title: Reduction of ferrylmyoglobin by the spin trap N-tert-butyl-alpha-phenylnitrone (PBN) in aqueous solution and during freezing.
abstract: The hypervalent muscle pigment ferrylmyoglobin, formed by activation of metmyoglobin by hydrogen peroxide, was found to be reduced in a second-order reaction by N-tert-butyl-alpha-phenylnitrone (PBN, often used as a spin trap). In acidic aqueous solution at ambient temperature, the reduction is relatively slow (deltaH++ = 65+/-2kJ x mol(-1) and deltaS++ = -54+/-7 J x mol(-1). K(-1) for pH = 5.6), but phase transitions during freezing of the buffered solutions accelerates the reaction between ferrylmyoglobin and PBN. In these heterogenous systems at low temperature (but not when ice-formation was inhibited by glycerol), a PBN-derived radical intermediate was detected by ESR-spectroscopy, identified as a nitroxyl radical by a parallel nitrogen hyperfine coupling constant of 31.8 G, and from microwave power saturation behavior concluded not to be located in the heme-cleft of the protein. The acceleration of the reaction is most likely caused by a lowering of the pH during the freezing of the buffered solutions whereby ferrylmyoglobin becomes more oxidizing.
authors.affiliation: Department of Dairy and Food Science, Royal Veterinary and Agricultural University, Frederiksberg C, Denmark.
authors.forename: M V
authors.initials: MV
authors.lastname: Kröger-Ohlsen
authors.forename: M L
authors.initials: ML
authors.lastname: Andersen
authors.forename: L H
authors.initials: LH
authors.lastname: Skibsted
mesh_terms: D003497:Cyclic N-Oxides; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D005615:Freezing; D005990:Glycerol / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008786:Metmyoglobin / Q000737:chemistry*; D009589:Nitrogen Oxides / Q000737:chemistry*; D010084:Oxidation-Reduction; D012996:Solutions; D013053:Spectrophotometry; D013113:Spin Labels; D013816:Thermodynamics; D014867:Water
chemical_list: D003497:Cyclic N-Oxides; D005609:Free Radicals; D009589:Nitrogen Oxides; D012996:Solutions; D013113:Spin Labels; C028048:ferrylmyoglobin; D014867:Water; D008786:Metmyoglobin; C029217:phenyl-N-tert-butylnitrone; D006861:Hydrogen Peroxide; D005990:Glycerol