Riboflavin photosensitized oxidation of myoglobin.
The reaction of the fresh meat pigment oxymyoglobin, MbFe(II)O₂, and its oxidized form metmyoglobin, MbFe(III), with triplet-state riboflavin involves the pigment protein, which is oxidatively cleaved or dimerized as shown by SDS-PAGE and Western blotting. The overall rate constant for oxidation of MbFe(II)O₂ by ³Rib is (3.0 ± 0.5) × 10⁹ L·mol⁻¹·s⁻¹ and (3.1 ± 0.4) × 10⁹ L·mol⁻¹·s⁻¹ for MbFe(III) in phosphate buffer of pH 7.4 at 25 °C as determined by laser flash photolysis. The high rates are rationalized by ground state hydrophobic interactions as detected as static quenching of fluorescence from singlet-excited state riboflavin by myoglobins using time-resolved fluorescence spectroscopy and a Stern-Volmer approach. Binding of riboflavin to MbFe(III) has K(a) = (1.2 ± 0.2) × 10⁴ mol·L⁻¹ with ΔH° = -112 ± 22 kJ·mol⁻¹ and ΔS° = -296 ± 75 J·mol⁻¹·K⁻¹. For meat, riboflavin is concluded to be a photosensitizer for protein oxidation but not for discoloration.
Instituto de Química de São Carlos, Universidade de São Paulo , Av. Trabalhador São Carlense 400, CP 780, CEP 13560-970, São Carlos, SP, Brazil.
Juliana M
JM
Grippa
Andressa
A
de Zawadzki
Alberto B
AB
Grossi
Leif H
LH
Skibsted
Daniel R
DR
Cardoso
D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008027:Light; D009211:Myoglobin / Q000737:chemistry*; D010084:Oxidation-Reduction / Q000528:radiation effects*; D012256:Riboflavin / Q000737:chemistry*
D009211:Myoglobin; D012256:Riboflavin