Mild oxidation promotes myosin S2 cross-linking by microbial transglutaminase

The cross-linking of myosin, an important property in meat processing, has previously been studied in complex myofibril systems to address free radical and microbial transglutaminase (MTG) effects. In the present study, purified myosin from pork Longissimus muscle was modified with H₂O₂ and 10 µM Fe to determine the effects of oxidation on the subsequent cross-linking by MTG (E:S = 1:20) at 4 °C. When subjected to MTG, the degree of cross-linking in mildly oxidized myosin sample (1 mM H₂O₂) reached 87.6%, compared to 64.7% in MTG-treated nonoxidized myosin and 33.8% in excessively oxidized myosin (200 mM H₂O₂), based on the ε(γ-glutamyl)lysine bond, SDS-PAGE, and solubility analyses. Although S1 in myosin was always the principal cross-linking site, the S2 subfragment became a significant new region of cross-linking when stressed by 1 mM H₂O₂. These findings may guide the MTG application in meat processing where oxidation is not inhibited.