Ligand Energy Controls the Heme-Fe Valence in Aqueous Myoglobins

• Published in: Journal of the Physical Society of Japan Vol. 78; no. 4; p. 44802
• Main Authors: HARADA, Yoshihisa, TAGUCHI, Munetaka, SHIN, Shik, MIYAJIMA, Yoshiharu, TOKUSHIMA, Takashi, HORIKAWA, Yuka, CHAINANI, Ashish, SHIRO, Yoshitsugu, SENBA, Yasunori, OHASHI, Haruhiko, FUKUYAMA, Hidetoshi
• Format: Journal Article
• Language: English
• Published: Tokyo Physical Society of Japan 01-04-2009; The Physical Society of Japan
• Subjects: Analytical, structural and metabolic biochemistry; Biological and medical sciences; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Hemoproteins; Metalloproteins; Physics; Proteins; Myoglobin; charge-transfer energy; RXES; porphyrin; Heme; Ligands; Regulation; Charge transfer; Porphyrins
• ISSN: 0031-9015; 1347-4073
• DOI: 10.1143/jpsj.78.044802

We use resonant X-ray emission spectroscopy and model calculations to quantify the ligand: heme-Fe energy structure of aqueous myoglobins. For reduced (Fe2+) and oxidized (Fe3+) states, the removal or addition of an electron primarily involves charge changes on the ligand-site, and not the Fe-site. The results indicate a finite positive/negative charge-transfer energy δ between the heme-Fe 3d and ligand valence electronic states for Fe2+/Fe3+. Thus, the energy difference between the ligand and Fe 3d states (+δ or -δ) determines the charge properties of myoglobins. The study provides a reliable method for characterizing ligand-metal binding of biological systems in solution.