Abstract: In this study, the Longissimus dorsi muscle of Qinchuan cattle was injected with the proteasome inhibitor MG-132 immediately postmortem and then stored at 4 ℃. The effect of the ubiquitin-proteasome pathway (UPP) on protein degradation as well as changes in the proteasome activity, ubiquitin content and microstructure of the muscle during postmortem storage was explored in order to provide theoretical support for precise postmortem regulation of beef quality. With the extension of storage time, proteasome activity was lower and the contents of total soluble protein and ubiquitin were higher in the MG-132 group than in the control group. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) results showed that the band intensity of total soluble proteins between 40 and 250 kDa was greater in the MG-132 group than in the control group; muscle structure was better preserved in the MG-132 group, and the Z line and the boundary between light and dark bands were clearer than those in the control group. The contents of total soluble protein and ubiquitin showed a significantly positive correlation (P < 0.05). In conclusion, postmortem injection of MG-132 inhibited the proteasome activity and the degradation of ubiquitinated proteins in the UPP in Qinchuan beef, which in turn altered protein degradation and attenuated muscle damage. This suggests that the UPP has a potential role in meat quality formation; the proteasome not only degrades proteins by itself alone to destroy beef myofibrillar structure, but also influences postmortem beef protein degradation through mediating the UPP, ultimately affecting postmortem beef quality.

Key words: Bos taurus; proteasome inhibitor MG-132; proteasome; ubiquitin-proteasome pathway