The correlation of protein phosphorylation with protein degradation, oxidation, and endogenous enzyme activity in...

This investigation examined the correlation between phosphorylation levels of muscle proteins and textural characteristics, protein degradation, protein oxidation, and endogenous enzymatic activities in Esox lucius stored at 4 °C postmortem. Muscle quality gradually deteriorated during storage. Changes included a biphasic pH fluctuation (an initial decrease followed by an increase), increased myofibril fragmentation index (MFI), reduced shear force, elevated protein carbonyls, and diminished total sulfhydryl content. Endogenous proteases (μ-calpain, cathepsins B/L/D/H) remained active, and myofibrillar protein degradation occurred. As refrigeration time increased, phosphorylation of myofibrillar proteins (MP) gradually decreased, while phosphorylation of sarcoplasmic proteins (SP) increased. Correlation analysis showed that phosphorylation levels of MP and SP were significantly correlated with muscle texture, protein degradation, protein oxidation, and endogenous protease activity (P < 0.01 or P < 0.05). This suggests that protein phosphorylation may regulate postmortem changes in walleye muscle quality.