title: Reduction of ferrylmyoglobin by hydrogen sulfide. Kinetics in relation to meat greening.
abstract: The hypervalent meat pigment ferrylmyoglobin, MbFe(IV)═O, characteristic for oxidatively stressed meat and known to initiate protein cross-linking, was found to be reduced by hydrogen sulfide to yield sulfmyoglobin. Horse heart myoglobin, void of cysteine, was used to avoid possible interference from protein thiols. For aqueous solution, the reactions were found to be second-order, and an apparent acid catalysis could be quantitatively accounted for in terms of a fast reaction between protonated ferrylmyoglobin, MbFe(IV)═O,H(+), and hydrogen sulfide, H2S (k2 = (2.5 ± 0.1) × 10(6) L mol(-1) s(-1) for 25.0 °C, ionic strengh 0.067, dominating for pH < 4), and a slow reaction between MbFe(IV)═O and HS(-) (k2 = (1.0 ± 0.7) × 10(4) L mol(-1) s(-1) for 25.0 °C, ionic strengh 0.067, dominating for pH > 7). For meat pH, a reaction via the transition state {MbFe(IV)═O···H···HS}([symbol: see text]) contributed significantly, and this reaction appeared almost independent of temperature with an apparent energy of activation of 2.1 ± 0.7 kJ mol(-1) at pH 7.4, as a result of compensation among activation energies and temperature influence on pKa values explaining low temperature greening of meat.
authors: Instituto de Química de São Carlos, Universidade de São Paulo , Av. Trabalhador São-Carlense 400, CP 780, CEP 13560-970, São Carlos - SP, Brazil.
authors: Silvia H
authors: SH
authors: Libardi
authors: Helene
authors: H
authors: Pindstrup
authors: Daniel R
authors: DR
authors: Cardoso
authors: Leif H
authors: LH
authors: Skibsted
mesh_terms: D000818:Animals; D006736:Horses; D006862:Hydrogen Sulfide / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008460:Meat / Q000032:analysis*; D008786:Metmyoglobin / Q000737:chemistry*; D010084:Oxidation-Reduction
chemical_list: C028048:ferrylmyoglobin; D008786:Metmyoglobin; D006862:Hydrogen Sulfide