Phosphorylation prevents in vitro myofibrillar proteins degradation by μ-calpain

- Myofibrillar proteins treated by protein kinase A and alkaline phosphatase were degraded by μ-calpain.
- Degradation of myosin heavy chain, actin, desmin and troponin T was analysed.
- Phosphorylation prevents myofibrillar proteins degradation by μ-calpain.
- Dephosphorylation enhances myofibrillar proteins degradation by μ-calpain.

Myofibrillar proteins degradation contributes to meat tenderisation during post-mortem ageing. Protein phosphorylation has been revealed to be associated with meat tenderness in recent years. This study was undertaken to determine the impact of myofibrillar proteins phosphorylation on the degradation susceptibility by μ-calpain. Myofibrillar proteins were first incubated with protein kinase A (PKA) or alkaline phosphatase (AP) to increase or decrease the phosphorylation level, following μ-calpain hydrolysis. Myosin heavy chain, actin, desmin and troponin T showed different levels of degradation in control, AP and PKA groups under different Ca2+ concentrations. Generally, more degradation products were detected with the increase of Ca2+ concentration. Compared to the control, the protein degradation was higher in AP-treated group and lower in PKA-treated group. This study shows that phosphorylation prevents proteolytic susceptibility of myofibrillar proteins to degradation by μ-calpain, indicating that protein phosphorylation plays an important role in meat tenderisation during post-mortem ageing.