title: Crystallographic and spectroscopic studies of peroxide-derived myoglobin compound II and occurrence of protonated FeIV O.
abstract: High resolution crystal structures of myoglobin in the pH range 5.2-8.7 have been used as models for the peroxide-derived compound II intermediates in heme peroxidases and oxygenases. The observed Fe-O bond length (1.86-1.90 A) is consistent with that of a single bond. The compound II state of myoglobin in crystals was controlled by single-crystal microspectrophotometry before and after synchrotron data collection. We observe some radiation-induced changes in both compound II (resulting in intermediate H) and in the resting ferric state of myoglobin. These radiation-induced states are quite unstable, and compound II and ferric myoglobin are immediately regenerated through a short heating above the glass transition temperature (<1 s) of the crystals. It is unclear how this influences our compound II structures compared with the unaffected compound II, but some crystallographic data suggest that the influence on the Fe-O bond distance is minimal. Based on our crystallographic and spectroscopic data we suggest that for myoglobin the compound II intermediate consists of an Fe(IV)-O species with a single bond. The presence of Fe(IV) is indicated by a small isomer shift of delta = 0.07 mm/s from Mössbauer spectroscopy. Earlier quantum refinements (crystallographic refinement where the molecular-mechanics potential is replaced by a quantum chemical calculation) and density functional theory calculations suggest that this intermediate H species is protonated.
authors.affiliation: Department of Chemistry, University of Oslo, PO Box 1033, Blindern, Oslo N-0315, Norway.
authors.forename: Hans-Petter
authors.initials: HP
authors.lastname: Hersleth
authors.forename: Takeshi
authors.initials: T
authors.lastname: Uchida
authors.forename: Asmund K
authors.initials: AK
authors.lastname: Røhr
authors.forename: Thomas
authors.initials: T
authors.lastname: Teschner
authors.forename: Volker
authors.initials: V
authors.lastname: Schünemann
authors.forename: Teizo
authors.initials: T
authors.lastname: Kitagawa
authors.forename: Alfred X
authors.initials: AX
authors.lastname: Trautwein
authors.forename: Carl Henrik
authors.initials: CH
authors.lastname: Görbitz
authors.forename: K Kristoffer
authors.initials: KK
authors.lastname: Andersson
mesh_terms: D000818:Animals; D018360:Crystallography, X-Ray / Q000379:methods*; D006418:Heme / Q000737:chemistry; D006736:Horses; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D008968:Molecular Conformation; D009206:Myocardium / Q000378:metabolism; D009211:Myoglobin / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D010545:Peroxides / Q000737:chemistry; D011522:Protons; D011789:Quantum Theory; D015204:Spectroscopy, Mossbauer / Q000379:methods*; D013059:Spectrum Analysis, Raman / Q000379:methods*
chemical_list: D009211:Myoglobin; D010545:Peroxides; D011522:Protons; D006418:Heme; D007501:Iron; D010100:Oxygen