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.
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
Katsumasa
K
Kamiya
Shuji
S
Yamamoto
Kenji
K
Shiraishi
Atsushi
A
Oshiyama
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