Significant change in electronic structures of heme upon reduction by strong Coulomb repulsion between Fe d electrons.
We report total-energy electronic-structure calculations based on the density functional theory performed on a low-spin heme. We have found that the high-lying occupied and low-lying unoccupied states having Fe d and/or porphyrin pi orbital character are significantly rearranged upon the reduction of the heme. An analysis of these states shows that the remarkable elevation of the Fe d levels takes place due to the strong Coulombic repulsion between accommodated d electrons. Due to a peculiarity of the heme, this elevation could be controlled by lower-lying empty porphyrin pi states, leading to electron transfer from Fe d orbitals to the porphyrin pi ones in order to reduce the Coulomb-energy cost. This self-limiting mechanism provides a natural explanation not only for the present calculated results, but also for general electron delocalization appearing under various physiological conditions, regardless of the types of the hemes.
Kamiya
Katsumasa
K
Institute of Picobiology, Graduate School of Life Science, University of Hyogo, 3-2-1 Koto, Kamigori, Ako, Hyogo, 678-1297, Japan. kkamiya@sci.u-hyogo.ac.jp
Yamamoto
Shuji
S
Shiraishi
Kenji
K
Oshiyama
Atsushi
A
D000818:Animals; D002417:Cattle; D004579:Electron Transport; D004583:Electrons; D006418:Heme / Q000031:analogs & derivatives* / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D011789:Quantum Theory
C027728:heme a; D006418:Heme; D007501:Iron