title: Reduction of ferrylmyoglobin by beta-lactoglobulin.
abstract: Reduction of iron (IV) in ferrylmyoglobin in the presence of beta-lactoglobulin in aqueous solution is the result of two parallel reactions: (i) a so-called autoreduction, and (ii) reduction by beta-lactoglobulin in a second-order-reaction resulting in bityrosine formation in beta- lactoglobulin. In the pH-region investigated (5.4-7.4), the rate of reduction increased for both reactions with decreasing pH. The second order-reaction had for non-denatured beta-lactoglobulin the activation parameters: delta H* = 45 kJ.mol-1 and delta S not equal to = -93 J.mol-1.K-1 at pH = 7.0 and ionic strength 0.16 (NaCl). Reduction of ferrylmyoglobin by beta-lactoglobulin denatured by heat (86 degrees C for 3 min) or by hydrostatic pressure (300 MPa for 15 min) resulted in formation of higher molecular weight species as detected by size-exclusion chromatography and by SDS-PAGE. No molecular weight changes were observed for reduction of ferrylmyoglobin by native beta-lactoglobulin. Detection of bityrosine in the native beta-lactoglobulin fraction after oxidation with ferrylmyoglobin indicated intra-molecular bityrosine formation. In heat-denatured beta-lactoglobulin bityrosine formation could be of intra-molecular and/or of inter-molecular origin, the latter being confirmed by size-exclusion chromatography.
authors.affiliation: Department of Dairy and Food Science, Royal Veterinary and Agricultural University, Frederiksberg C, Denmark.
authors.forename: H
authors.initials: H
authors.lastname: Ostdal
authors.forename: B
authors.initials: B
authors.lastname: Daneshvar
authors.forename: L H
authors.initials: LH
authors.lastname: Skibsted
mesh_terms: D006861:Hydrogen Peroxide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D007700:Kinetics; D007782:Lactoglobulins / Q000737:chemistry*; D008786:Metmyoglobin / Q000737:chemistry*; D008970:Molecular Weight; D010084:Oxidation-Reduction; D011489:Protein Denaturation; D013057:Spectrum Analysis; D014443:Tyrosine / Q000737:chemistry
chemical_list: D007782:Lactoglobulins; C028048:ferrylmyoglobin; D008786:Metmyoglobin; D014443:Tyrosine; D006861:Hydrogen Peroxide; D007501:Iron