was largely dependent on protein bulk. A large rhombic splitting caused shifts to the blue, and showed a dependence of the porphyrin pi orbitals on the placement of the metal relative to the porphyrin plane. A structural basis for the degree of rhombic splitting and thermodynamic parameters for ligand binding is proposed.