Effect of Interaction between Protein Phosphorylation and S-Nitrosylation on Mutton Tenderness during Postmortem Storage

Postmortem mutton longissimus dorsi was minced and treated separately with phosphatase inhibitor, kinase inhibitor, S-nitrosoglutathione and nitric oxide synthase (NOS) inhibitor to control the degrees of phosphorylation and S-nitrosylation. The effect of interaction between protein phosphorylation and S-nitrosylation on mutton tenderness during postmortem storage were investigated by analyzing the changes in the phosphorylation level, S-nitrosylation level, pH, myofibrillar fragmentation index (MFI), desmin and troponin-T degradation of the treated mutton samples during storage at 4 ℃. The results indicated that phosphorylation levels were significantly higher (P < 0.05) in the phosphorylation-controlled group than in the phosphorylation and S-nitrosylation-controlled group in the early (0-12 h) and late (48-72 h) stages of storage, suggesting that protein S-nitrosylation inhibited its phosphorylation. When phosphorylation and S-nitrosylation modifications acted simultaneously, phosphorylation modification was dominant in affecting pH and its effect could be further enhanced by S-nitrosylation. On the contrary, S-nitrosylation played a major role in destroying the internal structure of myofibrillar proteins in mutton longissimus dorsi. When they occurred simultaneously, protein phosphorylation inhibited its S-nitrosylation; conversely, protein S-nitrosylation may promote the inhibitory effect of protein phosphorylation on desmin degradation. During postmortem storage, the interaction between protein phosphorylation and S-nitrosylation varied at different reaction periods, but both ultimately resulted in a decrease of troponin-T degradation. In conclusion, the interaction between protein phosphorylation and S-nitrosylation negatively influences the tenderness of mutton during postmortem aging.