Effect of the Electron Density of the Heme Fe Atom on the Nature of Fe-O2Bonding in Oxy Myoglobin

Yasuhiko Yamamoto, Kazuyasu Hasegawa, Tomokazu Shibata, Atsuya Momotake, Takashi Ogura, Sachiko Yanagisawa, Saburo Neya, Akihiro Suzuki, Yasuhiro Kobayashi, Makina Saito, Makoto Seto, Takehiro Ohta

Research output: Contribution to journalArticlepeer-review

Abstract

Mössbauer spectroscopy has been used to characterize oxygenated myoglobins (oxy Mbs) reconstituted with native and chemically modified 57Fe-enriched heme cofactors with different electron densities of the heme Fe atom (ρFe) and to elucidate the effect of a change in the ρFe on the nature of the bond between heme Fe and oxygen (O2), i.e., the Fe-O2 bond, in the protein. Quadrupole splitting (ΔEQ) was found to decrease with decreasing ρFe, and the observed ρFe-dependent ΔEQ confirmed an increase in the contribution of the ferric-superoxide (Fe3+-O2-) form to the resonance hybrid of the Fe-O2 fragment with decreasing ρFe. These observations explicitly accounted for the lowering of O2 affinity of the protein due to an increase in the O2 dissociation rate and a decrease in the autoxidation reaction rate of oxy Mb through decreasing H+ affinity of the bound ligand with decreasing ρFe. Therefore, the present study demonstrated the mechanism underlying the electronic control of O2 affinity and the autoxidation of the protein through the heme electronic structure. Carbon monoxide (CO) adducts of reconstituted Mbs (CO-Mbs) were similarly characterized, and we found that the resonance between the two canonical forms of the Fe-CO fragment was also affected by a change in ρFe. Thus, the nature of the Fe-ligand bond in the protein was found to be affected by the ρFe.

Original languageEnglish
Pages (from-to)1021-1027
Number of pages7
JournalInorganic chemistry
Volume60
Issue number2
DOIs
Publication statusPublished - 2021 Jan 18
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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