A theoretical evaluation of the ionization potentials for one-electron oxidized states of cytochrome c3

Abstract

The ionization potentials of one-electron oxidized states of cytochrome c 3 were evaluated by numerical calculations. In the ionization processes from cytochrome c 3 0+ to c 3 1+, four ionization potentials were observed with respect to four hemes involved in cytochrome c 3. Ab initio SCF MO calculations were carried out for the four heme complexes to obtain their ionization potentials under vacuum (IP vacuums). The electrostatic potentials (EPs) which the apo-protein and the aqueous solvent produce at the heme irons were calculated by the particle–particle/particle–mesh (PPPM) algorithm based on the self-consistent boundary (SCB) method. Final theoretical ionization potentials of cytochrome c 3 (IP proteins) were evaluated as the sum of IP vacuums and EPs. The calculated IP proteins successfully reproduced the order of corresponding experimental values. The maximum difference among IP proteins was 130 mV which was approximately twice as large as that of experimental ones. The small differences among IP proteins were given by the delicate cancellations of IP vacuums and EPs. We also discuss the detailed electronic structures of hemes in cytochrome c 3.